2,860,326 research outputs found
Selective ethylene trimerization by titanium complexes bearing phenoxy-imine ligands: NMR and EPR Spectroscopic studies of the reaction intermediates
The catalyst systems (FI)TiCl₃/MAO (FI = phenoxyimine ligand with an additional aryl–O–CH₃ donor) display exceptionally high activity in selective ethylene trimerization. By means of NMR and EPR spectroscopy, the nature of the Ti species formed in the catalyst systems (FI)TiCl₃/MAO, (FI)TiCl₃/MMAO, and (FI)TiCl₃/AlR₃/[Ph₃C]⁺[B(C₆F₅)₄]⁻ (R = Me, Et, ⁱBu) has been studied. It was shown that outer-sphere ion pairs of the type [(FI)TiIVMe₂]⁺[A]⁻ ([A]− = [MeMAO]⁻, [MeMMAO]⁻, [B(C₆F₅)₄]⁻) are formed at the initial stage of the reaction of (FI)TiCl₃ with MAO, MMAO, and AlMe₃/[Ph₃C]⁺[B(C₆F₅)₄]⁻. These ion pairs further partially convert into TiIII and TiII species. In the systems (FI)TiCl₃/MAO and (FI)TiCl₃/AlMe₃/[Ph₃C]⁺[B(C₆F5)₄]⁻, complexes with the proposed structures (FI)TiIIIMe₂, (FI)TiIICl, and [(FI)TiII(S)]⁺[A]⁻ ([A]− = [MeMAO]⁻, [B(C₆F₅)4)]⁻, S = solvent, vacancy) were observed (concentrations of TiIII species was lower than those of the TiII congeners). In contrast, in the system (FI)TiCl₃/MMAO, the concentrations of TiIII species (ion pairs of the type [(FI)TiIII(μ-H)(μ-Cl)AlⁱBu₂]⁺[MeMMAO]⁻) were higher than those of the TiII counterparts (ion pairs [(FI)TiII(S)]⁺[MeMMAO]⁻). The system (FI)TiCl₃/MMAO displays lower activity and selectivity in 1-hexene formation, in comparison to (FI)TiCl₃/MAO, due to undesirable PE generation. Probably, TiII and TiIV ion pairs are those participating in ethylene trimerization
Manipulation of Majorana fermion, Andreev reflection and Josephson current on topological insulators
We study theoretically charge transport properties of normal metal (N) /
ferromagnet insulator (FI) / superconductor (S) junction and S/FI/S junction
formed on the surface of three-dimensional topological insulator (TI), where
chiral Majorana mode (CMM) exists at FI/S interface. We find that CMM generated
in N/FI/S and S/FI/S junctions are very sensitively controlled by the direction
of the magnetization in FI region. Especially, the current-phase
relation of Josephson current in S/FI/S junctions has a phase shift neither 0
nor , which can be tuned continuously by the component of
perpendicular to the interface
Fractional Imputation in Survey Sampling: A Comparative Review
Fractional imputation (FI) is a relatively new method of imputation for
handling item nonresponse in survey sampling. In FI, several imputed values
with their fractional weights are created for each missing item. Each
fractional weight represents the conditional probability of the imputed value
given the observed data, and the parameters in the conditional probabilities
are often computed by an iterative method such as EM algorithm. The underlying
model for FI can be fully parametric, semiparametric, or nonparametric,
depending on plausibility of assumptions and the data structure.
In this paper, we give an overview of FI, introduce key ideas and methods to
readers who are new to the FI literature, and highlight some new development.
We also provide guidance on practical implementation of FI and valid
inferential tools after imputation. We demonstrate the empirical performance of
FI with respect to multiple imputation using a pseudo finite population
generated from a sample in Monthly Retail Trade Survey in US Census Bureau.Comment: 26 pages, 2 figure
Exploring the Referral and Usage of Science Fiction in HCI Literature
Research on science fiction (sci-fi) in scientific publications has indicated
the usage of sci-fi stories, movies or shows to inspire novel Human-Computer
Interaction (HCI) research. Yet no studies have analysed sci-fi in a top-ranked
computer science conference at present. For that reason, we examine the CHI
main track for the presence and nature of sci-fi referrals in relationship to
HCI research. We search for six sci-fi terms in a dataset of 5812 CHI main
proceedings and code the context of 175 sci-fi referrals in 83 papers indexed
in the CHI main track. In our results, we categorize these papers into five
contemporary HCI research themes wherein sci-fi and HCI interconnect: 1)
Theoretical Design Research; 2) New Interactions; 3) Human-Body Modification or
Extension; 4) Human-Robot Interaction and Artificial Intelligence; and 5)
Visions of Computing and HCI. In conclusion, we discuss results and
implications located in the promising arena of sci-fi and HCI research.Comment: v1: 20 pages, 4 figures, 3 tables, HCI International 2018 accepted
submission v2: 20 pages, 4 figures, 3 tables, added link/doi for Springer
proceedin
Key mechanistic features of swelling and blistering of helium-ion-irradiated tungsten
Helium-ion-induced swelling and blistering of single-crystal tungsten is investigated using a Helium Ion Microscope for site-specific dose-controlled irradiation (at 25 keV) with analysis by Helium Ion Microscopy, Atomic Force Microscopy and Transmission Electron Microscopy (cross-sectioning by Focused Ion Beam milling). We show that the blister cavity forms at a depth close to the simulated helium peak and that nanobubbles coalesce to form nanocracks within the envelope of the ion stopping range, swelling the blister shell. These results provide the first direct experimental evidence for the interbubble fracture mechanism proposed in the framework of the gas pressure model for blister formation
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