Femtosecond magneto-optical Kerr microscopy

We have developed a magneto-optical Kerr microscope that allows us to measure the ultrafast magnetization dynamics of ferromagnetic nanostructures. The magneto-optical signal can be recorded in a confocal reflection geometry with an accurate selection of the polarization. The magnetization dynamics is obtained from pump-probe measurements using frequency nondegenerate collinear pump and probe beams with a temporal resolution of 180 fs. Both probe and pump beams are focused to their diffraction limit, leading to an overall spatial resolution of 600 nm. The efficiency of the apparatus is tested by investigating the magnetization dynamics of individual CoPt(3) disks with a submicrometer diameter and a thickness of 15 nm.     

Forward and reverse product decompositions of depolarizing Mueller matrices

Because of the noncommutativity of the matrix product, the three factors into which a depolarizing Mueller matrix is decomposed, i.e., the diattenuator, the retarder, and the depolarizer, form six possible products grouped into two families, as already pointed out [J. Opt. Soc. Am. A13, 1106 (1996); Opt. Lett.29, 2234 (2004)]. We show that, apart from the generalized polar decomposition generating the first family of products, there exists a dual decomposition belonging to the second family. The mathematical procedure for this dual decomposition is given, and the symmetry existing between the two decompositions is pointed out. The choice of the most appropriate decomposition for a given practical optical arrangement is likewise discussed and illustrated by simple examples.     

A tandem cross-coupling/S(N)Ar approach to functionalized carbazoles

A novel route to functionalized carbazoles utilizing a tandem Suzuki cross-coupling/SNAr protocol is described. This process was found to be compatible with a variety of electron-withdrawing groups including aldehydes, esters, and sulfones. Using this method, a concise total synthesis (four steps, 50% overall yield) of the carbazole alkaloid glycosinine was achieved.     

A new manifold for the Morita reaction: diene synthesis from simple aldehydes and acrylates/acrylonitrile mediated by phosphines

Dienes have been formed with good stereoselectivity and in good yield from simple aldehydes and acrylates/acrylonitrile in the presence of a phosphine and a Lewis acid through a modification of the Morita reaction.     

Complex zeros of real ergodic eigenfunctions

We determine the limit distribution (as λ→∞) of complex zeros for holomorphic continuations φ_λ ^? to Grauert tubes of real eigenfunctions of the Laplacian on a real analytic compact Riemannian manifold (M,g) with ergodic geodesic flow. If \(\{\phi_{j_{k}}\}\) is an ergodic sequence of eigenfunctions, we prove the weak limit formula \(\frac{1}{\lambda_j}[Z_{\phi_{j_k}}^{\mathbb{C}}]\ \to\ \frac{i}{\pi} \partial\bar{\partial} |\xi|_g\), where \([Z_{\phi_{j_k}^{\mathbb{C}}}]\) is the current of integration over the complex zeros and where \(\overline{\partial}\) is with respect to the adapted complex structure of Lempert-Szöke and Guillemin-Stenzel.     

Rapid nucleic acid melting analyses using a microfabricated electrochemical platform

Microfabrication methods have been used to fabricate a new microscale platform that integrates thermal control and multi-electrode components to enable rapid, temperature-dependent electrochemical measurements on small-volume fluid samples. A wide range of biochemical phenomena can be characterized with the device, for example, when monitoring interactions at the working electrode between probe and target species which include an electroactive moiety. Employing square wave voltammetry, we have demonstrated the utility and reproducibility of the microplatform in melting studies on full-match, single-mismatch, and double-mismatch DNA structures of relevance to single-nucleotide polymorphism (SNP) discrimination. As shown, the small size of the reported device, low volume for the samples it can interrogate (∼10 μL), individual addressing of platform components and fast localized heating (settling times ∼5 s) combine to allow for efficient sample analyses. In addition, a straight-forward route exists, involving replication into array formats and integration with microfluidics, for extending the technology toward eventual high throughput work on drug discovery and medical diagnostics.     

Characterization of Polypropylene in Dibutoxymethane by High-Temperature Gel Permeation Chromatography with Triple Detection

This study presents the possibility of replacing the 1,2,4-trichlorobenzene (TCB) recommended by ASTM D 6474 for the analysis by gel permeation chromatography (GPC) of polypropylenes with dibutoxymethane (DBM, butylal), a halogen-free and less toxic solvent. The molecular weight distributions as well as the K and alpha parameters of the Mark-Houwink-Sakurada equation were measured for different types of commercial polypropylene samples solubilized in TCB and DBM, using a GPC system with triple detection (light scattering, differential refractive index, and viscometer). For the analyzed resins, covering typical applications of polypropylene, the GPC method in DBM provided results similar to those obtained in TCB.     

Development of an inverse heat conduction model and its application to determination of heat transfer coefficient during casting solidification

The interfacial heat transfer coefficient (IHTC) is required for the accurate simulation of heat transfer in castings especially for near net-shape processes. The large number of factors influencing heat transfer renders quantification by theoretical means a challenge. Likewise experimental methods applied directly to temperature data collected from castings are also a challenge to interpret because of the transient nature of many casting processes. Inverse methods offer a solution and have been applied successfully to predict the IHTC in many cases. However, most inverse approaches thus far focus on use of in-mold temperature data, which may be a challenge to obtain in cases where the molds are water-cooled. Methods based on temperature data from the casting have the potential to be used however; the latent heat released during the solidification of the molten metal complicates the associated IHTC calculations. Furthermore, there are limits on the maximum distance the thermocouples can be placed from the interface under analysis. An inverse conduction based method have been developed, verified and applied successfully to temperature data collected from within an aluminum casting in proximity to the mold. A modified specific heat method was used to account for latent heat evolution in which the rate of change of fraction solid with temperature was held constant. An analysis conducted with the inverse model suggests that the thermocouples must be placed no more than 2 mm from the interface. The IHTC values calculated for an aluminum alloy casting were shown to vary from 1,200 to 6,200 Wm^?2 K^?1. Additionally, the characteristics of the time-varying IHTC have also been discussed.