Appendice: Sur un théorème de Bloch et Kato (lettre à B. Perrin-Riou)

Sans résuméOblatum 21-VI-1993     

Microbubble drag reduction in rough walled turbulent boundary layers with comparison against polymer drag reduction

Experiments were conducted in the 12-inch diameter tunnel at the Applied Research Laboratory, Pennsylvania State University using the tunnel wall boundary layer to determine the influence of surface roughness on microbubble drag reduction. To accomplish this, carbon dioxide was injected through a slot at rates of 0.001 m³/s to 0.011 m³/s, and the resulting skin friction drag measured on a 317.5-mm long by 152.4-mm span balance. In addition to the hydrodynamically smooth balance plate, additional plates were covered with roughly 75, 150, and 300 micron grit. Over the speed range tested of 7.6, 10.7, and 13.7 m/s, the roughness ranged from smooth to fully rough. Not only was microbubble drag reduction achieved over the rough surfaces, but the % drag reduction at a given gas flow rate was larger for larger roughness. Scaling of the data is discussed. Comparison against results of a polymer drag reduction experiment, using the same facility, is made. Finally, a measure of the expected persistence of the phenomenon is given.     

Intramolecular interactions of L‐phenylalanine: Valence ionization spectra and orbital momentum distributions of its fragment molecules

Intramolecular interactions between fragments of L ‐phenylalanine, i.e., phenyl and alaninyl, have been investigated using dual space analysis (DSA) quantum mechanically. Valence space photoelectron spectra (PES), orbital energy topology and correlation diagram, as well as orbital momentum distributions (MDs) of L ‐phenylalanine, benzene and L ‐alanine are studied using density functional theory methods. While fully resolved experimental PES of L ‐phenylalanine is not yet available, our simulated PES reproduces major features of the experimental measurement. For benzene, the simulated orbital MDs for 1e_1g and 1a_2u orbitals also agree well with those measured using electron momentum spectra. Our theoretical models are then applied to reveal intramolecular interactions of the species on an orbital base, using DSA. Valence orbitals of L ‐phenylalanine can be essentially deduced into contributions from its fragments such as phenyl and alaninyl as well as their interactions. The fragment orbitals inherit properties of their parent species in energy and shape (ie., MDs). Phenylalanine orbitals show strong bonding in the energy range of 14‐20 eV, rather than outside of this region. This study presents a competent orbital based fragments‐in‐molecules picture in the valence space, which supports the fragment molecular orbital picture and building block principle in valence space. The optimized structures of the molecules are represented using the recently developed interactive 3D‐PDF technique. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011     

Sensitivity improvement in laser ablation inductively coupled plasma mass spectrometry achieved using a methane/argon and methanol/water/argon mixed gas plasma

The influence of the addition of carbon using methane or methanol/water to an inductively coupled plasma (ICP) via the carrier gas flow on the sensitivity in laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was studied. During the ablation of SRM NIST 610 with simultaneous addition of CH(4) (0.6-1.4 ml min(-1)), a sensitivity enhancement of more than one order of magnitude for selected analytes (e.g. (75)As(+)) was observed. In addition to the sensitivity enhancement for As, Te, I and Se, also all other measured elements showed a significantly enhanced sensitivity (minimum by a factor of 2). Potential mechanisms for the observed intensity enhancement include charge transfer reactions, a change in the ICP shape and a temperature increase in the plasma. Furthermore, the aspiration of a methanol-water mixture into a cooled spray chamber and the simultaneous addition to the laser ablated aerosol was investigated. This type of mixing leads to a sensitivity enhancement up to a factor of 20. To prevent clogging of the sampler cone and skimmer cone by carbon deposition, a fast cleaning procedure for the interface is tested during running ICP, which allows the application of such a set-up for specific applications.     

Urease inhibition and anti-leishmanial assay of substituted benzoylguanidines and their copper(II) complexes

