Synthesis and Characterization of Tris(diethyldithiocarbamato) cobalt(III) as an Undergraduate Inorganic Laboratory

The synthesis of tris(diethyldithiocarbamato) cobalt(III) by the reaction of sodium diethyldithio-carbamate and cobaltous chloride is described. The recovered crystals of the cobalt complex are characterized by magnetic susceptibility, IR and NMR spectroscopy, and cyclic voltammetry.     

A statistical learning strategy for closed-loop control of fluid flows

This work discusses a closed-loop control strategy for complex systems utilizing scarce and streaming data. A discrete embedding space is first built using hash functions applied to the sensor measurements from which a Markov process model is derived, approximating the complex system’s dynamics. A control strategy is then learned using reinforcement learning once rewards relevant with respect to the control objective are identified. This method is designed for experimental configurations, requiring no computations nor prior knowledge of the system, and enjoys intrinsic robustness. It is illustrated on two systems: the control of the transitions of a Lorenz’63 dynamical system, and the control of the drag of a cylinder flow. The method is shown to perform well.     

Stability and instability of nonlinear defect states in the coupled mode equations—Analytical and numerical study

Coupled backward and forward wave amplitudes of an electromagnetic field propagating in a periodic and nonlinear medium at Bragg resonance are governed by the nonlinear coupled mode equations (NLCME). This system of PDEs, similar in structure to the Dirac equations, has gap soliton solutions that travel at any speed between 0 and the speed of light. A recently considered strategy for spatial trapping or capture of gap optical soliton light pulses is based on the appropriate design of localized defects in the periodic structure. Localized defects in the periodic structure give rise to defect modes, which persist as nonlinear defect modes as the amplitude is increased. Soliton trapping is the transfer of incoming soliton energy to nonlinear defect modes. To serve as targets for such energy transfer, nonlinear defect modes must be stable. We therefore investigate the stability of nonlinear defect modes. Resonance among discrete localized modes and radiation modes plays a role in the mechanism for stability and instability, in a manner analogous to the nonlinear Schrödinger/Gross-Pitaevskii (NLS/GP) equation. However, the nature of instabilities and how energy is exchanged among modes is considerably more complicated than for NLS/GP due, in part, to a continuous spectrum of radiation modes which is unbounded above and below. In this paper we (a) establish the instability of branches of nonlinear defect states which, for vanishing amplitude, have a linearization with eigenvalues embedded within the continuous spectrum, (b) numerically compute, using Evans function, the linearized spectrum of nonlinear defect states of an interesting multiparameter family of defects, and (c) perform direct time-dependent numerical simulations in which we observe the exchange of energy among discrete and continuum modes.     

The electrochemical preparation of soluble electrically conducting polymers of 3-methoxythiophene with narrow distributions of molecular weight

Solutions of 3-methoxythiophene (MeOT) in dimethylformamide (DMF) were electrolyzed at controlled electrode potentials. The polymerizations were studied under homogeneous conditions in solutions in which the polymer was soluble in the medium, and no coating of the electrodes occurred. The reaction proceeded at high coulombic efficiency and a first order dependence on monomer concentration was observed. The molecular weights of the polymers were determined by gel permeation chromatography. All samples showed a narrow distribution of molecular weights, with M_w/M_n ranging from 1.01 to 1.07. The molecular weight was low (about 3000 Daltons) and did not change in magnitude during the course of the reaction from 10 to 86% conversion, or with change in electrode potential from 1.55 to 1.65 V vs. SCE. The data are interpreted on a model based upon the competitive formation of chemically unreactive bipolarons.     

The interaction of ultrathin films of Ni and Pd with W(110): an XPS study

The interaction of ultrathin films of Ni and Pd with W(110) has been examined using X-ray photoelectron spectroscopy (XPS) and the effects of annealing temperature and adsorbate coverage (film thickness) are investigated. The XPS data show that the atoms in a monolayer of Pd or Ni supported on W(110) are electronically perturbed with respect to the surface atoms of Pd(100) and Ni(100). The magnitude of the electronic perturbations is larger for Pd than for Ni adatoms. Our results indicate that the difference in Pd(3d_5/2) XPS binding energies between a pseudomorphic monolayer of Pd on W(110) and the surface atoms of Pd(100) correlates with the variations observed for the desorption temperature of CO (i.e., the strength of the Pd---CO bond) on these surfaces. A similar correlation is seen for the Ni(2p_3/2) XPS binding energies of Ni/W(110) and Ni(100) and the CO desorption temperatures from the surfaces. The shifts in XPS binding energies and CO desorption temperatures can be explained in terms of: (1) variations that occur in the Ni---Ni and Pd---Pd interactions when Ni and Pd adopt the lattice parameters of W(110) in a pseudomorphic adlayer; and (2) transfer of electron density from the metal overlayer to the W(110) substrate upon adsorption. Measurements of the Pd(3d_5/2) XP binding energy of Pd/W(110) as a function of film thickness indicate that the Pd---W interaction affects the electronic properties of several layers of Pd atoms.     

