Search for exotic baryons in 800 GeV pp-->pXi+/-piX reactions

We report the results of a high-statistics, sensitive search for narrow baryon resonances decaying to Xi-pi-, Xi-pi+, Xi+pi-, and Xi+pi+. The only resonances observed are the well known Xi0(1530) and Xi0(1530). No evidence is found for the states near 1862 MeV, previously reported by NA49 [Phys. Rev. Lett. 92, 042003 (2003)]. At the 95% confidence level, we find the upper limit for the production of a Gaussian enhancement with sigma=7.6 MeV in the Xi-pi- effective mass spectrum to be 0.3% of the number of observed Xi0(1530)-->Xi-pi+. We find similarly restrictive upper limits for an enhancement at 1862 MeV in the Xi-pi+, Xi+pi-, and Xi+pi+ mass spectra.     

Impurities in noncubic crystals: stabilization mechanisms for Jahn-Teller ions in layered perovskites

Mechanisms responsible for the local geometry around Jahn-Teller impurities in K2NiF4 type lattices are shown to be different from those generating the warping in cubic crystals. The present density functional theory calculations reveal that the elastic anisotropy of the host lattice (visible for closed shell impurities) and the electric field created by the rest of lattice ions upon active electrons make it possible to have d(9) ions in an elongated geometry but with a A(1g) ground state. The puzzling difference between equilibrium geometries for Cu2+ and Ni+ in layered perovskites can reasonably be understood.     

Variational transition state theory as a tool to determine kinetic selectivity in reactions involving a valley-ridge inflection point

Variational transition state theory has been used to calculate the kinetic isotope effects affecting product ratios in the reaction between (1)O(2) and d(6)-tetramethylethylene. The minimum energy path on the potential energy surface for this process reaches a valley-ridge inflection point and then bifurcates leading to the two final products. Using canonical variational transition state theory, two distinct dynamical bottlenecks were located corresponding to the H- and the D-abstraction, respectively. The calculated KIE at 263 K turns out to be 1.126. Analogously, a H/T KIE of 1.17 at the same temperature has been found for the reaction of (1)O(2) with the tritiated derivative of tetramethylethylene.     

Development of a Sequential Injection Analysis Device for the Determination of Total Polyphenol Index in Wine

A sequential injection analysis method is developed for the determination of the total polyphenol index in wines. The determination is based on the Folin-Ciocalteu reaction, which is monitored spectrophotometrically. Interactions between experimental variables and their optimal levels were investigated using factorial designs. The proposed system is fully computerised and is able to monitor polyphenol index in real samples of white, sweet and red wines. The calibration graph is linear from 5 to 200mg·L^–1 using Tannic acid as standard, with a detection limit of 3.2mg·L^–1. Interferences are studied. For validation purposes the proposed methodology was applied to the determination of the total polyphenol index in different types of wines and compared with earlier alternatives in order to assess their performance.     

Uniqueness of dilation invariant norms

Let be a nontrivial dilation. We show that every complete norm on that makes from into itself continuous is equivalent to . also determines the norm of both and with in a weaker sense. Furthermore, we show that even all the dilations do not determine the norm on .

     

Methyl group dynamics in a confined glass

We present a neutron scattering investigation on methyl group dynamics in glassy toluene confined in mesoporous silicates of different pore sizes. The experimental results have been analysed in terms of a barrier distribution model, such a distribution following from the structural disorder in the glassy state. Confinement results in a strong decreasing of the average rotational barrier in comparison to the bulk state. We have roughly separated the distribution for the confined state in a bulk-like and a surface-like contribution, corresponding to rotors at a distance from the pore wall respectively larger and smaller than the spatial range of the interactions which contribute to the rotational potential for the methyl groups. We have estimated a distance of 7 A as a lower limit of the interaction range, beyond the typical nearest-neighbour distance between centers-of-mass (4.7 A).     

