Is there potential for use of the Hall effect in analytical science?

This article describes the basic principles of the Hall effect and how it has been applied in solid state applications to measure both the magnetic field and material properties. This is followed by an outline of research undertaken in aqueous ionic solutions as a possible precursor to application in chemical studies. However, previous research has shown that factors such as the Nernst effect have reduced the success of reliably measuring the Hall voltage under these conditions. The possibility of a multi-sensing approach using both electrical and acoustic Hall voltages to overcome these challenges is discussed. The article concludes with a brief look at some early efforts to detect biomolecular interactions.     

Noncontact all-optical measurement of corneal elasticity

We report on a noninvasive and noncontact all-optical method to measure the elasticity of the cornea. We use a pulsed laser to excite surface acoustic waves (SAW) that propagate on the corneal surface, then use a phase-sensitive optical coherence tomography system to remotely record the SAWs from which the corneal elasticity is estimated. In addition, the system is able to provide real-time tomographic images of the cornea being examined, an important consideration for clinical studies. While precisely maintaining a range of intraocular pressures (IOP), a series of measurements is performed on ex vivo intact primate eyes. The measurement results not only demonstrate the feasibility of the proposed system to remotely measure the corneal elasticity, but also suggest a strong correlation between the corneal stiffness and the true IOP.     

A structure determination protocol based on combined analysis of 3D-ED data,powder XRD data,solid-state NMR data and DFT-D calculations reveals the structure of a new polymorph of l-tyrosine

We report the crystal structure of a new polymorph of l-tyrosine (denoted the β polymorph), prepared by crystallization from the gas phase following vacuum sublimation. Structure determination was carried out by combined analysis of three-dimensional electron diffraction (3D-ED) data and powder X-ray diffraction (XRD) data. Specifically, 3D-ED data were required for reliable unit cell determination and space group assignment, with structure solution carried out independently from both 3D-ED data and powder XRD data, using the direct-space strategy for structure solution implemented using a genetic algorithm. Structure refinement was carried out both from powder XRD data, using the Rietveld profile refinement technique, and from 3D-ED data. The final refined structure was validated both by periodic DFT-D calculations, which confirm that the structure corresponds to an energy minimum on the energy landscape, and by the fact that the values of isotropic ¹³C NMR chemical shifts calculated for the crystal structure using DFT-D methodology are in good agreement with the experimental high-resolution solid-state ¹³C NMR spectrum. Based on DFT-D calculations using the PBE0-MBD method, the β polymorph is meta-stable with respect to the previously reported crystal structure of l-tyrosine (now denoted the α polymorph). Crystal structure prediction calculations using the AIRSS approach suggest that there are three other plausible crystalline polymorphs of l-tyrosine, with higher energy than the α and β polymorphs.

A new polymorph of l-tyrosine is reported, with the crystal structure determined by combined analysis of 3D-ED data and powder XRD data, augmented by information from periodic DFT-D calculations and solid-state ¹³C NMR data.     

Solvent effects in the chlorination of tetrahydrothiophens with n-chlorosuccinimide

Depending simply on solvent, the reaction of N-chlorosuccinimide with tetrahydrothiophen can be arranged to give either 2-chloro-tetrahydrothiophen or 2,3-dichlorotetrahydrothiophen. In the latter case, a novel compound, 2-(4-chlorobutylthio)thiophen was isolated also. For 2-methyl- and 2,5-dimethyltetrahydrothiophen the solvent dependency was almost entirely eliminated, the principal reaction products being those resulting from dichlorination.     

Admissible estimation,Dirichlet principles and recurrence of birth-death chains on ℤ + p

Summary We establish a connection between admissible simultaneous estimation and recurrence of reversible Markov chains on ₊ ^p . Specifically, to each generalized Bayes estimator of the mean of a vector of p independent Poisson variables for a weighted quadratic loss, we associate a variational problem and a reversible birth and death chain on ₊ ^p . The variational problem is closely related to the Dirichlet principle for reversible chains studied recently by Griffeath, Liggett and Lyons. Under side conditions, admissibility of the estimator is equivalent to zero infimal energy in the variational problem and to recurrence of the Markov chain. This yields analytic and probabilistic criteria for inadmissibility which are applied to establish a broad class of results and previous conjectures.Research supported by an Australian National University Scholarship and A.D. White Fellowship at Cornell University and by NSF at Mathematical Sciences Research Institute, Berkeley and at Stanford