Sarah Alves

Generalization of the thermal lens model formalism to account for thermodiffusion in a single-beam Z-scan experiment: determination of the Soret coefficient

A generalization of the thermal lens model formalism is proposed to introduce and characterize the thermodiffusion phenomenon. The theory treats the case in which local heating generates a temperature gradient in a single-phase binary sample (a colloid, for instance) that yields, through thermodiffusion, concentration gradients in an initially homogeneous sample. The treatment generalizes the concept of a thermal lens to a material lens as a result of the coupling of a concentration variation with the optical properties of the medium. This formalism permits the use of the Z-scan technique to determine the Soret coefficient of samples. Applying this theory to the results of a Z-scan experiment with an ionic ferrofluid sample gives values that agree with those obtained from forced Rayleigh scattering measurements of the same material.

Investigation of the sign of the Soret coefficient in different ionic and surfacted magnetic colloids using forced Rayleigh scattering and single-beam Z -scan techniques

The sign of the Soret coefficient S T of a large set of ionic magnetic colloids (ionic ferrofluids (IFFs)) and surfacted magnetic colloids (surfacted ferrofluids (SFFs)) is determined using forced Rayleigh scattering and the single-beam Z -scan techniques. Different samples were investigated: acid and alkaline colloids with different values of pH; colloids with different concentrations of magnetic grains; colloids with grains of different typical diameters; colloids with magnetic grains with different coating natures; colloids with different non-polar and polar liquid carriers. Our results indicate that the sign of S T depends on the sign of the surface charge of grains in IFFs. In the case of water-based SFFs, the thermodiffusive behaviour is opposite to that of IFFs; that is, grains coated with a cationic surfactant behave like negatively charged IFF (alkaline) grains and grains coated with an anionic surfactant behave like positively charged IFF (acid) grains. SFFs with grains coated with non-ionic surfactants dispersed in non-polar fluid carriers behave like SFFs with grains coated with a cationic surfactant. The nature of the liquid carrier itself is not the only determinant factor, except apparently in the case of non-polar fluids, where only S T > 0 is found. These results cannot be explained with the available theories and it is highly probable that different mechanisms are present in the thermodiffusive behaviour of these complex fluids.

The effect of hydrophobic and hydrophilic fumed silica on the rheology of magnetorheological suspensions

We investigate magnetorheological fluids (MRFs) prepared with carbonyl iron powder and different types of hydrophobic and hydrophilic fumed silica. The rheological properties of the MRF suspensions were investigated with and without an applied magnetic field. The MRF samples prepared with hydrophobic silicas presented a more pronounced thixotropic effect and a higher recovery rate than those prepared with hydrophilic silicas. The application of a magnetic field to all the MRFs samples investigated leads to an increase in the viscosity and the thixotropic effect. MRF prepared with hydrophobic silicas presented smaller values of the viscosity than those prepared with hydrophilic silicas. At low applied magnetic fields, the type of the silica used to prepare the MRF leads to noticeable differences in the shear stress. However, these differences disappear at high magnetic fields. The results obtained showed that MRF samples prepared with the hydrophobic silica with the biggest particle diameter presented bett...

Impact of Selenium Supplementation in Neutropenia and Immunoglobulin Production in Childhood Cancer Patients

Essential to human health, selenium (Se) has enzymatic functions of fundamental importance to human biology due to its effects on DNA damage repair, its antioxidant properties, and cancer prevention. The best studied relationships between Se and the immune system is its role in the functions of neutrophils and of lymphocytes. Despite these observations, it is not yet clear by which mechanism Se is able to modify the immune status. This was a double-blind, crossover study: Group 1 received Se and Group 2 received placebo (30 days). After this, Group 1 received placebo and Group 2 received Se (30 days). Every 30 days, blood samples were collected for white blood cell count, red blood cell count, and Ig level measurement (IgA, IgG, IgE, IgM). Of the 36 patients, 17 were suffering from leukemia/lymphomas (LL) and 19 from solid tumors (ST). In the ST groups leukogram, a significant increase in neutrophils was observed after Se usage (P = .0192). During the analyzed period, Se minimized the triggering of neutropenia cases in both groups. IgA and IgG levels in ST patients were significantly higher than those identified in LL patients after Se usage (P = .0051 and P = .0055). For IgA, a significant increase in its production, after Se usage, was observed in the ST group when compared to the LL (P = .0011). The same did not occur to the IgM and IgE immunoglobulins. In our study, the supplementation with Se reduced the neutropenic cases (LL and ST patients) and reduced IgG and IgA levels in LL and increased in ST group.

Measurement of the nonlinear optical response of low-density lipoprotein solutions from patients with periodontitis before and after periodontal treatment: evaluation of cardiovascular risk markers

Abstract. The Z-Scan (ZS) technique in the thermal regime has been used to measure the nonlinear optical response of low-density lipoprotein (LDL). The ZS technique is carried out in LDL from 40 patients with chronic periodontitis before and after three, six, and 12 months of periodontal treatment. Clinical parameters such as probing depths, bleeding on probing, total and differential white blood cells counts, lipid profiles, cytokine levels, and antibodies against oxidized LDL are also determined and compared over time. Before the treatment, the ZS experimental results reveal that the LDL particles of these patients are heavily modified. Only after 12 months of the periodontal treatment, the ZS results obtained reveal behavioral characteristics of healthy particles. This conclusion is also supported by complementary laboratorial analysis showing that the periodontal treatment induces systemic changes in several inflammatory markers.

