1,709 research outputs found
A Validated Reversed-Phase HPLC Method for the Determination of Atorvastatin Calcium in Tablets
A Reversed-Phase Liquid Chromatographic (RP-LC) assay method was developed for the quantitative determination of atorvastatin calcium in the presence of its degradation products. The assay involved an isocratic elution of atorvastatin calcium in a LiChroCARTR 250*4 mm HPLC Cartridge LiChrospherR 100 RP-18 (5 ÎŒm) column using a mobile phase consisting of 0.1% acetic acid solution: acetonitrile (45:55, v/v), pH = 3.8. The flow rate was 0.8 mL/min and the analytes monitored at 246 nm. The assay method was found to be linear from 8.13 to 23.77 ÎŒg/mL. All the validation parameters were within the acceptance range. The developed method was successfully applied to estimate the amount of atorvastatin calcium in tablets.Fil: Simionato, Laura Daniela. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Ferello, L.. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Stamer. S.. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Repetto, M. F.. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Zubata, P. D.. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; ArgentinaFil: Segall, Adriana Ines. Universidad de Buenos Aires. Facultad de Farmacia y BioquĂmica. Departamento de TecnologĂa FarmacĂ©utica; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Houssay; Argentin
A molecular simulation analysis of producing monatomic carbon chains by stretching ultranarrow graphene nanoribbons
Atomistic simulations were utilized to develop fundamental insights regarding
the elongation process starting from ultranarrow graphene nanoribbons (GNRs)
and resulting in monatomic carbon chains (MACCs). There are three key findings.
First, we demonstrate that complete, elongated, and stable MACCs with fracture
strains exceeding 100% can be formed from both ultranarrow armchair and zigzag
GNRs. Second, we demonstrate that the deformation processes leading to the
MACCs have strong chirality dependence. Specifically, armchair GNRs first form
DNA-like chains, then develop into monatomic chains by passing through an
intermediate configuration in which monatomic chain sections are separated by
two-atom attachments. In contrast, zigzag GNRs form rope-ladder-like chains
through a process in which the carbon hexagons are first elongated into
rectangles; these rectangles eventually coalesce into monatomic chains through
a novel triangle-pentagon deformation structure under further tensile
deformation. Finally, we show that the width of GNRs plays an important role in
the formation of MACCs, and that the ultranarrow GNRs facilitate the formation
of full MACCs. The present work should be of considerable interest due to the
experimentally demonstrated feasibility of using narrow GNRs to fabricate novel
nanoelectronic components based upon monatomic chains of carbon atoms.Comment: 11 pages, 6 figures, Nanotechnology accepted versio
Raman frequency shift in oxygen functionalized carbon nanotubes
In terms of lattice dynamics theory, we study the vibrational properties of
the oxygen-functionalized single wall carbon nanotubes (O-SWCNs). Due to the
C-O and O-O interactions, many degenerate phonon modes are split and even some
new phonon modes are obtained, different from the bare SWCNs. A distinct Raman
shift is found in both the radial breathing mode and G modes, depending not
only on the tube diameter and chirality but also on oxygen coverage and
adsorption configurations. With the oxygen coverage increasing, interesting, a
nonmonotonic up- and down-shift is observed in G modes, which is contributed to
the competition between the bond expansion and contraction, there coexisting in
the functionalized carbon nanotube.Comment: 4 pages, 3 figures, 1 tabl
Spermidine biases the resolution of Holliday junctions by phage λ integrase
Holliday junctions are a central intermediate in diverse pathways of DNA repair and recombination. The isomerization of a junction determines the directionality of the recombination event. Previous studies have shown that the identity of the central sequence of the junction may favor one of the two isomers, in turn controlling the direction of the pathway. Here we demonstrate that, in the absence of DNA sequence-mediated isomer preference, polycations are the major contributor to biasing strand cleavage during junction resolution. In the case of wild-type phage λ excision junctions, spermidine plays the dominant role in controlling the isomerization state of the junction and increases the rate of junction resolution. Spermidine also counteracts the sequence-imposed bias on resolution. The spermidine-induced bias is seen equally on supercoiled and linear excisive recombination junction intermediates, and thus is not just an artefact of in vitro recombination conditions. The contribution of spermidine requires the presence of accessory factors, and results in the repositioning of Int's core-binding domains on junctions, perhaps due to DNA-spermidineâprotein interactions, or by influencing DNA conformation in the core region. Our results lead us to propose that spermidine together with accessory factors promotes the formation of the second junction isomer. We propose that this rearrangement triggers the activation of the second pair of Int active sites necessary to resolve Holliday junctions during phage λ Int-mediated recombination
From sensorimotor dependencies to perceptual practices: making enactivism social
