Experimental search for solar axions

A new technique has been used to search for solar axions using a single crystal germanium detector. It exploits the coherent conversion of axions into photons when their angle of incidence satisfies a Bragg condition with a crystalline plane. The analysis of approximately 1.94 kg.yr of data from the 1 kg DEMOS detector in Sierra Grande, Argentina, yields a new laboratory bound on axion-photon coupling of g_αγγ < 2.7 × 10⁻⁹GeV⁻¹, independent of axion mass up to 1 keV.     

Phase Transitions in a Traffic Flow Model

The terms phase transitions have been used since some years in the trafic modeling literarure to label a set of recurrent phenomena experimentally observed. This talk aims at the presentation of a system of p.d.e.s that models these phenomena, within the framework provided by phase transitions in systems of hyperbolic conservation laws.     

Assessment of the ageing of triterpenoid paint varnishes using fluorescence,Raman and FTIR spectroscopy

The assessment of the influence of natural and artificial ageing on the spectrofluorescence of triterpenoid varnishes dammar and mastic is the focus of this work. Both Fourier transform infrared (FTIR) microscopy using attenuated total reflectance and Raman spectroscopy have been employed for complementary molecular analysis of samples. Synchronous fluorescence spectroscopy, excitation emission spectroscopy, and statistical analysis of data have been used to monitor changes in the optical properties of varnish samples. Assessment of naturally and artificially aged samples using excitation emission spectroscopy suggests that extensive exposure to visible light does not lead to easily appreciable differences in the fluorescence of mastic and dammar; cluster analysis has been used to assess changes, which occur with artificial ageing under visible light, indicating that differences in the fluorescence spectra of aged triterpenoids may be insufficient for their discrimination. The results highlight significant differences between the initial fluorescence of films of dammar and mastic and the fluorescence, which develops with ageing and oxidation, and specific markers, which change with ageing in FTIR and Raman spectra, have been identified.     

Dihydrogen to dihydride isomerization mechanism in [(C5Me5)FeH2(Ph2PCH2CH2PPh2)]+ through the experimental and theoretical analysis of kinetic isotope effects

The isomerization of complex [Cp*Fe(dppe)(eta2-H2)]+, generated in situ by low-temperature protonation of Cp*Fe(dppe)H with either HBF4 or CF3COOH, to the dihydride tautomer trans-[Cp*Fe(dppe)(H)2]+ is irreversible and follows first-order kinetics in the -10 to +15 degrees C range with Delta H double dagger = 21.6 +/- 0.8 kcal mol(-1) and DeltaS double dagger = 5 +/- 3 eu. The isomerization rate constant is essentially independent of the nature and quantity of a strong acid. Density functional theory (DFT) calculations on various models, including the complete system at both the quantum mechanics/molecular mechanics (QM/MM) and full QM levels, probe the relative importance of steric and electronic effects for the relative stability of the nonclassical and classical isomers and identify two likely isomerization mechanisms: a "direct" pathway involving simultaneous H-H bond breaking and cis-trans isomerization and a "via Cp" pathway involving agostic C5Me5H intermediates. Both pathways are characterized by activation energies in close correspondence with the experimental value (21.3 and 22.2 kcal mol(-1), respectively). Further kinetic studies were carried out for the Cp*Fe(dppe)H + CF3COOD and Cp*Fe(dppe)D + CF3COOD systems at 273 K. The [Cp*Fe(dppe)(eta2-HD)]+ complex establishes a very rapid isotope redistribution equilibrium with the eta2-H2 and eta2-D2 analogues. The equilibrium constant value (K = 3.3 +/- 0.3) indicates a significant equilibrium isotope effect. Simulation of the rate data provides access to the individual isomerization rate constants kHH, kHD, and kDD for the three isotopomers, yielding kinetic isotope effects: kHH/kHD = 1.24 +/- 0.01 and kHD/kDD = 1.58 +/- 0.01 (and, consequently, kHH/kDD = 1.96 +/- 0.02). The analysis of the DFT-calculated frequencies, using the [Cp*Fe(dhpe)H2]+ model system, for the [Cp*Fe(dhpe)(eta2-XY)]+ isotopomers as well as transition states for the "direct" (TSdir) and "via Cp" (TSrot) pathways (X = H, D) allowed the computation of the expected isotope effects. A comparison with the experiment strongly suggests that the mechanism occurs via the "direct" pathway for the present system, although the small difference in the calculated energy barriers suggests that the "via Cp" pathway may be preferred in other cases.     

Characterization of Pd-Cu alloy nanoparticles on gamma-Al2O3-supported catalysts

Cu-Pd/Al2O3 bimetallic catalysts have been characterized by XRD, TEM, and EDX techniques. The surface structure has been investigated by FT-IR spectroscopy of low-temperature adsorbed CO in the reduced and in the oxidized state. Evidence has been provided of the formation of Cu-Pd alloy nanoparticles, both of the alpha-phase (disordered fcc) and of the beta-phase (ordered CsCl-type). IR spectra suggest that Cu likely decorates the edges while Pd mostly stays at the main faces. Part of copper disperses as Cu+ on the support even after reduction. The presence of copper seems to modify strongly the sate of oxidized Pd centers in oxidized high-Pd content materials. The redox chemistry of the system, where Pd is reduced more easily than Cu, appears to be very complex.     

