Dosimetria dos cones radiocir��rgicos Radionics de di��metros de 5 mm a 50 mm para um feixe de 6 MV de um acelerador linear Mevatron MD digital

Os par��metros dosim��tricos de um feixe de raios X de pequeno di��metro para um sistema de radiocirurgia comercial foram medidos em ��gua com um detector de diodo de Si do tipo p. As raz��es tecido-m��ximo, o fator de espalhamento total e os perfis dos feixes a profundidades de 5 e 10 cm foram medidos para 17 feixes de di��metros circulares de 5 mm a 50 mm, em incrementos de 2,5 mm. Os fatores de espalhamento totais ca��ram lentamente, de 0,947 para 0,888 entre os cones de 50 mm e 12,5 mm de di��metro (varia����o de 7%); para os cones entre 10 mm e 5 mm de di��metro, esta queda foi bem maior, de 0,854 para 0,666 (varia����o de 28%). Os valores obtidos para a rela����o tecido-m��ximo s��o consistentes com dados publicados. Os perfis dos feixes foram medidos nas dire����es x e y, e est��o dentro de 0,2 mm para todos os cones entre as duas dire����es. A medida da largura �� meia-altura se encontra dentro de 1 mm com o di��metro nominal dos cones.

Implanta����o de um programa de controle de qualidade de um acelerador linear de 6 MeV de f��tons

Este trabalho apresenta a parte operacional do processo final envolvido na implanta����o de um programa de controle de qualidade por meio de testes rotineiros mec��nicos e de radia����o. O programa de controle de qualidade, durante 35 meses, mostrou a estabilidade excelente deste acelerador.

An��lise das isotermas de adsor����o de Cu(II), Cd(II), Ni(II) e Zn(II) pela N-(3,4-dihidroxibenzil) quitosana empregando o m��todo da regress��o n��o linear

Adsorption of Cu(II), Ni(II), Pb(II) and Zn(II) ions from aqueous solutions by N-(3,4-dihydroxybenzyl) chitosan have been carried out. The Langmuir (L), Freundlich (F), Langmuir - Freundlich (LF), Redlich-Peterson (RP) and T��th (T) adsorption isotherms models have been applied to fit the experimental data. Nonlinear regression computational program "Enzefitte", which is a library of the more commonly used adsorption isotherm equations for obtaining tabular outuput suitable for plotting theoretical of fitted isotherms, has been used to estimate the adsorption parameters. These parameters were used to calculate the amount adsorbed q calc., a function of concentration (C).

C��lculo ab initio de intensidades Raman din��micas utilizando a teoria da resposta linear

In this paper a methodology for the computation of Raman scattering cross-sections and depolarization ratios within the Placzek Polarizability Theory is described. The polarizability gradients are derived from the values of the dynamic polarizabilities computed at the excitation frequencies using ab initio Linear Response Theory. A sample application of the computational program, at the HF, MP2 and CCSD levels of theory, is presented for H2O and NH3. The results show that high correlated levels of theory are needed to achieve good agreement with experimental data.

Alquilbenzeno sulfonato linear: uma abordagem ambiental e anal��tica

The environmental impact of detergents and other consumer products is behind the continued interest in the chemistry of the surfactants used. Of these, linear alkylbenzene sulfonates (LASs) are most widely employed in detergent formulations. The precursors to LASs are linear alkylbenzenes (LABs). There is also interest in the chemistry of these hydrocarbons, because they are usually present in commercial LASs (due to incomplete sulfonation), or form as one of their degradation products. Additionally, they may be employed as molecular tracers of domestic waste in the aquatic environment. The following aspects are covered in the present review: The chemistry of surfactants, in particular LAS; environmental impact of the production of LAS; environmental and toxicological effects of LAS; mechanisms of removal of LAS in the environment, and methods for monitoring LAS and LAB, the latter in domestic wastes. Classical and novel analytical methods employed for the determination of LAS and LAB are discussed in detail, and a brief comment on detergents in Brazil is given.

Utiliza����o do ��ndice de reten����o linear para caracteriza����o de compostos vol��teis em caf�� sol��vel utilizando GC-MS e coluna HP-Innowax

Gas chromatography coupled with mass spectrometry (GC-MS) is widely used for the characterization of volatile compounds. However, due to the complexity of the soluble coffee matrix, a complete identification of the components should not be based on mass spectra interpretation only. The linear index of retention (LRI) is frequently used to give support to mass spectra. The aim of this work is to investigate the characterization of the volatile compounds in soluble coffee samples by GC-MS using LRI values found with a HP-INNOWAX column. The method used allows a significant increase of the reliability of identifying compounds.

Vias de s��ntese linear e convergente: qual �� mais verde?

A comparative study of a convergent and the linear synthetic pathway with respect to their relative greenish allowed the quantification of the advantages of the former with respect to atomic productivity as well as robustness. The calculations show that convergent pathways provide a decrease of costs together with a decrease of E factor and an increase of atomic economy which means that greenish is accompanied by an economic advantage. The influence of other features of the convergent pathways synthesis on the improvement of the synthesis greenish is discussed qualitatively.

Utiliza����o do sensor linear de luz ILX554 em espectroscopia ��ptica

This technical note describes the construction of a low-cost optical detector. This device is composed by a high-sensitive linear light sensor (model ILX554) and a microcontroller. The performance of the detector was demonstrated by the detection of emission and Raman spectra of the several atomic systems and the results reproduce those found in the literature.

