Milling Bifurcations from Structural Asymmetry and Nonlinear Regeneration

This paper investigates multiple modeling choices for analyzing the rich and complex dynamics of high-speed milling processes. Various models are introduced to capture the effects of asymmetric structural modes and the influence of nonlinear regeneration in a discontinuous cutting force model. Stability is determined from the development of a dynamic map for the resulting variational system. The general case of asymmetric structural elements is investigated with a fixed frame and rotating frame model to show differences in the predicted unstable regions due to parametric excitation. Analytical and numerical investigations are confirmed through a series of experimental cutting tests. The principal results are additional unstable regions, hysteresis in the bifurcation diagrams, and the presence of coexisting periodic and quasiperiodic attractors which is confirmed through experimentation.     

Flow visualization of compressible vortex structures using density gradient techniques

Mathematical results are derived for the schlieren and shadowgraph contrast variation due to the refraction of light rays passing through two-dimensional compressible vortices with viscous cores. Both standard and small-disturbance solutions are obtained. It is shown that schlieren and shadowgraph produce substantially different contrast profiles. Further, the shadowgraph contrast variation is shown to be very sensitive to the vortex velocity profile and is also dependent on the location of the peak peripheral velocity (viscous core radius). The computed results are compared to actual contrast measurements made for rotor tip vortices using the shadowgraph flow visualization technique. The work helps to clarify the relationships between the observed contrast and the structure of vortical structures in density gradient based flow visualization experiments.Nomenclature a Unobstructed height of schlieren light source in cutoff plane, m - c Blade chord, m - f Focal length of schlieren focusing mirror, m - C _T Rotor thrust coefficient, T/( ² R ⁴) - I Image screen illumination, Lm/m ² - l Distance from vortex to shadowgraph screen, m - n _b Number of blades - p Pressure,N/m ² - p Ambient pressure, N/m ² - r, , z Cylindrical coordinate system - r _c Vortex core radius, m - Non-dimensional radial coordinate, (r/r _c ) - R Rotor radius, m - Tangential velocity, m/s - Specific heat ratio of air - Circulation (strength of vortex), m ²/s - Non-dimensional quantity, ² 8²p r _c ² - Refractive index of fluid medium - ₀ Refractive index of fluid medium at reference conditions - Gladstone-Dale constant, m ³/kg - Density, kg/m ³ - Density at ambient conditions, kg/m ³ - Non-dimensional density, (/ ) - Rotor solidity, (n _b c/ R) - Rotor rotational frequency, rad/s     

A Magneto-Mechanically Coupled Phase-Field Model at Large Deformation

The aggregate magneto-mechanical behavior of magneto-rheological elastomers (MREs) stems from the magnetic properties of the ferromagnetic inclusion and the mechanical properties of the matrix material. We propose a large deformation micro-magnetic theory, to predict the behavior and interaction of ferromagnetic particles inside an elastomeric matrix. A rate-type variational principle, with the magnetization as the order parameter is proposed. A large deformation Landau-Lifshitz-Gilbert equation for the time evolution of the magnetization, is obtained directly from the proposed variational principle. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Metabolite identification by liquid chromatography-mass spectrometry

Metabolite identification (Met ID) is important during the early stages of drug discovery and development, as the metabolic products may be pharmacologically active or toxic in nature. Liquid chromatography-mass spectrometry (LC-MS) has a towering role in metabolism research.This review discusses current approaches and recent advances in using LC-MS for Met ID. We critically assess and compare various mass spectrometers, highlighting their strengths and limitations. Citing appropriate examples, we cover recent LC and ion sources, isotopic-pattern matching, hydrogen/deuterium-exchange MS, data dependent analyses, MS^E, mass defect filter, 2D and 3D approaches for the elucidation of molecular formula, polarity switching, and background-subtraction and noise-reduction algorithms. A flow chart outlines a comprehensive strategy for Met ID, including a focus on reactive metabolites.     

Production of ROS by photosensitized anthracene under sunlight and UV-R at ambient environmental intensities

The aim of this study was to analyze the photostability and phototoxicity mechanism of anthracene (ANT) in a human skin epidermal cell line (HaCaT) at ambient environmental intensities of sunlight/UV‐R (UV‐A and UV‐B). Photomodification of ANT under sunlight/UV‐R exposure produced two photoproducts, anthrone and 9,10 anthracenedione. Generation of ¹O₂, O₂^?? and ^?OH was measured under UV‐R/sunlight exposure. Involvement of reactive oxygen species (ROS) was further substantiated by their quenching with free radical quenchers. Photodegradation of 2‐deoxyguanosine and linoleic acid peroxidation showed that ROS were mainly responsible for ANT phototoxicity. ANT generates significant amount of intracellular ROS in cell line. Maximum cell viability (85%) was reduced under sunlight exposure (30 min). Results of MTT assay accord NRU assay. ANT (0.01 μg mL^?1) induced cell‐cycle arrest at G1 phase. RT‐PCR demonstrated constitutive inducible mRNA expression of CYP 1A1 and 1B1 genes. Photosensitive ANT upregulates CYP 1A1 (2.2‐folds) and 1B1 (4.1‐folds) genes. Thus, the study suggests that ROS and DNA damage were mainly responsible for ANT phototoxicity. ANT exposure may be deleterious to human health at ambient environmental intensities reaching the earth’s surface through sunlight.     

Total synthesis of (-)-N-methylwelwitindolinone C isothiocyanate

We report the first total synthesis of (-)-N-methylwelwitindolinone C isothiocyanate. Our route features a number of key transformations, including an indolyne cyclization to assemble the [4.3.1]-bicyclic scaffold, as well as a late-stage intramolecular nitrene insertion to functionalize the C11 bridgehead carbon en route to the natural product.     

A fungal nonribosomal peptide synthetase module that can synthesize thiopyrazines

A nonribosomal peptide synthetase-like enzyme (NRPS325) from Aspergillus terreus was reconstituted in vitro and was shown to synthesize thiopyrazines using an unprecedented mechanism. Substrate promiscuity of NRPS325 toward different amino acids and free thiols was explored to produce >60 different thiopyrazine compounds.