Carbonates,thiocarbonates, and the corresponding monoalkyl derivatives: III. The 13C chemical shift tensors in potassium carbonate,bicarbonate and related monomethyl derivatives

The principal values of the 13C chemical shift tensors in potassium carbonate (K2CO3), trithiocarbonate (K2CS3), bicarbonate (KHCO3), methylcarbonate (KO2COCH3), S-methyl-monothiocarbonate (KO2CSCH3), O-methyl-monothiocarbonate (KOSCOCH3), S-methyl-dithiocarbonate (KOSCSCH3), and O-methyl-dithiocarbonate (KS2COCH3), were measured in solid-state nuclear magnetic resonance experiments. Chemical shift tensor calculations on the corresponding isolated anions were used to assign the chemical shift tensor orientations in the molecular frames of all anions. The correlation between experimental and calculated principal values improves significantly when the calculations are performed on isolated anions with proton-optimized X-ray geometries rather than on isolated anions with fully optimized geometries. Further considerable improvement in the correlation is achieved by utilizing the embedded ion method, which was recently developed to include electrostatic crystal potentials in chemical shift tensor calculations on ionic compounds. Similarities and differences in the chemical shift tensor orientations and principal values of the trigonal sp2 carbon atoms in the carbonate and thiocarbonate anions are compared with those known for condensed polyaromatic hydrocarbons.     

Self-assembling porphyrin-modified peptides

[structure: see text] We report the synthesis and characterization of a novel supramolecular assembly that features long-range electronic coupling between porphyrins covalently attached to a designed peptide scaffold. The resulting construct self-assembles to form extended organized aggregates in which the porphyrins engage in exciton coupling.     

Origin of the asymmetric magnetization reversal behavior in exchange-biased systems: competing anisotropies

The magnetization reversal in exchange-biased ferromagnetic-antiferromagnetic (FM-AFM) bilayers is investigated. Different reversal pathways on each branch of the hysteresis loop, i.e., asymmetry, are obtained both experimentally and theoretically when the magnetic field is applied at certain angles from the anisotropy direction. The range of angles and the magnitude of this asymmetry are determined by the ratio between the FM anisotropy and the interfacial FM-AFM exchange anisotropy. The occurrence of asymmetry is linked with the appearance of irreversibility, i.e., finite coercivity, as well as with the maximum of exchange bias, increasing for larger anisotropy ratios. Our results indicate that asymmetric hysteresis loops are intrinsic to exchange-biased systems and the competition between anisotropies determines the asymmetric behavior of the magnetization reversal.     

Measurement of geometric phase for mixed states using single photon interferometry

Geometric phase may enable inherently fault-tolerant quantum computation. However, due to potential decoherence effects, it is important to understand how such phases arise for mixed input states. We report the first experiment to measure mixed-state geometric phases in optics, using a Mach-Zehnder interferometer, and polarization mixed states that are produced in two different ways: decohering pure states with birefringent elements; and producing a nonmaximally entangled state of two photons and tracing over one of them, a form of remote state preparation.     

Ince-Gaussian series representation of the two-dimensional fractional Fourier transform

We introduce the Ince-Gaussian series representation of the two-dimensional fractional Fourier transform in elliptical coordinates. A physical interpretation is provided in terms of field propagation in quadratic graded-index media whose eigenmodes in elliptical coordinates are derived for the first time to our knowledge. The kernel of the new series representation is expressed in terms of Ince-Gaussian functions. The equivalence among the Hermite-Gaussian, Laguerre-Gaussian, and Ince-Gaussian series representations is verified by establishing the relation among the three definitions.     

Generation of hyperentangled photon pairs

We experimentally demonstrate the first quantum system entangled in every degree of freedom (hyperentangled). Using pairs of photons produced in spontaneous parametric down-conversion, we verify entanglement by observing a Bell-type inequality violation in each degree of freedom: polarization, spatial mode, and time energy. We also produce and characterize maximally hyperentangled states and novel states simultaneously exhibiting both quantum and classical correlations. Finally, we report the tomography of a 2 x 2 x 3 x 3 system (36-dimensional Hilbert space), which we believe is the first reported photonic entangled system of this size to be so characterized.     

A sorbent tube for oral malodour monitoring

Volatile sulphur compounds (VSCs) and particularly hydrogen sulphide are considered as the predominant gases causing oral malodour. In this paper, a simple alarm sensor has been developed for VSCs determination in mouth air. The device consists of a glass tube packed with a solid sensing phase. The VSCs react with the sensing phase to produce a change in the colour of the sensor visible with a naked eye.Different “reagents” were investigated to develop the sensing phase (neocuproine + Cu(II), bathocuproine + Cu(II), resazurin, 2,6-dichlorophenolindophenol and lead acetate), finding the neocuproine + Cu(II) as the best for our purposes. Also, different substrates such as Amberlite XAD-4 and XAD-7 and different trademarks of silica gel were tested as solid supports, being selected the silica gel.A device consisting of a glass tube packed with the sensing phase was optimized and tested with halitosis patients as a rapid illness test and the results compared with those obtained with a commercially available instrument, the Halimeter™, used for the determination of VSCs in mouth air. The results exhibited acceptable agreement between the proposed “qualitative” alarm sensor and a commercially available technique selected as reference, showing the possibility of using this “visual sensor” to control the halitosis and its evolution with an eventual treatment, by the own patient.     

Self-similar solutions of the porous medium equation in a half-space with a nonlinear boundary condition: existence and symmetry

We find existence of a nonnegative compactly supported solution of the problem Δu=u^α in , ∂u/∂ν=u on . Moreover, we prove that every nonnegative solution with finite energy is compactly supported and radially symmetric in the tangential variables.