Electroanalytical detection of pindolol: comparison of unmodified and reduced graphene oxide modified screen-printed graphite electrodes

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

c ̂-Axis resistivity in graphite-AlCl3 as found by CESR measurements

We report the absolute values of the c ̂-axis resistivity obtained from conduction electron spin resonance (CESR) experiments at various temperatures for a graphite-AlCl3 stage 2 compound. The agreement with d.c. measurements is quite good. The temperature dependence of the c ̂-axis resistivity previously obtained from CESR for graphite-AlCl3 is revised. © 1990.

Numerical analysis of a modified evacuated tubes solar collector

The need for renewable energy sources, facing the consequences of Climate Change, results in growing investment for solar collectors’ use. Research in this field has accompanied this expansion and evacuated tube solar collector stands as an important study focus. Thus, several works have been published for representing the stratification of the fluid inside the tubes and the reservoir, as well as analytical modeling for the heat flow problem. Based on recent publications, this paper proposes the study of solar water heating with evacuated tubes, their operation characteristics and operating parameters. To develop this work, a computational tool will be used - in this case, the application of computational fluid dynamics (CFD) software. In possession of the implemented model, a numerical simulation will be performed to evaluate the behavior of the fluid within this solar collector and possible improvements to be applied in the model.

Determination of Tetracycline in Environmental Water Samples at a Graphite-Polyurethane Composite Electrode

A bare graphite-polyurethane composite was evaluated in the tetracycline (TC) determination in natural water samples. Using differential pulse voltammetry (DPV), a linear response was observed in the range of 4.00-40.0 mu mol L-1 with limit of detection of 2.80 mu mol L-1, without the need of surface renewing between successive runs. During the tetracycline determination in water samples, recoveries between 92.6 and 100% were found. The results for TC determination in water samples after a pre-concentration stage agreed with spiked value at a 95% confidence level according to student t-test.

Saturated flow boiling heat transfer and critical heat flux in small horizontal flattened tubes

This paper presents experimental results for flow boiling heat transfer coefficient and critical heat flux (CHF) in small flattened tubes. The tested flattened tubes have the same equivalent internal diameter of 2.2 mm, but different aspect height/width ratios (H/W) of 1/4, 1/2, 2 and 4. The experimental data were compared against results for circular tubes using R134a and R245fa as working fluids at a nominal saturation temperature of 31 degrees C. For mass velocities higher than 200 kg/m(2)s, the flattened and circular tubes presented similar heat transfer coefficients. Such a behavior is related to the fact that stratification effects are negligible under conditions of higher mass velocities. Heat transfer correlations from the literature, usually developed using only circular-channel experimental data, predicted the flattened tube results for mass velocities higher than 200 kg/m(2)s with mean absolute error lower than 20% using the equivalent diameter to account for the geometry effect. Similarly, the critical heat flux results were found to be independent of the tube aspect ratio when the same equivalent length was kept. Equivalent length is a new parameter which takes into account the channel heat transfer area. The CHF correlations for round tubes predicted the flattened tube data relatively well when using the equivalent diameter and length. Furthermore, a new proposed CHF correlation predicted the present flattened tube data with a mean absolute error of 5%. (C) 2012 Elsevier Ltd. All rights reserved.

Residence Time Distribution Models Derived from Non-Ideal Laminar Velocity Profiles in Tubes

The theoretical E-curve for the laminar flow of non-Newtonian fluids in circular tubes may not be accurate for real tubular systems with diffusion, mechanical vibration, wall roughness, pipe fittings, curves, coils, or corrugated walls. Deviations from the idealized laminar flow reactor (LFR) cannot be well represented using the axial dispersion or the tanks-in-series models of residence time distribution (RTD). In this work, four RTD models derived from non-ideal velocity profiles in segregated tube flow are proposed. They were used to represent the RTD of three tubular systems working with Newtonian and pseudoplastic fluids. Other RTD models were considered for comparison. The proposed models provided good adjustments, and it was possible to determine the active volumes. It is expected that these models can be useful for the analysis of LFR or for the evaluation of continuous thermal processing of viscous foods.

