Maurizio Musso

Investigating the Effects of Simulated Martian Ultraviolet Radiation on Halococcus dombrowskii and Other Extremely Halophilic Archaebacteria

The isolation of viable extremely halophilic archaea from 250-million-year-old rock salt suggests the possibility of their long-term survival under desiccation. Since halite has been found on Mars and in meteorites, haloarchaeal survival of martian surface conditions is being explored. Halococcus dombrowskii H4 DSM 14522(T) was exposed to UV doses over a wavelength range of 200-400 nm to simulate martian UV flux. Cells embedded in a thin layer of laboratory-grown halite were found to accumulate preferentially within fluid inclusions. Survival was assessed by staining with the LIVE/DEAD kit dyes, determining colony-forming units, and using growth tests. Halite-embedded cells showed no loss of viability after exposure to about 21 kJ/m(2), and they resumed growth in liquid medium with lag phases of 12 days or more after exposure up to 148 kJ/m(2). The estimated D(37) (dose of 37 % survival) for Hcc. dombrowskii was > or = 400 kJ/m(2). However, exposure of cells to UV flux while in liquid culture reduced D(37) by 2 orders of magnitude (to about 1 kJ/m(2)); similar results were obtained with Halobacterium salinarum NRC-1 and Haloarcula japonica. The absorption of incoming light of shorter wavelength by color centers resulting from defects in the halite crystal structure likely contributed to these results. Under natural conditions, haloarchaeal cells become embedded in salt upon evaporation; therefore, dispersal of potential microscopic life within small crystals, perhaps in dust, on the surface of Mars could resist damage by UV radiation.

A novel skutterudite phase in the Ni–Sb–Sn system: phase equilibria and physical properties

A novel ternary phase, SnyNi4Sb12−xSnx, has been characterized and found to exhibit a wide range of homogeneity (at 250 °C, 2.4 ≤ x ≤ 5.6, 0 ≤ y ≤ 0.31; at 350 °C, 2.7 ≤ x ≤ 5.0, 0 ≤ y ≤ 0.27). SnyNi4Sb12−xSnx crystallizes in a skutterudite-based structure in which Sn atoms are found to occupy two crystallographically inequivalent sites: (a) Sn and Sb atoms randomly share the 24g site; and (b) a small fraction of Sn atoms occupy the 2a (0, 0, 0) position, with an anomalously large isotropic atomic displacement parameter. Eu0.8Ni4Sb5.8Sn6.2, Yb0.6Ni4Sb6.7Sn5.3 and Ni4As9.1Ge2.9 are isotypic skutterudites. Depending on the particular composition, metallic as well as semiconducting states appear. The crossover from semiconducting to metallic behaviour is discussed in terms of a temperature-dependent carrier concentration employing a simple model density of states with the Fermi energy slightly below a narrow energy gap. This model accounts for the peculiar temperature-dependent electrical resistivity. These skutterudites are characterized by a number of lattice vibrations, which were elucidated by Raman measurements and compared to the specific heat data. The Eu-containing compound exhibits long-range magnetic order at Tmag ≈ 6 K, arising from the Eu2+ ground state.

A Raman spectroscopic approach to the maturation process of fossil resins

Raman spectra of a range of differently aged samples of natural resins (recent resins, copals, fossils resins from Tertiary to Early Cretaceous age) were taken for a comparative study of the age-induced maturation processes of the resins. It can be shown that a decrease in band intensity at around 1640 cm−1 due to loss of ν(CC) stretching vibrations, together with other spectral details, is correlated with the increase in age of the resins. Copyright

The non-coincidence effect in highly diluted acetone-CCl I. Experimental results and theoretical predictions 4 binary mixtures

The concentration dependence of the first moments and peak frequencies of isotropic and anisotropic profiles of the υC=O mode in acetone–CCl4 binary mixtures is investigated. The emphasis is directed mainly towards the non-coincidence effect in the high dilution range, not accessed in previous experiments. Our results for the relative non-coincidence effect in non-isotopic binary mixtures appear largely consistent with the Logan theory. Moreover, the observation of the υC=O mode of the naturally present acetone–13C=O has been exploited to check the validity of the Logan theory for isotopic mixtures. It is verified that the observation of negative values for the non-coincidence effect, which is strictly related to that of a threshold concentration for the onset of this phenomenon, are artefacts due to the presence of spectral asymmetries in the υC=O mode.