A series of N,N',N'-trisubstituted guanidines (1-6) and their copper(II) complexes, [κ(2)(O,N)-C(6)H(5)CONHC(NHC(6)H(4)Cl)NR](2)Cu(ii) (R = iso-propyl (1a), n-butyl (2a), sec-butyl (3a), tert-butyl (4a), benzyl (5a), and para-tolyl (6a)) were synthesized and characterized using elemental analysis, FTIR and NMR spectroscopy. DFT studies were used to assess the location of the protons in the free ligands. However, calculations have shown that, in all cases, hydrogen bonding from either N-H group gives conformations that are very similar in energy. Single crystal XRD studies were used to characterize ligands 1 and 4 and the related complexes 1a and 4a. The structures reveal that these complexes are mononuclear in the solid state and that copper adopts a regular square planar geometry. In both metallic species, the N, N', N'-trisubstituted guanidine ligands chelate the Cu(II) atom using the oxygen and one nitrogen. The synthesized compounds were investigated for urease inhibition using thiourea as a standard drug. Most complexes exhibit a better activity than the respective guanidines and compound 1a was found to be the most active with IC(50) = 9.83 ± 0.07 μM (the IC(50) for thiourea is 21.0 ± 0.1 μM). The species were also screened for their anti-leishmanial activity. However, all of the compounds were devoid of any significant activity.     

Relativistic effects in spectroscopy and photophysics of heavy-metal complexes illustrated by spin–orbit calculations of [Re(imidazole)(CO)3(phen)]+

Spin–orbit coupling (SOC) is an essential factor in photophysics of heavy transition metal complexes. By enabling efficient population of the lowest triplet state and its strong emission, it gives rise to a very interesting photophysical behavior and underlies photonic applications such as organic light emitting diodes (OLED) or luminescent imaging agents. SOC affects excited-state characters, relaxation dynamics, radiative and nonradiative decay pathways, as well as lifetimes and reactivity. We present a new photophysical model based on mixed-spin states, illustrated by relativistic spin–orbit TDDFT and MS-CASPT2 calculations of [Re(imidazole)(CO)₃(1,10-phenanthroline)]⁺. An excited-state scheme is constructed from spin–orbit (SO) states characterized by their energies, double-group symmetries, parentages in terms of contributing spin-free singlets and triplets, and oscillator strengths of corresponding transitions from the ground state. Some of the predictions of the relativistic SO model on the number and nature of the optically populated and intermediate excited states are qualitatively different from the spin-free model. The relativistic excited-state model accounts well for electronic absorption and emission spectra of Re^I carbonyl diimines, as well as their complex photophysical behavior. Then, we discuss the SO aspects of photophysics of heavy metal complexes from a broader perspective. Qualitative SO models as well as previous relativistic excited-state calculations are briefly reviewed together with experimental manifestations of SOC in polypyridine and cyclometallated complexes of second- and third row d⁶ metals. It is shown that the relativistic SO model can provide a comprehensive and unifying photophysical picture.     

Modulating the photophysical properties of azamacrocyclic europium complexes with charge-transfer antenna chromophores

Two europium complexes with bis(bipyridine) azamacrocyclic ligands featuring pendant arms with or without π-conjugated donor groups are synthesized and fully characterized by theoretical calculations and NMR spectroscopy. Their photophysical properties, including two-photon absorption, are investigated in water and in various organic solvents. The nonfunctionalized ligand gives highly water-stable europium complexes featuring bright luminescence properties but poor two-photon absorption cross sections. On the other hand, the europium complex with an extended conjugated antenna ligand presents a two-photon absorption cross section of 45 GM at 720 nm but is poorly luminescent in water. A detailed solvent-dependent photophysical study indicates that this luminescence quenching is not due to the direct coordination of O-H vibrators to the metal center but to the increase of nonradiative processes in a protic solvent induced by an internal isomerization equilibrium.     

The effects of gate length variation and trapping effects on the transient response of AlGaN/GaN HEMT’s on SiC substrates

In AlGaN/GaN heterostructure field-effect transistors, the surface defects and dislocations may serve as trapping centers and affect the device performance via leakage current. In this paper we report results of our investigation of the trapping characteristics of Al_0.25Ga_0.75N/GaN HEMT using the Conductance Deep Level Transient Spectroscopy (CDLTS). Two deep level electronic defects were observed labeled E₁ and HL₁, with activation energies E_a1 = 1.36 eV and E_a2 = 0.63 eV. The hole-trap HL₁ is characterized for the first time in our studies. We identified the characteristics of the traps at the AlGaN/GaN interface adjoining the channel and the surface along the ungated region between the gate and the drain, as well as the effects of the surface traps.     

Reactivity of Lewis pairs (R2PCH2AlMe2)2 with carbon dioxide

Species R(2)PCH(2)AlMe(2) (R = Me, Ph) are stable Lewis adducts but still react with CO(2) both in solution and in the solid state. The CO(2) adducts undergo a rearrangement unprecedented for ambiphilic molecules to form aluminium carboxylates. A new spirocyclic compound was also obtained by double Lewis pair activation of CO(2).