Two-phase flow patterns and pressure drop inside horizontal tubes containing twisted-tape inserts

This paper presents an experimental study on two-phase flow patterns and pressure drop of R134a inside a 15.9 mm ID tube containing twisted-tape inserts. Experimental results were obtained in a horizontal test section for twisted-tape ratios of 3, 4, 9 and 14, mass velocities ranging from 75 to 250 kg/m(2) s and saturation temperatures of 5 and 15 degrees C. An unprecedented discussion on two-phase flow patterns inside tubes containing twisted-tape inserts is presented and the flow pattern effects on the frictional pressure drop are carefully discussed. Additionally, a new method to predict the frictional pressure drop during two-phase flow inside tubes containing twisted-tape inserts is proposed. (C) 2012 Elsevier Ltd. All rights reserved.

Determination of atenolol in environmental water samples and pharmaceutical formulations at a graphite-epoxy composite electrode

A bare graphite-epoxy composite was evaluated as an electrode material in the determination of atenolol in natural water samples and pharmaceutical formulations for which the analyte was spiked. Using a DPV procedure, a linear response was observed in the 4.45-84.7 mu mol L-1 range with a LOD = 2.23 mu mol L-1, without need of surface renewal between successive runs, and recoveries between 92.5 and 107.5% for pharmaceutical formulations. The results obtained from the proposed procedure agreed with HPLC results within a 95% confidence level. During the determination of atenolol in water samples, recoveries between 96.1 and 102.6% were found.

Determination of chlorine in food samples via the AlCl molecule using high-resolution continuum source molecular absorption spectrometry in a graphite furnace

Determination of chlorine using the molecular absorption of aluminum mono-chloride (AlCl) at the 261.418 nm wavelength was accomplished by high-resolution continuum source molecular absorption spectrometry using a transversely heated graphite tube furnace with an integrated platform. For the analysis. 10 mu L of the sample followed by 10 mu L of a solution containing Al-Ag-Sr modifier, (1 g L-1 each), were directly injected onto the platform. A spectral interference due to the use of Al-Ag-Sr as mixed modifier was easily corrected by the least-squares algorithm present in the spectrometer software. The pyrolysis and vaporization temperatures were 500 degrees C and 2200 degrees C, respectively. To evaluate the feasibility of a simple procedure for the determination of chlorine in food samples present in our daily lives, two different digestion methods were applied, namely (A) an acid digestion method using HNO3 only at room temperature, and (B) a digestion method with Ag, HNO3 and H2O2, where chlorine is precipitated as a low-solubility salt (AgCl), which is then dissolved with ammonia solution. The experimental results obtained with method B were in good agreement with the certified values and demonstrated that the proposed method is more accurate than method A. This is because the formation of silver chloride prevented analyte losses by volatilization. The limit of detection (LOD, 3 sigma/s) for Cl in methods A and B was 18 mu g g(-1) and 9 mu g g(-1), respectively, 1.7 and 3.3 times lower compared to published work using inductively coupled plasma optical emission spectrometry, and absolute LODs were 2.4 and 1.2 ng, respectively. (C) 2012 Elsevier B.V. All rights reserved.

Determination of tetracycline in environmental water samples at a graphite-polyurethane composite electrode

A bare graphite-polyurethane composite was evaluated in the tetracycline (TC) determination in natural water samples. Using differential pulse voltammetry (DPV), a linear response was observed in the range of 4.00-40.0 µmol L-1 with limit of detection of 2.80 µmol L-1, without the need of surface renewing between successive runs. During the tetracycline determination in water samples, recoveries between 92.6 and 100% were found. The results for TC determination in water samples after a pre-concentration stage agreed with spiked value at a 95% confidence level according to student t-test.

