The "non-nucleophilic" anion [Tf2N]- competes with the nucleophilic Br-: an unexpected trapping in the dediazoniation reaction in ionic liquids

Imidazolium ionic liquids containing [Tf2N]- anion are not as innocent as they are often considered; [Tf2N]- is more reactive than Br- in heterolytic dediazoniation reactions.     

Cation distribution in LiMgVO4 and LiZnVO4: structural and spectroscopic study

The room temperature cation occupancy in LiMgVO(4) and LiZnVO(4) crystallographic sites is obtained by means of the combined use of X-ray powder diffraction (XRPD), (7)Li and (51)V magic angle spinning nuclear magnetic resonance (MAS NMR), and micro-Raman measurements. In the LiMgVO(4) Cmcm orthorhombic structure, the 4c (C(2)(v) symmetry) tetrahedral vanadium site is fully ordered; on the contrary, the Li 4c tetrahedral site and the 4b (C(2)(h) symmetry) Mg octahedral site display about 22% of reciprocal cationic exchange. Higher cationic disorder is observed in LiZnVO(4): the three cations can distribute on the three tetrahedral and distinct sites of the R-3 structure. XRPD and MAS NMR analysis results highly agree for what concerns vanadium ion distribution on the three cationic sites (about 25, 26, and 47%). From the full profile fitting of XRPD patterns with the Rietveld method, it is also obtained that Li(+) displays a slightly preferred occupation of the T1 position (approximately 55%) and Zn(2+) of the T2 position (approximately 46%). The vibrational spectra of the two compounds are characterized by different peak positions and broadening of the Raman modes, reflecting the cation distribution and the local vibrational unit distortion. A comparison is also made with recent Raman results on Li(3)VO(4). High temperature XRPD measurements rule out possible structural transitions up to 673 K for both compounds.     

Investigation of the extraction and collimation of a beam in a circular accelerator using new crystal equipment

New crystalline equipment—an array of bent strips and fan reflector based on thin flat plates—has been used to investigate the extraction and collimation of a circulating beam in an accelerator with an energy of 50 and 1.3 GeV. It has been shown that new equipment can efficiently control the beam in a wide energy range. An extraction and collimation efficiency of 90%, which is a record for this method, has been achieved for 50-GeV protons.     

Particle motion in a photon gas: friction matters

The motion of a particle in the Tolman metric generated by a photon gas source is discussed. Both the case of geodesic motion and motion with nonzero friction, due to photon scattering effects, are analyzed. In the Minkowski limit, the particle moves along a straight line segment with a decelerated motion, reaching the endpoint at zero speed. The curved case shows a qualitatively different behavior; the geodesic motion consists of periodic orbits, confined within a specific radial interval. Under the effect of frictional drag, this radial interval closes up in time and in all our numerical simulations the particle ends up in the singularity at the center.     

Search for free neutron-antineutron oscillations

A search for free neutron-antineutron oscillations has been carried out at the Pavia Triga Mark II research reactor. A thin carbon target is crossed by a beam of thermal neutrons propagating in a 18.5 m long channel where the earth magnetic field is attenuated by a factor of 50. The total neutron current through the target is 3.2×10¹⁰ n/s. Possible antineutron annihilations are identified by a large track detector surrounding the target. A lower limit on the oscillation time of 4.7×10⁵ s (90% C.L.) has been reached.     

