The brain is a dynamic structure with the extracellular space (ECS) taking up almost a quarter of its volume. Signalling molecules, neurotransmitters and nutrients transit via the ECS, which constitutes a key microenvironment for cellular communication and the clearance of toxic metabolites. The spatial organization of the ECS varies during sleep, development and aging and is probably altered in neuropsychiatric and degenerative diseases, as inferred from electron microscopy and macroscopic biophysical investigations. Here we show an approach to directly observe the local ECS structures and rheology in brain tissue using super-resolution imaging. We inject single-walled carbon nanotubes into rat cerebroventricles and follow the near-infrared emission of individual nanotubes as they diffuse inside the ECS for tens of minutes in acute slices. Because of the interplay between the nanotube geometry and the ECS local environment, we can extract information about the dimensions and local viscosity of the ECS. We find a striking diversity of ECS dimensions down to 40 nm, and as well as of local viscosity values. Moreover, by chemically altering the extracellular matrix of the brains of live animals before nanotube injection, we reveal that the rheological properties of the ECS are affected, but these alterations are local and inhomogeneous at the nanoscale.

The recently discovered iron-based superconductors are potential candidates for high-field magnet applications. However, the critical current densities (Jc) of iron-based superconducting wires remain far below the level needed for practical applications. Here, we show that the transport Jc of Ba1−xKxFe2As2/Ag tapes is significantly enhanced by the combination process of cold flat rolling and uniaxial pressing. At 4.2 K, Jc exceeds the practical level of 105 A/cm2 in magnetic fields up to 6 T. The Jc-H curve shows extremely small magnetic field dependence and maintains a high value of 8.6 × 104 A/cm2 in 10 T. These are the highest values reported so far for iron-based superconducting wires. Hardness measurements and microstructure investigations reveal that the superior Jc in our samples is due to the high core density, more textured grains, and a change in the microcrack structure. These results indicate that iron-based superconductors are very promising for high magnetic field applications.

The intrinsic near-infrared photoluminescence observed in long single-walled carbon nanotubes is known to be quenched in ultrashort nanotubes due to their tiny size as compared to the exciton diffusion length in these materials (>100 nm). Here, we show that intense photoluminescence can be created in ultrashort nanotubes (∼40 nm length) upon incorporation of exciton-trapping sp defect sites. Using super-resolution photoluminescence imaging at <25 nm resolution, we directly show the preferential localization of excitons at the nanotube ends, which separate by less than 40 nm and behave as independent emitters. This unexpected observation opens the possibility to synthesize fluorescent ultrashort nanotubes-a goal that has been long thought impossible-for bioimaging applications, where bright near-infrared photoluminescence and small size are highly desirable, and for quantum information science, where high quality and well-controlled near-infrared single photon emitters are needed.

The isolation of individual boron nitride nanotubes (BNNTs) in aqueous phases has been achieved for the first time from raw materials based on the combination of peptide wrapping with a sonication procedure. Atomic force microscopic observations revealed the representative height and length of individual BNNTs. Fluorescence and infrared absorption spectra suggested the strong pi-pi interactions between BNNTs and the peptide. The absorption maxima of BNNTs were significantly blue-shifted from 200 nm for the original BNNTs to 193 nm. The modulation of the BNNT band gap with peptide wrapping promises potential applications of the peptide/BNNT complexes to various nanotechnologies.

We demonstrate that Ta sheathed SmO 1-x F x FeAs wires were successfully fabricated by the powder-in-tube (PIT) method for the first time. Structural analysis by mean of x-ray diffraction shows that the main phase of SmO 1-x F x FeAs was obtained by this synthesis method. The transition temperature of the SmO 0.65 F 0.35 FeAs wires was confirmed to be as high as 52 K. Based on magnetization measurements, it is found that a globe current can flow on macroscopic sample dimensions with J c of ~3.9×10 3 A/cm 2 at 5 K and self field, while a high J c about 2×10 5 A/cm 2 is observed within the grains, suggesting that a significant improvement in the globle J c is possible. It should be noted that the J c exhibits a very weak field dependence behavior. Furthermore, the upper critical fields (H c2 ) determined according to the Werthamer-Helfand-Hohenberg formula are (T= 0 K) ≈ 120 T, indicating a very encouraging application of the new superconductors. 1 NdFeAsO 0.9 F 0.1 superconductor from local and global measurements. Preprint at<

