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M Simões

Publications and source records attributed to M Simões.

At least 19 recordsLinked to original sources
PubMed2006

Corresponding states in nematic elasticity.

A comparative study of the temperature dependence of the elastic constants of the nematic liquid crystals known as PAA (p-azoxyanisole), MBBA 4'-methoxybenzylidene-4-n-butylaniline, and 5CB (4-n-pentyl-4'-cyanobiphenyl) will be made in this work. After a regularization of their values, and with use of a unique temperature scale, the experimental data of each of these parameters will be displayed along the lines of corresponding states that are not restricted to the neighborhoods of the nematic-isotropic phase transition point, as it would be the case in a usual corresponding states law, but encompass the entire nematic phase.

Journal Article↗
PubMed2006

Comparative antibacterial potential of selected aldehyde-based biocides and surfactants against planktonic Pseudomonas fluorescens.

The antimicrobial efficacy of two aldehyde-based biocides (glutaraldehyde, GTA, and ortho-phthalaldehyde, OPA) and two surfactants (cetyltrimethyl ammonium bromide, CTAB, and sodium dodecyl sulphate, SDS) was tested against planktonic Pseudomonas fluorescens. The antimicrobial effects were evaluated by respiratory activity as a measure of the oxygen uptake rate, adenosine triphosphate (ATP) release, outer membrane proteins (OMP) expression and cellular colour changes. The results were compared with the bacterial characteristics without chemical treatment. Tests in the presence of bovine serum albumin (BSA), in order to mimic a disinfection process in the real situation under dirty conditions, were performed according to the European Standard EN-1276. P. fluorescens was completely inactivated with OPA (minimum bactericidal concentration, MBC = 0.5 mM) and CTAB (MBC = 5 mM) and was resistant to GTA and SDS. Only CTAB promoted cellular disruption and consequent ATP release. The antimicrobial action of the chemicals tested was significantly reduced when BSA was introduced into the bacterial cultures, increasing markedly the MBC values. Additionally, the presence of BSA acted as a disruption protective agent when CTAB was applied and stimulated the bacterial respiratory activity when lower concentrations of SDS were tested. The OMP of the bacterial cells was affected by the application of both surfactants. OMP expression remained unaltered after biocide treatment. Bacterial colour change was noticed after treatment with biocides and surfactants. In summary, P. fluorescens was extremely resistant to GTA and SDS, with antimicrobial action being quenched markedly by the reaction with BSA.

Aldehydes↗
PubMed2005

Bend and splay elastic constants at a reentrant isotropic-calamitic-nematic phase transition.

By measuring the ratio between the major and minor axes of closed elliptical loops created by a magnetic field, the ratio between the bend (K33) and splay (K11) elastic constants of a lyotropic mixture of potassium laurate, decanol, and water in the calamitic nematic phase is measured as a function of temperature. Since these systems present two nematic-isotropic phase transitions--the usual one, at high temperatures, and a reentrant one, at low temperatures--such measurements are used to compare the behavior of these elastic constants at the neighborhoods of these two distinct regions, which have in common the vanishing of the order parameter. The experimental data have revealed the existence of two elastic constant branches, characterizing a distinct low- and high-temperature behavior. To explain such asymmetry we support that, because of the lyotropic nature of the compound, the micellar variation, which is mainly responsible for the reentrant phase, plays a distinct role at these two phase transitions.

Journal Article↗
PubMed2005

Viscosity peaks at the cholesteric-isotropic phase transitions.

In this work, the effective viscosity of the cholesteryl myristate and cholesteryl nonanoate liquid crystals is studied as a function of temperature at the region of their cholesteric-to-isotropic phase transition, where blue phases are found. Using a change of scale it is shown that the viscosity peaks that characterize these phase transitions are shape invariant, which suggests that large-scale fluctuations on the two-point correlation function give an important contribution to the observed viscosity. The consequences of this fact are investigated and, from the experimental data, the critical exponents associated with the diverging two-point correlation function are calculated. The results found for both compounds are essentially the same, being also in good agreement with the known values of the corresponding critical exponents of nematic-isotropic phase transition.

Journal Article↗
PubMed2005

Validation of respirometry as a short-term method to assess the efficacy of biocides.

