This research presents a detailed analysis and discussion of the crystallographic, flux pinning mechanism, the microstructure and superconducting properties of nano-Pt/nano-SiC co-added (in different ...addition levels) bulk MgB
2
samples. All disk-shaped MgB
2
bulk samples were manufactured using the conventional solid-state reaction method and the sintering process was implemented at 700 °C for 3 h in pure Ar atmosphere. Nano-Pt addition levels were 0.0; 0.5; 1.0; 3.0; 5.0; 7.0 wt% of MgB
2
powders and nano-SiC addition level was 10 wt% of MgB
2
powders. X-ray diffraction (XRD) analysis shows that Mg
2
Si, Pt
3
Si and Mg
2
PtSi impurity phases were detected in nano-Pt/nano-SiC co-added MgB
2
samples. These impurity phases created zones acting as influential pinning centers for the flux lines. The critical current density (
J
c
) indicated improvement at high field (
B
> 4 T) for 10 wt% nano-SiC added sample and all nano-Pt/nano-SiC co-added samples. The values of
J
c
in 6 T field at 5 K were calculated to be 3.1 × 10
3
A/cm
2
for pristine MgB
2
sample, 1.5 × 10
4
A/cm
2
for the 10 wt% nano-SiC added MgB
2
sample and 1.6 × 10
4
A/cm
2
for the 1.0 wt% nano-Pt and 10 wt% nano-SiC co-added MgB
2
sample. At applied magnetic fields higher than about 4 T at 5 K and 10 K, the best
J
c
performance among all samples is given by 1.0 wt% nano-Pt and 10 wt% nano-SiC co-added MgB
2
sample. The pristine MgB
2
sample has a the critical temperatures (
T
c
) of 38.1 K and
T
c
has dropped with nano-Pt/nano-SiC co-added bulk MgB
2
samples. The flux pinning mechanisms of both pristine and all nano-Pt/nano-SiC co-added bulk MgB
2
samples were seen to be the normal point pinning in magnetic fields lower than
B
max
(the field at which the pinning force reaches its maximum) at 15 K.
Fabrication methods are important way to improve structural and superconducting properties of MgB2 such as critical current, magnetic levitation force (MLF) and magnetic field trapping capability. ...Although the graded fabrication technique has been used for single-grain bulk YBCO superconductor to improve critical current and bulk superconducting properties, similar technique as regional doping has not been used for bulk MgB2, until now. In this study, nanoparticle silver doping was carried out in to the bulk MgTi0.06B2 superconductor by using in-situ solid state reaction and partial graded (regional) doping method together, to improve the radius independent uniform bulk current density and the magnetic levitation force as well as the structural properties of the MgB2 bulk superconductors. Both the Jc(0) self-field critical current and Fp (μ0H) pinning force density values enhanced in comparison with the inner region values, when the nanoparticle Ag doping is carried out in to the outer section of the sample. Addition to the enhancement of the structural and the micro electromagnetic properties as Jc(0) and Fp (μ0H), our study also focused on the improved of the bulk Jc and the radius of shielding current loop r, to improve bulk electromagnetic properties as the levitation force. It is seen that the structural properties enhanced and both the vertical levitation force and the lateral guidance force value increased with Ag doping to the outer section of MgTi0.06B2 sample. On the other hand, the increasing ratio of the lateral guidance force of 19.7% and the vertical levitation force of 10.8% of the sample with 3 wt% Ag-doped than the undoped one points out that the regional doping method to the outer section is very suitable for guidance force applications, which is important in the magnetic bearing application such as Maglev and magnetic energy storage systems.
•The regional nanoparticle Ag doping into bulk MgTi0.06B2.•The uniform bulk critical current improvement by the using regional doping method.•The structural and flux pinning properties enhanced by the regional Ag doping.•The increasing ratio of the lateral guidance force is higher than vertical force.