Theoretical models to predict the mechanical behavior of thick composite tubes

This paper shows theoretical models (analytical formulations) to predict the mechanical behavior of thick composite tubes and how some parameters can influence this behavior. Thus, firstly, it was developed the analytical formulations for a pressurized tube made of composite material with a single thick ply and only one lamination angle. For this case, the stress distribution and the displacement fields are investigated as function of different lamination angles and reinforcement volume fractions. The results obtained by the theoretical model are physic consistent and coherent with the literature information. After that, the previous formulations are extended in order to predict the mechanical behavior of a thick laminated tube. Both analytical formulations are implemented as a computational tool via Matlab code. The results obtained by the computational tool are compared to the finite element analyses, and the stress distribution is considered coherent. Moreover, the engineering computational tool is used to perform failure analysis, using different types of failure criteria, which identifies the damaged ply and the mode of failure.

Synthesis of self-assembled tubes in direct conjugated porphyrin-gold nanohybrid solution

We report on the formation of self-assembled meso-tetrakis (p-sulfonatofenyl) porphyrin (H2 TPP'S POT. 4-''IND. 4') tubes stabilized by gold nanoparticles (NPs) in basic solution and on their spectroscopic chareterization. The role of the gold NPs in the aggregation dynamics of free-base sulfonated porphyrin (H2TPP'S POT. 4-''IND. 4') is also investigated. The direct conjugation of the gold NPs to the H2TPPS4 molecule quenches the fluorescence intensity, while absorption peaks are blue-shifted, indicating predominant H-type aggregation. It is observed that porphyrin molecules adsorbed on the surface of the gold NP interact and form tubes of maximum diameter ∼1.5 μm and length >100 μm. Steady-state and time-resolved spectroscopic techniques confirm nonradiative energy transfer from porphyrin to gold NP.

Sviluppo di un tomografo multi-energy per lo studio pre-clinico di nuove metodiche diagnostiche finalizzate al riconoscimento precoce della patologia tumorale

A new multi-energy CT for small animals is being developed at the Physics Department of the University of Bologna, Italy. The system makes use of a set of quasi-monochromatic X-ray beams, with energy tunable in a range from 26 KeV to 72 KeV. These beams are produced by Bragg diffraction on a Highly Oriented Pyrolytic Graphite crystal. With quasi-monochromatic sources it is possible to perform multi-energy investigation in a more effective way, as compared with conventional X-ray tubes. Multi-energy techniques allow extracting physical information from the materials, such as effective atomic number, mass-thickness, density, that can be used to distinguish and quantitatively characterize the irradiated tissues. The aim of the system is the investigation and the development of new pre-clinic methods for the early detection of the tumors in small animals. An innovative technique, the Triple-Energy Radiography with Contrast Medium (TER), has been successfully implemented on our system. TER consist in combining a set of three quasi-monochromatic images of an object, in order to obtain a corresponding set of three single-tissue images, which are the mass-thickness map of three reference materials. TER can be applied to the quantitative mass-thickness-map reconstruction of a contrast medium, because it is able to remove completely the signal due to other tissues (i.e. the structural background noise). The technique is very sensitive to the contrast medium and is insensitive to the superposition of different materials. The method is a good candidate to the early detection of the tumor angiogenesis in mice. In this work we describe the tomographic system, with a particular focus on the quasi-monochromatic source. Moreover the TER method is presented with some preliminary results about small animal imaging.

Drift Tubes Trigger System of the CMS Experiment at LHC : Commissioning and Performances

In this thesis the performances of the CMS Drift Tubes Local Trigger System of the CMS detector are studied. CMS is one of the general purpose experiments that will operate at the Large Hadron Collider at CERN. Results from data collected during the Cosmic Run At Four Tesla (CRAFT) commissioning exercise, a globally coordinated run period where the full experiment was involved and configured to detect cosmic rays crossing the CMS cavern, are presented. These include analyses on the precision and accuracy of the trigger reconstruction mechanism and measurement of the trigger efficiency. The description of a method to perform system synchronization is also reported, together with a comparison of the outcomes of trigger electronics and its software emulator code.