This study shows that a short-term respirometric measurement based on the rate of oxygen uptake needed to oxidize glucose is a reliable and fast method to assess biocide efficacy against P. fluorescens cells. Respiratory activity using oxygen consumption rate, the determination of viable and nonviable cells using Live/Dead BacLight kit and colony formation units (CFU), were compared as indicators of the biocidal efficacy of ortho-phthalaldehyde (OPA). The results showed that determining the effect of OPA against P. fluorescens using the different methods leads to different conclusions. The minimum bactericidal concentration (MBC) was 80 mgl(-1), 100 mgl(-1) and 65 mgl(-1) respectively, using respiratory activity, viability using BacLight counts and culturability. The plate count method was shown to underestimate the biocidal action of OPA, whilst data from respirometry and viability using Live/Dead BacLight kit correlated strongly and were not statistically different when yellow cells were considered nonviable. Respirometry therefore represents an expeditious, non-destructive and accurate method to determine the antimicrobial action of biocides against aerobic heterotrophic bacteria.

Bacteriological Techniques↗
PubMed2004

Landau-de Gennes model for nonuniform configurations in nematic liquid crystalline elastomers.

Through a mean field theory, an elastic free energy describing the nonuniform elastic textures observed in nematic elastomers, is proposed. To construct it, an order parameter that describes the nematic-isotropic phase transition through the change of the elastic properties of the strain tensor at the transition point is introduced. The resulting elastic free energy can be written in a form that resembles the Frank free energy of the usual nematic liquid crystals, becoming equivalent to it when the size of the elastic nematic domains is a fixed constant along the whole sample. Using this approach, a model for nonhomogeneous deformations found by Macromolecules 33, 7675 (2000)] in elastomeric thin films of urethane/urea is proposed.

Journal Article↗
PubMed2003

Agreements and disagreements between theories and experiments in nematoviscosity.

In this work a set of viscosity data selected from the nematic liquid crystals literature is compared with the currently accepted microscopic (molecular) theories for the nematic viscosity. It is shown that the kinetic theory of Doi [N. Kuzuu and M. Doi, J. Phys. Soc. of Jpn. 52, 3486 (1983)] and the affine transformation theory of Hess [D. Baalss and S. Hess, Phys. Rev. Lett. 57, 86 (1986)] equally predict that Miesowicz's coefficients of a given sample are not independent but, as it has been believed for many years [H. Kneppe, F. Scheneider, and N. K. Sharma, Ber. Bunsenges Phys. Chem. 85, 784 (1981)], they are connected by a linear relationship. Such conjecture gains a strong positive support when it is applied to a set of experimental data that we have collected. However, when these data are used to obtain the values of the parameters used to build these theories, it is found that the values assumed by them are in flagrant disagreement with the physical interpretation that they are supposed to have.

Journal Article↗
PubMed2003

Periodic structures in a biaxial nematic phase.

In this work experimental and theoretical results will be used to show that under convenient conditions; appropriated geometry, well chosen boundary conditions, and suitable external fields, the elastic and dynamic behavior of a sample of a biaxial nematic liquid crystal can become similar to the one observed on usual uniaxial nematic liquid crystals. It is shown that this result can be used to determine the values of some combinations of the rheologic parameters of the biaxial phase.

Journal Article↗
PubMed2003

Cortisol, prolactin, growth hormone and neurovegetative responses to emotions elicited during an hypnoidal state.

The present study describes the responses of cortisol, prolactin and growth hormone (GH) to emotions elicited during sessions in which an hypnoidal state was induced. The purpose of the study was to provide answers for the following questions: 1) Do sessions with an emotional content have more hormonal surges than baseline, relaxation-only, sessions? 2) Does the induction of a fantasy of pregnancy and nursing elicit a prolactin response? 3) Are there any associations between surges of different hormones? 4) Are hormonal responses related to the intensity, type, or mode of expression of the emotions? For this purpose, thirteen volunteers and twelve patients with minor emotional difficulties were studied during sessions under hypnosis. The period of observation lasted for about three hours. Heart rate (HR), skin conductance (SC) and vagal tone (VT) were monitored. Serum cortisol, prolactin and growth hormone were sampled every 15 minutes. The volunteers had three types of sessions- "blank", consisting of relaxation only (12 sessions), "breast feeding", in which a fantasy of pregnancy and breast feeding was induced (12 sessions) and "free associations" in which the subjects were encouraged to evoke experiences or feelings (17 sessions). The patients had only sessions of free associations (38 sessions). Sessions of free associations had more hormonal surges than "blank" and "breast feeding" sessions. This was true for cortisol (8/17 v.3/24; p < 0.03), prolactin (7/17 v. 3/24; p < 0.05) and GH (9/17 v. 4/24; p < 0.02). During the 55 sessions of free associations (volunteers plus patients) there were 32 surges of cortisol, 18 of prolactin and 28 of GH. Cortisol and prolactin surges were negatively correlated (p < 0.03). GH had no significant association with either cortisol or prolactin. Visible emotions were positively associated with GH surges (p < 0.05). but not with cortisol or prolactin. Cortisol surges were correlated positively with evocations of real events (p < 0.01) and negatively with evocations containing defensive elements (p < 0.01). Cortisol correlated positively with shock and intimidation (p < 0.02) and negatively with rage (p < 0.04). The AUC of the cortisol peaks during shock and intimidation was significantly higher than that of the pool of all other cortisol peaks (12.4 micromol x min x l(-1) v. 7.1 micromol x min x l(-1); p < 0.005). Rage had a marginally significant positive association with prolactin surges (p=0.07). The distribution of GH surges did not show any significant association with types of emotions. The present study provides evidence that cortisol, prolactin and GH respond to psychological stress in humans. However, they are regulated differently from one another. Cortisol and prolactin surges appear to be alternative forms of response to specific emotions. GH surges depend on the intensity of the emotion, probably as a consequence of the associated muscular activity. The current paradigm of stress, implying corticotrophin-releasing hormone (CRH) as the initial step of a cascade of events, is insufficient to account for the diversity of hormonal changes observed in psychological stress in humans.

