Desymmetrization of a meso-allylic acetal by enantioselective conjugate elimination

An unprecedented enantioselective deprotonation/conjugate elimination sequence, which transforms an allylic meso-dioxepane into a chiral diene, is described. The best desymmetrization conditions (ee up to 70%) involve s-BuLi and sparteine at -78 degrees C in THF.     

Effective signal-to-noise ratio improvement by parametric image amplification

We show experimentally that parametric optical preamplification greatly improves the signal-to-noise ratio of an image if the detector has a poor quantum efficiency and/or a great level of readout noise. Results are fully consistent with the theory of quantum-noise-limited amplification.     

Asymptotics of the Fast Diffusion Equation via Entropy Estimates

We consider non-negative solutions of the fast diffusion equation u _t  = Δ u ^m with m ∈ (0, 1) in the Euclidean space , d ≧ 3, and study the asymptotic behavior of a natural class of solutions in the limit corresponding to t → ∞ for m ≧ m _c  = (d − 2)/d, or as t approaches the extinction time when m < m _c . For a class of initial data, we prove that the solution converges with a polynomial rate to a self-similar solution, for t large enough if m ≧ m _c , or close enough to the extinction time if m < m _c . Such results are new in the range m ≦ m _c where previous approaches fail. In the range m _c  < m < 1, we improve on known results.     

Physics and Performance of the Upgraded T2K’s Near Detector

Physics of Atomic Nuclei - Tokai-to-Kamioka (T2K) is a long-baseline neutrino oscillation experiment currently ongoing in Japan. T2K has been the first experiment to detect the appearance of...     

Asymptotic expansions of defective renewal equations with applications to perturbed risk models and processor sharing queues

We consider asymptotic expansions for defective and excessive renewal equations that are close to being proper. These expansions are applied to the analysis of processor sharing queues and perturbed risk models, and yield approximations that can be useful in applications where moments are computable, but the distribution is not.     

Unsupervised random forest: a tutorial with case studies

Unsupervised methods, such as principal component analysis, have gained popularity and wide‐spread acceptance in the chemometrics and applied statistics communities. Unsupervised random forest is an additional method capable of discovering underlying patterns in the data. However, the number of applications of unsupervised random forest in chemometrics has been limited. One possible cause for this is the belief that random forest can only be used in a supervised analysis setting. This tutorial introduces the basic concepts of unsupervised random forest and illustrates several applications in chemometrics through worked examples. Copyright © 2016 John Wiley & Sons, Ltd.     

Asymptotic behaviour for small mass in the two-dimensional parabolic-elliptic Keller-Segel model

The Keller-Segel system describes the collective motion of cells that are attracted by a chemical substance and are able to emit it. In its simplest form, it is a conservative drift-diffusion equation for the cell density coupled to an elliptic equation for the chemo-attractant concentration. This paper deals with the rate of convergence towards a unique stationary state in self-similar variables, which describes the intermediate asymptotics of the solutions in the original variables. Although it is known that solutions globally exist for any mass less 8π, a smaller mass condition is needed in our approach for proving an exponential rate of convergence in self-similar variables.     

Temporal and spatial assessment of normal cerebrospinal fluid dynamics with MR imaging

The purpose of this study was to measure normal cerebrospinal fluid (CSF) pulsations within the intracranial and upper cervical subarachnoid spaces and the ventricular system. Phase contrast cine MR sequences were performed in sagittal and axial planes on 13 volunteers with flow encoding in the craniocaudal direction. CSF pulsations displayed considerable variations in healthy subjects, depending both on measurements localization and subjects, with CSF peak velocities ranging from 0 to 7 cm/s. In the subarachnoid spaces, the highest velocities occurred in the anterior location and increased from the cerebellar pontine angle cisterns towards the lower cervical spaces. In the ventricular system, the highest velocities occurred through the aqueduct of Sylvius. CSF flow within the third ventricle seemed to reflect a circular motion. There was a caudal net CSF flow in the aqueduct whereas in the upper cervical spaces net CSF flow was caudal anteriorly and cranial laterally. Velocity profiles of CSF pulsations demonstrated arterial morphology. After the R wave, caudal systolic motion was first observed in the posterior subarachnoid spaces, soon after in the anterior subarachnoid spaces and later in the ventricular system. Considering the morphology of CSF pathways, three successively initiated phenomena may explain the temporal course of CSF motion: the systolic expansion of the main arteries at the base of the brain, the systolic expansion of the cerebrospinal axis and, finally, the systolic expansion of the choroid plexuses.