Quench characteristics of a stabilizer-free 2G HTS conductor

The prospect of medium/high field superconducting magnets using second generation (2G) HTS tapes is approaching reality with continued enhancement in the performance of these conductors. While the cryogenic stability and quench propagation are fundamental issues for the design and safe operation of superconducting magnets, there is insufficient understanding and experimental data for 2G HTS conductors, in particular for the high field scenario at low temperature (<77 K) where the current sharing regime is much larger than in low temperature superconductors. The present work includes a systematic characterization of the relevant thermal-electrical properties used for both qualitative discussion and numerical analysis. Direct measurements of one dimensional adiabatic quench initiation and propagation of a stabilizer-free 2G conductor have been carried out with spatial-temporal recording of temperature and voltage following the deposition of varying local heat pulses to the conductor at different temperatures between 30 K and 77 K carrying different transport currents. The minimum quench energy, and the heat generation in the minimum propagation zone (MPZ) have been obtained as a function of temperature and transport current. The results show quench features unique to HTS such as an increasing MPZ with transport current and higher quench energies at lower temperatures. The experimental results are discussed in the context of current sharing over a large temperature range

The development of high field magnets utilizing Bi-2212 wind & react insert coils

Wind & react Bi-2212 inserts have been manufactured and tested inside a wide-bore NbTi-Nb3Sn magnet providing a background field up to 20T at 4.2K. A pair of six-layer concentric coils both achieved critical currents of 350 A (JE = 200 A/mm2) in a 20T background field. A thicker 14-layer insert made from 119m of round wire had a critical quench current IQ of 287A (JE = 162 A/mm2) at the same field and contributed to a combined central field of 22.5 T. This is a record for a fully superconducting magnet at 4.2 K. The 14-layer coil, equipped with an external protective shunt, was used for an extensive series of quench measurements and endured >150 quenches without damage. Minimum quench energies were found to be in the range of 200-500mJ in background fields of 15-20T when the coil carried 70-95% of its critical quench current

One-step growth and shaping by a dual plasma reactor of diamond nanocones arrays for the assembling of stable cold cathodes

Arrays of conical-shaped nanodiamond structures are formed on silicon substrate by a single-step CVD process from CH4/H-2 mixtures. The formation of these nanocones has been found to depend on interplay between growing and etching during the CVD process carried out in a dual-mode MW/RF plasma reactor. Morphology and structure of the conical-like systems can be controlled by varying the process parameters, and have been investigated by scanning electron microscopy (SEM), reflection high energy electron diffraction (RHEED) and micro-Raman spectroscopy. The Field Emission (FE) properties of different diamond nanocones arrays have been investigated and compared with those of analogous systems in order to assess the feasibility of the present nano-materials as electron emitters for cold cathodes. The FE behavior is discussed taking into account the structure of the different diamond nanocones

All-thiol-stabilized Ag-44 and Au12Ag32 nanoparticles with single-crystal structures

通讯作者地址: Zheng, NF (通讯作者) Xiamen Univ, Collaborat Innovat Ctr Chem Energy Mat, State Key Lab Phys Chem Solid Surfaces, Xiamen 361005, Peoples R China.Noble metal nanoparticles stabilized by organic ligands are important for applications in assembly, site-specific bioconjugate labelling and sensing, drug delivery and medical therapy, molecular recognition and molecular electronics, and catalysis. Here we report crystal structures and theoretical analysis of three Ag-44(SR)(30) and three Au12Ag32(SR)(30) inter-metallic nanoclusters stabilized with fluorinated arylthiols (SR = SPhF, SPhF2 or SPhCF3). The nanocluster forms a Keplerate solid of concentric icosahedral and dodecahedral atom shells, protected by six Ag-2(SR)(5) units. Positive counterions in the crystal indicate a high negative charge of 4(-) per nanoparticle, and density functional theory calculations explain the stability as an 18-electron superatom shell closure in the metal core. Highly featured optical absorption spectra in the ultraviolet-visible region are analysed using time-dependent density functional perturbation theory. This work forms a basis for further understanding, engineering and controlling of stability as well as electronic and optical properties of these novel nanomaterials.Ministry of Science and Technology of China 2011CB932403 ,2009CB930703 , National Nature Science Foundation of China 21131005 ,21021061 ,20925103 , Academy of Finlan

Structural Evolution of Atomically Precise Thiolated Bimetallic [Au12+nCu32(SR)(30+n)](4-) (n=0, 2, 4, 6) Nanoclusters

