Towards focusing using photonic crystal flat lens

We report on the numerical simulation and fabrication of a two-dimensional flat lens based on negative refraction in photonic crystals. The slab acting as a lens is made of an hole array (operating at the wavelength of 1.5 μm) etched in a InP/InGaAsP/InP semiconductor layer. We first study the key issues for the achievement of a negative refractive index taking advantage of folding of dispersion branches with main emphasis in dispersion properties rather than the opening of forbidden gaps. The diffraction and refraction regimes are analysed according to the comparison of the wave-vector with respect to the relevant dimensions of the hole array. In the second stage, we illustrate technological challenges in terms of e-beam lithography on a sub-micron scale and deep reactive ion etching for an indium phosphide based technology.     

Etude du couplage 2J(N15?H) en série hétérocyclique. Application à la détermination des constantes d'équilibres prototropiques rapides

The fast tautomeric equilibrium of (N¹⁵)-4-phenylisoxazolin-5-one ( 2 ) has been investigated by a study of ²J(N¹⁵? H₃) coupling. Comparison of the observed values for 2 and for the two fixed forms (N¹⁵)-2-methyl-4-phenylisoxazolin-5-one ( 3 ) and (N¹⁵)-4-phenyl-5-methoxyisoxazol ( 4 ) indicates a considerable amount of enolic type structure for 2 in basic media.     

染料J聚集体Langmuir_Blodgett膜光致发光谱的温度影响与多声子跃迁

在2 0 一3 0 0 K 的范围内测量了三种花青染料聚集体L a n g m i u r 一B lo d g e t t (L B ) 膜的光致发光谱. 随着温度下降零声子线J 峰强度的增大, 观察到声子伴带的异常加强. 分析表明生长不均匀的聚集体L B 膜具有低维晶体的特性, 声子祸合强, 且无辐射跃迁起着重要的作用. 关键词：     

Mechanism of UV laser-induced absorption in fused silica fibers

An alteration of absorption spectra of fused silica fibers under delivery of high-power (ultraviolet) UV laser radiation (4th harmonic of the Nd:YAG laser, wavelength 266 nm) was studied in comparison with their photoluminescent properties. Tested fibers were produced by various technologies based on PMCVD methods. The nature of defects responsible for UV absorption in fibers and the mechanisms of their photogeneration are discussed.     

Characterization of a model Phillips catalyst by mass spectrometry

A model Phillips catalyst for ethylene polymerization, prepared by spin coating a Cr(III)(Cr(acac)3) precursor on a silicon wafer, was submitted to an oxidative activation. Laser ablation Fourier transform mass spectrometry provided direct information on molecular species at the silicon wafer surface during activation. At 350 degrees C the chromium precursor was degraded, while chromium oxide species were formed. The chromium concentration decreased with temperature. The activated model catalyst was active for ethylene polymerization. Using complementary techniques (Fourier transform infrared spectroscopy, laser desorption/ionization mass spectrometry), the polymer was identified as crystalline polyethylene. After 1 h of polymerization at 160 degrees C, dome-like structures were observed by atomic force microscopy. Their morphologies were constituted of regions of parallel aligned lamellae of polymer.     

Low-field NMR water proton longitudinal relaxation in ultrahighly diluted aqueous solutions of silica-lactose prepared in glass material for pharmaceutical use

Low-field (0.02–4 MHz) proton nuclear magnetic resonance (NMR) longitudinal relaxometry was applied to ultrahighly diluted aqueous solutions in order to detect physical modifications induced in the solvent by the dilution process. A mixture of silica-lactose (1.67·10⁻⁵ M silica, 2.92·10⁻² M lactose) was initially solubilized in water or in saline, then submitted to eighteen iterative centesimal dilutions in water or in saline under vigorous vortex agitation and rigorously controlled atmospheric conditions, and compared to similarly treated pure water and saline as controls. Several independent series of samples were measured according to a blind protocol (total of 140 code-labelled samples). A slight frequency dispersion (about 4%) was found within the 0.02–4 MHz range, centered around 0.55 MHz, and ascribed to combined effects of silica and trace paramagnetic contaminants, both concentrated and in a reduced motion at the borosilicate wall tube interface. The iterative dilution-agitation process in pure water and saline induced no significant effect on relaxivity. Slightly increased relaxivity compared to solvent was found in the initial silica-lactose dilution (especially in saline, about 4%), which vanished unexpectedly slowly upon dilution, as adjusted to an arbitrary log-linear model. Statistical analysis was applied to succeed in discriminating solutions from their solvents beyond the 10⁻¹² level of dilution. No clear explanation emerged, but post-experiment chemical analysis revealed high amounts (6 ppm) of released silica from the glass material used, with excess in silicalactose samples, and lower amounts of trace paramagnetic contaminants in highly diluted silica-lactose samples, which could provide a clue.     

Mechanism of two-electron oxidation of deoxyguanosine 5'-monophosphate by a platinum(IV) complex

Many transition metal complexes mediate DNA oxidation in the presence of oxidizing radiation, photosensitizers, or oxidants. The final DNA oxidation products vary depending on the nature of metal complexes and the structure of DNA. Here we propose a mechanism of oxidation of a nucleotide, deoxyguanosine 5'-monophosphate (dGMP) by trans-d,l-1,2-diaminocyclohexanetetrachloroplatinum (trans-Pt(d,l)(1,2-(NH(2))(2)C(6)H(10))Cl(4), [Pt(IV)Cl(4)(dach)]; dach = diaminocyclohexane) to produce 7,8-dihydro-8-oxo-2'-deoxyguanosine 5'-monophosphate (8-oxo-dGMP) stoichiometrically. The reaction was studied by high-performance liquid chromatography (HPLC), (1)H and (31)P nuclear magnetic resonance (NMR), and electrospray ionization mass spectrometry (ESI-MS). The proposed mechanism involves Pt(IV) binding to N7 of dGMP followed by cyclization via nucleophilic attack of a phosphate oxygen at C8 of dGMP. The next step is an inner-sphere, two-electron transfer to produce a cyclic phosphodiester intermediate, 8-hydroxyguanosine cyclic 5',8-(hydrogen phosphate). This intermediate slowly converts to 8-oxo-dGMP by reacting with solvent H(2)O.     

The nonnegative MINQUE estimate

The purpose of this paper is to give a characterization of the nonnegative MINQUE estimate for variance components. A similar characterization has been given by Pukelsheim but only in some special cases. The proof presented here uses results from convex programming and emphasizes certain geometrical aspects of the nonnegative MINQUE estimate problem.