Analysis of collisional alignment and orientation studied by scattering of spin-polarized electrons from laser excited atoms

A general framework using density matrices is developed for the analysis of atomic excitation by spin-polarized electrons. This framework is applied to the specific case of the 3S _1/2→3P _3/2 transition in Na, as studied by the time-reversed, superelastic process. The scattering is characterized in terms of physical parameters describing the collisionally excitedp-state, i.e., its angular momentum (L _⊥), linear polarization (P _lin), and alignment angle (γ), with these parameters defined separately for singlet and triplet excitation. An expression for the scattering intensity is derived which is valid for arbitrary electron polarization and atomic state preparation. Specific examples are discussed with a view toward complete determination of the relevant scattering amplitudes and phases. Recent experimental results are reevaluated for comparison with theoretical calculations, and suggestions are made for future experiments.     

Videofluoroscopic and Laryngoscopic Evaluation of the Upper Airway and Larynx of Professional Bassoon Players

The bassoon is a demanding double-reed woodwind instrument requiring exquisite control of airflow and air pressure to the reed to produce desired tonal characteristics. Little information is available from direct visualization of the vocal tract and larynx of the bassoonist while playing. Of particular interest is the mechanism(s) of vibrato. This study was undertaken to understand more fully the mechanics of the upper airway in bassoonists during music production. Four adult bassoon players served as subjects. Three players were studied with both sound-synchronized videofluoroscopy and fiber-optic nasal endoscopy. The other subject was studied only by fiber-optic endoscopy. All subjects were evaluated while playing various scales and standard passages common in music pedagogy. The results from this study revealed several findings on the mechanics of upper airway activity during playing: (1) firm velopharyngeal closure was a prerequisite for maximal containment of air pressure and regulation of airflow in the oropharyngeal regions; (2) changes in the pitch and intensity were associated with differential expansion of the pharynx; (3) tongue activity was notable because of its shaping the size and shape of the airway, its role in regulating airflow to the reed, and its contributions to conditioning airflow in vibrato; and (4) slight vocal fold displacements from subglottal airflow and epiglottic movements from tongue base activity contributed to airway changes during vibrato. These seemed to further condition subglottal pressure trains derived primarily from expiration.     

Diels-alder reactions with 2-(Arylsulfinyl)-1,4-benzoquinones: effect of aryl substitution on reactivity, chemoselectivity, and pi-facial diastereoselectivity

Diels-Alder reactions of (SS)-2-(2'-methoxynaphthylsulfinyl)-1, 4-benzoquinone (1b), 2-(p-methoxyphenylsulfinyl)-1,4-benzoquinone (1c), and 2-(p-nitrophenylsulfinyl)-1,4-benzoquinone (1d) with cyclopentadiene are reported. These cycloadditions allowed the highly chemo- and stereoselective formation of both diastereoisomeric endo-adducts resulting from reaction on the unsubstituted double bond C(5)-C(6) of quinones working under thermal and Eu(fod)(3)- or BF(3).OEt(2)-catalyzed conditions. The synthesis of endo-adduct [4aS,5S,8R,8aR,SS]-9d resulting from cycloaddition on the substituted C(2)-C(3) double bond was achieved in a chemo- and diastereoselective way from quinone 1d in the presence of ZnBr(2). The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group.     

Effect of surface orientation and sulfur coverage on the oxidation of carbon on Ni surfaces

The reaction between adsorbed oxygen and segregated carbon on a cylindrical nickel single-crystal has been examined with Auger electron spectroscopy (AES) and temperature programmed desorption (TPD), for a range of surface orientation, oxygen exposure, and sulfur coverage. It was found that for small oxygen exposures, surface carbon and surface oxygen react during TPD to form a CO desorption peak, labeled β₁. The β₁ CO peak temperature and peak shape vary with orientation. At higher oxygen coverages, the CO desorption peak split into low-temperature and high-temperature peaks. The behavior of the β₁ CO desorption peak for large oxygen exposures is consistent with a model of the carbon-oxygen recombination reaction in which the morphologies of the initial carbon and oxygen phases change during oxygen exposure as a result of repulsive lateral interactions. High oxygen exposures result in the formation of large regions of contact between the two phases; this is believed to produce the low-temperature β₁ CO desorption peak. Small segregated-sulfur coverages, and low oxygen exposures, caused the β₁ CO peak to shift to lower temperatures for all orientations. Sulfur is believed to cause more frequent contact between carbon and oxygen for small oxygen exposures because it compresses the adsorbed oxygen and segregated carbon into the sulfur-free areas of the surface. Large coverages of segregated sulfur inhibited carbon segregation on some, and oxygen adsorption on most, orientations. The absence of reactant species explains the disappearance of the β₁ CO peak during TPD from orientations which had a high sulfur coverage.     

Alignment locking to suspended Fabry-Perot cavity

In this paper we report on the alignment locking of an in vacuum 77 m long suspended mirror Fabry-Perot cavity. Lock was achieved by mode-matching a 500 mW Nd:YAG NPRO onto a pre-mode cleaner, the output of which was then mode-matched to the suspended cavity. The longitudinal locking was achieved by feeding back to the laser frequency actuator to follow the cavity resonance. Subsequent implementation of a hybrid auto-alignment system enhanced the stability of the circulating power inside the cavity. Preliminary results are presented.     

Time domain investigation on vibrational dephasing and spectral diffusion in CO-doped solid N2

Infrared picosecond accumulated photon echo experiments have been performed for the first time, using the Orsay Free Electron Laser, on the v = 0-->v = 1 transition of CO in solid nitrogen. The vibrational dephasing time is found to be exceptionally long ( T2>/=120 ns) at low temperature. The analysis of the observed spectral diffusion leads one to assume different energy transfer mechanisms depending on the CO concentration.