Plasmonic edge states: an electrostatic eigenmode description

We consider periodic arrangements of metal nanostructures and study the effect of periodicity on the localised surface plasmon resonance of the structures within an electrostatic eigenmode approximation. We show that within this limit, the collective surface plasmon resonances of the periodic structures can be expressed in terms of superpositions of the eigenmodes of uncoupled nanostructures that exhibit a standing--wave character delocalised across the entire periodic structure. The formalism derived successfully enables the design and accounts for the observation of plasmonic edge-states in periodic structures

Optical chirality from dark-field illumination of planar plasmonic nanostructures

Dark-field illumination is shown to make planar chiral nanoparticle arrangements exhibit circular dichroism in extinction analogous to true chiral scatterers. Circular dichrosim is experimentally observed at the maximum scattering of single oligomers consisting rotationally symmetric arrangements of gold nanorods, with strong agreement to numerical simulation. A dipole model is developed to show that this effect is caused by a difference in the geometric projection of a nanorod onto the handed orientation of electric fields created by a circularly polarized dark-field that is normally incident on a glass substrate. Owing to this geometric origin, the wavelength of the peak chiral response is also experimentally shown to shift depending on the separation between nanoparticles. All presented oligomers have physical dimensions less than the operating wavelength, and the applicable extension to closely packed planar arrays of oligomers is demonstrated to amplify the magnitude of circular dichroism. The realization of strong chirality in these oligomers demonstrates a new path to engineer optical chirality from planar devices using dark-field illumination

Treatment of chronic lateral ankle instability: a modified brostrom technique using three suture anchors

Ankle sprains are very common injuries seen in the athletic and young population. Majority of patients will improve with a course of rest and physical therapy. However, with conservative management about twenty percent of all patients will go on to develop chronic lateral ankle instability. This manuscript describes our detailed surgical technique of a modification to the original Brostrom procedure using three suture anchors to anatomically reconstruct the lateral ankle ligaments to treat high demand patients who have developed chronic lateral ankle instability. The rationale for this modification along with patient selection and workup are discussed. Both the functional outcomes at the two year follow up along with the complications and the detailed postoperative rehabilitation protocol for the high demand athletes are also presented. This modified Brostrom procedure is shown in both illustrative format and intra-operative photos

Treatment of chronic lateral ankle instability: a modified broström technique using three suture anchors

Ankle sprains are very common injuries seen in the athletic and young population. Majority of patients will improve with a course of rest and physical therapy. However, with conservative management about twenty percent of all patients will go on to develop chronic lateral ankle instability. This manuscript describes our detailed surgical technique of a modification to the original Broström procedure using three suture anchors to anatomically reconstruct the lateral ankle ligaments to treat high demand patients who have developed chronic lateral ankle instability. The rationale for this modification along with patient selection and workup are discussed. Both the functional outcomes at the two year follow up along with the complications and the detailed postoperative rehabilitation protocol for the high demand athletes are also presented. This modified Broström procedure is shown in both illustrative format and intra-operative photos

Catalytic mechanism and pH dependence of a methyltransferase ribozyme (MTR1) from computational enzymology

A methyltransferase ribozyme (MTR1) was selected in vitro to catalyze alkyl transfer from exogenous O6-methylguanine (O6mG) to a target adenine N1, and recently, high-resolution crystal structures have become available. We use a combination of classical molecular dynamics, ab initio quantum mechanical/molecular mechanical (QM/MM) and alchemical free energy (AFE) simulations to elucidate the atomic-level solution mechanism of MTR1. Simulations identify an active reactant state involving protonation of C10 that hydrogen bonds with O6mG:N1. The deduced mechanism involves a stepwise mechanism with two transition states corresponding to proton transfer from C10:N3 to O6mG:N1 and rate-controlling methyl transfer (19.4  kcal·mol-1 barrier). AFE simulations predict the pKa for C10 to be 6.3, close to the experimental apparent pKa of 6.2, further implicating it as a critical general acid. The intrinsic rate derived from QM/MM simulations, together with pKa calculations, enables us to predict an activity-pH profile that agrees well with experiment. The insights gained provide further support for a putative RNA world and establish new design principles for RNA-based biochemical tools.</p

Structure and mechanism of a methyl transferase ribozyme

Known ribozymes in contemporary biology perform a limited range of chemical catalysis, but in vitro selection has generated species that catalyze a broader range of chemistry; yet, there have been few structural and mechanistic studies of selected ribozymes. A ribozyme has recently been selected that can catalyze a site-specific methyl transfer reaction. We have solved the crystal structure of this ribozyme at a resolution of 2.3 Å, showing how the RNA folds to generate a very specific binding site for the methyl donor substrate. The structure immediately suggests a catalytic mechanism involving a combination of proximity and orientation and nucleobase-mediated general acid catalysis. The mechanism is supported by the pH dependence of the rate of catalysis. A selected methyltransferase ribozyme can thus use a relatively sophisticated catalytic mechanism, broadening the range of known RNA-catalyzed chemistry. [Image: see text

Merging multiple-partial-depth data time series using objective empirical orthogonal function fitting

Author Posting. © IEEE, 2010. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 35 (2010): 710-721, doi:10.1109/JOE.2010.2052875.In this paper, a method for merging partial overlapping time series of ocean profiles into a single time series of profiles using empirical orthogonal function (EOF) decomposition with the objective analysis is presented. The method is used to handle internal waves passing two or more mooring locations from multiple directions, a situation where patterns of variability cannot be accounted for with a simple time lag. Data from one mooring are decomposed into linear combination of EOFs. Objective analysis using data from another mooring and these patterns is then used to build the necessary profile for merging the data, which is a linear combination of the EOFs. This method is applied to temperature data collected at a two vertical moorings in the 2006 New Jersey Shelf Shallow Water Experiment (SW06). Resulting profiles specify conditions for 35 days from sea surface to seafloor at a primary site and allow for reliable acoustic propagation modeling, mode decomposition, and beamforming.This work was supported by the U.S. Office of Naval Research (ONR) under Grants N00014-04-1-0146 and N00014-05-1- 0482, theONRPostdoctoral FellowshipAward under Grant N00014-08-1-0204, and by E. Livingston and T. Pawluskiewicz. The work of P. F. J. Lermusiaux and P. J. Haley was supported by the ONR under Grants N00014-07-1-1061, N00014-07-1-0501, and N00014-08-1-1097 to the Massachusetts Institute of Technology