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When the wavelength of the Raman scattered light coincides with the absorption spectrum of the sample, a phenomenon known as Raman self-absorption occurs. If the absorption wavelength range matches completely with the Raman wavenumber range for a given excitation line (high absorption), this process causes spectra with poor signal-to-noise-ratio, making the acquisition nearly impossible. When the absorption of the sample and the Raman scattered are partially coincident (low absorption), smaller modifications in the band-profile of the Raman spectrum are expected difficult to be detected. If a different excitation wavelength is available in order to avoid or minimize this phenomenon, a correction method is customary. The correction methods developed so far in quantitative analysis are still very complex and require the knowledge of several sampling parameters. In this work, we present a very simple but reliable method based on the Beer-Lambert law to correct low self-absorption effects. This method uses simple concepts, a straightforward methodology and the concentration of the Raman active component in the liquid matrix is the only parameter required to perform the correction. This method may be extremely useful in different fields in which Raman spectroscopy is used to obtain molecular and structural information from a band profile analysis. As an example, the method is applied here to successfully correct the Raman spectra of different CuSO4 aqueous solutions excited at 532 nm.

We have carried out a systematic study of abiotic precipitation at different temperatures of several Mg and Ca carbonates (calcite, nesquehonite, hydrocalcite) present in carbonaceous chondrites. This study highlights the capability of Raman spectroscopy as a primary tool for performing full mineralogical analysis. The precipitation reaction and the structure of the resulting carbonates were monitored and identified with Raman spectroscopy. Raman spectroscopy enabled us to confirm that the precipitation reaction is very fast (minutes) when Ca(II) is present in the solution, whereas for Mg(II) such reactions developed at rather slow rates (weeks). We also observed that both the composition and the reaction mechanisms depended on temperature, which might help to clarify several issues in the fields of planetology and geology, because of the environmental implications of these carbonates on both terrestrial and extraterrestrial objects.

Measurements of the refractive index from 293 to 321 K at four fixed wavelengths, from 587.6 to 404.7 nm, are reported for valeric acid (pentanoic acid), caproic acid (hexanoic acid), oenantic acid (heptanoic acid), caprylic acid (octanoic acid), and pelargonic acid (nonanoic acid). We also report the temperature and wavelength dependencies of the refractive index obtained from a least-squares routine. The agreement between the measured and calculated refractive indices lies within the experimental uncertainty.

Measurements of the refractive index from 288 to 318 K at five fixed wavelengths, from 656.3 to 404.7 nm, are reported for benzene, toluene (methylbenzene), o-xylene (1,2-dimethylbenzene), m-xylene (1,3-dimethylbenzene), and p-xylene (1,4-dimethylbenzene). We also report the temperature and wavelength dependencies of the refractive index obtained from a least-squares routine. The agreement between the measured and calculated refractive indices lies within the experimental uncertainty.

A general method to include temperature effects into the equation of state (EOS) of solids is discussed. A universal model based on a pseudo-spinodal approach is used to predict the pressure and temperature dependencies of the thermodynamic properties for a variety of solids: n -H 2 , Ar, Kr, Xe, NaCl, LiF, NaF, KCl, CsCl, Li, Na, K, Rb, Cs, Al, Fe, Cu, Zn, Ag, Cd, Pt, Au, and Pb. The predictive capabilities of the complete EOS are discussed and compared with available models.

Enterotoxigenic Bacteroides fragilis (ETBF) strains have been reported as a cause of diarrhoeal diseases. Diarrhoea is an important cause of morbidity and mortality in children from developing countries. This study was conducted to determine the prevalence and antimicrobial susceptibility of ETBF in children from Leon, Nicaragua. Faecal specimens from 106 children under ten years of age with diarrhoea and 60 asymptomatic, age-matched controls were examined for presence of ETBF using an assay based on immunomagnetic separation (IMS) in combination with PCR (IMS-PCR) and HT29/C1 cell assay. ETBF was present in nine children with diarrhoea (8.4%) and was more often identified in children ≤1 year (7/63, 11.1%) but all ETBF positive children were under 2 years of age. ETBF was isolated as the only pathogen in five of nine positive children (55.5%). The agar dilution method was used to determine the antimicrobial susceptibility pattern of the ETBF strains. All strains were resistant to ampicillin (range 8–1024 mg/L) and one strain was also resistant to clindamycin MIC 256 mg/L. All the other antimicrobial agents were active against the strains (MIC50and MIC90): 8 and 16 mg/L for cefoxitin, 0.004 and 0.008 mg/L for imipenem, 0.5 and 0.5 mg/L for clindamycin and for metronidazole, 2 and 4 mg/L for chloramphenicol. A majority (77%) of the ETBF strains were β-lactamase producers.

Some experimental studies indicate that the isothermal compressibility, κT, of molecular liquids follows a power law up to very high pressures along isothermal paths. We show here that the high-pressure behavior of κT can be characterized from surface tension and κT data measured at low pressures. Our method is based on a pseudospinodal hypothesis. Comparison with experimental is satisfactory up to very high pressures for different molecular liquids. The results are also studied in terms of the reduced bulk modulus. B. Our method reproduces adequately the intersections experimentally found for the isotherms of B versus molar volume of molecular liquids.

Experimental and theoretical studies suggest that the thermal expansion coefficients α p of liquids follow a power law up to extremely high pressures along isothermal paths. Accurate experiments reveal that intersections between α p isotherms occur at high pressure for many liquids. It is shown how the high-pressure behavior of α p can be accurately predicted for real liquids from surface tension and low-pressure α p measurements. The method proposed here is based on the assumption that the spinodal curve does exist and can be estimated from surface tension measurements using Furth's hole theory.

Molar densities have been measured by using an expansion technique at pressures up to 104 MPa and temperatures from 198 to 298 K for the mixture {x CS2 + (1-x) Si(CH3)4}(1) over the whole composition range. Several thennodynamic properties (isothermal compressibility, thermal expansivity, and molar internal energy, enthalpy and entropy increments relative to liquid at saturation) have been directly obtained from the experimental densities. The isothermal compressibility and the thermal expansivity are both smooth functions of pressure, temperature and composition, although the isotherms of the thermal expansivity exhibit a characteristic crossover at high pressures. The intersection of isotherms of thermal expansivity seems to occur at a single point of the (p,αp) diagram, showing a nearly linear dependence with the composition.

The Deiters equation of state has been used to predict the vapor-liquid equilibrium and second virial coefficient for several pure substances. The equation of state depends on three characteristic parameters which can be calculated from the critical constants. A general procedure to determine the characteristic parameters is reported. The predictions are very satisfactory, being within the experimental uncertainties in most cases.

Vapour pressures and excess volumes for the hexafluorobenzene—n-hexadecane system and vapour pressures for the hexafluorobenzene—benzene—n-hexadecane system have been measured at 298.15 K. Thermodynamic consistency of the data has been checked using a Pade approximation for the binary system, and a new expression for the excess Gibbs energy of the ternary system. The new expression compares favourably with others previously proposed in the literature.

Solutions containing both poly(4-vinylpyridine) (P4VP) and poly(acrylic acid) (PAA) in 50% v/v metanol-water have been studied at room temperature by means of fluorescence studies, spectrophotometry and potentiometry. The results show the formation of a polycomplex between the polymers. Its stoichiometry is 0.5–0.6 PAA:1 P4VP and only slightly depends on polymer concentration for a range of very dilute solutions (10−3–10−4 M in monomeric units). The polycomplex is largely stabilized through hydrogen bonds but there is some proton transfer and the resulting coulombic interactions also contribute to the stabilization. The role of hydrophobic interactions is also discussed.