Identification and quantification of phosphatidylcholines containing very-long-chain polyunsaturated fatty acid in bovine and human retina using liquid chromatography/tandem mass spectrometry

The retina is one of the vertebrate tissues with the highest content in polyunsaturated fatty acids (PUFA). A large proportion of retinal phospholipids, especially those found in photoreceptor membranes, are dipolyunsaturated molecular species. Among them, dipolyunsaturated phosphatidylcholine (PC) molecular species are known to contain very-long-chain polyunsaturated fatty acids (VLC-PUFA) from the n-3 and n-6 series having 24-36 carbon atoms (C24-C36) and four to six double bonds. Recent interest in the role played by VLC-PUFA arose from the findings that a protein called elongation of very-long-chain fatty acids 4 (ELOVL4) is involved in their biosynthesis and that mutations in the ELOVL4 gene are associated with Stargardt-like macular dystrophy (STD3), a dominantly inherited juvenile macular degeneration leading to vision loss. The aim of the present study was to develop an HPLC-ESI-MS/MS method for the structural characterisation and the quantification of dipolyunsaturated PC molecular species containing VLC-PUFA and validate this methodology on retinas from bovines and human donors. Successful separation of phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS), PC, lyso-phosphatidylcholine (LPC) and sphingomyelin (SM) was achieved using a silica gel column and a gradient of hexane/isopropanol/water containing ammonium formate as a mobile phase. A complete structural characterisation of intact phosphatidylcholine species was obtained by collision-induced dissociation (CID) in the negative mode. Fatty acid composition and distribution can be clearly assigned based on the intensity of sn-2/sn-1 fragment ions. The PC species were characterised on bovine retina, 28 of which were dipolyunsaturated PC species containing one VLC-PUFA (C24-C36) with three to six double bonds. VLC-PUFA was always in the sn-1 position while PUFA at the sn-2 position was exclusively docosahexaenoic acid (DHA, C22:6n-3). Most of these VLC-PUFA-containing dipolyunsaturated PCs were detected and quantified in human retinas. The quantitative analysis of the different PC molecular species was performed in the positive mode using precursor ion scanning of m/z 184 and 14:0/14:0-PC and 24:0/24:0-PC as internal standards. The relationship between the MS peak intensities of different PC species and their carbon chain length was included for calibration. The main compounds represented were those having VLC-PUFA with 32 carbon atoms (C32:3, C32:4, C32:5 and C32:6) and 34 carbon atoms (C34:3, C34:4, C34:5 and C34:6). Dipolyunsaturated PCs with 36:5 and 36:6 were detected but in smaller quantities. In conclusion, this new HPLC-ESI-MS/MS method is sensitive and specific enough to structurally characterise and quantify all molecular PC species, including those esterified with VLC-PUFA. This technique is valuable for a precise characterisation of PC molecular species containing VLC-PUFA in retina and may be useful for a better understanding of the pathogenesis of STD3.     

Further assessment of forward pressure level for in situ calibration

Quantifying ear-canal sound level in forward pressure has been suggested as a more accurate and practical alternative to sound pressure level (SPL) calibrations used in clinical settings. The mathematical isolation of forward (and reverse) pressure requires defining the The?venin-equivalent impedance and pressure of the sound source and characteristic impedance of the load; however, the extent to which inaccuracies in characterizing the source and/or load impact forward pressure level (FPL) calibrations has not been specifically evaluated. This study examined how commercially available probe tips and estimates of characteristic impedance impact the calculation of forward and reverse pressure in a number of test cavities with dimensions chosen to reflect human ear-canal dimensions. Results demonstrate that FPL calibration, which has already been shown to be more accurate than in situ SPL calibration, can be improved particularly around standing-wave null frequencies by refining estimates of characteristic impedance. Better estimates allow FPL to be accurately calculated at least through 10 kHz using a variety of probe tips in test cavities of different sizes, suggesting that FPL calibration can be performed in ear canals of all sizes. Additionally, FPL calibration appears a reasonable option when quantifying the levels of extended high-frequency (10-18 kHz) stimuli.     

Near-field optical characterization of interacting and non-interacting gold nanoparticles embedded in a silica thin film

By near-field optics, we characterized the local optical properties of clusters of gold nanoparticles randomly distributed under a 50 nm-thick SiO₂ thin film. A local field enhancement is visible above isolated clusters. A few hundred nanometers away from them, we observed a polarization-dependent pattern with elliptical lobes oriented in the incident polarization direction. A simple simulation shows that the observed near-field images can be represented by the sum of the field of an oscillating dipole and the incident field. When the cluster density is larger, the measured near-field images show numerous bright and dark spots. The position of the bright spots does not necessarily coincide with the gold clusters showing the presence of coupling effects between them.