The discovery of iron-based superconductors, the first non-cuprate family of superconductors with T c above 40 K, has stimulated enormous interest in the field of superconductivity since last year. This remarkable discovery not only offers the opportunity to study the origin of superconductivity, but also opens up new possibilities of application. One of the most fascinating and useful properties of superconductors is the ability to carry electrical current with zero resistance. Here, we report the successful fabrication of dense Sr 0.6 K 0.4 Fe 2 As 2 superconducting wires using the ex situ powder-in-tube (PIT) method and demonstrate a transport J c of 3750 A cm −2 at 4.2 K. The connectivity of grains was improved upon doping (Ag or Pb) and the transport property of Sr 0.6 K 0.4 Fe 2 As 2 wires was enhanced for a lead-doped sample, especially in low fields, to a best I c of 37.5 A. Our results suggest that grain boundary properties require much greater attention when looking for applications of the high-T c iron-based superconductors.

Abstract:We report the realization of grain alignment in Sn-added Sr 1-x K x Fe 2 As 2 superconducting tapes with Fe sheath prepared by ex-situ powder-in-tube method. At 4.2 K, high transport critical current densities J c of 2.5×10 4 A/cm 2 (I c = 180 A) in self-field and 3.5×10 3 A/cm 2 (I c = 25.5 A) in 10 T have been measured. These values are the highest ever reported so far for Fe-based superconducting wires and tapes. We believe the superior J c in our tape samples are due to well textured grains and strengthened intergrain coupling achieved by Sn addition. Our results demonstrated an encouraging prospect for application of iron based superconductors.* Author to whom correspondence should be addressed; E-mail: ywma@mail.iee.ac.cn 2 The discovery of superconductivity in LaFeAsO 1-x F x and related compounds, with a higher transition temperature, T c of ~55 K, has triggered great research interests from both theoretical and applied aspects [1][2][3][4][5][6][7]. In addition to T c , these iron based superconductors were reported to have a very high upper critical field, B c2 , and low B c2 anisotropy, making them potential candidates for a wide array of future applications [8][9][10][11]. The early results indicate that the global critical current is limited by intergrain currents over the grain boundaries in polycrystalline bulk and wires [12][13][14][15][16][17][18]. Recent experiments revealed that high-angle grain boundary largely deteriorates critical current density J c in Ba(Fe 1-x Co x ) 2 As 2 bicrystals [19,20]. These results suggest that the discovered iron based superconductors are exhibiting weak link grain boundary behavior similar to high-T c cuprate superconductors. An effective method to overcome the weak link problem is to engineering textured grains in iron based superconductors to minimize deterioration of the critical current density across high-angle grain boundaries.Recently Co-doped Ba122 coated conductors have been grown by several groups utilizing the existing YBCO coated conductor technology and have reached a self-field J c over 1 MA/cm 2 [21][22][23]. However, the technology has the shortcoming of low production rate, complexity and high equipment cost. Furthermore, it is hard to be applied to the volatile elements in iron based superconductors such as alkali metals doped 122 phase and F doped 1111 phase. Cold deformation process is a well-developed technique used to enhance the degree of grain alignment and critical current density of Bi2223 superconductors [24,25]. It is unsurprising that this technique may also be suitable for iron based superconductors too. Besides grain alignment, adding metallic elements is another effective way to improve the grain connectivity of the iron based superconductors. For example, we have reported that the superconducting properties of the 122 phase iron based superconductor can be significantly increased by Ag or Pb addition [26,27]. Recently Togano et al [28] reported further improvement in transport critical current in the Ba122 wires with A...

Nb-sheathed Sr0.6K0.4Fe2As2 superconducting wires have been fabricated using the powder-in-tube (PIT) method for the first time and the superconducting properties of the wires have been investigated. The transition temperature (Tc) of the Sr0.6K0.4Fe2As2 wires is confirmed to be as high as 35.3 K. Most importantly, Sr0.6K0.4Fe2As2 wires exhibit a very weak Jc-field dependence behavior even the temperature is very close to Tc. The upper critical field Hc2(0) value can exceed 140 T, surpassing those of MgB2 and all the low temperature superconductors. Such high Hc2 and superior Jc-field performance make the 122 phase SrKFeAs wire conductors a powerful competitor potentially useful in very high field applications.Comment: 15 pages, 6 figure