Search results for "Deriva"
showing 10 items of 1423 documents
One-pot synthesis of fluorinated 2-amino-pyrimidine-N-oxides. Competing pathways in the four-atom side-chain rearrangements of 1,2,4-oxadiazoles
2006
Abstract Trifluoromethylated 2-amino-pyrimidine N-oxides have been synthesized by reaction of the 3-amino-5-methyl-1,2,4-oxadiazole with trifluoromethyl-β-diketones in the presence of perchloric acid, followed by hydrolysis. In this ring-to-ring transformation an initial formation of (unisolated) 1,2,4-oxadiazole-pyrimidinium salts, and subsequent ring-opening at the oxadiazole moiety occurs. Isolation of 2-(hydroxyamino)-pyrimidine from the reaction mixture evidenced the presence of a competing pathway where the N(4) nitrogen of the oxadiazole is involved in the formation of a regioisomeric pyrimidinium salt. The effect of the trifluoromethyl group on the product distribution is discussed.…
Ageing behaviour and analytical characterization of the Jatobá resin collected from Hymenaea stigonocarpa Mart.
2009
Abstract This paper reports the results of an analytical study to characterize the trunk resin collected from the Hymenaea stigonocarpa Mart. species from the region of Minas Gerais (Brazil), popularly known as Jatoba resin. Hymenaea resins are reported to have been used in artistic applications such as protective varnishes in polychromed sculptures and paintings. Therefore, the identification of the main chemical changes that take place in the resin when it is prepared as a thin film exposed to atmospheric effects have been considered herein. Changes due to the degradation effect of light have been studied on a series of specimens prepared as a thin films and subjected to accelerated UV li…
Tangents to fractal curves and surfaces
2010
International audience; The aim of our work is to specify and develop a geometric modeler, based on the formalism of iterated function systems with the following objectives: access to a new universe of original, various, aesthetic shapes, modeling of conventional shapes (smooth surfaces, solids) and unconventional shapes (rough surfaces, porous solids) by defining and controlling the relief (surface state) and lacunarity (size and distribution of holes). In this context we intend to develop differential calculus tools for fractal curves and surfaces defined by IFS. Using local fractional derivatives, we show that, even if most fractal curves are nowhere differentiable, they admit a left and…
Johdatus fraktaaliderivaattoihin ja niiden sovelluksiin
2014
Fraktaaliderivaatta on derivaatta, jonka kertaluku on reaali- tai kompleksiluku. Fraktaaliderivaatta voidaan määritellä usealla eri tavalla, mutta mikään määritelmä ei ole selkeästi muita parempi. Koska fraktaaliderivaatan ominaisuudet riippuvat valitusta määritelmästä, ominaisuuksia ei voida suoraan yleistää kaikille fraktaaliderivaatoille. Tämän tutkielman tarkoitus on antaa lukijalle perustiedot reaalilukukertaisista fraktaaliderivaatoista ja niiden määritelmäsidonnaisista ominaisuuksista. Tutkielmassa esitellään kolme yleisimmin viitattua määritelmää: Grünwald-Letnikov, Riemann-Liouville ja Caputo. Grünwald-Letnikovin määritelmä yleistää klassisen derivaatan määritelmän suoraan reaali- …
Tuning the Electrochemistry of Free-Base Porphyrins in Acidic Nonaqueous Media: Influence of Solvent, Supporting Electrolyte, and Ring Substituents
2016
International audience; A detailed study of reduction potentials, electroreduction mechanisms and acid-base chemistry was carried out on two series of free-base porphyrins in nonaqueous media. The first series is represented by four-pyrrole substituted tetraphenylporphyrin (TPP) derivatives, two of which are planar and two of which are nonplanar in their non-protonated form. The second comprises porphyrins with 0-4 meso-phenyl groups on the macrocycle. Equilibrium constants for conversion of each neutral porphyrin to its diprotic [H4P] 2+ form were determined and the electrochemistry was then elucidated as a function of: (i) type of nonaqueous solvent, (ii) anion of supporting electrolyte, …
Evolutionary game theory of continuous traits from a causal perspective
2023
Modern evolutionary game theory typically deals with the evolution of continuous, quantitative traits under weak selection, allowing the incorporation of rich biological detail and complicated nonlinear interactions. While these models are commonly used to find candidates for evolutionary endpoints and to approximate evolutionary trajectories, a less appreciated property is their potential to expose and clarify the causal structure of evolutionary processes. The mathematical step of differentiation breaks a nonlinear model into additive components which are more intuitive to interpret, and when combined with a proper causal hypothesis, partial derivatives in such models have a causal meanin…
On Descriptive Characterizations of an Integral Recovering a Function from Its $$L^r$$-Derivative
2022
The notion of Lr-variational measure generated by a function F ∈ Lr[a, b] is introduced and, in terms of absolute continuity of this measure, a descriptive characterization of the HKr -integral recovering a function from its Lr-derivative is given. It is shown that the class of functions generating absolutely continuous Lr-variational measure coincides with the class of ACGr -functions which was introduced earlier, and that both classes coincide with the class of the indefinite HKr-integrals under the assumption of Lr-differentiability almost everywhere of the functions consisting these classes
El problema del acortamiento de curvas asociado a una densidad
2016
A lo largo de la presente Tesis, se estudia el flujo por la curvatura media asociado a una densidad (FCMpsi) de una hipersuperficie, en una variedad riemanniana con densidad. Los principales resultados se obtienen para el caso particular en el que la dimensión de la variedad ambiente es dos y las subvariedades son curvas. A dicho problema, se le llamará problema del acortamiento de curvas asociado a una densidad (PACpsi). En el capítulo uno, se presentan los conceptos básicos para desarrollar y comprender el trabajo de la Tesis. Se da la definición del problema a abordar, se introducen las herramientas necesarias para su estudio y se calculan las fórmulas de variación de las cantidades geom…
Investigation of photoluminescence and amplified spontaneous emission properties of cyanoacetic acid derivative (KTB) in PVK amorphous thin films
2018
This work was supported by European Regional Development Fund within the Project No. 1.1.1.1/16/A/046 and A.Riekstins SIA “Mikrotīkls” donation, administered by University of Latvia Foundation.
Single hollow fiber SLM extraction of polyamines followed by tosyl chloride derivatization and HPLC determination
2007
Determination of polyamines in biological fluids possesses medical diagnostic relevance. Despite the vast panel of analytical methods developed for polyamines they are not applied in routine clinical usage, mainly due to the time and labor consuming sample preparation step and complicated derivatization procedures. Thus, new simpler methods are needed. This paper describes a single hollow fiber SLM extraction method of polyamines followed by simple pre-column derivatization with tosyl chloride and HPLC-UV analysis. The influence of different parameters such as the extraction time, organic phase composition, acceptor pH, donor pH, acceptor volume, donor volume and stirring speed on the trans…