A queueing system with linear repeated attempts,bernoulli schedule and feedback

We analyse a single-server retrial queueing system with infinite buffer, Poisson arrivals, general distribution of service time and linear retrial policy. If an arriving customer finds the server occupied, he joins with probabilityp a retrial group (called orbit) and with complementary probabilityq a priority queue in order to be served. After the customer is served completely, he will decide either to return to the priority queue for another service with probability ϑ or to leave the system forever with probability =1−ϑ, where 0≤ϑ<1. We study the ergodicity of the embedded Markov chain, its stationary distribution function and the joint generating function of the number of customers in both groups in the steady-state regime. Moreover, we obtain the generating function of system size distribution, which generalizes the well-knownPollaczek-Khinchin formula. Also we obtain a stochastic decomposition law for our queueing system and as an application we study the asymptotic behaviour under high rate of retrials. The results agree with known special cases. Finally, we give numerical examples to illustrate the effect of the parameters on several performance characteristics.     

Diffractively produced charm final states in 800-GeV/c pp collisions

We report the first observation of diffractively produced open charm in 800-GeV/c pp collisions of the type pp-->pD*X. We measure cross sections of sigma(diff)(D*+) = (0.185+/-0.044+/-0.054) (mu)b and sigma(diff)(D(*-)) = (0.174+/-0.034+/-0.029) (mu)b. Our measurements are based on 4.3x10(9) events recorded by FNAL E690 in the fixed-target run of 1991. We compare our results with previous fixed-target charm experiments.     

Correlations in a Mozart's music score (K-73x) with palindromic and upside-down structure

In this work, we study long-range correlations in a “Scherzo-Duetto di Mozart” score (K-73x) for two violins. This is a fascinating piece, as the second violin part is upside down on the same sheet below the first violin, and some parts are like a palindrome. Given such ingenious structure, it is expected the existence of long-range correlations in the score structure. In order to quantify long-range correlations, we considered the music score as a sequence of integer numbers, each of them corresponding to last common denominator units of note. By using detrended fluctuation analysis (DFA), correlations are quantified by means of the scaling exponent that reflects the type of correlations for a given distance between neighbors note. The following conclusions can be drawn from the analysis: (a) For about 10-25 neighbor note distances, correlations are similar to 1/f-noise. This is an interesting finding since it has been shown that pleasant sounds for humans display a behavior similar to 1/f noise. (b) As the neighbor note distance increases, the long-range correlations decays continuously. For some score sections, the music score behaves like non-correlated (i.e., purely random) noise. Summing up, the results show that the studied Mozart's score contains a certain degree of correlation for relatively small note distances, and becomes close to non-correlated behavior for long note distances. We considered also the sequence constructed by considering the distance between the simultaneously played notes of the two violins. Interestingly, for relatively small neighbor note distances, a scaling behavior similar to that found for individual violins is also displayed. In some sense, this is an expression of the specific structure (palindromes plus upside down construction) used by Mozart in the composition of this music score. Although we focused on a particular high-art music score, our results suggest that modern methods borrowed from statistical physics can be useful for the systematic study of music composition techniques.     

Synthesis of carbon nanotubes by CVD: Effect of acetylene pressure on nanotubes characteristics

The effect of acetylene partial pressure on the structural and morphological properties of multi-walled carbon nanotubes (MWCNTs) synthesized by CVD on iron nanoparticles dispersed in a SiO₂ matrix as catalyst was investigated. The general growing conditions were: 110 cm³/min flow rate, 690 °C synthesis temperature, 180 Torr over pressure and two gas compositions: 2.5% and 10% C₂H₂/N₂. The catalyst and nanotubes were characterized by HR-TEM, SEM and DRX. TGA and DTA were also carried out to study degradation stages of synthesized CNTs. MWCNTs synthesized with low acetylene concentration are more regular and with a lower amount of amorphous carbon than those synthesized with a high concentration. During the synthesis of CNTs, amorphous carbon nanoparticles nucleate on the external wall of the nanotubes. At high acetylene concentration carbon nanoparticles grow, covering all CNTs’ surface, forming a compact coating. The combination of CNTs with this coating of amorphous carbon nanoparticles lead to a material with high decomposition temperature.