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Single-crystal superconductors of the general formula (LRE)–Ba–Cu–O (light rare earth, LRE = Nd, Sm, Eu and Gd) have considerable potential for engineering applications because of their ability to trap magnetic fields significantly higher than those achievable with permanent magnets. But the lack of a process by which these materials can be fabricated reliably and economically in the form of large single grains has severely hindered their development. We report a practical processing method for the fabrication in air of single-crystal (RE)BCO. The technique is economical and offers considerable freedom in terms of the processing parameters and reproducibility in growth of oriented single grains. The process is based primarily on the development of a new type of generic seed crystal that can effectively promote the epitaxial nucleation of any (RE)BCO system, and secondly on suppressing the formation of RE–Ba solid solution in a controlled manner within large grains processed in air.

Transport measurements performed on a cross-sectional slice prepared from a bulk GdBa 2 Cu 3 O 7- x -Ag single-grain superconductor of 25 mm in diameter are described and the results presented. The sample, which was fabricated via the buffer-assisted top-seeded infiltration growth process, was capable of trapping a maximum magnetic field of ~ 1 T at 77 K. Transport measurements on superconducting, bulk single-grain RE-Ba-Cu-O [(RE)BCO] samples are generally very challenging due to their large critical current densities and poor mechanical properties. We present a straightforward and reliable approach to prepare reproducibly specimens from the parent single grain and results of transport property measurements on these samples in a commercial Physical Property Measurement System (PPMS). Critical current densities determined via magnetic and transport measurements are compared and discussed.

A new melt processing route for the fabrication of large grain Gd-Ba-Cu-O (GdBCO) bulk superconductors has been developed based on the use of novel GdBa4Cu3O8−δ (Gd-143) and GdBa6Cu3O10−δ (Gd-163) precursor compositions. The new processing route enables the fabrication of large single grains from precursor powders that contain high concentrations of Ba. The superconducting properties and microstructures of GdBCO single grains with extra Ba fabricated via this new processing route are reported. Most importantly, the possible formation of a new form of Gd1+xBa2−xCu3O7−δ solid solution (Gd-123ss) with x < 0 in single grains fabricated from the Ba-rich precursor are discussed for the first time based on the superconducting, chemical, and structural properties of the large GdBCO grains.

We have applied the seeded infiltration and growth (IG) technique to the processing of samples containing Ag in an attempt to fabricate Ag-doped Y-Ba-Cu-O (YBCO) bulk superconductors with enhanced mechanical properties. The IG technique has been used successfully to grow bulk Ag-doped YBCO superconductors of up to 25 mm in diameter in the form of single grains. The distribution of Ag in the parent Y-123 matrix fabricated by the IG technique is observed to be at least as uniform as that in samples grown by conventional top seeded melt growth (TSMG). Fine Y-211 particles were observed to be embedded within the Y-123 matrix for the IG processed samples, leading to a high critical current density, Jc, of over 70 kA/cm2 at 77.3 K in self-field. The distribution of Y-211 in the IG sample microstructure, however, is inhomogeneous, which leads to a variation in the spatial distribution of Jc throughout the bulk matrix. A maximum-trapped field of around 0.43 T at 1.2 mm above the sample surface (i.e. including 0.7 mm for the sensor mould thickness) is observed at liquid nitrogen temperature, despite the relatively small grain size of the sample (20 mm diameter × 7 mm thickness).

Trapped fields of over 20 T are, in principle, achievable in bulk, single-grain high temperature cuprate superconductors. The principle barriers to realizing such performance are, firstly, the large tensile stresses that develop during the magnetization of such trapped-field magnets as a result of the Lorentz force, which lead to brittle fracture of these ceramic-like materials at high fields and, secondly, catastrophic thermal instabilities as a result of flux movement during magnetization. Moreover, for a batch of samples nominally fabricated identically, the statistical nature of the failure mechanism means the best performance (i.e. trapped fields of over 17 T) cannot be attained reliably. The magnetization process, particularly to higher fields, also often damages the samples such that they cannot repeatedly trap high fields following subsequent magnetization. In this study, we report the sequential trapping of magnetic fields of ~ 17 T, achieving 16.8 T at 26 K initially and 17.6 T at 22.5 K subsequently, in a stack of two Ag-doped GdBa2Cu3O7-{\\delta} bulk superconductor composites of diameter 24 mm reinforced with (1) stainless-steel laminations, and (2) shrink-fit stainless steel rings. A trapped field of 17.6 T is, in fact, comparable with the highest trapped fields reported to date for bulk superconducting magnets of any mechanical and chemical composition, and this was achieved using the first composite stack to be fabricated by this technique.

A trapped magnetic field of greater than 3 T has been achieved in a single grain GdBa2Cu3O7-{\\delta} (GdBaCuO) bulk superconductor of diameter 30 mm by employing pulsed field magnetisation (PFM). The magnet system is portable and operates at temperatures between 50 K and 60 K. Flux jump behaviour was observed consistently during magnetisation when the applied pulsed field, Ba, exceeded a critical value (e.g. 3.78 T at 60 K). A sharp dBa/dt is essential to this phenomenon. This flux jump behaviour enables the magnetic flux to penetrate fully to the centre of the bulk superconductor, resulting in full magnetization of the sample without requiring an applied field as large as that predicted by the Bean model. We show that this flux jump behaviour can occur over a wide range of fields and temperatures, and that it can be exploited in a practical quasi-permanent magnet system.

