Defect conformal blocks from Appell functions

We develop a group theoretical formalism to study correlation functions in defect conformal field theory, with multiple insertions of bulk and defect fields. This formalism is applied to construct the defect conformal blocks for three-point functions of scalar fields. Starting from a configuration with one bulk and one defect field, for which the correlation function is determined by conformal symmetry, we explore two possibilities, adding either one additional defect or bulk field. In both cases it is possible to express the blocks in terms of classical hypergeometric functions, though the case of two bulk and one defect field requires Appell’s function F4.

Structural and electronic properties of SnO2 doped with non-metal elements

Crystal structure and electronic properties of SnO2 doped with non-metal elements (F, S, C, B, and N) were studied using first-principles calculations. The theoretical results show that doping of non-metal elements cannot change the structure of SnO2 but result in a slight expansion of the lattice volume. The most obvious finding from the analysis is that F-doped SnO2 has the lowest defect binding energy. The doping with B and S introduced additional defect energy levels within the forbidden bandgap, which improved the crystal conductivity. The Fermi level shifts up due to the doping with B, F, and S, while the Fermi level of SnO2 doped with C or N has crossed the impurity level. The Fermi level of F-doped SnO2 is inside the conduction band, and the doped crystal possesses metallicity. The optical properties of SnO2 crystals doped with non-metal elements were analyzed and calculated. The SnO2 crystal doped with F had the highest reflectivity in the infrared region, and the reflectance of the crystals doped with N, C, S, and B decreased sequentially. Based on this theoretical calculations, F-doped SnO2 is found to be the best photoelectric material for preparing low-emissivity coatings.

Annihilation of Highly-Charged Topological Defects

We studied numerically external stimuli enforced annihilation of a pair of daughter nematic topological defect (TD) assemblies bearing a relatively strong topological charge |m|=3/2. A Landau- de Gennes phenomenological approach in terms of tensor nematic order parameter was used in an effectively two-dimensional Cartesian coordinate system, where spatial variations along the z-axis were neglected. A pair of {m=3/2,m=−3/2} was enforced by an appropriate surface anchoring field, mimicking an experimental sample realization using the atomic force microscope (AFM) scribing method. Furthermore, defects were confined within a rectangular boundary that imposes strong tangential anchoring. This setup enabled complex and counter-intuitive annihilation processes on varying relevant parameters. We present two qualitatively different annihilation paths, where we either gradually reduced the relative surface anchoring field importance or increased an external in-plane spatially homogeneous electric field E. The creation and depinning of additional defect pairs {12,−12} mediated the annihilation in such a geometry. Furthermore, we illustrate the absorption of TDs by sharp edges of the confining boundary, accompanied by m=±1/4↔∓1/4 winding reversal of edge singularities, and also E-driven zero-dimensional to one-dimensional defect core transformation.

Study of Structural and Electronic properties of Non-metal Elements doped SnO2

The crystal structure, electronic properties of F, S, C, B and N doped SnO2 were studied with the First-Principle Method. The theoretical results show that doping of non-metal elements did not change the structure of SnO2 but result in slight lattice volume expansion. The dope of the non-metal elements of B, F, and S cause the Fermi level to shift upThe most obvious finding to emerge from the analysis is that F-doped SnO2 has the lowest defect binding energy, stable crystal structure, and the easiest doping. The B, F, and S element doped SnO2 can modulate the fermi level. The doping of the B and S elements introduced additional defect energy levels to appear within the forbidden band-gap，which improved the crystal conductivity. Analysis of the energy band structure of SnO2 crystals doped with C and N elements shows that the Fermi level has crossed the impurity level. The Fermi level of F doped SnO2 is inside the conduction band, and the doped crystal has metallicity. The optical properties of SnO2 crystals doped with non-metallic elements were analyzed and calculated. The SnO2 crystal doped with F element had the highest reflectivity in the infrared region, and the reflectance of the crystals doped with N, C, S, and B elements decreased sequentially. Based on this theoretical calculations, F doped SnO2 is found to be the best photoelectric material for for preparing low-e thin film.

Fabrication of Defect-Free P84® Polyimide Hollow Fiber for Gas Separation: Pathway to Formation of Optimized Structure

The elimination of the additional defect healing post-treatment step in asymmetric hollow fiber manufacturing would result in a significant reduction in membrane production cost. However, obtaining integrally skinned polymeric asymmetric hollow fiber membranes with an ultrathin and defect-free selective layer is quite challenging. In this study, P84® asymmetric hollow fiber membranes with a highly thin (~56 nm) defect-free skin were successfully fabricated by fine tuning the dope composition and spinning parameters using volatile additive (tetrahydrofuran, THF) as key parameters. An extensive experimental and theoretical study of the influence of volatile THF addition on the solubility parameter of the N-methylpyrrolidone/THF solvent mixture was performed. Although THF itself is not a solvent for P84®, in a mixture with a good solvent for the polymer, like N-Methyl-2-pyrrolidone (NMP), it can be dissolved at high THF concentrations (NMP/THF ratio > 0.52). The as-spun fibers had a reproducible ideal CO2/N2 selectivity of 40, and a CO2 permeance of 23 GPU at 35 °C. The fiber production can be scaled-up with retention of the selectivity.

