Electromagnetic behaviour and thermal stability of a conduction-cooled, no-insulated 2G-HTS coil at intermediate temperatures

The electromagnetic and thermal properties of a double pancake coil made of second generation high temperature superconductor, 2G-HTS, have been studied. The coil was wound with no-insulation between turns (NI coil) and was later impregnated with epoxy resin and glued to a copper support plate. The coil was thermally anchored to the cryocooler cold finger and cooled by conduction. After several thermal cycles no degradation of its superconducting properties was observed. The coil was operated under high vacuum and high currents (up to 400 A in steady conditions) at different temperatures in the range between 5 K and 77 K, with special focus on the analysis above 30 K. The charge and discharge characteristics, and the experimentally measured and numerically estimated critical currents, have been studied. The different loss contributions during current ramp and the thermal contact conductance between different parts of the double pancake coil have been measured. The implications of these two factors on the thermal stability and the behaviour of the whole cryogenic system are discussed

Improved copper–epoxy adhesion by laser micro- and nano-structuring of copper surface for thermal applications

The objective of this work is the enhancement of metal-to-metal bonding to provide high thermal conductivity together with electrical insulation, to be used as heat sinks at room and cryo-genic temperatures. High thermal conductive metal (copper) and epoxy resin (Stycast 2850FT) were used in this study, with the latter also providing the required electrical insulation. The copper surface was irradiated with laser to induce micro- and nano-patterned structures that result in an improvement of the adhesion between the epoxy and the copper. Thus, copper-to-copper bonding strength was characterized by means of mechanical tensile shear tests. The effect of the laser processing on the thermal conductivity properties of the Cu/epoxy/Cu joint at different temperatures, from 10 to 300 K, is also reported. Using adequate laser parameters, it is possible to obtain high bonding strength values limited by cohesive epoxy fracture, together with good thermal conductivity at ambient and cryogenic temperatures. © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Large enhancement of thermal conductance at ambient and cryogenic temperatures by laser remelting of plasma-sprayed Al2O3 coatings on Cu

Joints of high thermal contact conductance and electrical insulation have been obtained by coating copper supports with thin alumina (Al2O3) layers (of 140–150 µm thickness). This has been achieved by a combination of plasma spraying process and the subsequent coating remelting by a near-Infrared (n-IR) laser. With a proper optimization of the laser processing conditions, it is possible to transform the metastable ¿-Al2O3 phase of the as-sprayed coatings to stable a-Al2O3, and to achieve denser alumina coatings. This results in a large enhancement of the thermal conductance of the joints, enabling their application as heat sinks at cryogenic and ambient temperatures. The process proposed in this work is scalable for the formation of alumina coatings on large metallic pieces of complex geometries. © 202

Dimensionality of collective pinning in 2H-NbSe2 single crystals

Quantum Matter and Optic

Properties and antibacterial activity of MnFe2O4 nanoparticles obtained by pulsed laser ablation in liquid

In this study, MnFe2O4 nanoparticles (NPs) were fabricated via pulsed laser ablation in liquid. Chemical and structural composition, microstructure, magnetic and antibacterial properties were characterized. Spinel was found as the main crystalline phase, while Fe2O3 and Mn2O3 were observed as the major secondary phases, all identified by X-ray diffractometry (XRD). Observation by Transmission Electron Microscopy (TEM) indicated that most of the nanoparticles were spherical in shape and found in agglomerates, most likely because of their magnetic nature. Moreover, Fast Fourier Transform of selective area electron diffraction patterns pointed at the existence of crystalline particles. The coercive field (Hc) and saturation magnetization (Ms) values determined for these NPs were found to increase with decreasing temperature. Their antibacterial properties were evaluated using the viable bacteria counting technique (colony) for MnFe2O4 concentrations of 100 and 300 μg/mL with Bacillus subtilis, Salmonella typhimurium, Pseudomonas aeruginosa, Klebsiella pneumoniae and Escherichia coli strains

