Application of low-pressure gas chromatography-ion-trap mass spectrometry to the analysis of the essential oil of Turnera diffusa (Ward.) Urb.

Turnera diffusa Willd. var. afrodisiaca (Ward) Urb. (syn. T. aphrodisiaca) belongs to the family of Turneraceae and is an aromatic plant growing wild in the subtropical regions of America and Africa. It is widely used in the traditional medicine as e.g. anti-cough, diuretic, and aphrodisiac agent. This work presents a 3 min chromatographic analysis using low-pressure (LP) gas chromatography (GC)-ion-trap (IT) mass spectrometry (MS). The combination of a deactivated 0.6 m x 0.10 mm i.d., restrictor with a wide-bore CP-Wax 52 capillary column (10 m x 0.53 mm i.d., 1 mum) reduces the analysis time by a factor of 3-7 in comparison to the use of a conventional narrow bore column. Chromatographic conditions have been optimized to achieve the fastest separation with the highest signal/noise ratio in MS detection. These results allow fast and reliable quality control of the essential oil to be achieved. (C) 2003 Elsevier B.V. All rights reserved.

An HPLC-PAD method to analyse flavonoid glycosides and styrylpyrones from Cryptocarya species (Lauraceae)

An HPLC-PAD method has been developed in order to evaluate simultaneously the main secondary metabolites, flavonoid glycosides and styrylpyrones, of leaves of Cryptocarya moschata. The sample preparation, consisting of extraction, liquid-liquid extraction and centrifugation, requires minimum sample manipulation but produces high yields with reproducibility, selectivity and simplicity. HPLC on a C, column presents each class of metabolites grouped and with good resolution of the main compounds. The experimental conditions can be used to study inter- and intra-specific variability of secondary metabolites in Cryptocarya spp. Copyright (c) 2005 John Wiley A Sons, Ltd.

Using shifts in the electronic emission curve to evaluate polymer surface degradation

The polymer surface degradation and/or modification evolution of Teflon FEP and Mylar C films caused by a low energy electron beam were analyzed using a new method that consists in measuring the second crossover energy shift in the electronic emission curve. Upon prolonged irradiation, the second crossover energy shifts irreversibly to lower values in Teflon FEP but to higher values in Mylar C, indicating distinct mechanisms of surface degradation for the two polymers. The method represents a relatively inexpensive way to monitor early stages of surface degradation since the secondary electron emission comes from a maximum depth below the geometric surface of 100 mn in insulators. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

Phase separation suppression in InGaN epitaxial layers due to biaxial strain

Phase separation suppression due to external biaxial strain is observed in InxGa1-xN alloy layers by Raman scattering spectroscopy. The effect is taking place in thin epitaxial layers pseudomorphically grown by molecular-beam epitaxy on unstrained GaN(001) buffers. Ab initio calculations carried out for the alloy free energy predict and Raman measurements confirm that biaxial strain suppress the formation of phase-separated In-rich quantum dots in the InxGa1-xN layers. Since quantum dots are effective radiative recombination centers in InGaN, we conclude that strain quenches an important channel of light emission in optoelectronic devices based on pseudobinary group-III nitride semiconductors. (C) 2002 American Institute of Physics.

Structural behaviour of three-pile caps subjected to axial compressive loading

This work presents a comparative analysis about the behaviour of pile caps supported by 3 piles subjected to axial loading. Piles with 20 cm and 30 cm diameters were analysed. The main reinforcement was maintained in all the specimens, however, the arrangement of the secondary reinforcement varied. The main reinforcement consisted of steel bars connecting the piles. The secondary reinforcement was made up of: (a) bars going through the piles and through the projection of the column, (b) bars forming a network, and (c) vertical and horizontal stirrups. The main objective was the observation of the pile cap behaviour regarding the cracks and the modes of rupture. The real scale specimens were subjected to experimental tests until failure by rupture. Instruments were placed with the aim to obtain the displacement of the bases, the strains in the main and secondary reinforcement bars, in the compression struts, in the lower and upper nodal zones and in the sides of the caps. None of the caps reached failure by rupture with a load less than 1.12 times the theoretical load. The specimens ruptured due to the cracking of the compression strut and/or the yielding of the reinforcement bars in one direction.

A Transmission Problem for Euler-Bernoulli beam with Kelvin-Voigt Damping

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A linear optimization approach to the combined production planning model

Two fundamental processes usually arise in the production planning of many industries. The first one consists of deciding how many final products of each type have to be produced in each period of a planning horizon, the well-known lot sizing problem. The other process consists of cutting raw materials in stock in order to produce smaller parts used in the assembly of final products, the well-studied cutting stock problem. In this paper the decision variables of these two problems are dependent of each other in order to obtain a global optimum solution. Setups that are typically present in lot sizing problems are relaxed together with integer frequencies of cutting patterns in the cutting problem. Therefore, a large scale linear optimizations problem arises, which is exactly solved by a column generated technique. It is worth noting that this new combined problem still takes the trade-off between storage costs (for final products and the parts) and trim losses (in the cutting process). We present some sets of computational tests, analyzed over three different scenarios. These results show that, by combining the problems and using an exact method, it is possible to obtain significant gains when compared to the usual industrial practice, which solve them in sequence. (C) 2010 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.

