Unleash electron transfer in C-H functionalization by mesoporous carbon-supported palladium interstitial catalysts

The functionalization of otherwise unreactive C–H bonds adds a new dimension to synthetic chemistry, yielding useful molecules for a range of applications. Arylation has emerged as an increasingly viable strategy for functionalization of heteroarenes which constitute an important class of structural moieties for organic materials. However, direct bisarylation of heteroarenes to enable aryl-heteroaryl-aryl bond formation remains a formidable challenge, due to the strong coordination between heteroatom of N or S and transitional metals. Here we report Pd interstitial nanocatalysts supported on ordered mesoporous carbon as catalysts for a direct and highly efficient bisarylation method for five-membered heteroarenes that allows for green and mild reaction conditions. Notably, in the absence of any base, ligands and phase transfer agents, high activity (turn-over frequency, TOF, up to 107 h−1) and selectivity (>99%) for the 2,5-bisarylation of five-membered heteroarenes are achieved in water. A combination of characterization reveals that the remarkable catalytic reactivity here is attributable to the parallel adsorption of heteroarene over Pd clusters, which breaks the barrier to electron transfer in traditional homogenous catalysis and creates dual electrophilic sites for aryl radicals and adsorbate at C2 and C5 positions. The d-band filling at Pd sites shows a linear relationship with activation entropy and catalytic activity. The ordered mesopores facilitate the absence of a mass transfer effect. These findings suggest alternative synthesis pathways for the design, synthesis and understanding of a large number of organic chemicals by ordered mesoporous carbon supported palladium catalysts.publishedVersio

GeoGauss: Strongly Consistent and Light-Coordinated OLTP for Geo-Replicated SQL Database

Multinational enterprises conduct global business that has a demand for geo-distributed transactional databases. Existing state-of-the-art databases adopt a sharded master-follower replication architecture. However, the single-master serving mode incurs massive cross-region writes from clients, and the sharded architecture requires multiple round-trip acknowledgments (e.g., 2PC) to ensure atomicity for cross-shard transactions. These limitations drive us to seek yet another design choice. In this paper, we propose a strongly consistent OLTP database GeoGauss with full replica multi-master architecture. To efficiently merge the updates from different master nodes, we propose a multi-master OCC that unifies data replication and concurrent transaction processing. By leveraging an epoch-based delta state merge rule and the optimistic asynchronous execution, GeoGauss ensures strong consistency with light-coordinated protocol and allows more concurrency with weak isolation, which are sufficient to meet our needs. Our geo-distributed experimental results show that GeoGauss achieves 7.06X higher throughput and 17.41X lower latency than the state-of-the-art geo-distributed database CockroachDB on the TPC-C benchmark

Lorentz force particle analyzer

International audienceA new contactless technique is presented for the detection of micron-sized insulating particles in the flow of an electrically conducting fluid. A transverse magnetic field brakes this flow and tends to become entrained in the flow direction by a Lorentz force, whose reaction force on the magnetic-field-generating system can be measured. The presence of insulating particles suspended in the fluid produce changes in this Lorentz force, generating pulses in it; these pulses enable the particles to be counted and sized. A two-dimensional numerical model that employs a moving mesh method demonstrates the measurement principle when such a particle is present. Two prototypes and a three-dimensional numerical model are used to demonstrate the feasibility of a Lorentz force particle analyzer (LFPA). The findings of this study conclude that such an LFPA, which offers contactless and on-line quantitative measurements, can be applied to an extensive range of applications. These applications include measurements of the cleanliness of high-temperature and aggressive molten metal, such as aluminum and steel alloys, and the clean manufacturing of semiconductors. Published by AIP Publishing

A note on the exponent set of primitive minimally strong digraphs

AbstractWe obtain a lower bound for e(n), the least integer (greater than or equal to 5) that is not the exponent of any nXn primitive, nearly reducible matrix. The main result is that under certain hypotheses about the distance between n and the nearest prime number we have that e(n)>n2⧸3

Structure of H-classes in the semigroup of nonnegative matrices

AbstractThis paper investigates the structure of the H-classes in the semigroup Nn of nonnegative matrices. We obtain two sets of equivalent conditions for any two matrices A,B to satisfy AHB in Nn. We establish a one-to-one and onto correspondence between the H-class HA and the group WA0 of the greatest cone independent submatrix A0 of A. We find WA0 can be made up from the groups of the connective submatrices of A0

On block cocyclic pairs of nonnegative matrices

AbstractIn this paper we introduce the concept of an (n1,…,nk) block cocyclic pair of nonnegative matrices which is a generalization of the concept of a cocyclic pair given by Johnson and Bru (Linear Algebra Appl. 141 (1990) (227–240), as well as of the concept of a block cocyclic pair given by Bru et al. (Linear Algebra Appl. 236 (1996) 231-143). Then we generalize the results of Johnson and Bru concerning the cocyclic pair and also the results of Bru et al. concerning the block cocyclic pair

Green's relations in the matrix semigroup Mn(S)

AbstractWe investigate Green's relations in the multiplicative semigroup of matrices Mn(S), where S is any strong ideal subset of R+. First we characterize the structures of R, L, D, and H classes in Mn(S). Our results generalize the corresponding known results in the semigroup Mn(R+). Then we prove that J = D in Mn(S∗), where S∗ is any strong ideal subset of R+ which has no elements less than 1 except 0