Detailed study of the ac susceptibility of Sr2RuO4 in oriented magnetic fields

We have investigated the ac susceptibility of the spin triplet superconductor Sr$_2$RuO$_4$ as a function of magnetic field in various directions at temperatures down to 60 mK. We have focused on the in-plane field configuration (polar angle $\theta \simeq 90^{\circ}$), which is a prerequisite for inducing multiple superconducting phases in Sr$_2$RuO$_4$. We have found that the previous attribution of a pronounced feature in the ac susceptibility to the second superconducting transition itself is not in accord with recent measurements of the thermal conductivity or of the specific heat. We propose that the pronounced feature is a consequence of additional involvement of vortex pinning originating from the second superconducting transition.Comment: Accepted for publication in Phys. Rev.

Inter- and Intragranular Effects in Superconducting Compacted Platinum Powders

Compacted platinum powders exhibit a sharp onset of diamagnetic screening at $T \simeq 1.9$ mK in zero magnetic field in all samples investigated. This sharp onset is interpreted in terms of the intragranular transition into the superconducting state. At lower temperatures, the magnetic ac susceptibility strongly depends on the ac field amplitude and reflects the small intergranular critical current density $j_{c}$. This critical current density shows a strong dependence on the packing fraction f of the granular samples. Surprisingly, $j_{c}$ increases significantly with decreasing f ($j_{c}(B=0, T=0) \simeq 0.07$ A/cm$^{2}$ for f = 0.67 and $j_{c}(B=0, T=0) \simeq 0.8$ A/cm$^{2}$ for f = 0.50). The temperature dependence of $j_{c}$ shows strong positive curvature over a wide temperature range for both samples. The phase diagrams of inter- and intragranular superconductivity for different samples indicate that the granular structure might play the key role for an understanding of the origin of superconductivity in the platinum compacts.Comment: 11 pages including 9 figures. To appear in Phys. Rev. B in Nov. 0

A study of supercooling of the disordered vortex phase via minor hysteresis loops in 2H-NbSe_2

We report on the observation of novel features in the minor hysteresis loops in a clean crystal of NbSe_2 which displays a peak effect. The observed behavior can be explained in terms of a supercooling of the disordered vortex phase while cooling the superconductor in a field. Also, the extent of spatial order in a flux line lattice formed in ascending fields is different from (and larger than) that in the descending fields below the peak position of the peak effect; this is attributed to unequal degree of annealing of the state induced by a change of field in the two cases.Comment: 5 pages of text + 6 figures, submitted to Phys. Rev.

Flux pinning in high-Tc superconductors under transport current cycles

Giordano, J.L. Departamento de Ciencias de la Ingenierıa, Universidad de Talca,Chile

Warehousing for manufacturing improvment „ATN”.