ULTRA-VIOLET-LASER-INDUCED CHEMILUMINESCENCE OF NACD AND NAHG EXCIMERS

A single line UV Ar++ laser has been used for the photochemical production of NaCd and NaHg excimers, detected by their characteristic bound–free emission in the blue spectral region. Selected laser lines excited specific levels in the C 1Πu electronic state of the Na2 molecule. The chemical reaction of the excited sodium dimer with Cd or Hg atoms produced NaCd and NaHg excimers. We suggest a simple model for the explanation of the observed spectra, based on recent ab initio theoretical calculations.

Concentration dependence of the band profile parameters for the ν3(12C=O) Raman band of acetone in acetone–CCl4 binary mixtures: Experimental and Monte Carlo simulation results and their interpretation

The concentration dependence of specific band profile parameters, i.e., bandwidth and asymmetry, of the isotropic and anisotropic components of the ν3(12C=O) Raman band of acetone is investigated in the acetone–CCl4 binary mixtures. Emphasis is mainly placed upon the comparison of the results obtained from Monte Carlo simulations with the experimental results obtained by Raman spectroscopy. The results on the concentration dependence of the bandwidth are interpreted within the lineshape theory of Bratos and Tarjus, while the results on the concentration dependence of the band asymmetry are examined with the help of the theoretical predictions given by Knapp and by Knapp and Fischer. We have found a good qualitative agreement between all the results.

The non-coincidence effect in highly diluted acetone-CCl4 binary mixtures II. Experimental, theoretical and Monte Carlo simulation results

The concentration dependence of the Raman non-coincidence effect is investigated for the υ3(12C=O) band of the acetone–CCl4 binary mixtures. Emphasis is placed mainly upon a comparison of the results obtained from Monte Carlo simulations with those from Raman measurements. There is very good quantitative agreement between the results of the simulations and the experiments for the concentration dependence of the first moments of the isotropic and anisotropic bands, and hence the non-coincidence effect. These results on the observed and simulated concentration dependence of the non-coincidence effect are compared with those derived from the theory of Logan. This work confirms the validity of the theoretical treatment of chemical binary mixtures proposed by Logan, at least for this particular case of a polar solute dissolved in a non-polar solvent. To our knowledge these Monte Carlo simulations of spectral observables have been performed for chemical mixtures for the first time.

Isotropic Raman line shapes near gas–liquid critical points: The shift, width, and asymmetry of coupled and uncoupled states of fluid nitrogen

In order to improve the experimental database about the additional nonrotational broadening of vibrational line shapes observable when a simple fluid approaches its gas–liquid critical point, we improved the pioneering measurements of Clouter and Kiefte [for their own review see Phys. Rev. A 33, 2749 (1986)] on the critical behavior of the polarized Raman line of fluid nitrogen by using the isotopic mixture (14N2).975−(14N15N).025, giving special attention to the fact that the isotropic line shape of liquid N2 (ν≈2327 cm−1) is affected by intermolecular vibrational resonance couplings. Using a highest-resolution double monochromator and modern CCD detection techniques, we were able to follow the temperature dependencies of the line shape parameters (i.e., shift, width, and asymmetry) of the coupled 14N2 and, depending on the S/N ratio available, of the uncoupled 14N15N in the range 45 K≲T≲300 K with up to mK resolution (1) in the β-solid phase, (2) in the coexisting liquid and gas phases, and (3) along t...

The non-coincidence effect in N,N-dimethylformamide-CCl4 highly diluted binary mixtures. Experimental and theoretical results

We report results on the concentration dependence of the non-coincidence effect in the v(C=O) mode in N,N-dimethylformamide-CCl4 mixtures. This study has been mainly addressed to the investigation of the experimentally observed sign inversion for this quantity in the low concentration range of chemical mixtures, which is also reported in the literature. We argue that the sign inversion of the non-coincidence effect in N,N-dimethylformamide-CCl4 mixtures is an artefact originated by the presence of an intrinsic asymmetry which with dilution moves from the blue to the red side of the band. The Logan theory for the thermodynamic state dependence of the non-coincidence effect in chemical mixtures offers a valuable tool for the interpretation of the results in the whole concentration range. Different models are compared and discussed.

Interferometric determination of the refractive index of liquid sulphur dioxide

The absolute refractive index of liquid sulphur dioxide (SO2) was determined with an uncertainty of ±0.0007 with the help of a Michelson interferometer and a computer-controlled rotatory stage supporting a rectangular fused silica cell, containing the liquid. The measurements were performed at temperatures around 20 °C for the laser line wavelengths 632.8, 514.5 and 488.0 nm. The experimental data were fitted to the simple Cauchy dispersion formula. The results calculated from this formula are consistent within the experimental uncertainty with published values obtained at other wavelengths and/or other temperatures.