Three-dimensional polarized Monte Carlo atmospheric radiative transfer model (3DMCPOL): 3D effects on polarized visible reflectances of a cirrus cloud

A polarized atmospheric radiative transfer model for the computation of radiative transfer inside three-dimensional inhomogeneous mediums is described. This code is based on Monte Carlo methods and takes into account the polarization state of the light. Specificities introduced by such consideration are presented. After validation of the model by comparisons with adding-doubling computations, examples of reflectances simulated from a synthetic inhomogeneous cirrus cloud are analyzed and compared with reflectances obtained with the classical assumption of a plane parallel homogeneous cloud (1D approximation). As polarized reflectance is known to saturate for optical thickness of about 3, one could think that they should be less sensitive to 3D effects than total reflectances. However, at high spatial resolution (80 m), values of polarized reflectances much higher than the ones predicted by the 1D theory can be reached. The study of the reflectances of a step cloud shows that these large values are the results of illumination and shadowing effects similar to those often observed on total reflectances. In addition, we show that for larger spatial resolution (10 km), the so-called plane-parallel bias leads to a non-negligible overestimation of the polarized reflectances of about 7–8%.     

Determination of the ground state rotational constants for formaldehyde: H212CO and H213CO

The two isotopic species CH₂DCOOH and CH₂DCOOD of acetic acid have been investigated with microwave spectroscopy in order to determine the equilibrium configuration of the methyl group, which was found to be eclipsed with respect to the carbonyl group. Centrifugal distortion constants free from internal rotation effects have been determined. A r_s structure for the four hydrogens and a partial r₀ structure for the whole molecule are given.     

Hadronic gauge couplings in meson decays

The branching ratiosR(J→ππρ)≡Γ(J→ππρ)/Γ(J→ππ) for naturalJ ^P mesons have been evaluated under the assumption that theT(J→ππρ) amplitudes are generated by the gauge principle for ρ-mesons originally proposed by Sakurai in his approach to VMD. The ratios are predicted to increase withJ and are compatible with the present-day data. This suggests that the hadronic interactions of the photon proceed exclusively through its hadronic (VMD) component.     

Spin dependence of heavy quark fragmentation

We propose that the non-perturbative part of the fragmentation function describing the transition from a heavy quark to a heavy meson is proportional to the square of the produced meson wave function at the origin, taking into account hyperfine interactions. We analyze the effects of this proposal on the number of pseudoscalar mesons compared to the number of vector mesons produced and find a good agreement with experimental data. Finally, we discuss further experimental checks for our hypothesis.     

Properties and structure of AsTe glasses (II). Local order parameters and structural model

Diffraction measurements on bulk and thin films AsTe glasses are reported, throughout the whole range of stability. FNP distances and areas, average valence angles and compactness are determined from the Fourier transform. For As-rich glasses important differences are found between short-range order in both vitreous and crystalline states. An interpretation at the molecular scale is proposed. It takes account of the particular topological properties of the AsTe molecules, which are evidenced by hand-made models. The proposed structure consists of a network of AsTe_3/2 units which are interconnected through “AsAs locks”. It is shown that these “locks” play a crucial role in the stability of the As-rich glasses in favoring strongly the covalent bonds. On the other hand, in Te-rich glasses there is no similar locking mechanism. The presence of threefold-coordinated tellurium sites enhances the metallic character, and weakens the difference between crystalline and vitreous states. The structural models which are proposed enable us to explain the anomalies and the discontinuities of most thermodynamic properties which are described in paper I.     

Time resolved luminescence of CdS at high excitation

We report a study at low temperature of the time resolved luminescence of CdS, excited by two photon absorption. Concerning the so called EHP-LO and P bands, we confirm our results previously obtained on CdSe[1, 2]. (a) At high excitation a broad band (peak position at λ > 495 nm) occurs due to radiative recombination in an electron hole plasma, assisted by the emission of one LO phonon. (b) The simultaneous kinetics of the P line (λ ? 490.5 nm) and A-LO line (λ ? 492.5 nm) are conflicting with the interpretation of the P line as resulting of radiative exciton-exciton collisions. We interpret the P line as due to biexciton recombination.We have studied the luminescence in the (I₂-I₁) region (486nm < λ < 490nm) at low excitation. We observe clearly the following, (a) A broad band (488 nm < λ < 490.5 nm) which corresponds to the gain observed in previous experiments of pulse and probe spectroscopy and interpreted as direct recombination in an electron hole liquid (EHL). (b) After the disappearance of the EHL band, one single line (M_D), which shifts continuously towards the I₂ position during the time resolved kinetics. We suggest it to be connected with the high excitation effect on donor impurities (bound polyexcitons).     

Metalation of 4-oxazolinyloxazole derivatives. A convenient route to 2,4-bifunctionalized oxazoles

The synthesis of an array of 5-phenyloxazole derivatives bearing a variety of hydroxyalkyl groups at the C-2 position of the heterocyclic nucleus and possessing a formyl or a carboxyl function at C-4 is reported. These bifunctionalized compounds have been efficiently prepared by addition of carbonylated electrophiles to the 2-lithio derivative of 5-phenyloxazole preliminarily equipped with an oxazoline unit at the 4-position of the oxazole nucleus. It is demonstrated that this protocol offers a double advantage since it suppresses the troublesome electrocyclic ring-opening reaction and allows access to the target compounds by simple chemical transformation of the oxazoline ring system.     

TeV strings and the neutrino-nucleon cross section at ultrahigh energies

In scenarios with the fundamental unification scale at the TeV one expects string excitations of the standard model fields at accessible energies. We study the neutrino-nucleon cross section in these models. We show that duality of the scattering amplitude forces the existence of a tower of massive leptoquarks that mediate the process in the s channel. Using the narrow-width approximation we find a sum rule for the production rate of resonances with different spin at each mass level. We show that these contributions can increase substantially the standard model neutrino-nucleon cross section, although they seem insufficient to explain the cosmic ray events above the Greisen-Zatsepin-Kuz'min cutoff energy.     

A structural and theoretical investigation of equatorial cis and trans uranyl phosphinimine and uranyl phosphine oxide complexes UO2Cl2(Cy3PNH)2 and UO2Cl2(Cy3PO)2

Phosphinimine ligands (Cy3PNH) readily react with UO2Cl2(THF)3 (THF=tetrahydrofuran) to give UO2Cl2(Cy3PNH)2, which contains strong U-N interactions and exists as cis and trans isomers in the solid and solution state. Solution NMR experiments and computational analysis both support the trans form as the major isomer in solution, although the cis isomer becomes more stabilized with an increase in the dielectric constant of the solvent. Mayer bond orders, energy decomposition analysis, and examination of the molecular orbitals and total electron densities support a more covalent bonding interaction in the U-NHPCy3 bond compared with the analogous bond of the related U-OPCy3 compounds.