Single grain, (RE)BCO bulk superconductors in large or complicated geometries are required for a variety of potential applications, such as motors and generators and magnetic shielding devices. As a result, top, multi-seeded, melt growth (TMSMG) has been investigated over the past two years in an attempt to enlarge the size of (RE)BCO single grains specifically for such applications. Of these multi-seeding techniques, so-called bridge seeding provides the best alignment of two seeds in a single grain growth process. Here we report, for the first time, the successful growth of YBCO using a special, 45{\\deg} - 45{\\deg}, arrangement of bridge-seeds. The superconducting properties, including trapped field, of the multi-seeded YBCO grains have been measured for different bridge lengths of the 45{\\deg}- 45{\\deg} bridge-seeds. The boundaries at the impinging growth front and the growth features of the top, multi-seeded surface and cross-section of the multi-seeded, samples have been analysed using optical microscopy. The results suggest that an impurity-free boundary between the two seeds of each leg of the bridge-seed can form when 45{\\deg}- 45{\\deg} bridge-seeds are used to enlarge the size of YBCO grains.

The ability of large grain, REBa\\(_{2}\\)Cu\\(_{3}\\)O\\(_{7-\\delta}\\) [(RE)BCO; RE = rare earth] bulk superconductors to trap magnetic field is determined by their critical current. With high trapped fields, however, bulk samples are subject to a relatively large Lorentz force, and their performance is limited primarily by their tensile strength. Consequently, sample reinforcement is the key to performance improvement in these technologically important materials. In this work, we report a trapped field of 17.6 T, the largest reported to date, in a stack of two, silver-doped GdBCO superconducting bulk samples, each of diameter 25 mm, fabricated by top-seeded melt growth (TSMG) and reinforced with shrink-fit stainless steel. This sample preparation technique has the advantage of being relatively straightforward and inexpensive to implement and offers the prospect of easy access to portable, high magnetic fields without any requirement for a sustaining current source.

Large RNAs and ribonucleoprotein complexes have powerful therapeutic potential, but effective cell-targeted delivery tools are limited. Aptamers that internalize into target cells can deliver siRNAs (<15 kDa, 19–21 nt/strand). We demonstrate a modular nanostructure for cellular delivery of large, functional RNA payloads (50–80 kDa, 175–250 nt) by aptamers that recognize multiple human B cell cancer lines and transferrin receptor-expressing cells. Fluorogenic RNA reporter payloads enable accelerated testing of platform designs and rapid evaluation of assembly and internalization. Modularity is demonstrated by swapping in different targeting and payload aptamers. Both modules internalize into leukemic B cell lines and remained colocalized within endosomes. Fluorescence from internalized RNA persists for ≥2 h, suggesting a sizable window for aptamer payloads to exert influence upon targeted cells. This demonstration of aptamer-mediated, cell-internalizing delivery of large RNAs with retention of functional structure raises the possibility of manipulating endosomes and cells by delivering large aptamers and regulatory RNAs. Large RNAs and ribonucleoprotein complexes have shown potential as novel therapeutic agents, but their targeted delivery to cells is still challenging. Here the authors present a modular aptamer nanostructure for intracellular delivery of RNAs up to 250 nucleotides to cancer cells.

The rates of sexually transmitted infections (STIs) continue to rise across Australia among 16- to 29-year-olds. Timely testing is needed to reduce transmission, but sexual health clinics are at capacity. This demand, coupled with barriers to getting tested faced by young people, has led to web-based services as a pragmatic solution. However, for young people to use these services, they must be acceptable, attractive, and usable. Social marketing principles combined with end user engagement can be used to guide the development of a web-based service and create a marketing strategy to attract them to the service. Working closely with end users and guided by social marketing, this project explored messaging, design elements (imagery), and promotional strategies that will support high usage of a web-based STI/blood-borne virus (BBV) testing service for young people in Victoria, Australia. Young people were recruited to participate in half-day workshops via youth organizations and targeted Meta (Facebook/Instagram) advertisements. An initial web-based survey was deployed to inform workshop content. Workshops were held in metropolitan, outer metropolitan, and regional Victoria. Young people were presented with a range of \"image territories\" developed by a social marketing firm and social marketing messages that were informed by the literature on communicating health messages. Participants discussed the feelings and reactions evoked by the content. Data collected through mixed methods (transcribed notes, audio recording, and physical outputs) were thematically analyzed to understand features of messaging and imagery that would attract young people to use the service. A total of 45 people completed the initial survey with 17 participating in focus group workshops (metropolitan: n=8, outer metropolitan: n=6, and regional: n=3). Young people preferred messages that highlight the functional benefits (confidential, affordable, and accessible) of a web-based service and include professional imagery and logos that elicit trust. Young people indicated that the service should be promoted through digital communications (eg, dating apps and social media), with endorsement from government or other recognized institutions, and via word-of-mouth communications. This study has highlighted the value of applying social marketing theory with end user engagement in developing a web-based STI/BBV testing service. Through the voices of young people, we have established the foundations to inform the design and marketing for Victoria's first publicly funded web-based STI/BBV testing clinic. Future research will measure the reach and efficacy of social marketing, and how this service complements existing services in increasing STI/BBV testing uptake among young Victorians.