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Biomedical subjects

E A Oliveira

Publications and source records attributed to E A Oliveira.

At least 19 recordsLinked to original sources
PubMed2006

Transitions in the orientational order of liquid crystals induced by periodic patterned substrates.

The orientational order of liquid crystals (LCs) induced by periodic patterned substrates has been investigated with cells coated by azopolymer films that could be photoaligned in a controlled way. Two regimes were observed depending on the period of the patterns: (i) above 3.0 microm the LC follows the direction imposed by the patterned substrate since the energy stored in the surface potential minimizes the elastic energy of the LC medium. (ii) For periods smaller than 1.0 microm a homogeneous in-plane state was induced and the LC did not follow the orientation imposed by the surface. This in-plane transition could be explained qualitatively by a theoretical model based on the competition between the Frank-Oseen elastic energy and the phenomenological surface potential. The results also suggest an out-of-plane transition for the LC director as the period was reduced. These results agree with data in the literature for patterned substrates with completely distinct architectures. This indicates that for a particular LC sample the overall behavior depends basically on the texture period instead of the texture architecture. The textures were characterized with a scanning near-field optical microscope (SNOM), which allowed simultaneous morphological and optical images in the submicrometer range.

Journal Article↗
PubMed2005

Effect of microtextured substrates on the molecular orientation of a nematic liquid-crystal sample.

The in-plane orientation of a nematic liquid-crystal sample, confined by two periodic microtextured substrates, is theoretically analyzed by means of the Frank-Oseen continuum elastic theory and a suitable surface term. In addition, an easy optical method to produce such textures using photopolymeric films is presented. It is shown that, in the limit of large pattern period, the orientation depends only on the ratio of the splay and bend elastic constants K1/K3 and on the easy axis direction of the individual stripes. In the particular case for which K1 = K3, the stability depends only on the easy axis direction for a general pattern period.

Journal Article↗
PubMed2005

Removal of metal ions from aqueous solutions by sorption onto rice bran.

A new sorbent (raw rice bran) was investigated for heavy metal ions removal from aqueous solutions. Rice bran characterisation was carried out in order to identify the functional groups possibly involved in the metal binding. The binding process was studied in terms of binding capacity and metal affinity. The adsorption equilibrium was well described by the Freundlich isotherm model. The negative Gibbs free energy values obtained in this study with rice bran confirm the feasibility of the process and the spontaneous nature of sorption.

Ions↗
PubMed2004

Surface-induced orientational phase transition in a lyotropic liquid crystal observed by nonlinear optical techniques.

We have observed a phase transition from a uniaxial to a biaxial nematic phase in a lyotropic liquid crystal as a function of decreasing film thickness. The results, obtained by optical second-harmonic generation experiments in a wedged cell geometry, are supported by additional Z -scan measurements and can be interpreted by wall-induced ordering effects.

Journal Article↗
PubMed2004

Diagnostic accuracy of fetal renal pelvis anteroposterior diameter as a predictor of uropathy: a prospective study.

OBJECTIVE: The purpose of this study was to assess the accuracy of prenatal ultrasound measurement of anteroposterior renal pelvis diameter (APD) to discriminate between significant uropathy and idiopathic renal pelvis dilatation. METHODS: One-hundred-and-three neonates who were found to have fetal renal pelvis dilatation, defined as presence of an APD > or = 5 mm, underwent systematic investigation for uropathies and were prospectively followed. An ultrasound scan was performed after the first week of postnatal life and all infants underwent a voiding cystourethrogram. Neonates with an APD larger than 10 mm underwent renal scintigraphy. Ultrasound scans, clinical examination and laboratory reviews were scheduled at 6-month intervals. Receiver-operating characteristics (ROC) curves were constructed to determine the best cut-offs for APD to identify renal units with significant uropathy as well as those requiring surgical intervention. Significant uropathy was defined as the presence of well-established urinary tract abnormalities or when there was abnormal renal scintigraphy. RESULTS: The estimated area under the curve for APD was 0.900 (95% CI, 0.841-0.942) indicating excellent power to discriminate between idiopathic pelvis dilatation and significant uropathy. The sensitivity and specificity for the 7.5 mm cut-off point were 97.9% and 40.6%, respectively. To identify infants who required surgical intervention, the calculated area under the curve was 0.953 (95% CI, 0.908-0.980). CONCLUSION: Our results suggest that measurement of APD is an excellent test to identify fetuses with significant uropathy, as well as those requiring postnatal intervention.

