Excitation of the dynamical dipole in the charge asymmetric reaction O + Sn

The γ-ray emission from the dynamical dipole formed in heavy-ion collisions during the process leading to fusion was measured for the N/Z asymmetric reaction ¹⁶O + ¹¹⁶Sn at beam energies of 8.1 and 15.6 MeV/nucleon. High-energy γ-rays and charged particles were measured in coincidence with the heavy recoiling residual nuclei. The data are compared with those from the N/Z symmetric reaction ⁶⁴Ni + ⁶⁸Zn at bombarding energies of 4.7 and 7.8 MeV/nucleon, leading to the same CN with the same excitation energies as calculated from kinematics. The measured yield of the high-energy γ-rays from the ¹⁶O-induced reaction is found to exceed that of the thermalized CN and the excess yield increases with bombarding energy. The data are in rather good agreement with the predictions for the dynamical dipole emission based on the Boltzmann–Nordheim–Vlasov model. In addition, a comparison with existing data in the same mass region is performed to extract information on the dipole moment dependence.     

The role of ion pairing in the chromatographic study of propranolol analogues

Summary The partition coefficients, logP _app ^RPLC, for a series of propranolol analogues have been determined by reversed phase high performance liquid chromatography. The hydrochloride salts and free base logP _app ^RPLC show that charged and uncharged species can partition into the reversed phase. An extrathermodynamic relationship was found for logP _app ^RPLC measured in two different column stationary phases, C8 and PMOS, suggesting that the same set of compounds experience a similar trend in these elution systems. The importance of using phosphate and/or MOPS buffer is due to the fact that the latter can avoid ion-pairing partitioning, but the former does play the same role for PMOS column when the free base is considered.     

C ∞ regularity of solutions of an equation of Levi’s type in R 2 n +1

We study the regularity of the solutions u of a class of P.D.E., whose prototype is the prescribed Levi curvature equation in ℝ^{2 n +1}. It is a second-order quasilinear equation whose characteristic matrix is positive semidefinite and has vanishing determinant at every point and for every function u∈C ². If the Levi curvature never vanishes, we represent the operator ℒ associated with the Levi equation as a sum of squares of non-linear vector fields which are linearly independent at every point. By using a freezing method we first study the regularity properties of the solutions of a linear operator, which has the same structure as ℒ. Then we apply these results to the classical solutions of the equation, and prove their C ^∞ regularity. Received: October 10, 1998; in final form: March 5, 1999?Published online: May 10, 2001     

NMR molecular characterization of lubricating base oils: Correlation with their performance

The NMR technique was used to characterize some base oils of different nature (mineral, saturated polyolefins, hydrocracked and from waxes hydroisomerization) at the molecular level. Base oils are used in the formulation of lubricants with the addition of suitable additives which improve the final products performance. The studied base oils are used particularly in the formulation of engine oils. In this paper we have compared two “NMR editing” techniques which allow one to quantify the CH_n (n = 0?3) fractions of an “average” base oil molecule: 1) the gated spin echo (GASPE) and 2) the distortionless enhancement by polarization transfer (DEPT). We found that the quantitative data obtained from GASPE have a better accuracy than those from DEPT and so we chose GASPE to study the molecular characteristics of the aliphatic moieties of the base oils. On the basis of the GASPE data and of the average molecular mass obtained via VPO (Vapor Pressure Osmometry), the average number of branches and aliphatic rings were calculated. Moreover, on the basis of GASPE the distribution of side chain lengths and the positions of the methyl groups along the straight chain (methyls are the only groups for which the positions are directly obtained from NMR spectra) were obtained. A confirmation of the reliability of the NMR approach was achieved by comparing the branching degree, found with the NMR approach, of some base oils with their heats of fusion measured with the Differential Scanning Calorimetry (DSC). The heats of fusion are expected to be directly related to the length of straight CH₂ sequence and therefore to be lower for more branched molecules. We found that for base oils with similar aliphatic moieties, the heats of fusion are lower for more branched base oil molecules with a nearly linear correlation. The exception to this rule is represented by the two olefinic oils. Besides, we found that the fraction of the methyls on aliphatic chains longer than three carbons, determined with GASPE, correlates very well with the pour points values, with the only exception of the mineral oil.     

Comparison between CP/MAS 13C-NMR and pyrolysis-GC/MS in the structural characterization of humins and humic acids of soil and sediments

The chemical structure of humins (HUs) and humic acids (HAs) of terrestrial and marine environments was investigated by cross-polarization magic angle spinning ¹³C-nuclear magnetic resonance spectroscopy (CP/ MAS ¹³C-NMR) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Samples of HUs and HAs were obtained from sediments of the Adriatic Sea, the Lagoon of Ravenna (Adriatic Sea) and the Bubano Lake as well as from an agricultural soil. HUs displayed pyrograms and NMR spectra different from those of related HAs. According to NMR spectra HUs were more aliphatic and contained fewer carboxyl groups than HAs, while pyrolysates of HUs were characterized by higher levels of products arising from carbohydrates and lower levels of lignin methoxyphenols with respect to HAs. The relative content of paraffinic carbons determined by NMR was in good agreement with the relative abundance of unbranched aliphatic hydrocarbons released by pyrolysis. Both techniques evidenced the importance of polymethylene structures in HUs. Received: 5 January 1998 / Revised: 24 March 1998 / Accepted: 25 March 1998     

Thermally and optically stimulated luminescence of glass mosaic tesserae

A series of experiments on the luminescence signals from the glassy matrix of mosaic tesserae has been conducted. The results presented show the relationship between the 280–390 °C thermoluminescence (TL) peak and the optically stimulated luminescence (OSL) emitted under illumination by 450 nm light. We have proposed an appropriate laboratory protocol with repeated irradiations and illuminations of the same aliquot of the sample that allowed for establishing a correlation between TSL and OSL emissions, both very likely associated to the same trap. PACS 78.66.Jg; 87.66.Sq; 78.60.Kn     

Iodonium zwitterions

The first example of a diaryl zwitterionic iodonium compound having the anionic function directly on the aromatic ring is described. Compound 2, Ph-I(+)-C₆H₄-4-SO₂N(−)SO₂CF₃, is obtained in excellent yield and its X-ray structure was determined. 2 and the many analogues that can be prepared have excellent potential as photoacid generators (PAGs) in microlithography.     

Nuclear magnetic resonance studies of surface interactions between trifluoromethanesulfonic acid and silica

The nature of the interaction between trifluoromethanesulfonic acid (triflic acid) and the surface groups of silica as a support has been investigated by¹H and¹⁹F-NMR studies. The¹⁹F-NMR spin-lattice relaxation time (T ₁) dependence on temperature suggests that the dominant relaxation mechanism for¹⁹F is a combination of spin-rotation (SR) interactions, one of which seems to be quenched by cage-like structures. This mechanism is activated by the treatment followed to stabilize the acid on silica. Hydrogen proton relaxation seems instead to be driven by dipolar interactions and the formation of hydrogen bridges. Activation energies have been estimated for various cases, assuming an Arrhenius-type temperature dependence for the correlation times of molecular motion. A linear dependence of¹H chemical shift on inverse temperature was also found, which is interpreted as thermal weakening of hydrogen bonding. The results support the conclusion that the stability of triflic acid on silica is due to the formation of strong hydrogen bridges between the sulfonic groups of triflic acid and the silica surface hydroxyls, provided a network structure similar to that observed for pure acid is obtained in which strong interactions between acid molecules occur. The acid seems to be organized as solid-like “drops” on the silica surface, which accounts for the long residence time on the silica surface.