218 research outputs found
Shielding superconductors with thin films
Determining the optimal arrangement of superconducting layers to withstand
large amplitude AC magnetic fields is important for certain applications such
as superconducting radiofrequency cavities. In this paper, we evaluate the
shielding potential of the superconducting film/insulating film/superconductor
(SIS') structure, a configuration that could provide benefits in screening
large AC magnetic fields. After establishing that for high frequency magnetic
fields, flux penetration must be avoided, the superheating field of the
structure is calculated in the London limit both numerically and, for thin
films, analytically. For intermediate film thicknesses and realistic material
parameters we also solve numerically the Ginzburg-Landau equations. It is shown
that a small enhancement of the superheating field is possible, on the order of
a few percent, for the SIS' structure relative to a bulk superconductor of the
film material, if the materials and thicknesses are chosen appropriately.Comment: 7 pages, 5 figure
ABC-SysBio-approximate Bayesian computation in Python with GPU support.
Motivation: The growing field of systems biology has driven demand for flexible tools to model and simulate biological systems. Two established problems in the modeling of biological processes are model selection and the estimation of associated parameters. A number of statistical approaches, both frequentist and Bayesian, have been proposed to answer these questions. Results: Here we present a Python package, ABC-SysBio, that implements parameter inference and model selection for dynamical systems in an approximate Bayesian computation (ABC) framework. ABC-SysBio combines three algorithms: ABC rejection sampler, ABC SMC for parameter inference and ABC SMC for model selection. It is designed to work with models written in Systems Biology Markup Language (SBML). Deterministic and stochastic models can be analyzed in ABC-SysBio
The T210M Substitution in the HLA-a*02:01 gp100 Epitope Strongly Affects Overall Proteasomal Cleavage Site Usage and Antigen Processing
MHC class I-restricted epitopes, which carry a tumor-specific mutation resulting in improved MHC binding affinity, are preferred T cell receptor targets in innovative adoptive T cell therapies. However, T cell therapy requires efficient generation of the selected epitope. How such mutations may affect proteasome-mediated antigen processing has so far not been studied. Therefore, we analyzed by in vitro experiments the effect on antigen processing and recognition of a T210M exchange, which previously had been introduced into the melanoma gp100209–217tumor epitope to improve the HLA-A*02:01 binding and its immunogenicity. A quantitative analysis of the main steps of antigen processing shows that the T210M exchange affects proteasomal cleavage site usage within the mutgp100201–230 polypeptide, leading to the generation of an unique set of cleavage products. The T210M substitution qualitatively affects the proteasome-catalyzed generation of spliced and non-spliced peptides predicted to bind HLA-A or -B complexes. The T210M substitution also induces an enhanced production of the mutgp100209–217 epitope and its N-terminally extended peptides. The T210M exchange revealed no effect on ERAP1-mediated N-terminal trimming of the precursor peptides. However, mutant N-terminally extended peptides exhibited significantly increased HLA-A*02:01 binding affinity and elicited CD8+ T cell stimulation in vitro similar to the wtgp100209–217 epitope. Thus, our experiments demonstrate that amino acid exchanges within an epitope can result in the generation of an altered peptide pool with new antigenic peptides and in a wider CD8+ T cell response also towards N-terminally extended versions of the minimal epitope
Thermodynamic route of Nb3Sn nucleation: Role of oxygen
Intermetallic Nb3Sn alloys have long been believed to form through Sn
diffusion into Nb. However, our observations of significant oxygen content in
Nb3Sn prompted an investigation of alternative formation mechanisms. Through
experiments involving different oxide interfaces (clean HF-treated, native
oxidized, and anodized), we demonstrate a thermodynamic route that
fundamentally challenges the conventional Sn diffusion mechanism for Nb3Sn
nucleation. Our results highlight the critical involvement of a SnOx
intermediate phase. This new nucleation mechanism identifies the principles for
growth optimization and new synthesis of high-quality Nb3Sn superconductors
ABC-SysBio—approximate Bayesian computation in Python with GPU support
Motivation: The growing field of systems biology has driven demand for flexible tools to model and simulate biological systems. Two established problems in the modeling of biological processes are model selection and the estimation of associated parameters. A number of statistical approaches, both frequentist and Bayesian, have been proposed to answer these questions
Surface oxides, carbides, and impurities on RF superconducting Nb and Nb3Sn: A comprehensive analysis
Surface structures on radio-frequency (RF) superconductors are crucially
important in determining their interaction with the RF field. Here we
investigate the surface compositions, structural profiles, and valence
distributions of oxides, carbides, and impurities on niobium (Nb) and
niobium-tin (Nb3Sn) in situ under different processing conditions. We establish
the underlying mechanisms of vacuum baking and nitrogen processing in Nb and
demonstrate that carbide formation induced during high-temperature baking,
regardless of gas environment, determines subsequent oxide formation upon air
exposure or low-temperature baking, leading to modifications of the electron
population profile. Our findings support the combined contribution of surface
oxides and second-phase formation to the outcome of ultra-high vacuum baking
(oxygen processing) and nitrogen processing. Also, we observe that
vapor-diffused Nb3Sn contains thick metastable oxides, while electrochemically
synthesized Nb3Sn only has a thin oxide layer. Our findings reveal fundamental
mechanisms of baking and processing Nb and Nb3Sn surface structures for
high-performance superconducting RF and quantum application
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