A Chiral Nonracemic Enolate with Dynamic Axial Chirality: Direct Asymmetric Alkylation of α-Amino Acid Derivatives (SYNTHETIC ORGANIC CHEMISTRY-Fine Organic Synthesis)

The structure of enolate was long believed to be achiral. However, a chiral nonracemic enolate with a racemization barrier of 16 kcal/mol at -78 oC was found to be the crucial intermediate for the asymmetric -methylation of 1 to give 2 in 81% ee and 96% yield. The asymmetric -methylation occurs in other amino acid derivatives (Val, Leu, Trp, His, Tyr, Dopa) in 78-93% ee

Characteristics and problems of unplugged computer science curriculum for young children: comparative and practical research based on the curriculum in four countries

With the progress of computer science education in recent years, more and more educators have brought attention to computer science education among young children. Among all these strategies, the unplugged form has been shown to be more effective in teaching. However, recent studies have focused more on the impact of unplugged computer science courses on young children and less on whether these courses are appropriate for the developmental stage of young children. Therefore, this research summarized the curriculum characteristics by comparing different series of unplugged courses for young children from four nations. Then, in a 7-day workshop conducted in China\u27s urban areas, we explored the issues that arise in the implementation of these courses. This research reveals that, although the existing courses cater to a young age range, four issues can still be found, including difficulty, ability difference, too much cooperation, and emphasis on abstraction. Some of these issues may be handled by instructors, while others need consideration of the connection between curriculum design and the physical and cognitive development levels of young children. Furthermore, this research explored the acceptance of unplugged computer science among Chinese young children as well as its impact on their computational thinking level, achieving positive results

Estimates on compressed neural networks regression

When the neural element number nn of neural networks is larger than the sample size mm, the overfitting problem arises since there are more parameters than actual data (more variable than constraints). In order to overcome the overfitting problem, we propose to reduce the number of neural elements by using compressed projection AA which does not need to satisfy the condition of Restricted Isometric Property (RIP). By applying probability inequalities and approximation properties of the feedforward neural networks (FNNs), we prove that solving the FNNs regression learning algorithm in the compressed domain instead of the original domain reduces the sample error at the price of an increased (but controlled) approximation error, where the covering number theory is used to estimate the excess error, and an upper bound of the excess error is given

Reflective imaging improves spatiotemporal resolution and collection efficiency in light sheet microscopy

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nature Communications 8 (2017): 1452, doi:10.1038/s41467-017-01250-8.Light-sheet fluorescence microscopy (LSFM) enables high-speed, high-resolution, and gentle imaging of live specimens over extended periods. Here we describe a technique that improves the spatiotemporal resolution and collection efficiency of LSFM without modifying the underlying microscope. By imaging samples on reflective coverslips, we enable simultaneous collection of four complementary views in 250 ms, doubling speed and improving information content relative to symmetric dual-view LSFM. We also report a modified deconvolution algorithm that removes associated epifluorescence contamination and fuses all views for resolution recovery. Furthermore, we enhance spatial resolution (to <300 nm in all three dimensions) by applying our method to single-view LSFM, permitting simultaneous acquisition of two high-resolution views otherwise difficult to obtain due to steric constraints at high numerical aperture. We demonstrate the broad applicability of our method in a variety of samples, studying mitochondrial, membrane, Golgi, and microtubule dynamics in cells and calcium activity in nematode embryos.This work was supported by the Intramural Research Program of the National Institute of Biomedical Imaging and Bioengineering at the National Institutes of Health. P.L. and H.S. acknowledge summer support from the Marine Biological Laboratory at Woods Hole, through the Whitman- and Fellows- program. P.L. acknowledges support from NIH National Institute of Biomedical Imaging and Bioengineering (NIBIB) of the National Institutes of Health (NIH) under grant number R01EB017293. C.S. acknowledges funding from the National Institute of General Medical Sciences of NIH under Award Number R25GM109439 (Project Title: University of Chicago Initiative for Maximizing Student Development [IMSD]) and NIBIB under grant number T32 EB002103. Partial funding for the computation in this work was provided by NIH grant numbers S10 RRO21039 and P30 CA14599. A.U. and I.R.-S. were supported by the NSF grant number 1607645