Adult↗
PubMed2003

Monitoring the effects of biocide treatment of Pseudomonas fluorescens biofilms formed under different flow regimes.

The effectiveness of glutaraldehyde (GTA), a very common biocide for controlling biofilms formed by Pseudomonas fluorescens on stainless steel slides, in laminar and turbulent flow, was investigated. Tests were performed using a concentration of biocide of 200 mg L(-1) and a range of exposure times. The GTA action was assessed by means of activity tests and dry weight of the biofilms. The physical stability of the biofilm without biocide application and after exposure to GTA for different periods of time was also studied and evaluated through the variation of the mass of the deposit after submission to different rotation velocities. The results showed that, in all the situations studied, biofilms were not controlled after the treatment with biocide, since they remained on the metal surface and were still active. The results also demonstrated that the physical stability of the biofilms increased with biocide application.

Biofilms↗
PubMed2002

Geometric approach to the Miesowicz coefficients at the region of the crystalline-nematic transition and a universal relation for their ratio.

In this work the ratios between the Miesowicz coefficients of rigid calamitic nematic liquid crystals will be studied. It will be shown that the microscopic theory that describes these coefficients, the kinetic theory [M. Doi and S. F. Edwards, The Theory of Polymer Dynamics (Oxford Press, New York, 1986)], suggests that some ratios between the Miesowicz coefficients would have a universal character, that does not depend on the nematic material being examined. A set of experimental data has been collected from the liquid crystal literature and, once these data are rescaled in a common temperature scale, they point to the existence of such a universality. Nevertheless, only in the neighborhoods of the nematic-isotropic transition, do the theoretical calculations of the kinetic theory and the experimental data predict the same profile for this universality; when the region of the crystalline-nematic transition is approached theory and experiment present severe discrepancies. The reason for this disagreement is studied and it is proposed that it results from the fact that the kinetic theory does not take into account the packing properties of the nematic medium. A different approach to the calculation of these ratios is proposed and it is shown that it describes the experimental data for all temperatures.

Journal Article↗
PubMed2001

Maier-Saupe and Onsager approaches as limits of the nematic-isotropic phase transition.

Through a virial expansion, the long and small range properties of the interaction between ellipsoidal nematic molecules are put together in a unique approach that combines the essentials of some classical models that describe the nematic-isotropic phase transition. The Lennard-Jones potential that mediates the interaction between the centers of the mass of molecules, the long range Maier-Saupe interaction that favors their alignment and the molecular hard core that hinders their close approximation, as in the Onsager model, are combined in a unique approach that exhibits two phases transitions; the gaseous-liquid transition and the nematic-isotropic phase transition. As a conclusion, the Onsager and Maier-Saupe approaches were considered limits of the actual physical situation.

Journal Article↗
PubMed2001

Induction of orientational order in the isotropic phase of a nematic liquid crystal.