Proponents of enactivism should be interested in exploring what notion of action best captures the type of action-perception link that the view proposes, such that it covers all the aspects in which our doings constitute and are constituted by our perceiving. This article proposes and defends the thesis that the notion of sensorimotor dependencies is insufficient to account for the reality of human perception, and that the central enactive notion should be that of perceptual practices. Sensorimotor enactivism is insufficient because it has no traction on socially dependent perceptions, which are essential to the role and significance of perception in our lives. Since the social dimension is a central desideratum in a theory of human perception, enactivism needs a notion that accounts for such an aspect. This article sketches the main features of the Wittgenstein-inspired notion of perceptual practices as the central notion to understand perception. Perception, I claim, is properly understood as woven into a type of social practices that includes food, dance, dress, music, etc. More specifically, perceptual practices are the enactment of culturally structured, normatively rich techniques of commerce of meaningful multi- and inter-modal perceptible material. I argue that perceptual practices explain three central features of socially dependent perception: attentional focus, aspectsâ saliency, and modal-specific harmony-like relations
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Imputation versus prediction: applications in machine learning for drug discovery
Imputation is a powerful statistical method that is distinct from the predictive modelling techniques more commonly used in drug discovery. Imputation uses sparse experimental data in an incomplete dataset to predict missing values by leveraging correlations between experimental assays. This contrasts with quantitative structureâactivity relationship methods that use only descriptor â assay correlations. We summarize three recent imputation strategies â heterogeneous deep imputation, assay profile methods and matrix factorization â and compare these with quantitative structureâactivity relationship methods, including deep learning, in drug discovery settings. We comment on the value added by imputation methods when used in an ongoing project and find that imputation produces stronger models, earlier in the project, over activity and absorption, distribution, metabolism and elimination end points. </jats:p
Egalitarian justice and expected value
According to all-luck egalitarianism, the differential distributive effects of both brute luck, which defines the outcome of risks which are not deliberately taken, and option luck, which defines the outcome of deliberate gambles, are unjust. Exactly how to correct the effects of option luck is, however, a complex issue. This article argues that (a) option luck should be neutralized not just by correcting luck among gamblers, but among the community as a whole, because it would be unfair for gamblers as a group to be disadvantaged relative to non-gamblers by bad option luck; (b) individuals should receive the warranted expected results of their gambles, except insofar as individuals blamelessly lacked the ability to ascertain which expectations were warranted; and (c) where societal resources are insufficient to deliver expected results to gamblers, gamblers should receive a lesser distributive share which is in proportion to the expected results. Where all-luck egalitarianism is understood in this way, it allows risk-takers to impose externalities on non-risk-takers, which seems counterintuitive. This may, however, be an advantage as it provides a luck egalitarian rationale for assisting ânegligent victimsâ
Impact of time-ordered measurements of the two states in a niobium superconducting qubit structure
Measurements of thermal activation are made in a superconducting, niobium
Persistent-Current (PC) qubit structure, which has two stable classical states
of equal and opposite circulating current. The magnetization signal is read out
by ramping the bias current of a DC SQUID. This ramping causes time-ordered
measurements of the two states, where measurement of one state occurs before
the other. This time-ordering results in an effective measurement time, which
can be used to probe the thermal activation rate between the two states.
Fitting the magnetization signal as a function of temperature and ramp time
allows one to estimate a quality factor of 10^6 for our devices, a value
favorable for the observation of long quantum coherence times at lower
temperatures.Comment: 14 pages, 4 figure
Band gap engineering by functionalization of BN sheet
From first principles calculations, we investigate the stability and physical
properties of single layer h-BN sheet chemically functionalized by various
groups viz. H, F, OH, CH3, CHO, CN, NH2 etc. We find that full
functionalization of h-BN sheet with these groups lead to decrease in its
electronic band gap, albeit to different magnitudes varying from 0.3 eV to 3.1
eV, depending upon the dopant group. Functionalization by CHO group, in
particular, leads to a sharp decrease in the electronic band gap of the
pristine BN sheet to ~ 0.3 eV, which is congenial for its usage in transistor
based devices. The phonon calculations on these sheets show that frequencies
corresponding to all their vibrational modes are real (positive), thereby
suggesting their inherent stability. The chemisorption energies of these groups
to the B and N atoms of the sheet are found to lie in the range of 1.5 -6 eV.Comment: 15 pages, 2 figures PRB(submitted
Multi-component Transparent Conducting Oxides: Progress in Materials Modelling
Transparent conducting oxides (TCOs) play an essential role in modern
optoelectronic devices through their combination of electrical conductivity and
optical transparency. We review recent progress in our understanding of
multi-component TCOs formed from solid-solutions of ZnO, In2O3, Ga2O3 and
Al2O3, with a particular emphasis on the contributions of materials modelling,
primarily based on Density Functional Theory. In particular, we highlight three
major results from our work: (i) the fundamental principles governing the
crystal structures of multi-component oxide structures including (In2O3)(ZnO)n,
named IZO, and (In2O3)m(Ga2O3)l(ZnO)n, named IGZO; (ii) the relationship
between elemental composition and optical and electrical behaviour, including
valence band alignments; (iii) the high-performance of amorphous oxide
semiconductors. From these advances, the challenge of the rational design of
novel electroceramic materials is discussed.Comment: Part of a themed issue of Journal of Physics: Condensed Matter on
"Semiconducting Oxides". In Press (2011
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