The objective of the study was to investigate the effect of pre-synchronisation on the occurrence of the oestrus and pregnancy rate after fixed time artificial insemination (FTAI) in synchronised ...ewes during the anoestrous season. Kivircik ewes (n = 84) were randomly assigned to one of the two treatment groups with (PRE; n = 42) or without (SYN; n = 42) pre-synchronisation. In the SYN group, the ewes were subjected to a 7-d short-term protocol (P4 insertion-6d-PGF2α-1d-P4 removal + eCG). In the PRE group, the same short-term protocol as in the SYN group was applied with 7 days apart for a pre-synchronised synchronisation protocol. A cervical FTAI was performed with fresh semen at 54 h after sponge removal. At the beginning of the synchronisation protocol, the oestrous response (66.7% vs. 0.0%) and cyclicity rates (64.3% vs. 14.3%) based on progesterone (P4) were higher in the PRE group compared to those in the SYN group, respectively (P < 0.01). However, the oestrous response after synchronisation was lower within 96 h (57.1% vs. 95.2%; P < 0.01) in the PRE group compared to that in the SYN group. Although the pregnancy rate after the FTAI was significantly (P < 0.05) lower in the PRE group (14.3%) than the SYN group (35.7%), the overall pregnancy rate after natural mating was not different (95.2%) between the groups. In conclusion, the pre-synchronisation decreased the oestrous response leading to a lower pregnancy rate after the FTAI in the synchronised ewes during the anoestrous season. Thus, attention should be paid to two consecutive administrations of eCG in a pre-synchronisation and synchronisation protocol in ewes.
Infrared (IR) laser-line scanning has been widely used to induce different surface microstructures in a broad range of materials. In this work, this laser configuration was applied on the surface of ...MgTi0.06B2 bulk samples in order to ascertain its effects on their superconducting properties, particularly on the magnetic levitation forces. The microstructural changes produced by this type of laser treatment were investigated by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). It was observed that the thermal treatment induced by the laser improves grain connectivity in a layer of material just below the irradiated surface, in agreement with the observed improvement in critical current density values, Jc, which were estimated from isothermal magnetic hysteresis loops. A significant increment of both vertical (Fz) and lateral (Fx) magnetic levitation forces was achieved. Numerical calculations were performed to understand the experimental behaviour and to clarify how an improvement of Jc near the surface can improve the magnetic levitation force of these materials. In addition, the same studies were carried out in similar bulk samples but with nano-sized silver particle additions of 3 and 6 wt %, in the outer ring of the bulk, observing also an improvement of the levitation forces, albeit less than in samples without Ag because of the better performance of the original samples after laser treatment. These results are relevant to those studying superconductor fabrication and material fabrication modelling, essential for the development of technological applications of superconductors, and are based on microstructure control via application of a recently developed laser-line scan method.
•Infra-red laser-line scanning was applied on the surface of MgTi0.06B2 bulk samples.•The vertical and lateral levitation forces enhance after laser treatment.•Laser improves grain connectivity and Jc values near the surface of the material.•Numerical calculations show reasonable agreement with experimental values.•No fundamental change in the pinning mechanisms has occurred by Ag addition.
Two algorithms used in microwave radiometry for radio-frequency interference (RFI) detection and mitigation are the pulse detection algorithm and the kurtosis detection algorithm. The relative ...performance of the algorithms is compared both analytically and empirically. Their probabilities of false alarm under RFI-free conditions and of detection when RFI is present are examined. The downlink data rate required to implement each algorithm in a spaceborne application is also considered. The kurtosis algorithm is compared to a pulse detection algorithm operating under optimal RFI detection conditions. The performance of both algorithms is also analyzed as a function of varying characteristics of the RFI. The RFI detection probabilities of both algorithms under varying subsampling conditions are compared and validated using data obtained from a field campaign. Implementation details, resource usage, and postprocessing requirements are also addressed for both algorithms.
Radio-frequency interference (RFI) is a major limiting factor in passive microwave remote sensing and radio astronomy. A digitally based radiometer system has been developed to improve RFI mitigation ...through the use of high temporal and spectral resolution. The system includes a pulse-blanking algorithm that is capable of removing pulsed time-domain sources in real time. Cross-frequency mitigation is also possible in postprocessing through the use of the system's high spectral resolution. Several experiments have been conducted at L- and C-bands in recent years. Datasets from two particular campaigns are analyzed in this paper: ground-based observations at L-band in Canton, Michigan that emphasize pulse blanking and an airborne campaign at C-band over Texas and the Gulf of Mexico that emphasizes cross-frequency mitigation. Results and analyses are presented to quantify the RFI mitigation performance achieved.
