Feature matching aims at generating correspondences across images, which is widely used in many computer vision tasks. Although considerable progress has been made on feature descriptors and fast matching for initial correspondence hypotheses, selecting good ones from them is still challenging and critical to the overall performance. More importantly, existing methods often take a long computational time, limiting their use in real-time applications. This paper attempts to separate true correspondences from false ones at high speed. We term the proposed method (GMS) grid-based motion Statistics, which incorporates the smoothness constraint into a statistic framework for separation and uses a grid-based implementation for fast calculation. GMS is robust to various challenging image changes, involving in viewpoint, scale, and rotation. It is also fast, e.g., take only 1 or 2 ms in a single CPU thread, even when 50K correspondences are processed. This has important implications for real-time applications. What's more, we show that incorporating GMS into the classic feature matching and epipolar geometry estimation pipeline can significantly boost the overall performance. Finally, we integrate GMS into the well-known ORB-SLAM system for monocular initialization, resulting in a significant improvement. Keywords Feature matching • Epipolar geometry • Visual SLAM • Structure-from-motion • GMS 1 Introduction Feature matching is one of the most fundamental problems in the computer vision community. It aims to generate correspondences across different views of an object or scene, which is widely used in many vision tasks such as structurefrom-motion (Schonberger and Frahm 2016) and Visual SLAM (Davison et al. 2007; Mur-Artal et al. 2015). Typical solutions rely on feature detectors (Harris and stephens 1988), descriptors (Lowe 2004), and matchers (Muja and Communicated by Jiri Matas.

A strategy is reported for controlling the architecture of poly­(disulfide)­s by ring-opening polymerization. Aryl thiol initiators shift the ring–chain equilibrium to yield cyclic polymers, while alkyl thiols favor linear ones. Control over polymerization enables synthesis of large polymers (630 kDa) and catalytic depolymerization to recycle monomers. This work provides a new avenue to create dynamic covalent polymers with controlled geometry and length, allowing better characterization of structure–property relationships to expand their materials potentials.

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Coffee consumption in China has seen a significant rise in recent years. This study seeks to explore the determinants of coffee consumption in China with a specific focus on fair trade coffee. In a survey of 564 respondents in Wuhan City, consumers' willingness to pay (WTP) for fair trade labeled coffee was measured. This study uses an interval regression to investigate individual demographic and consumption characteristic impacts on WTP. Results show that on average, consumers were willing to pay 22% more for a medium cup of fair trade coffee compared with traditional coffee. In addition, other variables that indicated a higher WTP included female consumers, consumers who made their own coffee, and consumers who planned to consume more coffee in the following year.

Dynamic effects are an important determinant of chemical reactivity and selectivity, but the deliberate manipulation of atomic motions during a chemical transformation is not straightforward. Here, we demonstrate that extrinsic force exerted upon cyclobutanes by stretching pendant polymer chains influences product selectivity through force-imparted nonstatistical dynamic effects on the stepwise ring-opening reaction. The high product stereoselectivity is quantified by carbon-13 labeling and shown to depend on external force, reactant stereochemistry, and intermediate stability. Computational modeling and simulations show that, besides altering energy barriers, the mechanical force activates reactive intramolecular motions nonstatistically, setting up “flyby trajectories” that advance directly to product without isomerization excursions. A mechanistic model incorporating nonstatistical dynamic effects accounts for isomer-dependent mechanochemical stereoselectivity.

The primary sequence in biopolymers carries the information to direct folded secondary structures, to modulate their stabilities, and to control the resultant functions. Our ability to encode such information into nonbiological oligomers and polymers, however, is still limited. Here, we describe a C 2-symmetric aryl-triazole foldamer that assembles into a chloride-templated 2:2 double helix, and the discovery that its interconversion with the simpler 1:1 single helix can be driven by solvent quality, temperature, and concentration. We use single-site substitutions in the 13-residue sequence (two terminal sites and one central site) to reveal that the stability of the double helix is largely dictated by the differences in the anion binding power between single and double helices as well as the location of the modified residues. Specifically, placement of stabilizing CH···Cl– hydrogen-bonding interactions at the chain ends in the form of bisamide phenylene residues is found to highly favor the double helix. While the burial of π surfaces and the solvophobic effect also help to stabilize the double helix, their role was found to be less sensitive to the modifications considered. This understanding of how chemical information is programmed into the primary sequence provides a powerful tool for controlling structure and properties of abiological foldamers.

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