Surface-reflection elimination in polarization imaging of superficial tissue

A major drawback in polarization gating of light backscattered from tissue is that surface reflections dominate the image. An optically flat plate and matching fluid applied to the tissue surface, combined with off-axis detection, were previously used to address this problem. This approach is often inappropriate or inconvenient for practical use and more importantly can affect the tissue's optical properties. A method is demonstrated that combines images obtained with linearly and circularly polarized light to produce a polarization-gated image that is free from surface reflections and does not require optically flat plates or matching fluid.     

Direct measurement of the spatial Wigner function with area-integrated detection

We demonstrate experimentally a novel technique for characterizing transverse spatial coherence by using the Wigner distribution function. The method is based on the measurement of interference between a pair of rotated and displaced replicas of the input beam with an area-integrating detector, and it provides an optimal signal-to-noise ratio in regimes when array detectors are not available. We analyze the quantum-optical picture of the presented measurement for single-photon signals and discuss possible applications in quantum information processing.     

Universal quadratures for boundary integral equations on two-dimensional domains with corners

We describe the construction of a collection of quadrature formulae suitable for the efficient discretization of certain boundary integral equations on a very general class of two-dimensional domains with corner points. The resulting quadrature rules allow for the rapid high-accuracy solution of Dirichlet boundary value problems for Laplace’s equation and the Helmholtz equation on such domains under a mild assumption on the boundary data. Our approach can be adapted to other boundary value problems and certain aspects of our scheme generalize to the case of surfaces with singularities in three dimensions. The performance of the quadrature rules is illustrated with several numerical examples.     

设计阻挫

所谓几何阻挫,是指缘起材料晶格几何结构的一类现象。阻挫系统中,如果近邻作用无法同时满足能量极小,就会出现几何阻挫。最简单的自旋阻挫系统由三个位于正三角形顶点且两两之间反铁磁耦合的伊辛(Ising)自旋组成,无论何种自旋构型都无法使所有近邻自旋满足反铁磁排列。相对于此,复杂情况下的自旋阻挫往往是系统晶格结构以及特定自旋相互作用叠加的结果。在阻挫之茫茫世界中,自旋相互作用之间的竞争会导致许多新奇物理现象。就像自旋液体,即便温度极低,自旋涨落却依然很强,使之无法弛豫到基态,皆因于此。     

4‐Anilino‐3‐nitro­pyridine

The structure of the title compound, C₂₂H₁₈N₆O₄, (I), comprises two unique mol­ecules that separately form hydrogen‐bonded polymer chains via N—H?N interactions. Molecular independence arises due to a difference in the dihedral angles between the linked rings, i.e. 52.19 (4) and 46.17 (5)°.     

4,6‐Di­chloro‐2‐(methyl­thio)­pyrimidine

The structure of the title compound, C₃₀H₂₄Cl₁₂N₁₂S₆, (I), comprises six symmetry unique mol­ecules that vary only slightly in their N—C—S—C torsion angle. All the mol­ecules are planar to within less than 3.1°.     

Nanocrystalline TiO2 films studied by optical, XRD and FTIR spectroscopy

We report the deposition of thin titanium dioxide films on Si(1 0 0) and silica glass at low temperatures between 200 and 350 °C by a technique of ultraviolet-assisted injection liquid source chemical vapor deposition (UVILS-CVD) with 222 nm radiation. The composition and optical properties of the films deposited have been studied using a variety of standard characterisation methods. A strong absorption peak around 438 cm⁻¹, corresponding to Ti-O stretching vibration, was observed by Fourier transform infrared spectroscopy for different deposition temperatures. Nanostructured films on Si wafers were observed by atomic force microscopy while X-ray diffraction results showed that crystalline TiO₂ layers could be formed at deposition temperatures as low as 210 °C. The deposition kinetics and influence of the substrate temperature on the film are discussed. The activation energy for this photo-CVD process at temperatures between 200 and 350 °C was found to be 0.435 eV. This is much lower than the value (E_a=5.64 eV) obtained by conventional thermal CVD. The thicknesses of the films grown, from several nanometers to micrometers can be accurately controlled by changing the number of drops introduced by the injection liquid source. Under optimum deposition conditions, refractive index values as high as 2.5 and optical transmittance of between 85% and 90% in the visible region of the spectrum can be obtained.     

Structure of 2,2′-bis(3-allyl-4-cyanatophenyl)isopropylidene

The structure of the title compound (I) was determined by direct methods using MoK diffractometer data, and refined by full-matrix least squares toR=0.066 for 1536 reflections (I3 (I)). The structure shows a central tetrahedral carbon atom surrounded by two methyl and two 3-allyl-4-cyanatophenyl groups. The geometry of the cyanato group in this molecule compares well with those in 2,2-bis(4-cyanatophenyl)isopropylideneII) and 4-chloro-3,5-dimethyl-phenylcyanate (III), the only other examples of organic compounds bearing the cyanato moiety in the Cambridge Crystallographic Database (V.3).     

Crystal structure, vibrational spectra, and thermal decomposition and nitrogen adsorption behaviour of a new tetramanganese(II) dipyrophosphate decahydrate, Mn4(P2O7)2·10H2O

A new manganese(II) pyrophosphate, Mn₄(P₂O₇)₂·10H₂O, has been synthesized and characterized by single-crystal X-ray diffraction [orthorhombic space group Pnma, with unit cell parameters of a=9.3288(3) ?, b=25.9532(9) ?, c=8.4783(3) ?; Z=4]. All the pyrophosphate anions show non-linear P–O–P bonds with an average angle of 128.60°. The framework of this new pyrophosphate is made up of packed layers of MnO₆ octahedra connected by double-tetrahedra P₂O₇ groups and a layer of Mn(H₂O)₆ units. The [P₂O₇]⁴⁻ anions adopt a bent, near-staggered conformation. The absence of coincidences for the majority of the IR and Raman bands is in accord with the centrosymmetric structure of the material. The vibrational spectra have been interpreted in part on the basis of factor group effects. The structural changes occurring during heating have been investigated by TG-ATD. When Mn₄(P₂O₇)₂ ^.10H₂O is gradually heated, it decomposes into an intermediate hydrated salt at 96°C and then to anhydrous Mn₂P₂O₇ at 325°C. This thermal behaviour is different from that of Zn₄(P₂O₇)₂·10H₂O. The crystal structure of the new managenese(II) pyrophosphate is compared with the known structures of Zn₄(P₂O₇)₂·10H₂O, Mn₂P₂O₇·2H₂O and anhydrous Mn₂P₂O₇. The adsorption and desorption isotherms of Mn₄(P₂O₇)₂·10H₂O, Zn₄(P₂O₇)₂·10H₂O and MnKHP₂O₇·2H₂O have been investigated by BET measurements and the results show that the capacity for N₂ sorption of the Mn(II) salt is two times lower than is that of the Zn(II) isotype and two or three times higher than is that of MnKHP₂O₇·2H₂O.     

Crystal structure of 6-nitrobenzo(a)pyrene

In 6-nitrobenzo(a)pyrene, an environmental pollutant, the nitro substituent lies at 69.5(1) to the mean plane of the aromatic moiety. The C–C bond distances range from 1.341(3) to 1.443(3) Å. The crystal is in the monoclinic space group, P2₁/c, with a = 8.3239(3) Å, b = 8.9530(3) Å, c = 18.0678(5) Å, = 99.264(2) and Z = 4. Molecules are assembled in sheets in the unit cell through stacking and alternating C–H O interactions.