First demonstration of “white-light” laser cooling of a stored ion beam

“White-light” cooling of an ion beam confined in a storage ring has been demonstrated at Test Storage Ring in Heidelberg. Measurements aimed at comparing “white-light” with single-mode laser cooling show that “white-light” cooling gives lower temperatures at higher ion densities both in a coasting and in a bunched beam. This revised version was published online in July 2006 with corrections to the Cover Date.     

Formation of the polycrystalline FeSi phase with the CsCl structure in codeposited thin Fe x Si1 ? x films ( x = 0.5–0.6)

Specific features of the phase formation in the Fe-Si system within the Fe _x Si_{1 − x} (x = 0.5–0.6) concentration range have been investigated. The data obtained by conversion electron M?ssbauer spectroscopy suggest that, for the Fe-Si system in the concentration range x > 0.55, a polycrystalline FeSi phase with the CsCl structure is formed under thermodynamically equilibrium conditions upon annealing at T = 250°C; in this case, the excess (overstoichiometric) Fe atoms are incorporated into the Si sublattice. Previously, the CsCl-FeSi phase was observed only in epitaxially stabilized FeSi/Si(100) layers. Original Russian Text ? A.V. Zenkevich, D.E. Lauer, V.P. Filippov, 2007, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2007, Vol. 71, No. 9, pp. 1313–1315.     

Dual photochemistry of anthracene-9,10-endoperoxide studied by femtosecond spectroscopy

The dual photochemistry of anthracene-9,10-endoperoxide (APO) was investigated in a fs UV pump-supercontinuum probe experiment, along with anthracene (AC) and anthraquinone (AQ) for comparison. Excitation of APO at 282 nm leads to 100% product formation by two competing photoreaction channels. Cycloreversion generates with a ～25% quantum yield (QY) (1)O(2) and AC vibrationally excited in the singlet electronic ground state (hot AC). 1-2% of the AC is generated in the lowest triplet state, but no AC is generated in electronically excited singlet states. Generation and cooling of hot AC are modeled using solution phase and broadened gas-phase AC absorption spectra at various temperatures. Results indicate ultrafast generation of hot AC within 3 ps, much faster than reported before for derivatives of anthracene endoperoxide, and subsequent cooling with an 18 ps time constant. The homolytic O-O cleavage pathway generates a biradical, which converts into electronically excited diepoxide (DE). Our data indicate a 1.5 ps time constant that we tentatively assign to the biradical decay and DE formation. Cooling of DE in this electronically excited state takes place with a ～21 ps time constant. Excitation of AQ at 266 nm is followed by an ultrafast population of the T(1)(nπ*) triplet state of AQ with a time constant of (160 ± 60) fs.     

Visualizing Loglinear Models

Abstract

We consider visual methods based on mosaic plots for interpreting and modeling categorical data. Categorical data are most often modeled using loglinear models. For certain loglinear models, mosaic plots have unique shapes that do not depend on the actual data being modeled. These shapes reflect the structure of a model, defined by the presence and absence of particular model coefficients. Displaying the expected values of a loglinear model allows one to incorporate the residuals of the model graphically and to visually judge the adequacy of the loglinear fit. This procedure leads to stepwise interactive graphical modeling of loglinear models. We show that it often results in a deeper understanding of the structure of the data. Linking mosaic plots to other interactive displays offers additional power that allows the investigation of more complex dependence models than provided by static displays.     

Experimental investigation of a low-cost solid state detector with high spatial resolution for ultracold neutrons

An ultracold-neutron detector based on a commercial CMOS webcam was investigated for the first time at the instrument PF2 of the Institut Laue-Langevin. In this feasibility study two different neutron converters, ¹⁰B and ⁶Li, were compared. For a standard high-definition videochip with an active area of 3.2 mm × 4.8 mm, a spatial resolution of ≈ 0.3 μm is possible to obtain. For a 430 nm thin ⁶Li converter, positioned in front of the webcam, a detection efficiency of (47.1 ± 0.6)% was found.     

Application of the FAKE molecular-orbital method to diatomic molecules XY (X,Y = H,F, Cl,Br, I)

Theoretical Chemistry Accounts - The FAKE (fast, accurate kinetic energy) method of semiempirical molecular orbital calculation is applied to diatomic molecules XY (X, Y= H, F, Cl, Br, I). The...     

Irreversible or reversible self-assembly procedures yield robust zirconium (IV)-porpyrinphosphonate cones or microm-long fibers of monomolecular thickness

Stepwise, irreversible self-assembly of porphyrinphosphonates by zirconium(IV) produces cones of 20 nm height and similar widths. Side-on growth cannot be prevented. Reversible fiber growth without metal ions gave micrometer long fibers on mica of 2 nm width, because charge repulsion allowed only for end-on growth.