通讯作者地址: Zheng, NF (通讯作者)A series of all-thiol stabilized bimetallic Au-Cu nanoclusters, [Au12+nCu32(SR)(30+n)](4-) (n = 0, 2, 4, 6 and SR = SPhCF3), are successfully synthesized and characterized by X-ray single-crystal analysis and density functional theory (DFT) calculations. Each cluster consists of a Keplerate two-shell Au-12@Cu-20 core protected by (6 - n) units of Cu-2(SR)(5) and n units of Cu2Au(SR)(6) (n = 0, 2, 4, 6) motifs on its surface. The size and structural evolution of the clusters is atomically controlled by the Au precursors and countercations used in the syntheses. The clusters exhibit similar optical absorption properties that are not dependent on the number of surface Cu2Au(SR)(6) units. Although DFT suggests an electronic structure with an 18-electron superatom shell closure, the clusters display different thermal stabilities. [Au12+nCu32(SR)(30+n)](4-) clusters with n = 0 and 2 are more stable than those with n = 4 and 6. Moreover, an oxidation product of the clusters, [Au13Cu12(SR)(20)](4-), is structurally identified to gain insight into how the clusters are oxidized.MOST of China 2011CB932403 NSFC of China 21131005 21390390 21333008 Academy of Finlan

Ligand-Stabilized Au13Cux (x=2, 4, 8) Bimetallic Nanoclusters: Ligand Engineering to Control the Exposure of Metal Sites

通讯作者地址: Zheng, NF (通讯作者) Xiamen Univ, Collaborat Innovat Ctr Chem Energy Mat, State Key Lab Phys Chem Solid Surfaces, Xiamen 361005, Peoples R China.Three novel bimetallic Au-Cu nanoclusters stabilized by a mixed layer of thiolate and phosphine ligands bearing pyridyl groups are synthesized and fully characterized by X-ray single crystal analysis and density functional theory computations. The three clusters have an icosahedral Au-13 core face-capped by two, four, and eight Cu atoms, respectively. All face-capping Cu atoms in the clusters are triply coordinated by thiolate or pyridyl groups. The surface ligands control the exposure of Au sites in the clusters. In the case of the Au13Cu8 cluster, the presence of 12 2-pyridylthiolate ligands still leaves open space for catalysis. All the 3 clusters are 8-electron superatoms displaying optical gaps of 1.8-1.9 eV. The thermal decomposition studies suggest that the selective release of organic ligands from the clusters is possible.MOST of China 2011CB932403 ,2011CB201301 ,2009CB930703 , NSFC 21227001 ,21131005 ,21021061 ,20925103 ,20923004 , Fundamental Research Funds for the Central Universities 201012104

Nanotechnology, governance, and public deliberation: What role for the Social Sciences?

In this article we argue that nanotechnology represents an extraordinary opportunity to build in a robust role for the social sciences in a technology that remains at an early, and hence undetermined, stage of development. We examine policy dynamics in both the United States and United Kingdom aimed at both opening up, and closing down, the role of the social sciences in nanotechnologies. We then set out a prospective agenda for the social sciences and its potential in the future shaping of nanotechnology research and innovation processes. The emergent, undetermined nature of nanotechnologies calls for an open, experimental, and interdisciplinary model of social science research

Phytoextraction as a tool for green chemistry

The unique chemical and physical properties of metals mean that they are extensively utilized by industry in a huge variety of applications, including electronics, materials, industrial catalysts and chemicals. The increased consumer demand from a growing population worldwide with rising aspirations for a better life has resulted in concerns over the security of supply and accessibility of these valuable elements. As such, there is a growing need to develop alternative methods to recover them from waste repositories, current or historic, both for hazard avoidance and potentially, as a new source of metals for industry. Phytoextraction (the use of plants for the recovery of metals from waste repositories) is a green and novel technique for metal recovery, which, if done with the goal of resource supply rather than hazard mitigation, is termed “phytomining”. The ability for plants to form metallic nanoparticles as a consequence of phytoextraction could make the recovered metal ideally suited for utilization in green chemical technologies, such as catalysis. This review focuses on a multidisciplinary approach to elemental sustainability and highlights important aspects of metal lifecycle analysis, metal waste sources (including mine tailings), phytoextraction and potential green chemical applications that may result from the integration of these approaches

Nanogel as a Novel Platform for Smart Drug Delivery System

Abstract Nanogels are one of the techniques in nanotechnology which has been most prevalent in successful medication delivery inside the body and in addition topical treatment. The nanoparticulate frameworks are materials having under 100 nm in any event in one measurement. The quest for this review article is to briefly portray the current advancement of nanogel medication delivery framework as far as medication loading and swelling of medication from nanogels. A few crosslinking techniques have been utilized as a part of the best approach to frame the hydrogel network structures, which can be characterized in two noteworthy gatherings of artificially and physically-instigated crosslinking. Nanogels based materials have high medication loading limit, biocompatibility and biodegradability which are the key focuses to plan and medication delivery framework adequately. Recently different types of nanogel along with the synthetic procedure, mechanism of drug release from nanogel carrier and applications are mainly focused. Keywords: nanogels, classification, mechanism of drug release, applications Cite This Article: Nilesh S. Zarekar, Vishal J. Lingayat, and Vishal V. Pande, "Nanogel as a Novel Platform for Smart Drug Delivery Syste