The performance of the Shapiro-Wilk (S-W) test of normality for the detection of pulsed sinusoidal radio frequency interference (RFI) in microwave radiometry is analyzed. The study is motivated by ...the fact that the S-W test has been shown in the statistical literature to be effective in detecting a wide variety of non-Gaussian signal types. The basic properties of the S-W test statistic are reviewed, and the implementation of the test in digital hardware is discussed. Because the properties of the test statistic are difficult to obtain analytically, Monte Carlo simulations are utilized to compute performance. Results show that the test can provide reasonable performance in detecting pulsed sinusoidal RFI and that quantization of data has only a minimal impact on the sensitivity achieved. Detection performance is also compared with that of the kurtosis test for normality. It is shown that the S-W test produces comparable but degraded sensitivity compared to that of the kurtosis test in most cases while avoiding the ldquoblind spotrdquo associated with the kurtosis test for pulsed interferers having 50% duty cycle. Test performance is also shown to be improved if a priori knowledge of expected RFI pulse lengths is incorporated.
•Bulk samples welded by using a melt processed solder material with a pressure source.•The structural and physical properties of welded samples were investigated in welding region.•The welding ...process had no negative effect on magnetoresistivity properties.•30 wt% 211 addition ratio is optimum for welding region and whole welded sample.
Although the welding techniques have been used to join for bulk YBCO superconductors with a sintered superconductor, similar technique as a Ag2O added bulk YBCO superconductor fabricated by melt-powder-melt-growth process (MPMG) for using as a solder material has not been used, until now. Also, physical and the bulk superconducting properties of the welded samples have not been investigated. In this study, two 20 wt% Y211 and two 30 wt% Y211 added YBCO main samples were fabricated by cold top seeding-melt-growth (TSMG) method by using an Nd123 seed. Two main samples having the same Y211 addition and welding sample positioned between the main samples stacked and welded thermally with a pressure source simultaneously. It can be seen from the levitation force measurement, making before the welding process, that the 30 wt% Y211 added samples have the larger the maximum repulsive forces values than the 20 wt% Y211 added and Ag2O added welding samples but at the same order. After the welding process the welded samples cut into the specimens, to investigate micro structure and electromagnetic properties, positioned above, on and below of the welding region of the each welded Y123 samples. From the SEM analysis a continuous structural phase was obtained between the solder material and the main samples with a good integration without any boundary gap or defects. The welding process had no negative noticeable effect on Tc of the samples under zero magnetic field, while superconducting transition width (∆Tc) of the specimen cutting from the 30 wt% Y211 added sample (Y30-ab) is smaller the specimen cutting from the 20 wt% Y211 added sample (Y20-ab) under applied magnetic field points out that Y30-ab is more resistant to the applied field than the Y20-ab because of the 211 addition. In addition, 30 wt% 211 addition ratio is more efficient for welding region and whole welded sample in terms of the supplying uniform superconducting properties as Jc. The obtained results on welded joined bulk superconductor can be beneficial to increase application potential of these superconducting materials in real scale magnetic systems.
