189 research outputs found
Palladium-catalyzed difluoromethylation of heteroaryl chlorides, bromides and iodides.
A palladium-catalyzed difluoromethylation of a series of heteroaryl chlorides, bromides and iodides under mild conditions is described. A wide range of heteroaryl halides such as pyridyl, pyrimidyl, pyrazyl, funanyl, thienyl, pyazolyl, imidazolyl, thiazolyl, and oxazolyl halides were efficiently difluoromethylated, thus providing medicinal chemists an alternative choice for the preparation of drug candidates with the difluoromethylated heteroarene unit
Revisiting Scalarization in Multi-Task Learning: A Theoretical Perspective
Linear scalarization, i.e., combining all loss functions by a weighted sum,
has been the default choice in the literature of multi-task learning (MTL)
since its inception. In recent years, there is a surge of interest in
developing Specialized Multi-Task Optimizers (SMTOs) that treat MTL as a
multi-objective optimization problem. However, it remains open whether there is
a fundamental advantage of SMTOs over scalarization. In fact, heated debates
exist in the community comparing these two types of algorithms, mostly from an
empirical perspective. To approach the above question, in this paper, we
revisit scalarization from a theoretical perspective. We focus on linear MTL
models and study whether scalarization is capable of fully exploring the Pareto
front. Our findings reveal that, in contrast to recent works that claimed
empirical advantages of scalarization, scalarization is inherently incapable of
full exploration, especially for those Pareto optimal solutions that strike the
balanced trade-offs between multiple tasks. More concretely, when the model is
under-parametrized, we reveal a multi-surface structure of the feasible region
and identify necessary and sufficient conditions for full exploration. This
leads to the conclusion that scalarization is in general incapable of tracing
out the Pareto front. Our theoretical results partially answer the open
questions in Xin et al. (2021), and provide a more intuitive explanation on why
scalarization fails beyond non-convexity. We additionally perform experiments
on a real-world dataset using both scalarization and state-of-the-art SMTOs.
The experimental results not only corroborate our theoretical findings, but
also unveil the potential of SMTOs in finding balanced solutions, which cannot
be achieved by scalarization.Comment: Accepted at NeurIPS 202
Cavity Quantum Electrodynamics Effects with Nitrogen Vacancy Center Spins in Diamond and Microwave Resonators at Room Temperature
Cavity quantum electrodynamics (C-QED) effects, such as Rabi splitting, Rabi
oscillations and superradiance, have been demonstrated with nitrogen vacancy
center spins in diamond in microwave resonators at cryogenic temperature. In
this article we explore the possibility to realize strong collective coupling
and the resulting C-QED effects with ensembles of spins at room temperature.
Thermal excitation of the individual spins by the hot environment leads to
population of collective Dicke states with low symmetry and a reduced
collective spin-microwave field coupling. However, we show with simulations
that the thermal excitation can be compensated by spin-cooling via optical
pumping. The resulting population of Dicke states with higher symmetry implies
strong coupling with currently available high-quality resonators and enables
C-QED effects at room temperature with potential applications in quantum
sensing and quantum information processing.Comment: 9 pages, 6 figure
Structural basis for ubiquitylation by HOIL-1
The linear ubiquitin chain assembly complex synthesises linear Ub chains which constitute a binding and activation platform for components of the TNF signalling pathway. One of the components of LUBAC is the ubiquitin ligase HOIL-1 which has been shown to generate oxyester linkages on several proteins and on linear polysaccharides. We show that HOIL-1 activity requires linear tetra-Ub binding which enables HOIL-1 to mono-ubiquitylate linear Ub chains and polysaccharides. Furthermore, we describe the crystal structure of a C-terminal tandem domain construct of HOIL-1 comprising the IBR and RING2 domains. Interestingly, the structure reveals a unique bi-nuclear Zn-cluster which substitutes the second zinc finger of the canonical RING2 fold. We identify the C-terminal histidine of this bi-nuclear Zn-cluster as the catalytic base required for the ubiquitylation activity of HOIL-1. Our study suggests that the unique zinc-coordinating architecture of RING2 provides a binding platform for ubiquitylation targets
Synthesis, crystal structure and bioactivity of phenazine-1-carboxylic acylhydrazone derivatives
A phenazine-1-carboxylic acid intermediate was synthesized from the reaction of aniline and 2-bromo-3-nitro-benzoic acid. It was then esterified and reacted with hydrazine hydrate to afford phenazine-1-carboxylic hydrazine. Finally, 10 new hydrazone compounds 3a–3j were obtained by the condensation reaction of phenazine-1-carboxylic acid hydrazide and the respective aldehyde-containing compound. The structures were characterized by 1H and 13C NMR spectroscopy, MS and single crystal X-ray diffraction. The antitumor activity of the target compounds in vitro (HeLa and A549) was determined by thiazolyl blue tetrazolium bromide. The results showed that compound (E)-N′-(2-hydroxy-4-(2-(piperidine-1-yl) ethoxy) benzyl) phenazine-1-carbonyl hydrazide 3d exhibited good cytotoxic activity
Two-dimensional germanium islands with Dirac signature on Ag2Ge surface alloy
Two-dimensional (2D) Dirac materials have attracted intense research efforts
due to their promise for applications ranging from field-effect transistors and
low-power electronics to fault-tolerant quantum computation. One key challenge
is to fabricate 2D Dirac materials hosting Dirac electrons. Here, monolayer
germanene is successfully fabricated on a Ag2Ge surface alloy. Scanning
tunneling spectroscopy measurements revealed a linear energy dispersion
relation. The latter was supported by density functional theory calculations.
These results demonstrate that monolayer germanene can be realistically
fabricated on a Ag2Ge surface alloy. The finding opens the door to exploration
and study of 2D Dirac material physics and device applications
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