Area Under Curve↗
PubMed2003

Manipulation of anchoring strength in an azo-dye side chain polymer by photoisomerization.

The generation of surface anisotropy by photochemical means has been proposed as an attractive method to align liquid crystals. In this paper, we present an experimental study of the alignment induced on a liquid crystal by a polymer film containing azo-dye groups in the side chain. Optical measurements were performed in nematic liquid crystal cells to determine the azimuthal and zenithal anchoring strengths as a function of the irradiation energy and chromophores concentration. It was observed that the director tends to align perpendicular to the polarization direction of the incident light and the orientation process consists essentially of a rotation of the director in the plane parallel to the boundary surfaces. However, the concentration of azo-dye groups in the polymer film must exceed a minimum value to get a macroscopical effect on the liquid crystal alignment. It is shown that the azimuthal anchoring strength can be varied two orders of magnitude by controlling the irradiation energy and azo-dye concentration.

Journal Article↗
PubMed2001

Dynamical behavior of a nematic lyotropic liquid crystal in flat confined samples.

We investigate the dynamical behavior of the director in the surface layer of lyotropic nematic liquid crystals in an external magnetic field. The characteristic time of the orientation process is obtained from optical measurements for samples of different thickness (200, 50, and 10 microm). The boundary surfaces are glass plates coated with rubbed polymer [polymethylmethcrylate (PMMA)], to introduce an easy axis. Drastic changes in the dynamical behavior are observed when the thickness is decreased and the experimental results indicate a uniaxial to biaxial transition due to the confinement of the nematic sample.

Journal Article↗
PubMed2001

Multicystic dysplastic kidney detected by fetal sonography: conservative management and follow-up.

The most common cystic lesion recognized antenatally is multicystic dysplastic kidney (MCDK). Recently, conservative management without nephrectomy has been advocated. The purpose of this study was to report our experience in the conservative management of unilateral MCDK. Between 1989 and 1997, 20 children with MCDK detected by prenatal ultrasonography (US) were prospectively followed. At birth, US confirmed the prenatal findings in all cases. All patients were submitted to radioisotope scans and a micturating cystogram. Follow-up US examinations were performed annually. Mean age at diagnosis during the prenatal period was 31 weeks of gestation (range 24-38). Median follow-up time was 33 months (range 7-91). Follow-up US was performed in 19 children; 13 (68%) showed partial involution, 4 (21%) complete involution, and 2 (11%) an increase in unit size. The mean age at complete or partial involution of the lesion was 18 months. No children developed hypertension or tumors, and all maintained normal growth. In conclusion, the natural history of MCDK is usually benign, and serial US examinations show that affected kidneys frequently show involution with time.

Female↗
PubMed2001

[Risk behavior in adolescence]

OBJECTIVE: The present article reviews the methods and criteria used to assess risk behavior in adolescents. METHODS: Non-systematic review of scientific literature, as well as the assessment of the clinical and research experience accumulated by the Adolescent Outpatient Clinic of the Hospital de Clínicas de Porto Alegre. RESULTS: Physicians can apply a comprehensive healthcare model by using a psychosocial approach, trying to understand the influence the media exerts on adolescents, and trying to establish a confidentiality relationship with them. The major factors that should be evaluated regarding risk behavior among adolescents include clinical and nutritional aspects, as well as sexuality, violence, mental health and alcohol and drug use issues. CONCLUSIONS: Health care providers should use their sensitivity and expertise, in addition to establishing ethically clear approaches to evaluate risk factors. The authors suggest a route of investigation of risk behavior that should be used in routine consultation.

Journal Article↗
PubMed2001

Outcome of fetal urinary tract anomalies associated with multiple malformations and chromosomal abnormalities.

