Methylamine is an abundant amine compound detected in the atmosphere which can affect the nature of atmospheric aerosol surfaces, changing their chemical and optical properties. Molecular dynamics simulation results show that methylamine accommodation on water is close to unity with the hydrophilic head group solvated in the interfacial environment and the methyl group pointing into the air phase. A detailed analysis of the hydrogen bond network indicates stronger hydrogen bonds between water and the primary amine group at the interface, suggesting that atmospheric trace gases will likely react with the methyl group instead of the solvated amine site. These findings suggest new chemical pathways for methylamine acting on atmospheric aerosols in which the methyl group is the site of orientation specific chemistry involving its conversion into a carbonyl site providing hydrophilic groups for uptake of additional water. This conversion may explain the tendency of aged organic aerosols to form cloud condensation nuclei. At the same time, formation of NH 2 radical and formaldehyde is suggested to be a new source for NH 2 radicals at aerosol surfaces, other than by reaction of absorbed NH 3 . The results have general implications for the chemistry of other amphiphilic organics, amines in particular, at the surface of atmospherically relevant aerosols. Published by AIP Publishing. [http://dx

Though numerous segmentation algorithms have been proposed to segment brain tissue from magnetic resonance (MR) images, few of them consider combining the tissue segmentation and bias field correction into a unified framework while simultaneously removing the noise. In this paper, we present a new unified MR image segmentation algorithm whereby tissue segmentation, bias correction and noise reduction are integrated within the same energy model. Our method is presented by a total variation term introduced to the coherent local intensity clustering criterion function. To solve the nonconvex problem with respect to membership functions, we add auxiliary variables in the energy function such as Chambolle's fast dual projection method can be used and the optimal segmentation and bias field estimation can be achieved simultaneously throughout the reciprocal iteration. Experimental results show that the proposed method has a salient advantage over the other three baseline methods on either tissue segmentation or bias correction, and the noise is significantly reduced via its applications on highly noise-corrupted images. Moreover, benefiting from the fast convergence of the proposed solution, our method is less time-consuming and robust to parameter setting.

Mountainous landscapes are particularly vulnerable and sensitive to climate change and human activities, and a clear understanding of how ecosystem services (ES) and their relationships continuously change over time, across space, and along altitude is therefore essential for ecosystem management. Chongqing, a typical mountainous region, was selected to assess the long-term changes in its key ES and their relationships. From 1992 to 2018, the temporal variation in water yield (WY) revealed that the maximum and minimum WYs occurred in 1998 and 2006, which coincided with El Niño-Southern Oscillation and severe drought events, respectively. Soil export (SE) and WY were consistent with precipitation, which reached their highest values in 1998. During this period, carbon storage (CS) and habitat quality (HQ) both decreased significantly. ES in Chongqing showed large variations in altitude. Generally, WY and SE decreased with increasing altitude, while CS and HQ increased. For spatial distribution, WY and SE showed positive trends in the west and negative trends in the east. In regard to CS and HQ, negative trends dominated the area. Persistent tradeoffs between WY and soil conservation (SC) were found at all altitude gradients. The strong synergies between CS and HQ were maintained over time.