The present investigation focuses on methods to further improve the Jc values of disk-shaped bulk MgB2 superconductors by optimizing the sintering conditions. We prepared two sets of bulk MgB2 ...material from commercial high-purity powders of Mg metal and amorphous B using a single-step solid-state reaction process. To optimize the sintering time, a set of samples was sintered at 775 °C with sintering duration ranging between 1 and 10 h (pure Ar atmosphere). A second set of samples was produced similarly at 775, 780, 785, 795, 800 and 805 °C (3 h, pure argon atmosphere). X-ray diffraction analysis showed that both sets of samples were single phase MgB2. Magnetization measurements confirmed a sharp superconducting transition with Tc,onset ≈ 38.2 K–38.8 K. The critical current density (Jc) values for MgB2 samples produced for 1 h were the highest in all processed materials, i.e., the high Jc value of 270,000 A/cm2 and 125,000 A/cm2 (20 K, self-field and 1 T) were achieved in the sample produced at 775 °C, without any additional doping. In contrast, the second series of samples clearly indicated that at 805 °C (3 h) the highest Jc of 245,000 A/cm2 and 110,000 A/cm2 (20 K, self-field and 1 T) were achieved. AFM and EBSD observations indicated that largest amount of fine grains do exist in the sample sintered at 775 °C, but the narrowest distribution of grains does exist in the sample sintered at 800 °C. The present results clearly demonstrate a strong relation between the microstructure and the pinning performance. The optimization of the sintering conditions is crucial to improve the performance of bulk MgB2 samples.
•We had successfully improved the performance of sintered, pure bulk MgB2 materials.•EBSD observations clarified that the grain sizes are in the 100–500 nm range.•The high Jc value at 20 K, 0 T and 1 T are 2.70 × 105 A/cm2 and 1.25 × 105 A/cm2.•Samples sintered at 800 °C and 805 °C exhibit the largest amount of small grains.•The grain boundary pinning is dominant in pure, bulk MgB2 materials.
Neutrons are powerful tools for investigating the structure and properties of materials used in science and technology. Recently, laser-driven neutron sources (LDNS) have attracted the attention of ...different communities, from science to industry, in a variety of applications, including radiography, spectroscopy, security, and medicine. However, the laser-driven ion acceleration mechanism for neutron generation and for establishing the scaling law on the neutron yield is essential to improve the feasibility of LDNS. In this paper, we report the mechanism that accelerates ions with spectra suitable for neutron generation. We show that the neutron yield increases with the fourth power of the laser intensity, resulting in the neutron generation of3×1011in4πat a maximum, with1.1×1019Wcm−2, 900 J, 1.5 ps lasers. By installing a “hand-size” moderator, which is specially designed for the LDNS, it is demonstrated that the efficient generation of epithermal (0.1–100 eV) neutrons enables the single-shot analysis of composite materials by neutron resonance transmission analysis (NRTA). We achieve the energy resolution of 2.3% for 5.19-eV neutrons 1.8 m downstream of the LDNS. This leads to the analysis of elements and isotopes within sub-μstimes and allows for high-speed nondestructive inspection.
We have succeeded in getting 1 H NMR signals at 47.8 MHz (1.12 T) from a single-sided HTS bulk magnet activated by pulse-field magnetization. Diffusion NMR using an inhomogeneous outer field was also ...demonstrated on the surface. This kind of NMR relaxometry can not get the information of molecular structures, which conventional NMR using a homogeneous magnetic field can acquire. However, the relaxation of nuclear spin magnetization is still observable. A higher magnetic field gradient generated by the small HTS bulk magnet, 67 T/m at a 5 mm distance from the surface, can be effectively used to observe the self-diffusion coefficient of liquids in higher spatial resolution, 44 μm. The easy accessibility to the strong field gradient is one of the unique properties ofcompact HTS bulk magnets. We believe that single-sided (unilateral) diffusion NMR will become the new application of HTS bulk magnets.