A trimeric Rab7 GEF controls NPC1-dependent lysosomal cholesterol export

SummaryCholesterol import in mammalian cells is mediated by the LDL receptor pathway. Here, using an endogenous cholesterol reporter in a genome-wide CRISPR screen we identify >70 genes involved in LDL-cholesterol import. We characterise C18orf8 as a core component of the mammalian Mon1-Ccz1 guanidine exchange factor (GEF) for Rab7, required for complex stability and function. C18orf8-deficient cells lack Rab7 activation and show severe defects in late endosome morphology and endosomal LDL trafficking, resulting in cellular cholesterol deficiency. Unexpectedly, free cholesterol accumulates within swollen lysosomes, suggesting a critical additional defect in lysosomal cholesterol export. We find that active Rab7 interacts with the NPC1 cholesterol transporter and licenses lysosomal cholesterol export. This process is abolished in C18orf8-, Ccz1- and Mon1A/B-deficient cells and restored by a constitutively active Rab7. The trimeric Mon1-Ccz1-C18orf8 (MCC) GEF therefore plays a central role in cellular cholesterol homeostasis coordinating Rab7 activation, endosomal LDL trafficking and NPC1-dependent lysosomal cholesterol export.

On the Origin of Charge Compensation in Aluminum-Implanted n-Type 4H-SiC by Analysis of Hall Effect Measurements

Aluminum implanted 4H-SiC often shows an unexpected increase of the free hole density at elevated temperatures in Hall Effect measurements. Here we show that this phenomenon cannot solely be traced down to the Hall scattering factor and the presence of excited acceptor states. It is necessary to assume an additional defect center in the lower half of the band gap with ionization energies higher than that of aluminum to explain this behavior. Therefore, we investigated ion-implanted square van-der-Pauw samples with Hall Effect and complementary SIMS measurements. An analysis of the data using the neutrality equation reveals compensation ratios of 20 % to 90 %, depending on the aluminum concentration and the concentration of the deep defect center of up to 50 % of the doping.

Approach to UK SMR Component Design

The United Kingdom (UK) Small Modular Reactor (SMR) is being developed by a Rolls-Royce led consortium to provide a market driven, affordable, low carbon energy, generation capability. The UK SMR is a Pressurised Water Reactor (PWR) design based on proven technology with a high level of safety achieved through multiple active and passive systems. This paper presents the approach that has been taken in the early design phases of the pressure vessels for the UK SMR. It considers the key design principles e.g. standardisation, simplification and design for manufacture, inspection and assembly which are being applied to enable the cost and lead-time reductions which are necessary for the UK SMR to be a viable alternative to larger conventional nuclear plants. The Reactor Pressure Vessel (RPV) is used as an example to illustrate some of the key design requirements which need to be addressed. Nuclear components are required to be designed and constructed to standards which are commensurate with the significance of the safety functions which they perform. This paper covers the practice established in the UK of designing to Incredibility of Failure for those components with catastrophic failure modes such as the RPV. It describes the additional features including more stringent materials specification and testing, additional defect tolerance studies and the qualification of manufacturing inspections which need to be addressed in the design to satisfy the high reliability claim.

Comparison and Characterization of Acid Functionalization of Multi Walled Carbon Nanotubes Using Various Methods

Functionalization of multiwalled carbon nanotubes (MWCNT) is one of several methods used to improve the compatibility of CNT. Even though acid functionalised method is effective, the strong acids such as H2SO4/HNO3 were normally employed and long hours of sonication is used to disperse the CNTs in the solution frequently can damage the nanotube, thus limiting their great performance as mechanical and electrical reinforcements. Here we are reporting comparison between three methods used in acid functionalized treatments of MWCNT. The first method, MWCNT was functionalized using ultra sonication water bath and followed by reflux (Method A). The second method, MWCNT was functionalized using ultrasonication water bath only for 2 hours (Method B). Finally, the third method MWCNT was functionalized using ultrasonication water bath only for 6 hours (Method C). Raman spectroscopy measurements were used to examine the general relationship between the chemical treatment and the amount of non-graphitic carbon. Electron microscopy analysis revealed that MWCNT functionalized using Method C suffered the highest degree degradation such as, nanotube shortening and additional defect generation in the graphitic network. Method B proved to be the most effective for this aim.