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P Parras

Publications and source records attributed to P Parras.

6 recordsLinked to original sources
PubMed2006

Small-angle x-ray scattering study of flow alignment of a thermotropic liquid crystal in the nematic and smectic phases.

The capillary flow alignment of the thermotropic liquid crystal 4-n-octyl-4'-cyanobiphenyl in the nematic and smectic phases is investigated using time-resolved synchrotron small-angle x-ray scattering. Samples were cooled from the isotropic phase to erase prior orientation. Upon cooling through the nematic phase under Poiseuille flow in a circular capillary, a transition from the alignment of mesogens along the flow direction to the alignment of layers along the flow direction (mesogens perpendicular to flow) appears to occur continuously at the cooling rate applied. The transition is centered on a temperature at which the Leslie viscosity coefficient alpha3 changes sign. The configuration with layers aligned along the flow direction is also observed in the smectic phase. The transition in the nematic phase on cooling has previously been ascribed to an aligning-nonaligning or tumbling transition. At high flow rates there is evidence for tumbling around an average alignment of layers along the flow direction. At lower flow rates this orientation is more clearly defined. The layer alignment is ascribed to surface-induced ordering propagating into the bulk of the capillary, an observation supported by the parallel alignment of layers observed for a static sample at low temperatures in the nematic phase.

Journal Article↗
PubMed1993

[Evaluation of a new automated system for the determination of antifungal sensitivity].

BACKGROUND: To evaluate a new semi-automatized system (ATB-Fungus, Bio Mérieux, Spain) for antifungal in vitro susceptibility testing in yeast. METHODS: We studied the susceptibility of 91 yeast strains (22 Candida albicans, 18 Candida parapsilopsis, 18 Candida krusei, 17 Candida tropicalis, 11 Candida glabrata, 5 Candida guillermondii) against amphotericin B, flucytosine, ketoconazole, miconazole, econazole and nystatin, by means of "ATB-fungus" and agar diffusion and only against systemic usage antifungal agents by agar-dilution method. RESULTS: The correlation between "ATB-fungus" and diffusion method and agar dilution was 100% for amphotericin B, except for Candida krusei and C. tropicalis strains. This correlation rate was lower for fluocytosine and ketoconazole, without major differences between species. There is an absolute concordance between the system under evaluation and agar diffusion method regarding nystatin. For the two azole drugs remaining (miconazole and econazole) the correlation found for Candida glabrata was 100% and for C. parapsilopsis 95% with agar diffusion method. Candida glabrata was the single species that showed better correlation with all three methods, while major differences were seen with C. krusei and C. tropicalis. CONCLUSIONS: Although "ATB-fungus" seems to be a nearly well standardized method for antifungal susceptibility testing, more studies are required for assessing its reproducibility and also to determine when, how and for which antifungal agents would be a valid procedure.

Antifungal Agents↗
PubMed1993

[Comparison of ATB STREP, AMS-Vitek GPS-TA, and disk diffusion for the detection of a high level of aminoglycoside resistance in Enterococcus spp].

BACKGROUND: The absence of the synergic effect between beta-lactam and aminoglucoside versus Enterococcus is predicted by the presence of a high level of resistance to aminoglucoside. There are several commercial systems which include wells for the performance of this determination for streptomycin and gentamicin. METHODS: A comparative study of two commercial systems, Vitek GPS-TA and ATB STREP (Biomérieux) and disk diffusion versus the Mueller-Hinton agar dilution method used as a method of reference. Two hundred ninety strains of Enterococcus spp. from blood, wounds, pus, fluids from paracentesis and urine were studied. RESULTS: By the reference method, 17 presented high level of resistance only to gentamicin, 45 only to streptomycin, 46 to both and 182 were sensitive to the two antibiotics. The sensitivity of ATB STREP, Vitek GPS-TA and disk diffusion was respectively for high level of resistance to gentamicin of 96.8, 100 and 100% and specificity of 99.5, 99.1 and 96.5%. For high level of resistance to streptomycin sensitivity was 78.2, 100 and 100% and specificity 96, 79.4 and 72.4% respectively. CONCLUSIONS: The authors consider the three methods valid for the determination of high level of resistance to gentamicin, presenting excellent correlation between the results of the reference methods. However, for high level of resistance to streptomycin with ATB STREP 1/5 of the resistant strains would not be detected due to low sensitivity. With Vitek GPS-TA and disk diffusion, although excellent sensitivity was presented, a high percentage of false positives were obtained due to low specificity, thus the authors recommend that before a results of resistance be decided the same should be confirmed by another alternative method (agar dilution, macrodilution in tubes or death-time curve).

Diffusion↗
PubMed1992

In vitro susceptibility of 245 yeast isolates to amphotericin B, 5-fluorocytosine, ketoconazole, fluconazole and itraconazole.

The in vitro activity of amphotericin B, 5-fluorocytosine, ketoconazole, fluconazole and itraconazole was tested against 245 yeast strains isolated from clinical specimens (68 Candida albicans, 74 Candida tropicalis, 43 Candida krusei, 28 Candida glabrata, 19 Candida parapsilosis, 8 Candida lusitaniae and 5 Candida guilliermondii). An agar dilution method was employed to carry out testing. Minimal inhibitory concentrations to restrain 90% of isolate growth (MIC90) ranged from 0.12 to 2 mg/l for amphotericin B and for 5-fluorocytosine, from 0.03 to 8 mg/l for ketoconazole, from 0.05 to 50 mg/l for itraconazole and from 0.1 to > 100 mg/l for fluconazole. Among the azole derivatives, the most active was ketoconazole, followed by itraconazole. Only 1 strain of C. albicans was resistant to amphotericin B (MIC > 4 mg/l). Both C. tropicalis and C. krusei responded poorly to fluconazole and the former to itraconazole as well. The species most susceptible to the antifungal agents tested was C. glabrata and the most resistant were C. tropicalis and C. krusei.

Amphotericin B↗
PubMedDate not supplied

Determination of serum levels of dietary thiocyanate.

A spectrophotometric method was used to determine thiocyanate (SCN-) levels in human serum, in an attempt to relate serum levels of this ion to the dietary intake of vegetables of the genus Brassica. Thiocyanate ion was measured before and after a one-week period during which the subjects ate a diet rich in these vegetables. We also determined the serum increase in SCN- 2 h after the administration of 0.5 g KSCN.

Adult↗