Laser-driven ion accelerators have the advantages of compact size, high density, and short bunch duration over conventional accelerators. Nevertheless, it is still challenging to simultaneously ...enhance the yield and quality of laser-driven ion beams for practical applications. Here we propose a scheme to address this challenge via the use of emerging multi-petawatt lasers and a density-modulated target. The density-modulated target permits its ions to be uniformly accelerated as a dense block by laser radiation pressure. In addition, the beam quality of the accelerated ions is remarkably improved by embedding the target in a thick enough substrate, which suppresses hot electron refluxing and thus alleviates plasma heating. Particle-in-cell simulations demonstrate that almost all ions in a solid-density plasma of a few microns can be uniformly accelerated to about 25% of the speed of light by a laser pulse at an intensity around 10(22) W/cm(2). The resulting dense block of energetic ions may drive fusion ignition and more generally create matter with unprecedented high energy density.
Bulk high-temperature superconductors (HTSs) enable the opportunity to develop several unique applications in electrical power that are not feasible with superconducting or normal wires. The large ...current carrying capacity and low thermal conductivity of the HTSs allows relatively short lengths to carry large currents to low-temperature devices without introducing heat to the device. Such current leads can dramatically reduce the refrigeration requirements for devices such as SMES. The HTSs make a relatively sharp transition to a highly resistive state when the critical current density is exceeded, and this effect has suggested their use for resistive fault current limiters. The bulk HTSs may also take the form of large single-grained superconductors within which circulating currents may flow at large current density without loss. They are capable of developing magnetizations, similar to that of permanent magnets, but with much larger magnetic fields. In this case, they may be used as field-trapping components. Applications in this case include brushless synchronous motors, laboratory magnets, magnetic separation, and magnetron sputtering. The bulk HTSs may also be used as diamagnetic objects in magnetic circuits to provide new types of power devices. One application that uses this effect is an inductive fault current limiters, in which the HTS shields an iron core in an inductive circuit until some current level is exceeded. This transition increases the component from low impedance to high impedance. The diamagnetic property may also be used to create low-loss magnetic bearings for use in efficient energy-storage flywheel devices or sensitive instrumentation. The combination of diamagnetic shielding and field trapping has suggested their use in motor designs analogous to hysteresis motors. Laboratory prototypes for all of these devices have been constructed and tested, and in some cases the devices have been field tested in actual power systems. Improvements in HTS properties, such as flux pinning, mechanical strength, and the ability to grow large grains, have greatly improved the economics of applications that use bulk HTS.
The structures and functional activities of metalloproteinases from snake venoms have been widely studied because of the importance of these molecules in envenomation. Batroxase, which is a ...metalloproteinase isolated from Bothrops atrox (Pará) snake venom, was obtained by gel filtration and anion exchange chromatography. The enzyme is a single protein chain composed of 202 amino acid residues with a molecular mass of 22.9kDa, as determined by mass spectrometry analysis, showing an isoelectric point of 7.5. The primary sequence analysis indicates that the proteinase contains a zinc ligand motif (HELGHNLGISH) and a sequence C164I165M166 motif that is associated with a “Met-turn” structure. The protein lacks N-glycosylation sites and contains seven half cystine residues, six of which are conserved as pairs to form disulfide bridges. The three-dimensional structure of Batroxase was modeled based on the crystal structure of BmooMPα-I from Bothrops moojeni. The model revealed that the zinc binding site has a high structural similarity to the binding site of other metalloproteinases. Batroxase presented weak hemorrhagic activity, with a MHD of 10μg, and was able to hydrolyze extracellular matrix components, such as type IV collagen and fibronectin. The toxin cleaves both α and β-chains of the fibrinogen molecule, and it can be inhibited by EDTA, EGTA and β-mercaptoethanol. Batroxase was able to dissolve fibrin clots independently of plasminogen activation. These results demonstrate that Batroxase is a zinc-dependent hemorrhagic metalloproteinase with fibrin(ogen)olytic and thrombolytic activity.