Din��mica n��o-linear e reagente limitante: um exemplo de bifurca����o transcr��tica

The nonlinear analysis of a general mixed second order reaction was performed, aiming to explore some basic tools concerning the mathematics of nonlinear differential equations. Concepts of stability around fixed points based on linear stability analysis are introduced, together with phase plane and integral curves. The main focus is the chemical relationship between changes of limiting reagent and transcritical bifurcation, and the investigation underlying the conclusion.

O USO DE UM SENSOR DE LUZ LINEAR COMO RECURSO DID��TICO PARA DEMONSTRAR PRINC��PIOS DE DIFRA����O E ESPECTROSCOPIA

This article presents a discussion on light diffraction by slits and grids as well as the development of an experimental apparatus which provides quantitative observation of the phenomenon. We conducted a brief historical survey on the evolution of the wave theory of light and the role of diffraction in the context of optical spectroscopy. We also reviewed the use of Huygens’ principle to calculate the intensity pattern obtained when light is diffracted by slits and compared the predictions with experimental results obtained using the apparatus developed. Finally, the use of the apparatus in an optical spectroscopy experiment was demonstrated.

Analysis of the nucleotide sequence of the coat protein and 3'-untranslated region of two Brazilian Potato virus Y isolates

Two Brazilian Potato virus Y (PVY) isolates were biologically characterized as necrotic (PVY-NBR) and common (PVY-OBR) based upon symptoms on test plants. Additional characterization was performed by sequencing a cDNA corresponding to the 3' terminal region of the viral genome. The sequence consisted of 195 nucleotides (nt) coding part of the nuclear inclusion body b (NIb) gene, 804 nt of the coat protein (CP) gene, and 328 nt (PVY-OBR) or 326 nt (PVY-NBR) of the 3'-untranslated region (UTR). Translation of the sequence resulted in one single open reading frame with part of the NIb and a CP of 267 amino acids. The two isolates shared 95.1% similarity in the CP amino acid sequence. The CP and the 3'-UTR sequence of the Brazilian isolates were compared to those of other PVY isolates previously reported and unrooted phylogenetic trees were constructed. The trees revealed a separation of two distinct clusters, one comprising most of the common strains and the other comprising the necrotic strains. PVY-OBR was clustered in the common group and PVY-NBR in the necrotic one.

Sequence analysis of the capsid protein gene of an isolate of Apple stem grooving virus, and its survey in Southern Brazil

Apple stem grooving virus (ASGV) is one of the most important viruses infecting fruit trees. This study aimed at the molecular characterization of ASGV infecting apple (Malus domestica) plants in Santa Catarina (SC). RNA extracted from plants infected with isolate UV01 was used as a template for RT-PCR using specific primers. An amplified DNA fragment of 755 bp was sequenced. The coat protein gene of ASGV isolate UV01 contains 714 nucleotides, coding for a protein of 237 amino acids with a predicted Mr of approximately 27 kDa. The nucleotide and the deduced amino acid sequences of the coat protein gene showed identities of 90.9% and 97.9%, respectively, with a Japanese isolate of ASGV. Very high amino acid homologies (98.7%) were also found with Citrus tatter leaf capillovirus (CTLV), a very close relative of ASGV. These results indicate low coat protein gene variability among Capillovirus isolates from distinct regions. In a restricted survey, mother stocks in orchards and plants introduced into the country for large scale fruit production were indexed and shown to be infected by ASGV (20%), usually in a complex with other (latent) apple viruses (80%).

PCR amplification and sequence analyses of reverse transcriptase-like genes in Crinipellis perniciosa isolates

Reverse transcriptase (RT) sequence analysis is an important technique used to detect the presence of transposable elements in a genome. Putative RT sequences were analyzed in the genome of the pathogenic fungus C. perniciosa, the causal agent of witches' broom disease of cocoa. A 394 bp fragment was amplified from genomic DNA of different isolates of C. perniciosa belonging to C-, L-, and S-biotypes and collected from various geographical areas. The cleavage of PCR products with restriction enzymes and the sequencing of various RT fragments indicated the presence of several sequences showing transition events (G:C to A:T). Southern blot analysis revealed high copy numbers of RT signals, forming different patterns among C-, S-, and L-biotype isolates. Sequence comparisons of the predicted RT peptide indicate a close relationship with the RT protein from thegypsy family of LTR-retrotransposons. The possible role of these retrotransposons in generating genetic variability in the homothallic C. perniciosa is discussed.

Generaliza����o de um modelo linear de imped��ncia eletroqu��mica

Em geral, a fun����o de um modelo de imped��ncia para processos de eletrodo simples �� deduzida de um modelo el��trico equivalente, denominado circuito de Randles. Neste trabalho estudou-se a generaliza����o dessa fun����o, mediante a introdu����o de um par��metro n��o-el��trico, relacionado com a flexibilidade do ��ngulo de fase e da magnitude. A fun����o foi ajustada ��s medidas experimentais de imped��ncia obtidas de um sistema constitu��do de uma liga Ti-10%Al (m/m) em solu����o de cloreto de s��dio 0,9%, variando-se a amplitude de perturba����o. Verificou-se que a fun����o generalizada foi adequada para descrever a imped��ncia do sistema analisado, reduzindo as distor����es entre a curva experimental e a curva te��rica. Al��m disso, os melhores resultados foram obtidos para sinais de perturba����o do sistema com amplitude igual a 10 mV.