The orientational properties of an isotropic dense liquid composed by anisotropic molecules, such as a liquid crystal in an isotropic phase, is studied. Using a Langevin-like equation it will be shown that the rotational motion of each molecule can be divided in two elements describing two kinds of physical motion. The first describes the Brownian rotational motion and another the coherent rotation induced by the external fields. It will be shown that, even at the isotropic phase, an order parameter describing the mean degree of alignment of the molecules around a given point can be defined. This order parameter also separates the order coming from the coherent motion from the order generated by the anisotropy in the thermal fluctuations. At the end the proposed model is compared with an experiment and it is shown that the coherent motion is enough to explain the experimental results.

Journal Article↗
PubMed2001

Arising of magnetic walls in the vicinities of the Frèedericksz transition.

In this paper, the dynamical formation of twist-bend periodic walls at the neighborhoods of the Frèedericksz critical point of a nematic sample of liquid crystals is studied. The theory that describes the arising of these periodic structures affirms that the mode with the fastest initial growth will fix the observed properties of these patterns. But, just above the Frèedericksz threshold there is a region where this leading mode becomes null and, therefore, a homogeneous bending of the director may be detected. This prediction was not confirmed by the experiment, and walls with very well defined wavelength were found. We will show here that the fastest growing mode cannot be defined around the Frèedericksz threshold and, therefore, a new way to compute the observed periodicity must be formulated. We assume that the observed wall results from a sum of a continuum and nonsharp distribution of modes in which the null mode is at the center.

Journal Article↗
PubMed2001

Relevance of the rates of PCNA, Ki-67 and p53 expression according to the epithelial compartment in cervical lesions.

In order to assess further biological evidence for similarities among the "diagnostic classes" of cervical lesions, which are now a matter of international discussion in the search for a uniform classification, the purpose of this study was to characterize the immunoexpression of cell proliferation markers (proliferating cell nuclear antigen, PCNA and Ki-67) and protein p53. Each marker was individually quantified in basal, intermediate, and superficial epithelial compartments presenting chronic cervicitis (CC) accompanied by the cytopathic effects of infection by human papillomavirus (CCHPV) or not (CC), as well as in cervical intraepithelial neoplasia (CIN) grades I, II, and III. A total of 100 patients were evaluated and the positive nuclei were counted separately, including all extensions of the available epithelium. The percentage of PCNA- and Ki-67-positive cells increased with increasing grade of the cervical lesions, although PCNA immunoreactivity was always greater than the immunoreactivity observed with Ki-67 antigen. The immunoexpression of p53 protein was found to be weak, with no remarkable behavior in any specific "diagnostic class". The differences in cell proliferation markers found herein further emphasize the progressive loss of epithelial layer organization in the course of the development of preneoplastic changes in cervical squamous epithelium. Furthermore, difficulties in morphologically distinguishing "borderline lesions" persist when cell cycle markers are studied, further supporting the suggestion to consider the lesions of CCHPV and CIN I together as only one diagnostic class. Conversely, the different immune profile found between CIN II and III further supports the validity of the subdivision of CIN into three groups.

Biomarkers, Tumor↗
PubMed1999

Forbidden walls.

In this paper the presence of periodic twist-bend walls in the upper vicinity of the Frèedericksz critical point of a nematic calamitic sample is reported. According to the existing theory, the formation of these structures could not happen in this region of the magnetic field. The length of the periodicity of these walls as well as the time spent with their formation have been measured, and it was demonstrated that the coherent motion of the nematic material cannot drive their construction. We assume that the mechanism responsible for their appearance results from the magnification of some selected random fluctuations occurring at the neighborhood of the Frèedericksz critical point.

Journal Article↗
PubMed1998

[Myocardial protection against cold stress with pravastatin].

The CARE study showed that the myocardial infarction recurrence rate in patients with moderate cholesterol blood level decreases early during pravastatin treatment. Our goal is to evaluate the possible role of pravastatin in preventing the myocardial lesions induced by cold stress. Twenty Wistar-EPM rats were divided into four groups: Control (CON); PR (Pravastatin) treated with 10 mg/kg/d for 15 days; S (Stress group) in which the rats were submitted to cold stress (-8 degrees C for four hours); and PR + S group treated with pravastatin like PR group and also submitted to the cold stress. The animals were sacrificed and heart fragments were removed for optic and electronic microscopic analysis. The variable considered was mitochondria abnormality (edema, lyses and vacuolization) that was interpreted as crystolyses indices (CI) (n degree of abnormal mitochondria/n degree total of mitochondria). The following crystolyses indices, were found for each group respectively: CON, 2.0%; S, 95.5%; PR, 19.9% and PR + S group, 27.7%*(*p < 0.01). In conclusion, pravastatin prevented myocardial lesions induced by cold stress significantly.

Animals↗