The purpose of this study was to identify prognostic factors and describe the outcome of prenatally detected renal anomalies associated with multiple malformations and chromosomal defects. Forty-one fetuses were included in the analysis. Prenatal ultrasound reports, neonatal records and autopsy information were retrospectively reviewed. Prognostic factors associated with fetal echography and clinical and laboratory findings on admission were studied. Data were analyzed by univariate analysis in which variables associated with adverse outcome were identified by the Chi-square test or Fisher exact test. The abnormalities associated with renal anomalies were divided into three groups: chromosomal defects (21%), previously described syndromes and conditions (24%), and new sporadic conditions (55%). Of 41 children admitted, 30 (76%) died during the perinatal period. The presence of oligohydramnios was significantly associated with an adverse outcome (OR=11, p=0.05). Male gender was a protective factor against death during the perinatal period (OR=0.11, p=0.01). In conclusion, prenatally detected renal anomalies associated with multiple malformations and chromosomal defects had a poor prognosis. The presence of oligohydramnios increased the risk of death, and male gender had a protective role against poor outcome.

Abnormalities, Multiple↗
PubMed2000

Primary megaureter detected by prenatal ultrasonography: conservative management and prolonged follow-up.

With the widespread use of obstetric echography the incidence of fetal hydronephrosis has been reported more frequently. Consequently, many uropathies have been detected in asymptomatic neonates. The authors report their experience with prenatally detected primary non-refluxing megaureter. Newborns with fetal hydronephrosis were investigated by ultrasonography and micturating cystourethrogram after the beginning of chemoprophylaxis. If primary megaureter was identified, after 1 month the children underwent 99tm-DMSA, diuretic 99tm-DTPA, and intravenous urography. Eight infants with primary megaureter (bilateral in 3 cases) were identified, for a total of 11 renal units for study. All children were submitted to non-operative management. We performed ultrasonography and diuretic 99tm-DTPA during follow-up, which lasted on average 75 months. The mean cross-sectional diameter of the dilated ureter was 13.6 mm during neonatal period, and reached 8.4 mm at the end of follow-up. The renal function and the diuretic renogram remained stable throughout follow-up. Two neonates presented transitory hypertension. Our results support the notion that conservative management is safe for primary megaureter detected in asymptomatic neonates, with most cases showing spontaneous regression during a prolonged follow-up.

Female↗
PubMed1999

Prognostic factors in fetal hydronephrosis: a multivariate analysis.

With the increasing use of obstetric echography fetal hydronephrosis has been reported more frequently. The purpose of this study was to identify prognostic factors associated with adverse outcome, such as renal failure and death, in fetal hydronephrosis. One hundred and forty-eight children with fetal hydronephrosis were admitted, submitted to a systematic protocol, and prospectively followed. Prognostic factors associated with fetal echography and clinical and laboratory findings on admission were studied. The median follow-up was 39 months. The analysis was conducted in two steps. In a univariate analysis, variables associated with adverse outcome were identified by the Kaplan-Meier method. The variables that were significantly associated with adverse outcome were then included in a multivariate analysis. This analysis, using the multivariate Cox's model, was performed to identify variables that were independently associated with a worse prognosis. Only variables that remained independently associated with adverse outcome were included in the final model. After final adjustment by Cox's multivariate model, three variables were identified as independent predictors of adverse outcome: oligohydramnios, prematurity, and glomerular filtration rate lower than 20 ml/min. Thus, in the presence of oligohydramnios, prematurity, and abnormal renal function, the medical team must plan appropriate follow-up for infants at health centers prepared to investigate and treat uropathies in newborns.

Algorithms↗
PubMed1999

Surface breaking in lyotropic nematic liquid crystals induced by a magnetic field.

The twist deformation induced by a magnetic field H in a lyotropic liquid crystal is analyzed. Our results show the existence of three regimes for the surface deformation related to two critical values for the external magnetic field. The first, for low magnetic field, is an elastic one in which the surface deformation disappears when the field is removed. In a second regime, a permanent deformation of the lyotropic liquid crystal is induced by the distorting field. This regime is characterized by a threshold for H, called H(*)(c). In the third regime, the sample is uniformly oriented along H. Also this regime has a well defined threshold value, H(**)(c), and the alignment remains even when the distorting field is removed. To interpret the experimental data recently published, we proposed a phenomenological model according to which there is an elastic coupling between the surface layer of thickness l and the bulk. This elastic coupling has a saturation for a given value of the deformation of the bulk with respect to the surface layer.