Simultaneous quantification of 17 trace elements in blood by dynamic reaction cell inductively coupled plasma mass spectrometry (DRC-ICP-MS) equipped with a high-efficiency sample introduction system

A quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) equipped with a dynamic reaction cell (DRC) and coupled with a desolvating nebulization system (APEX-IR) was employed to determine 17 elements (Al, As, Ba, Cd, Co, Cr, Li, Mn, Mo, Ni, Pb, Sb, Se, Sn, Sr, V, and Zr) in blood samples. Ammonia (for Al, Cr, Mn, and V) and O₂ (for As and Se) were used as reacting gases. Selection of the best flow rate of the gases and optimization of the quadrupole dynamic bandpass tuning parameter (RPq) were carried out, using digested blood diluted 1 + 9 with deionized water and spiked with 1 μg L⁻¹ of Al, Cr, Mn, V and 5 μg L⁻¹ of As and Se. Detection limits were determined in digested blood using the 3σ criterion. The desolvating system allowed a sufficient sensitivity to be achieved to determine elements at levels of ng L⁻¹ without detriment of signal stability. The accuracy of the method was tested with the whole blood certified reference material (CRM), certified for Al, As, Cd, Co, Cr, Mn, Mo, Ni, Pb, Sb, Se, and V, and with indicative values for Ba, Li, Sn, Sr, and Zr. The addition calibration approach was chosen for analysis. In order to confirm the DRC data, samples were also analyzed by means of sector field inductively coupled plasma mass spectrometry (SF-ICP-MS), operating in medium (m/Δm = 4000) and high (m/Δm = 10,000) resolution mode and achieving a good agreement between the two techniques.     

A comprehensive PIV measurement campaign on a fully equipped helicopter model

The flow field around a helicopter is characterised by its inherent complexity including effects of fluid?Cstructure interference, shock?Cboundary layer interaction, and dynamic stall. Since the advancement of computational fluid dynamics and computing capabilities has led to an increasing demand for experimental validation data, a comprehensive wind tunnel test campaign of a fully equipped and motorised generic medium transport helicopter was conducted in the framework of the GOAHEAD project. Different model configurations (with or without main/tail rotor blades) and several flight conditions were investigated. In this paper, the results of the three-component velocity field measurements around the model are surveyed. The effect of the interaction between the main rotor wake and the fuselage for cruise/tail shake flight conditions was analysed based on the flow characteristics downstream from the rotor hub and the rear fuselage hatch. The results indicated a sensible increment of the intensity of the vortex shedding from the lower part of the fuselage and a strong interaction between the blade vortex filaments and the wakes shed by the rotor hub and by the engine exhaust areas. The pitch-up phenomenon was addressed, detecting the blade tip vortices impacting on the horizontal tail plane. For high-speed forward flight, the shock wave formation on the advancing blade was detected, measuring the location on the blade chord and the intensity. Furthermore, dynamic stall on the retreating main rotor blade in high-speed forward flight was observed at r/R?=?0.5 and 0.6. The analysis of the substructures forming the dynamic stall vortex revealed an unexpected spatial concentration suggesting a rotational stabilisation of large-scale structures on the blade.     

On network form and function

Moving from the observation that drainage network configurations minimizing total energy dissipation are stationary solutions of the general equation describing landscape evolution, we review theoretical and observational evidence on river patterns and their scale-invariant structure. Exact results complemented by numerical annealing of the basic equation in the presence of additive noise suggest that configurations at (or very close to) the global minimum of energy dissipation differ from dynamically accessible states, which have rather different scaling properties and conform much better to natural forms. Thus we argue that, at least in the fluvial landscape, Nature works through imperfect searches for dynamically accessible optimal configurations. We also show that optimal networks are spanning loopless configurations only under precise physical requirements. This is stated in a form applicable to generic networks, suggesting that other branching structures occurring in Nature (e.g. scale-free and looping) may possibly arise through optimality to selective pressures. Indeed, we show that this is the case.     

Chemical composition and antibacterial activity of the essential oil of Espeletia nana

The essential oil of the leaves of Espeletia nana Cuatrec., obtained by hydrodistillation, was analyzed by GC-MS, which allowed the identification of 24 components, which made up 99.9% of the oil. The most abundant compounds were a-pinene (38.1%), beta-pinene (17.2%), myrcene (15.0%), spathulenol (4.2%), bicyclogermacrene (4.0%), a-zingiberene (4.0%), and gamma-himachalene (3.7%). Antibacterial activity was tested against Gram-positive and Gram-negative bacteria using the agar disk diffusion method. Activity was observed only against Gram-positive bacteria. MIC values were determined for Staphylococcus aureus ATCC 25923 (200 microg/mL) and Enterococcusfaecalis ATCC 29212 (600 microg/mL).     

On the stable set of associated prime ideals of a monomial ideal

It is shown that any set of nonzero monomial prime ideals can be realized as the stable set of associated prime ideals of a monomial ideal. Moreover, an algorithm is given to compute the stable set of associated prime ideals of a monomial ideal.