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Superconducting screening on different length scales in high-quality bulk MgB2 superconductor
High quality bulk MgB2 exhibit a structure of voids and agglomeration of
crystals on different length-scales. Because of this, the superconducting
currents percolate between the voids in the ensuing structure. Magnetic
measurements reveal that the superconducting currents circulate on at least
three different length-scales, of ~1 micrometre, ~10 micrometre and whole of
the sample (~millimetre). Each of these screenings contributes to the measured
irreversible magnetic moment (Dm). The analysis of the field dependence of Dm
for samples of subsequently decreasing size showed that the critical current
obtained using the simple critical state model is erroneous. This leads to the
artefact of the sample size-dependent critical current and irreversibility
field. Our data analysis enables the separation of the contribution of each of
the screening currents to Dm. The field dependence of each of the currents
follows a stretched exponential form. The currents flowing around whole of the
sample give a dominant contribution to Dm in the intermediate fields (1T < H <
4T at 20K) and they can be used to obtain the value of Jc from critical state
model, which corresponds to the transport Jc
The induced representations of Brauer algebra and the Clebsch-Gordan coefficients of SO(n)
Induced representations of Brauer algebra from with are discussed. The induction coefficients
(IDCs) or the outer-product reduction coefficients (ORCs) of with up to a normalization factor are
derived by using the linear equation method. Weyl tableaus for the
corresponding Gel'fand basis of SO(n) are defined. The assimilation method for
obtaining CG coefficients of SO(n) in the Gel'fand basis for no modification
rule involved couplings from IDCs of Brauer algebra are proposed. Some
isoscalar factors of for the resulting irrep
with
$\sum\limits_{i=1}^{4}\lambda_{i}\leq .Comment: 48 pages latex, submitted to Journal of Phys.
Nodeless superconductivity in IrPtTe with strong spin-orbital coupling
The thermal conductivity of superconductor IrPtTe
( = 0.05) single crystal with strong spin-orbital coupling was measured down
to 50 mK. The residual linear term is negligible in zero magnetic
field. In low magnetic field, shows a slow field dependence. These
results demonstrate that the superconducting gap of IrPtTe is
nodeless, and the pairing symmetry is likely conventional s-wave, despite the
existence of strong spin-orbital coupling and a quantum critical point.Comment: 5 pages, 4 figure
Current Path Properties of the Transport Anisotropy at Filling Factor 9/2
To establish the presence and orientation of the proposed striped phase in
ultra-high mobility 2D electron systems at filling factor 9/2, current path
transport properties are determined by varying the separation and allignment of
current and voltage contacts. Contacts alligned orthogonal to the proposed
intrinsic striped phase produce voltages consistent with current spreading
along the stripes; current driven along the proposed stripe direction results
in voltages consistent with channeling along the stripes. Direct comparison is
made to current spreading/channeling properties of artificially induced 1D
charge modulated systems, which indicates the 9/2 direction.Comment: 10 pages, 4 figure
Microscopic origin of local moments in a zinc-doped high- superconductor
The formation of a local moment around a zinc impurity in the high-
cuprate superconductors is studied within the framework of the bosonic
resonating-valence-bond (RVB) description of the model. A topological
origin of the local moment has been shown based on the phase string effect in
the bosonic RVB theory. It is found that such an moment distributes
near the zinc in a form of staggered magnetic moments at the copper sites. The
corresponding magnetic properties, including NMR spin relaxation rate, uniform
spin susceptibility, and dynamic spin susceptibility, etc., calculated based on
the theory, are consistent with the experimental measurements. Our work
suggests that the zinc substitution in the cuprates provide an important
experimental evidence for the RVB nature of local physics in the original (zinc
free) state.Comment: The topological reason of local moment formation is given. One figure
is adde
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Highly Stable Luminous "snakes" from CsPbX3 Perovskite Nanocrystals Anchored on Amine-Coated Silica Nanowires
CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) are known for their exceptional optoelectronic properties, yet the material's instability toward polar solvents, heat, or UV irradiation greatly limits its further applications. Herein, an efficient in situ growing strategy has been developed to give highly stable perovskite NC composites (abbreviated CsPbX3@CA-SiO2) by anchoring CsPbX3 NCs onto silica nanowires (NWs), which effectively depresses the optical degradation of their photoluminescence (PL) and enhances stability. The preparation of surface-functionalized serpentine silica NWs is realized by a sol-gel process involving hydrolysis of a mixture of tetraethyl orthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES), and trimethoxy(octadecyl)silane (TMODS) in a water/oil emulsion. The serpentine NWs are formed via an anisotropic growth with lengths up to 8 μm. The free amino groups are employed as surface ligands for growing perovskite NCs, yielding distributed monodisperse NCs (∼8 nm) around the NW matrix. The emission wavelength is tunable by simple variation of the halide compositions (CsPbX3, X = Cl, Br, or I), and the composites demonstrate a high photoluminescence quantum yield (PLQY 32-69%). Additionally, we have demonstrated the composites CsPbX3@CA-SiO2 can be self-woven to form a porous 3D hierarchical NWs membrane, giving rise to a superhydrophobic surface with hierarchical micro/nano structural features. The resulting composites exhibit high stability toward water, heat, and UV irradiation. This work elucidates an effective strategy to incorporate perovskite nanocrystals onto functional matrices as multifunctional stable light sources
Investigation of iterative image reconstruction in three-dimensional optoacoustic tomography
Iterative image reconstruction algorithms for optoacoustic tomography (OAT),
also known as photoacoustic tomography, have the ability to improve image
quality over analytic algorithms due to their ability to incorporate accurate
models of the imaging physics, instrument response, and measurement noise.
However, to date, there have been few reported attempts to employ advanced
iterative image reconstruction algorithms for improving image quality in
three-dimensional (3D) OAT. In this work, we implement and investigate two
iterative image reconstruction methods for use with a 3D OAT small animal
imager: namely, a penalized least-squares (PLS) method employing a quadratic
smoothness penalty and a PLS method employing a total variation norm penalty.
The reconstruction algorithms employ accurate models of the ultrasonic
transducer impulse responses. Experimental data sets are employed to compare
the performances of the iterative reconstruction algorithms to that of a 3D
filtered backprojection (FBP) algorithm. By use of quantitative measures of
image quality, we demonstrate that the iterative reconstruction algorithms can
mitigate image artifacts and preserve spatial resolution more effectively than
FBP algorithms. These features suggest that the use of advanced image
reconstruction algorithms can improve the effectiveness of 3D OAT while
reducing the amount of data required for biomedical applications
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