This multidisciplinary study paves way to investigate the crucial of fundamental characteristic properties including the bulk density, electrical, superconducting, flux pinning mechanism, crystal ...structure quality and strength quality of interaction between the superconducting grains in the Bi2.1Sr2.0Ca1.1Cu2.0Oy (Bi-2212) superconducting materials with the partial replacement of gallium foreign impurity by bismuth nanoparticles in the crystal structure. Characterizations of polycrystalline ceramic materials prepared by standard ceramic route in the atmospheric air are performed by means of conventional experimental measurement methods such as powder X-ray diffraction, Archimedes water displacement, dc electrical resistivity versus temperature and critical current density examinations. All the bulk Bi-site Ga partial replaced materials exhibit the Bi-2212 superconducting phase within the different fraction levels (%73.1–94.8), moderate self-field critical current densities 54–96 A/cm2 and wide-ranging offset and onset critical transition temperature range of 45.65 K–84.52 K and 70.06 K-85.00 K. As for the experimental findings of bulk density and related degrees of granularity (porosity) parameters, the bulk density parameter is found to be between 5.76 g/cm3 and 6.12 g/cm3 when the corresponding residual porosity value is also obtained to be in a range of 8.57 %–2.86%. Moreover, the mobile hole carrier concentrations in the short-range-ordered antiferromagnetic CuO2 layers are found to be in the range from 0.085 until 0.152. Additionally, the role of Ga/Bi partial substitution in the crystal lattice on the normal state resistivity, residual resistivity, residual resistivity ratio, vibrational mode intensities, texturing, superconducting volume fractions, mobile hole carrier concentrations, average crystallite sizes, Lotgering indices and cell parameters are discussed in details. All the experimental results and theoretical approaches show that the characteristic properties tend to improve regularly with the increment in the Ga foreign impurity level until x = 0.05 due to the increment in the crystal structure quality and interaction between the superconducting grains. After the critical Ga/Bi substitution level of x = 0.05, every feature degrades considerably.
Display omitted
•Defining optimum trivalent Bi/Ga replacement level for Bi-2212 ceramic materials.•Transition of intrinsic over-doped state into optimally doped state with Ga impurity.•Formation of more effective and strong electron-phonon couplings at Fermi level.•Role of Bi/Ga substitution on strengths of ability and quality of crystal structure.•Change in ability and strength of artificial flux pinning centers with Ga content.
The higher magnetic levitation force and related stiffness values are very important for Maglev and magnetic bearing applications. Also, larger superconducting surface area is needed for continuous ...and larger magnetic mediums with different geometries and dimensions in real scale industrial applications of superconducting systems. In this study, the cylindrical YBCO superconductors were fabricated by top−seeded melt growth (TSMG) method in single and two−seeded forms with different seed distances and then the magnetic force and stiffness measurements were carried out by three axes magnetic force measurement system in different cooling heights (CH) of 20 mm and 75 mm. Additionally, a new analytical method, based on the magnetic dipole approximation, is proposed to calculate the levitation force in this study, named as Modified Advanced Frozen Image Method (MAFI), since although the Advanced Frozen Image Method in literature can calculate the levitation force with hysteresis, this method does not include the size effect of the superconductor. In the experimental studies, it is seen that the maximum levitation force values obtained by PMG with three PMs (named PMG−1) are more than two times higher than that of obtained with single PM for all samples with different distance of seeds, because of the higher magnetic flux distribution of related PMG arrangement than the single PM. In addition, the maximum magnetic levitation force value firstly increased and then decreased due to current coupling effect weakness by increasing distance of seeds. The calculated analytical levitation force results are not compatible with the experimental results without current coupling effect, but a well agreement is observed when the current coupling effect is taken into account in calculations. Also the MAFI method was tested with different dimensions of superconductors and the obtained results indicated the success of the proposed method. The maximum levitation force values obtained with MAFI method increased with increasing dimensions of HTS and PMs. Thus, one can say that the MAFI method is useful for the levitation force calculations between multi−seeded superconductors and PMGs with different dimensions and for different CHs. As a result, the analytical levitation force values obtained with the MAFI method are agree with the experimental levitation force sufficiently and this method can give fast calculation results without any divergence problem. This method can be thought as an alternative to the numerical calculation methods, having serious divergence problems for much amount and bigger size superconducting samples, therefore it will be useful to clarify bulk superconducting properties as supporter to the experimental studies.
•Single and two seeded YBCOs with different seed distance were fabricated.•Levitation force and Stiffness of seeded YBCOs were investigated.•Levitation force firstly increased then decreased with increasing distance of seeds.•The Frozen Image method was improved with size and hysteresis together.•Obtained analytical force values agree well with the experimental levitation force.
PDF