M.Ramazanova Noliktavas sistēmas pilnveidošana uzņēmumā „ATN”. Bakalaura darbs bez pielikumiem sastāv no 69 lapaspusēm, 11 attēliem, 6 tabulām, 4 formulām, ka arī no 3 pielikumiem un 23 informācijas avotiem. Bakalaura darba temats ir „Noliktavas sistēmas pilnveidošana uzņēmumā „ATN”. Bakalaura darba mērķis ir izanalizēt uzņēmuma noliktavas sistēmas funkcionēšanu saimniecības procesā, pamatojoties uz teorētiskām atziņām, izcelt trūkumus un izstrādāt priekšlikumus SIA „ATN” noliktavas sistēmas pilnveidošanai. Bakalaura darba mērķa sasniegšanai pielietotas literatūras referatīva analīze, matemātiskā, grafiska un anketēšanas metodes. Bakalaura darbs sastāv no četrām daļām, pirmajā nodaļā tiek apskatīta kravas/pasūtījuma organizēšana un nodošana uz noliktavu un ar to saistītas problēmas. Mīnētas arī galvenās izmaksas noliktavu uzturēšana uzņēmumā un noliktavas iekārtošanas un uzturēšanas motivācijas iemesli. Otrā nodaļa ir par kravas sagatavošanu, transportēšanu un piegādi klientam. Trešajā nodaļā tiek aplūkota noliktavas sistēmas ievešana uzņēmumā, tāpat ir noskaidrots, cik svarīgi preču īpašniekam novērtēt glabāja¬mo preču vidējo daudzumu, līdz ar to novēršot noliktavas iespējamās dīk¬stāves vai tās telpu deficītu. Novērtējums balstās uz kritiskā punkta ana¬līzi. Ceturtajā, pēdēja nodaļā tiek aprakstīts un analizēts uzņēmums. Ir dots klasificējums uzņēmuma noliktavām, veikti nepieciešamie aprēķini, balstoties uz teorētisko daļu un pielietojot grafisko metodi, noteikti apgrozījuma un preču apjoma minimumi. Autore novērtē, cik lielā mērā uzņēmums savā darbībā saskārās ar ekonomiskiem, tiesiskiem, sociāliem un kultūras aspektiem, ka arī izdara SWOT analīzi. Tātad, darba teorētiskajā daļā tika apskatīts, kā šos jautājumus (problēmas) var risināt teorētiskā skatījumā. Darba praktiskajā daļā tika imitētas problēmas reālā uzņēmumā, kurā darba teorētiskajā daļā apskatītie jautājumi tika risināti praktiskā skatījumā. Risinājuma rezultātā tika iegūts priekšstats par situāciju uzņēmumā attiecībā uz izvirzītajām problēmām. Bakalaura darba beigās autore sniedz kopavilkumu un priekšlikumus par SIA „ATN” noliktavas sistēmas pilnveidošanai, kuri dod iespēju pārskatīt esošo noliktavas saimniecību no noliktavas loģistikas un to uzlabošanas iespējas skatījuma. Šis darbs var kļūt par piemēru līdzīgai izpētei citos uzņēmumos. Pētījuma avoti: vispārēja un speciālā literatūra par noliktavu organizēšanu un loģistiku, materiāli no Interneta tīkla, SIA „ATN” nepublicētie materiāli, autores veiktās aptaujas rezultāti.M.Ramazanova “ATN” enterprise's warehouse systems improvement Bachelor paper consists of 69 pages, 11 images, 6 tables, 4 formulas, as well as 3 appendixes and 23 information sources. Bachelor paper's object is “ATN” enterprise's warehouse systems improvement. Bachelor paper's target is to analyze enterprise's warehouse systems, that functions in usual work process, on the basis of the epistemology, and also to exposure the shortcomings and to work out some proposals for SIA „ATN” system improving. To achieve the target of bachelor paper lecture analysis, mathematic, graphic conducting of people survey were used. Bachelor paper consists of four parts. First part is about cargo/order organization, shipping to warehouse and related problems. There you can find major costs of stock keeping, establishing warehouse and motivation for maintenance. The second part is about cargo processing and its shipping to the customer. The third part is about integrating warehouse system in company structure, the aspects of how is important for owner to evaluate stock quantity, thus helping to eliminate downtime of warehouse or shortfall of premises. Evaluation is based on analysis of critical point. Fourth part is about describing and analyzing the company. There is a classification of manufacture warehouse is given, and on the basis of theoretical part and using the graphic method value’s minimum of turnover is revealed. Necessary calculations also are made. Author has evaluated how much manufacture in it’s work process inculcate economical, lawgiving, social and cultural aspects and work out the SWOT analyzing. In result of theoretical part of work the decision is found on theoretical view. Practical part of current work real manufacture’s problems referred and decided. In result of the decision the concept of situation in manufacture acquired attaching to the problems mentioned. In the end of the bachelor paper its author gives a summary and some proposals for improving the warehouse system of SIA “ATN”. Those proposals give a possibility to revise the present warehouse service from the warehousing logistics point of view. The current work can serve as an example to a similar research for another enterprises. SIA „ATN” warehouse systems improvement, which gives a possibility to overview current warehouse establishment from the logistic and improving view. The current work can serve as an example to a similar research for another enterprises. Research sources: general and special literature of warehousing logistic and organizing, Internet sources materials, SIA „ATN” internal documents and materials of author’s researches