RESUMO
The aim of this article is to show a way to extend the usefulness of the Generalized Bernoulli Method (GBM) with the purpose to apply it for the case of variational problems with functionals that depend explicitly of all the variables. Moreover, after expressing the Euler equations in terms of this extension of GBM, we will see that the resulting equations acquire a symmetric form, which is not shared by the known Euler equations. We will see that this symmetry is useful because it allows us to recall these equations with ease. The presentation of three examples shows that by applying GBM, the Euler equations are obtained just as well as it does the known Euler formalism but with much less effort, which makes GBM ideal for practical applications. In fact, given a variational problem, GBM establishes the corresponding Euler equations by means of a systematic procedure, which is easy to recall, based in both elementary calculus and algebra without having to memorize the known formulas. Finally, in order to extend the practical applications of the proposed method, this work will employ GBM with the purpose to apply it for the case of solving isoperimetric problems.
RESUMO
The aim of this article is to show the way to get both, exact and analytical approximate solutions for certain variational problems with moving boundaries but without resorting to Euler formalism at all, for which we propose two methods: the Moving Boundary Conditions Without Employing Transversality Conditions (MWTC) and the Moving Boundary Condition Employing Transversality Conditions (METC). It is worthwhile to mention that the first of them avoids the concept of transversality condition, which is basic for this kind of problems, from the point of view of the known Euler formalism. While it is true that the second method will utilize the above mentioned conditions, it will do through a systematic elementary procedure, easy to apply and recall; in addition, it will be seen that the Generalized Bernoulli Method (GBM) will turn out to be a fundamental tool in order to achieve these objectives.
RESUMO
We present a combined experimental and theoretical study to analyze the structure, electronic properties, and aggregation behavior of hydroxylated multiwalled carbon nanotubes (OH-MWCNT). Our MWCNTs have average diameters of ~2 nm, lengths of approximately 100-300 nm, and a hydroxyl surface coverage θ~0.1. When deposited on the air/water interface the OH-MWCNTs are partially soluble and the floating units interact and link with each other forming extended foam-like carbon networks. Surface pressure-area isotherms of the nanotube films are performed using the Langmuir balance method at different equilibration times. The films are transferred into a mica substrate and atomic force microscopy images show that the foam like structure is preserved and reveals fine details of their microstructure. Density functional theory calculations performed on model hydroxylated carbon nanotubes show that low energy atomic configurations are found when the OH groups form molecular islands on the nanotube's surface. This patchy behavior for the OH species is expected to produce nanotubes having reduced wettabilities, in line with experimental observations. OH doping yields nanotubes having small HOMO-LUMO energy gaps and generates a nanotube â OH direction for the charge transfer leading to the existence of more hole carriers in the structures. Our synthesized OH-MWCNTs might have promising applications.
Assuntos
Nanotubos de Carbono/química , Elétrons , Hidroxilação , Estrutura Molecular , Teoria QuânticaRESUMO
PIP: Hematological status of pregnant women from low and middle economic classes before and after similar hematinic therapy were compared. Subjects were 88 economically indigent and 88 middle-class women. Both groups came from the same ethnic background. Before treatment mean values for hemoglobin and nutrients were significantly lower in the poor pregnant women, except for serum folate which was similar. The only parasitic infestations found were whipworm (Trichuris trichiura) in 10% of the poor group and 2% of the middle-class group. Treatment of 40 poor and 33 middle-class patients was with oral doses of 130 mg of ferrous fumarate. The other 48 poor and 55 middle-class patients also received 2.5 mg of folic acid orally daily. At term, after treatment, there was still a statistically but lesser difference between the 2 groups, with the exception of serum iron. Total iron binding capacity was similar in both groups. The frequency of preeclampsia was 4% in the middle-class and 5% in the poor patients. At term, despite the iron dosage, anemia frequency and iron deficiency remained the same in both groups. Those taking folic acid improved so that the 2 classes were equal. Low serum folate levels for those of the middle class not taking folic acid were 25%. It is concluded that all pregnant women in this population should receive both iron and folic acid supplementation throughout pregnancy. For women with an iron deficiency at the beginning of pregnancy, 120 mg/day was not enough. There was the possibility of impaired iron absorption in these patients.^ieng