Improved cyclic reduction for solving queueing problems

The cyclic reduction technique (Buzbee et al., 1970), rephrased in functional form (Bini and Meini, 1996), provides a numerically stable, quadratically convergent method for solving the matrix equation X = ∑^{+ ∞} _i=0 X_i A_i, where the A_i's are nonnegative k × k matrices such that ∑^{+ ∞} _i=0 A_i is column stochastic. In this paper we propose a further improvement of the above method, based on a point-wise evaluation/interpolation at a suitable set of Fourier points, of the functional relations defining each step of cyclic reduction (Bini and Meini,1996). This new technique allows us to devise an algorithm based on FFT having a lower computational cost and a higher numerical stability. Numerical results and comparisons are provided. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of double core chromophore-functionalized nanothreads by compressing azobenzene in a diamond anvil cell

Carbon nanothreads are likely the most attracting new materials produced under high pressure conditions. Their synthesis is achieved by compressing crystals of different small aromatic molecules, while also exploiting the applied anisotropic stress to favor nontopochemical paths. The threads are nanometric hollow structures of saturated carbon atoms, reminiscent of the starting aromatic molecule, gathered in micron sized bundles. The examples collected so far suggest that their formation can be a general phenomenon, thus enabling the design of functionalities and properties by suitably choosing the starting monomer on the basis of its chemical properties and crystal arrangement. The presence of heteroatoms or unsaturation within the thread is appealing for improving the processability and tuning the electronic properties. Suitable simple chromophores can fulfill these requirements and their controlled insertion along the thread would represent a considerable step forward in tailoring the optical and electronic properties of these mechanically extraordinary materials. Here, we report the synthesis and extensive characterization of double core nanothreads linked by azo groups. This is achieved by compressing azobenzene in a diamond anvil cell, the archetype of a wide class of dyes, and represents a fundamental step in the realization of nanothreads with tailored photochemical and photophysical properties.

One-step high-pressure synthesis of 2D crystalline double nanothreads linked by azo groups.     

Bronchoalveolar lavage fluid protein composition in patients with sarcoidosis and idiopathic pulmonary fibrosis: a two-dimensional electrophoretic study

We used two-dimensional (2-D) electrophoresis to analyze the protein composition of fluid recovered by bronchoalveolar lavage (BALF) from patients with sarcoidosis and idiopathic pulmonary fibrosis, two forms of interstitial lung disease with different cellular composition and cytokine profile in BALF. They are also characterized by different pathogenesis and clinical evolution, idiopathic pulmonary fibrosis being less favorable than sarcoidosis due to rapidly progressive pulmonary fibrosis. Thirty-eight proteins or protein fragments, never previously assigned in BALF samples, were identified by various methods including mass fingerprinting of tryptic digests. Comparison of the BALF protein maps of the two groups of patients showed 32 spots with statistically significant disease-related variations in relative abundance. In sarcoidosis we found an increase in the amount of several plasma proteins, while in idiopathic pulmonary fibrosis we observed a statistically significant increase in low-molecular-weight proteins, many of which are involved in inflammatory processes (such as MIF and calgranulin) or antioxidant response (such as antioxidant peroxysomal enzyme and thioredoxin peroxidase 2). 2-D electrophoresis allowed us to identify new BALF proteins and to characterize protein composition in patients with sarcoidosis and idiophatic pulmonary fibrosis. Comparison of the gels of the two diseases showed that they differ in BALF protein profiles as they do in type of immune response.     

Hyperbolic-like elastic scattering of spinning particles by a Schwarzschild black hole

The scattering of spinning test particles by a Schwarzschild black hole is studied. The motion is described according to the Mathisson–Papapetrou–Dixon model for extended bodies in a given gravitational background field. The equatorial plane is taken as the orbital plane, the spin vector being orthogonal to it with constant magnitude. The equations of motion are solved analytically in closed form to first-order in spin and the solution is used to compute corrections to the standard geodesic scattering angle as well as capture cross section by the black hole.     

Solving Toeplitz Least Squares Problems by Means of Newton's Iteration

We extend the algorithm of [4], based on Newton's iteration and on the concept of -displacement rank, to the computation of the generalized inverse A ⁺ of an m×n Toeplitz matrix A. We introduce new strategies for the dynamical control of the truncation level at each step of the iteration. Numerical experiments and an application to a problem of image restoration are shown. An object-oriented implementation in C++ is described.