Simulation of a Large-Eddy-Break-up Device (LEBU) in a Moderate Reynolds Number Turbulent Boundary Layer

A well-resolved large eddy simulation (LES) of a large-eddy break-up (LEBU) device in a spatially evolving turbulent boundary layer is performed with, Reynolds number, based on free-stream velocity and momentum-loss thickness, of R e _θ ≈ 4300. The implementation of the LEBU is via an immersed boundary method. The LEBU is positioned at a wall-normal distance of 0.8 δ (δ denoting the local boundary layer thickness at the location of the LEBU) from the wall. The LEBU acts to delay the growth of the turbulent boundary layer and produces global skin friction reduction beyond 180δ downstream of the LEBU, with a peak local skin friction reduction of approximately 12 %. However, no net drag reduction is found when accounting for the device drag of the LEBU in accordance with the towing tank experiments by Sahlin et al. (Phys. Fluids 31, 2814, 1988). Further investigation is performed on the interactions of high and low momentum bulges with the LEBU and the corresponding output is analysed, showing a ‘break-up’ of these large momentum bulges downstream of the LEBU. In addition, results from the spanwise energy spectra show consistent reduction in energy at spanwise length scales for \(\lambda _{z}^{+} > 1000\) independent of streamwise and wall-normal location when compared to the corresponding turbulent boundary layer without LEBU.     

Dislocation-based micropolar single crystal plasticity: Comparison of multi- and single criterion theories

Two new formulations of micropolar single crystal plasticity are presented within a geometrically linear setting. The construction of yield criteria and flow rules for generalized continuum theories with higher-order stresses can be done in one of two ways: (i) a single criterion can be introduced in terms of a combined equivalent stress and inelastic rate or (ii) or individual criteria can be specified for each conjugate stress/inelastic kinematic rate pair, a so-called multi-criterion theory. Both single and multi-criterion theories are developed and discussed within the context of dislocation-based constitutive models. Parallels and distinctions are made between the proposed theories and some of the alternative generalized crystal plasticity models that can be found in the literature. Parametric numerical simulations of a constrained thin film subjected to simple shear are conducted via finite element analysis using a simplified 2-D version of the fully 3-D theory to highlight the influence of specific model components on the resulting deformation under both loading and unloading conditions. The deformation behavior is quantified in terms of the average stress-strain response and the local shear strain and geometrically necessary dislocation density distributions. It is demonstrated that micropolar single crystal plasticity can qualitatively capture the same range of behaviors as slip gradient-based models, while offering a simpler numerical implementation and without introducing plastic slip rates as generalized traction-conjugate velocities subject to an additional microforce balance.     

A multiplexed post-translational modification monitoring approach on a matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometer

Post-translational modifications (PTMs) of proteins are essential for proper function, as they regulate many aspects of a protein's activity and interaction with substrates. When analyzing modified peptides derived from such proteins by mass spectrometry, these modifications can dissociate, producing either a marker ion or neutral loss characteristic of the modification, which have conventionally been monitored with a precursor ion scan or neutral loss scan, respectively. Although powerful, both precursor ion scans and neutral loss scans can only screen for one particular modification at a time. This has led to the development of multiple neutral loss monitoring (MNM) for neutral losses and multiple precursor ion monitoring (MPM) for marker ions on electrospray instruments. Here, we report their implementation on a matrix-assisted laser desorption/ionization (MALDI) instrument as well as the inception of a novel scan strategy termed targeted multiple precursor ion monitoring (tMPM). This latter scan strategy has been developed on a MALDI tandem time-of-flight (TOF/TOF) mass spectrometer for the identification of multiple PTMs via their associated marker ions by manipulating certain components of the instrument, notably the timed ion selector and the delayed extraction source 2. Targeted MPM combined with a second approach, multiple neutral loss monitoring (MNM), is shown to be a successful approach in the identification of PTMs, identifying multiple modified peptides in a complex sample matrix.     

Do (pentaarylcyclopentadienyl)molybdenum(VI) dioxo species catalyse alkene epoxidations? Insights from kinetics data

A (perarylcyclopentadienyl)molybdenum(VI) dioxo complex is shown to catalyse epoxidation of cyclooctene by t-butylhydroperoxide, but decomposition to a much more active non-cyclopentadienyl containing catalyst occurs as the reaction proceeds.     

A Structurally-Tunable 3-Hydroxyflavone Motif for Visible Light-Induced Carbon Monoxide-Releasing Molecules (CORMs)

Molecules that can be used to deliver a controlled amount of carbon monoxide (CO) have the potential to facilitate investigations into the roles of this gaseous molecule in biology and advance therapeutic treatments. This has led to the development of light-induced CO-releasing molecules (photoCORMs). A goal in this field of research is the development of molecules that exhibit a combination of controlled CO release, favorable biological properties (e.g., low toxicity and trackability in cells), and structural tunability to affect CO release. Herein, we report a new biologically-inspired organic photoCORM motif that exhibits several features that are desirable in a next-generation photoCORM. We show that 3-hydroxyflavone-based compounds are easily synthesized and modified to impart changes in absorption features and quantum yield for CO release, exhibit low toxicity, are trackable in cells, and can exhibit both O₂-dependent and -independent CO release reactivity.