Cu and Fe metallic ions-mediated oxidation of low-density lipoproteins studied by NMR, TEM and Z-scan technique.

In this work we report on a study of the morphological changes of LDL induced in vitro by metallic ions (Cu(2+) and Fe(3+)). These modifications were characterized by transmission electron microscopy, nuclear magnetic resonance and the Z-scan technique. The degree of oxidative modification of LDL was determined by the TBARS and lipid hydroperoxides assays. It is shown that distinct pathways for modifying lipoproteins lead to different morphological transformations of the particles characterized by changes in size and/or shape of the resulting particles, and by the tendency to induce aggregation of the particles. There were no evidence of melting of particles promoted by oxidative processes with Cu and Fe.

Plasma and urine DNA levels are related to microscopic hematuria in patients with bladder urothelial carcinoma

a) Objective: An increase in cell-free DNA was observed in the plasma of many cancer patients. This major biomarker can be used to differentiate patients with malignant neoplasms from those with benign neoplasms or healthy patients. Depending on the characteristic of the tumor, there are qualitative variations in the circulating cell-free DNA. Today, studies on the concentration of fragments of circulating cell-free DNA and their respective sizes in patients with bladder cancer are not plentiful in the literature. A 100% effective plasma tumor marker, which would help in the diagnosis and follow-up of bladder cancer, is yet to be developed; therefore, cell-free DNA levels in the plasma may represent a valuable biomarker for the diagnosis, prognosis and follow-up of patients with this type of tumor. b) Design and methods: In this study we analyze the kinetics of plasma and urine DNA concentrations in patients with bladder cancer, relating them to the other clinical laboratory variables. c) Results: Patients with hematuria showed a positive correlation with urine DNA. d) Conclusion: An increase in plasma and urine DNA was unprecedentedly reported over time, a fact that may come in handy in the prognosis of patients. Furthermore, microscopic haematuria is correlated with plasma and urinary DNA levels.

Advances in the non-linear optical investigation of lyotropic-like low-density human lipoproteins in the native and oxidised states

The Z-Scan optical technique was recently used to measure the non-linear optical response of human lipoproteins, in particular low-density lipoprotein (LDL) particles, regarding their oxidative (atherogenic) state. The higher is the oxidation degree of the LDL particle, the smaller is their non-linear optical response. The main physical process involved in this phenomenon is the increase in the thermal diffusivity of the aqueous LDL solution, as a function of the oxidation degree. The responsible for the heat diffusion across the sample are the hydroperoxides generated by the oxidation. Other human lipoproteins were shown to present non-linear optical responses in the thermal timescale regime. The non-linear optical response of LDL solutions may be used in the development of new tools to quantify the atherogenic particles in the human blood.

The validation of the Z-Scan technique for the determination of plasma glucose

Glucose is the main energy source for the human body. The concentration of blood glucose is regulated by several hormones including both antagonists: insulin and glucagon. The quantification of glucose in the blood is used for diagnosing metabolic disorders of carbohydrates, such as diabetes, idiopathic hypoglycemia and pancreatic diseases. Currently, the methodology used for this determination is the enzymatic colorimetric with spectrophotometric. This study aimed to validate the use of measurements of nonlinear optical properties of plasma glucose via the Z-Scan technique. For this we used samples of calibrator patterns that simulate commercial samples of patients (ELITech ©). Besides calibrators, serum glucose levels within acceptable reference values (normal control serum - Brazilian Society of Clinical Pathology and Laboratory Medicine) and also overestimated (pathological control serum - Brazilian Society of Clinical Pathology and Laboratory Medicine) were used in the methodology proposal. Calibrator dilutions were performed and determined by the Z-Scan technique for the preparation of calibration curve. In conclusion, Z-Scan method can be used to determinate glucose levels in biological samples with enzymatic colorimetric reaction and also to apply the same quality control parameters used in biochemistry clinical.

Effect of dicationic ionic liquids on lyotropic liquid crystals formed by a binary system composed of Triton-X 100 and water

ABSTRACT In this work, binary mixtures of a non-ionic surfactant (Triton X-100) and water were studied with concentrations of 30%wt H2O, showing, lamellar mesophase at temperatures below 10oC. Different dicationic ionic liquids were used for doping these mesophases: 1,n-bis(3-methylimidazolium-1-yl)alkane, 1,n-bis(1-methylpyrrolidinium-1-yl)alkane and 1,n-bis(pyridinium-N-yl)alkane dibromide, where n = 6 and 8. Polarized Optical Microscopy and Small-Angle X-ray Scattering were used for identifying the mesophases and the influence of different dicationic ionic liquids on the lyotropic liquid crystals phase transitions. The addition of dicationic ionic liquids to the lyotropic liquid crystals samples led to changes in transition temperature and in mesophase structure itself (such as characteristic distances).