Journal Article↗
PubMed1998

Features of primary vesicoureteric reflux detected by investigation of foetal hydronephrosis.

Primary vesicoureteric reflux (VUR) diagnosed on investigation of foetal hydronephrosis accounts for many antenatally detected uropathies. In order to study foetal VUR and its consequences, newborns with foetal hydronephrosis were investigated by ultrasound, micturating cystourethrogram and 99mTechnetium-dimercapto-succinic acid (DMSA), after beginning of chemoprophylaxis. Twenty-eight infants with VUR (bilateral in 15 cases) were identified giving a total 43 renal units for study. There was a predominance of males (86%), moderate/severe reflux (84%) and renal damage (51%). Presence of renal damage was correlated with the severity of reflux. VUR should be investigated in cases of foetal hydronephrosis and our results support that renal damage is frequently congenital and not secondary to urinary tract infection.

Female↗
PubMed1995

Action of immobilized xanthine oxidase on purines.

Xanthine oxidase was covalently immobilized on polyacrylamide gel beads, polyamide-11 and dacron. Hypoxanthine (15 ml of 200 microM), prepared in 0.1 M phosphate buffer, pH 8.0, was circulated through a column containing 1.0 g derivatized enzyme at a flow rate of 1.0 ml/min at 28 degrees C. Specific activities of 0.660, 0.072 and 0.016 Units/mg of protein were demonstrable for the polyacrylamide gel beads, dacron and polyamide-11 derivatives, respectively. The action of these water insoluble enzyme derivatives on 6-mercaptopurine (15 ml of 660 microM) was also investigated, under the same experimental conditions, showing specific activities of 0.063 Units/mg, 0.574 muUnits/mg and 0.118 muUnits/mg, respectively. The 6-mercaptopurine oxidative pathway catalyzed by immobilized xanthine oxidase on dacron stopped at the intermediate compound, 6-mercapto-8-hydroxypurine, so that no 6-thiouric acid was produced, whereas the immobilized preparations using polyacrylamide gel beads and polyamide-11 behaved like the soluble enzyme, namely, 6-thiouric acid was the final product. The behavior of dacron-xanthine oxidase compound was similar to that previously described for the derivatives obtained with carboxymethylcellulose and chitosan. The hypoxanthine oxidative pathway catalyzed by xanthine oxidase immobilized on these three supports was similar to the soluble enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzymes, Immobilized↗
PubMed1994

L-malic acid production by entrapped Saccharomyces cerevisiae into polyacrylamide gel beads.

The yeast Saccharomyces cerevisiae was entrapped within polyacrylamide gel beads by employing a procedure that uses sodium dodecylsulfate as a detergent to improve the spherical configuration of the beads. The resulting preparation showed a rate of fumarate bio-conversion to L-malic acid about 60 times higher than that found for the free cells. Almost all fumarate was converted in 30 min of incubation. The thermal stability of the immobilized cells did not significantly differ from the free cells. An optimal pH of 5.7 was found for the immobilized preparation and no succinic acid was detected as a byproduct in the incubation mixture.

Acrylic Resins↗
PubMed1991

Immobilization of protein on ferromagnetic Dacron.

Ferromagnetic Dacron (polyethyleneterephthalate) is proposed as a matrix to immobilize proteins covalently. Dacron in powder was magnetized by reacting ferrous (Fe+2) and ferric (Fe+3) ions with its hydrazide form at pH 8.3. Ferromagnetic hydrazide Dacron was converted to ferromagnetic azide Dacron and amyloglucosidase (E.C. 3.2.1.3) was covalently bound through the latter group. The catalytic property of the enzyme was preserved (8% of the specific activity estimated for the soluble enzyme) and all the magnetic amyloglucosidase Dacron derivative was recovered by using a magnetic field. No activity was detected in the supernatant.

Enzymes, Immobilized↗