SAE 1045 steel/WC-Co/Ni-Cu-Ni/SAE 1045 steel joints prepared by dynamic diffusion bonding: Microelectrochemical studies in 0.6 M NaCl solution

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A BEM formulation based on Reissner's theory to perform simple bending analysis of plates reinforced by rectangular beams

In this work, the plate bending formulation of the boundary element method (BEM), based on the Reissner's hypothesis, is extended to the analysis of plates reinforced by rectangular beams. This composed structure is modelled by a zoned plate, being the beams represented by narrow sub-regions with larger thickness. The integral equations are derived by applying the weighted residual method to each sub-region, and summing them to get the equation for the whole plate. Equilibrium and compatibility conditions are automatically imposed by the integral equations, which treat this composed structure as a single body. In order to decrease the number of degrees of freedom, some approximations are considered for both displacements and tractions along the beam width. The accuracy of the proposed model is illustrated by simple examples whose exact solution are known as well as by more complex examples whose numerical results are compared with a well-known finite element code.

Design, construction, and performance of a real-time holographic refractometry prototype for liquid analysis

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Mandibular cortical bone evaluation on cone beam computed tomography images of patients with bisphosphonate-related osteonecrosis of the jaw

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Pre-concentration of Cd(II), Cr(III), Cu(II) and Ni(II) on a column packed with free carboxymethylcellulose (CMCH)

Carboxymethylcellulose packed in to a glass column was used to pre-concentrate metallic cations from aqueous solutions. The pre-concentrated metal cations are directly eluted from the column using 5.0 mL of 1.0 mol L -1 hydrochloric acid. The optimum pre-concentration conditions are given (glass column, 16 cm length, 0.80 cm i.d., stationary phase height of 12 cm, flow-rate, 1.5 mL min -1). The recuperation efficiency achieved is greater than 95%, while the enrichment factor is 10 for 50 mL of solution (0.50 mg L -1 each).

Modal Analysis of a Beam with a Tip Rotor by Using a Fundamental Response

The shape modes of a damped-free beam model with a tip rotor are determined by using a dynamical basis that is generated by a fundamental spatial free response. This is a non-classical distributed model for the displacements in the transverse directions of the beam which turns out to be coupled through boundary conditions due to rotation. Numerical calculations are performed by using the Ritz-Rayleigh method with several approximating basis.

Determination of cadmium in river water samples by flame AAS after on-line preconcentration in mini-column packed with 2-aminothiazole-modified silica gel

A rapid and sensitive method was developed to determine trace levels of Cd2+ ions in an aqueous medium by flame atomic absorption spectrometry, using on-line preconcentration in a mini-column packed with 100 mg of 2-aminothiazol modified silica gel (SiAT). The Cd2+ ions were sorbed at pH 5.0. The preconcentrated Cd2+ ions were directly eluted from the column to the spectrometer's nebulizer-burner system using 100 μL of 2 mol L-1 hydrochloric acid. A retention efficiency of over 95% was achieved. The enrichment factor (calculated as the ratio of slopes of the calibration graphs) obtained with preconcentrations in a mini-column packed with SiAT (A = -1.3 × 10-3 + 1.8 × 10-3 [Cd2+]) and without preconcentrations (A = 4 × 10-5 + 3.5 × 10-3[Cd2+]), was 51 and the detection limit calculated was 0.38 μg L-1. The preconcentration procedure was applied to determine trace levels of Cd in river water samples. The optimum preconcentration conditions are discussed herein.

Robust control to parametric uncertainties in smart structures using linear matrix inequalities

The study of algorithms for active vibrations control in flexible structures became an area of enormous interest, mainly due to the countless demands of an optimal performance of mechanical systems as aircraft and aerospace structures. Smart structures, formed by a structure base, coupled with piezoelectric actuators and sensor are capable to guarantee the conditions demanded through the application of several types of controllers. This article shows some steps that should be followed in the design of a smart structure. It is discussed: the optimal placement of actuators, the model reduction and the controller design through techniques involving linear matrix inequalities (LMI). It is considered as constraints in LMI: the decay rate, voltage input limitation in the actuators and bounded output peak (output energy). Two controllers robust to parametric variation are designed: the first one considers the actuator in non-optimal location and the second one the actuator is put in an optimal placement. The performance are compared and discussed. The simulations to illustrate the methodology are made with a cantilever beam with bonded piezoelectric actuators.