ARDESIA: A fast silicon drift detector X-ray spectrometer for synchrotron applications

ARDESIA, a four-channel X-ray spectrometer based on silicon drift detectors (SDDs), is presented. It has been developed for synchrotron applications targeting especially X-ray fluorescence (XRF) and X-ray absorption spectroscopy (XAS) with good energy resolution at high count rates (a few Mcps per second). The main target applications are XRF and XAFS techniques. The system features a 2 × 2 monolithic array of 5-mm-pitch SDDs cooled with a double Peltier scheme and coupled to a four-channel CUBE charge preamplifier. Different digital pulse processors allowing operation in Mcps per second count rates are employed. The results of preliminary characterization measurements performed at both the LNF DAΦNE-Light DXR1 beamline and the ESRF LISA BM-08 are reported, in particular, XRF measurements on low atomic number elements (down to the Carbon K-line, 270 eV) and extended X-ray absorption fine structure of trace materials in pyrite.     

Dynamics of viscoelastic liquid filaments: Low capillary number flows

Many applications of viscoelastic free surface flows requiring formation of drops from small nozzles, e.g., ink-jet printing, micro-arraying, and atomization, involve predominantly extensional deformations of liquid filaments. The capillary number, which represents the ratio of viscous to surface tension forces, is small in such processes when drops of water-like liquids are formed. The dynamics of extensional deformations of viscoelastic liquids that are weakly strain hardening, i.e., liquids for which the growth in the extensional viscosity is small and bounded, are here modeled by the Giesekus, FENE-P, and FENE-CR constitutive relations and studied at low capillary numbers using full 2D numerical computations. A new computational algorithm using the general conformation tensor based constitutive equation [M. Pasquali, L.E. Scriven, Theoretical modeling of microstructured liquids: a simple thermodynamic approach, J. Non-Newtonian Fluid Mech. 120 (2004) 101–135] to compute the time dependent viscoelastic free surface flows is presented. DEVSS-TG/SUPG mixed finite element method [M. Pasquali, L.E. Scriven, Free surface flows of polymer solutions with models based on conformation tensor, J. Non-Newtonian Fluid Mech. 108 (2002) 363–409] is used for the spatial discretization and a fully implicit second-order predictor–corrector scheme is used for the time integration. Inertia, capillarity, and viscoelasticity are incorporated in the computations and the free surface shapes are computed along with all the other field variables in a fully coupled way. Among the three models, Giesekus filaments show the most drastic thinning in the low capillary number regime. The dependence of the transient Trouton ratio on the capillary number in the Giesekus model is demonstrated. The elastic unloading near the end plates is investigated using both kinematic [M. Yao, G.H. McKinley, B. Debbaut, Extensional deformation, stress relaxation and necking failure of viscoelastic filaments, J. Non-Newtonian Fluid Mech. 79 (1998) 469–501] and energy analyses. The magnitude of elastic unloading, which increases with growing elasticity, is shown to be the largest for Giesekus filaments, thereby suggesting that necking and elastic unloading are related.     

Pre-equilibrium effects and neck emission in 10-40 AMeV heavy ion collisions

New experimental results on pre-equilibrium effects and neck emission at Fermi energies are presented. Coulomb trajectory calculations have been performed to explain the observed IMF velocity distributions.     

Carbon-13 NMR studies of diphenyl dichalcogenides, (C6H5)2X2 (X = S,Se, Te)

The ¹³C NMR chemical shifts and spin-lattice relaxation times for diphenyl disulfide, diselenide and ditelluride have been measured and assigned. The shielding effects experienced by the carbon atoms re qualitatively discussed in terms of the inductive and mesomeeric properties of the dichalcogen group. The attempt to calculate the magnetic shielding tensors for the ¹³C nuclei in terms of the Pople theory gave unsatisfactory results.     

The conformation,UV-absorption spectra and photoelectron spectra of phenoxachalcogenins

The analysis of dipole moment data obtained for dibenzo-p-dioxin, phenoxathiin, phenoxaselenin and phenoxatellurin in benzene at 25°C in conjunction with EHT calculations of the ocnformational energies show that these molecules adopt a non-planar conformation in solution. Each of the phenoxachalcogenins is folded along the axis connecting the two heteroatoms. A butterfly flapping motion about the planar conformation canot be excluded. The uv and photoelectron spectroscopic data support the conclusions drawn from the dipole moment studies. The spectroscopic data were interpreted with the help of SCF-PPP-CI calculations.     

A new enantiodivergent synthesis of the Geissman-Waiss lactone

Intramolecular Michael reaction of methyl (R)-6-(tert-butoxycarbonylamino)oxy-4-hydroxy-2-hexenoate, in turn obtained from tert-butyl (R)-3-hydroxy-4-pentenoate, paved the way to the synthesis of both enantiomers of 2-oxa-6-azabicyclo[3.3.0]octan-3-one (the Geissman-Waiss lactone), a precursor for necine bases. Key intermediates in this approach were represented by enantiomeric bicyclic lactones incorporating a [1,2]-oxazinane nucleus, which has been conveniently used to install the pyrrolidine framework of the target compounds through a synthetic scheme featuring the reduction of the nitrogen-oxygen bond and an intramolecular S_N2 reaction.     

Hydrogenation of the ansa-Chain of Rifamycins. X-ray crystal structure of (16S)-16,17,18,19-tetrahydrorifamycin S

The catalytic hydrogenation of rifamycin S ( 2 ) over Pd/C, followed by oxidation with K₃[Fe(CN)₆], generates a pair of 16,17,18,19-tetrahydrorifamycins S ( 3/4 ), epimeric at C (16). The use of PtO₂ as catalyst leads to the hydrogenation also of the C(28)?C(29) bond giving, after oxidation by K₃[Fe(CN)₆], a mixture of the epimers (16R)- and (16S)-16,17,18,19,28,29-hexahydrorifamycins S ( 5/6 ). Furthermore, we synthesized the (16R)- and (16S)-3-bromo derivatives 7/8 and (16R)- and (16S)-3-(piperidin-1-yl) derivatives 9/10 . The determination of the X-ray crystal structure of the most abundant epimer 4 of the tetrahydrorifamycins allowed the assignment of the absolute configuration at C(16) of all derivative. A Structure-activity relationship study showed that in general the (16R)-epimers are more potent inhibitors of bacterial RNA polymerase than the (16S)-epimers.     

A Categorical Interpretation of the Intuitionistic,Typed, First Order Logic with Hilbert’s $${\varepsilon}$$-Terms

We introduce a typed version of the intuitionistic epsilon calculus. We give a categorical semantics of it introducing a class of categories which we call \({\varepsilon}\)-categories. We compare our results with earlier ones of Bell (Math Logic Quart 39(3):323–337, 1993).