482 research outputs found
CDM Accelerating Cosmology as an Alternative to LCDM model
A new accelerating cosmology driven only by baryons plus cold dark matter
(CDM) is proposed in the framework of general relativity. In this model the
present accelerating stage of the Universe is powered by the negative pressure
describing the gravitationally-induced particle production of cold dark matter
particles. This kind of scenario has only one free parameter and the
differential equation governing the evolution of the scale factor is exactly
the same of the CDM model. For a spatially flat Universe, as predicted
by inflation (), it is found that the
effectively observed matter density parameter is ,
where is the constant parameter specifying the CDM particle creation
rate. The supernovae test based on the Union data (2008) requires so that as independently derived from weak
gravitational lensing, the large scale structure and other complementary
observations.Comment: 6 pages, 3 figure
1-[2-(4-methyl-7-coumarinyloxy)ethyl]-4-(5-{1-[2-(4-methyl-7-coumarinyloxy)ethyl]-1h-1, 2, 3-triazol-4-yl}pentyl)-1h-1, 2, 3-triazole
Nature often produces compounds with a high degree of symmetry to reduce structural information and complexity. Synthesis of identical twin drugs, through the linkage of two identical pharmacophoric entities, is a classical strategy to produce more potent and/or selective drugs. Herein, two units of the privileged core of the coumarin hymecromone were linked together using âclick chemistryâ. Synthesis of 1-[2-(4-Methyl-7-coumarinyloxy)ethyl]-4-(5-{1-[2-(4-methyl- 7-coumarinyloxy)ethyl]-1H-1, 2, 3-triazol-4-yl}pentyl)-1H-1, 2, 3-triazole was achieved by coupling of two identical units of an azido coumarin with a symmetrical alkine using copper(I)-catalyzed alkyne-azide cycloaddition reaction, in good yields and with complete regioselectivity. © 2016 by the authors; licensee MDPI, Basel, Switzerland.2016
Checklist of horse flies (Diptera: Tabanidae) from Taquaruçu, Tocantins, Brazil, with new records for the state
A list of horse fly species is presented for the district of Taquaruçu, Palmas, Tocantins, Brazil. A total of 34 species and three varieties were recorded over one year of collections. From those, 21 species and one variety were new records for the state. © 2015 Check List and Authors
Replicate Periodic Windows in the Parameter Space of Driven Oscillators
In the bi-dimensional parameter space of driven oscillators, shrimp-shaped
periodic windows are immersed in chaotic regions. For two of these oscillators,
namely, Duffing and Josephson junction, we show that a weak harmonic
perturbation replicates these periodic windows giving rise to parameter regions
correspondent to periodic orbits. The new windows are composed of parameters
whose periodic orbits have periodicity and pattern similar to stable and
unstable periodic orbits already existent for the unperturbed oscillator. These
features indicate that the reported replicate periodic windows are associated
with chaos control of the considered oscillators
Effect of electromagnetic fields on the creation of scalar particles in a flat Robertson-Walker space-time
The influence of electromagnetic fields on the creation of scalar particles
from vacuum in a flat Robertson-Walker space-time is studied. The Klein Gordon
equation with varying electric field and constant magnetic one is solved. The
Bogoliubov transformation method is applied to calculate the pair creation
probability and the number density of created particles. It is shown that the
electric field amplifies the creation of scalar particles while the magnetic
field minimizes it.Comment: Important modifications, 20 pages, To appear in Eurpean Physical
Journal C. arXiv admin note: text overlap with arXiv:1108.033
Novel coumarins active against Trypanosoma cruzi and toxicity assessment using the animal model Caenorhabditis elegans
From 2nd Latin American Congress of Clinical and Laboratorial Toxicology
Porto Alegre, Brazil. 3-6 June 2018Background: Chagas disease (CD) is a tropical parasitic disease. Although the number of people infected is very
high, the only drugs available to treat CD, nifurtimox (Nfx) and benznidazole, are highly toxic, particularly in the
chronic stage of the disease. Coumarins are a large class of compounds that display a wide range of interesting
biological properties, such as antiparasitic. Hence, the aim of this work is to find a good antitrypanosomal drug with less toxicity. The use of simple organism models has become increasingly attractive for planning and simplifying efficient drug discovery. Within these models, Caenorhabditis elegans has emerged as a convenient and versatile tool with significant advantages for the toxicological potential identification for new compounds. Methods: Trypanocidal activity: Forty-two 4-methylamino-coumarins were assayed against the epimastigote form of Trypanosoma cruzi (Tulahuen 2 strain) by inhibitory concentration 50% (IC50). Toxicity assays: Lethal dose 50% (LD50) and Body Area were determined by Caenorhabditis elegans N2 strain (wild type) after acute exposure. Structure-activity relationship: A classificatory model was built using 3D descriptors. Results: Two of these coumarins demonstrated near equipotency to Nifurtimox (IC50 = 5.0 ± 1 ΌM), with values of:
11 h (LaSOM 266), (IC50 = 6.4 ± 1 ΌM) and 11 g (LaSOM 231), (IC50 = 8.2 ± 2.3 ΌM). In C. elegans it was possible to observe that Nfx showed greater toxicity in both the LD50 assay and the evaluation of the development of worms. It is possible to observe that the efficacy between Nfx and the synthesized compounds (11 h and 11 g) are similar. On the other hand, the toxicity of Nfx is approximately three times higher than that of the compounds. Results from the QSAR-3D study indicate that the volume and hydrophobicity of the substituents have a significant impact on the trypanocidal activities for derivatives that cause more than 50% of inhibition. These results show that the C. elegans model is efficient for screening potentially toxic compounds. Conclusion: Two coumarins (11 h and 11 g) showed activity against T. cruzi epimastigote similar to Nifurtimox, however with lower toxicity in both LD50 and development of C. elegans assays. These two compounds may be a feasible starting point for the development of new trypanocidal drugs
On exact solutions for quintessential (inflationary) cosmological models with exponential potentials
We first study dark energy models with a minimally-coupled scalar field and
exponential potentials, admitting exact solutions for the cosmological
equations: actually, it turns out that for this class of potentials the
Einstein field equations exhibit alternative Lagrangians, and are completely
integrable and separable (i.e. it is possible to integrate the system
analytically, at least by quadratures). We analyze such solutions, especially
discussing when they are compatible with a late time quintessential expansion
of the universe. As a further issue, we discuss how such quintessential scalar
fields can be connected to the inflationary phase, building up, for this class
of potentials, a quintessential inflationary scenario: actually, it turns out
that the transition from inflation toward late-time exponential quintessential
tail admits a kination period, which is an indispensable ingredient of this
kind of theoretical models. All such considerations have also been done by
including radiation into the model.Comment: Revtex4, 10 figure
Ação de inseticidas sobre os ovos e lagartas da broca-pequena-do-fruto do tomate, em bioensaio de laboratório
Evaluation of the addition of glycerol to Cupriavidus necator culture medium over Poly(3-hydroxybutyrate) production
- âŠ