► Batroxase is a weakly hemorrhagic metalloproteinase. ► Represent 1.2% (w/w) of the crude snake venom, pI 7.5 and molecular mass 22.9kDa. ► Batroxase presented thrombolytic and fibrin(ogen)olytic activity. ► Batroxase was characterized as a PIb class SVMP. ► Clinical use as fibrinolytic agent for the treatment of coagulation disorders.
•PIV technique successfully applied to He II noisy film boiling.•Large-scale boiling bubble is not a single bubble, but is composed of an infinite number of micro-bubbles.•In response to growth and ...collapse of bubble mass, a standing alternating flow is induced.•Three kinds of steady underlying flow components, thermal counter flow, plume and entrainment.
Noisy film boiling in nearly saturated He II caused by heating from a flat plate heater placed horizontally was investigated by applying visualization method and PIV (Particle Image Velocimetry) using hydrogen-deuterium solid particles as tracer particles. The images taken by a high-speed video to be used for the PIV were also used for visualization study, and the appearance of generation, growth and collapse processes of mass of tiny bubbles caused due to boiling and the qualitative aspect of the flow field could be understood. By the application of the PIV technique, the frequency of growth and collapse of bubble mass and the flow velocity field formed in the surrounding He II were measured. The output from the PIV was further examined separately for the time average and the time fluctuating components, and in each, independent flow components were identified. It was shown that the steady flow components include the plume above the heater and the entrainment towards the plume as well as the thermal counterflow. And the standing radially alternating flow is induced by repeatedly growing and collapsing bubble mass as a fluctuating flow. Their superposition forms the surrounding flow field.
•Mixed RE ions in ternary bulk RE-123 system are enhancing superconducting properties.•The superconductors prepared in air are able to step up to the industrial fabrication.•(Gd0.33,Y0.13,Er0.53)-123 ...sample exhibits the highest Jc and trapped field values.•FESEM identifies fine RE-211 particles responsible for the high Jc and TF values.•EDX analysis shows that these particles are rich in Er.
Ternary bulk REBa2Cu3Oy superconductors processed via oxygen-controlled melt growth (OCMG) have exhibited superior superconducting properties with respect to binary and single systems. However, the OCMG process is rather complicated, expensive, and difficult to scale-up into industrial level. To overcome these issues, we have studied the yet unexplored ternary bulk (Gd,Y,Er)Ba2Cu3Oy “(Gd,Y,Er)-123″ system, fabricated via trendy infiltration growth (IG) process. We studied the effect of varying Y-211 and Er-211 ratio (Gd: Y: Er = 0.33: 0.33-x: 0.33+x, where x = 0, 0.05, 0.1, 0.15 and 0.2) in the preform on the final superconducting properties and microstructure. We succeeded to fabricate (Gd,Y,Er)-123 single-grain bulks (diameter – 20 mm). The critical current density (Jc) and trapped field increased proportionally with the increased amount of Er-211 in the preform. Hall-probe measurements showed that the best bulk (x = 0.2) exhibited trapped field of 0.53 T at 77 K (applied field of 1 T) and self-field Jc values of 238 and 63 kA/cm2 at 50 and 77 K, respectively. FE-SEM micrographs revealed formation of two different types of secondary phases in the matrix (small and large). EDX analysis showed that the smaller 211 particles were Er-rich, while the larger ones were an irregular mixture of three RE-211 phases.
The hard X-ray Kβ″ emission line shows sensitivity with respect to a wide range of cation–ligand coordination, which we investigate in the cases of GeO2 and TiO2 on the basis of ab initio spectral ...calculations on amorphous and crystalline structures. In compressed amorphous GeO2, the sampling of a large number of instantaneous coordination polyhedra from an ab initio molecular dynamics trajectory reveals that the functional relation between the Kβ″ shift and coordination is close to linear between 4-fold and 7-fold coordination. A similar sensitivity of the Kβ″ emission line exists in the coordination range between six and nine of crystalline high-pressure TiO2 polymorphs. Our results demonstrate the potential of the Kβ″ emission line in research on the structure of amorphous oxide material.
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