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21.
AC impedance measurements of thin 100-nm polyaniline films electrosynthesized in various acidic electrolyte solutions known
to support different film morphologies are reported. By carefully defining experimental parameters obtained data could be
satisfactorily explained invoking a simple equivalent circuit assuming a double layer capacity assigned to the polymer/solution
interface, a pseudocapacity related to the internal redox capacity of the film, a film and a solution resistance and could be related to film morphologies. The data can be related
to structural/morphological features of PANI films in close agreement with generally accepted changes of PANI films as a function
of the degree of oxidation and type of anion present during electropolymerization. 相似文献
22.
Korn Md Andrade JB Jesus DS Lemos VA Bandeira ML Santos WN Bezerra MA Amorim FA Souza AS Ferreira SL 《Talanta》2006,69(1):16-24
Lead is recognized worldwide as a poisonous metal. Thus, the determination of this element is often required in environmental, biological, food and geological samples. However, these analyses are difficult because such samples contain relatively low concentrations of lead, which fall below the detection limit of conventional analytical techniques such as flame atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry. Several preconcentration procedures to determine lead have therefore been devised, involving separation techniques such as liquid-liquid extraction, solid phase extraction, coprecipitation and cloud point extraction. Citing 160 references, this paper offers a critical review of preconcentration procedures for determining lead using spectroanalytical techniques. 相似文献
23.
Afonso S. Bandeira 《Foundations of Computational Mathematics》2018,18(2):345-379
The largest eigenvalue of a matrix is always larger or equal than its largest diagonal entry. We show that for a class of random Laplacian matrices with independent off-diagonal entries, this bound is essentially tight: the largest eigenvalue is, up to lower order terms, often the size of the largest diagonal. entry. Besides being a simple tool to obtain precise estimates on the largest eigenvalue of a class of random Laplacian matrices, our main result settles a number of open problems related to the tightness of certain convex relaxation-based algorithms. It easily implies the optimality of the semidefinite relaxation approaches to problems such as \({{\mathbb {Z}}}_2\) Synchronization and stochastic block model recovery. Interestingly, this result readily implies the connectivity threshold for Erd?s–Rényi graphs and suggests that these three phenomena are manifestations of the same underlying principle. The main tool is a recent estimate on the spectral norm of matrices with independent entries by van Handel and the author. 相似文献
24.
25.
Afonso?S.?Bandeira Megan?E.?Lewis Dustin?G.?MixonEmail author 《Journal of Fourier Analysis and Applications》2018,24(4):935-956
We develop new discrete uncertainty principles in terms of numerical sparsity, which is a continuous proxy for the 0-norm. Unlike traditional sparsity, the continuity of numerical sparsity naturally accommodates functions which are nearly sparse. After studying these principles and the functions that achieve exact or near equality in them, we identify certain consequences in a number of sparse signal processing applications. 相似文献
26.
João Pedro A. Souza Dr. Leociley R. A. Menezes Dr. Francielle P. Garcia Dr. Débora B. Scariot Dr. Pamela T. Bandeira Mateus B. Bespalhok Dr. Siddhartha O. K. Giese Dr. David L. Hughes Prof. Dr. Celso V. Nakamura Prof. Dr. Andersson Barison Prof. Dr. Alfredo R. M. Oliveira Prof. Dr. Renan B. Campos Prof. Dr. Leandro Piovan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(58):14427-14437
Inspired by the synthetic and biological potential of organotellurium substances, a series of five- and six-membered ring organotelluranes containing a Te−O bond were synthesized and characterized. Theoretical calculations elucidated the mechanism for the oxidation-cyclization processes involved in the formation of the heterocycles, consistent with chlorine transfer to hydroxy telluride, followed by a cyclization step with simultaneous formation of the new Te−O bond and deprotonation of the OH group. Moreover, theoretical calculations also indicated anti-diastereoisomers to be major products for two chirality center–containing compounds. Antileishmanial assays against Leishmania amazonensis promastigotes disclosed 1,2λ4-oxatellurane LQ50 (IC50=4.1±1.0; SI=12), 1,2λ4-oxatellurolane LQ04 (IC50=7.0±1.3; SI=7) and 1,2λ4-benzoxatellurole LQ56 (IC50=5.7±0.3; SI=6) as more powerful and more selective compounds than the reference, being up to four times more active. A stability study supported by 125Te NMR analyses showed that these heterocycles do not suffer structural modifications in aqueous-organic media or at temperatures up to 65 °C. 相似文献
27.
Dr. Miguel A. Huertos Dr. Israel Cano Dr. Nuno A. G. Bandeira Dr. Jordi Benet‐Buchholz Prof. Dr. Carles Bo Prof. Dr. Piet W. N. M. van Leeuwen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16121-16127
The reaction of [CuI(HSC6H4PPh2)]2 with NaBH4 in CH2Cl2/EtOH led to air‐ and moisture‐stable copper hydride nanoparticles (CuNPs) containing phosphinothiolates as new ligands, one of which was isolated by crystallization. The X‐ray crystal structure of [Cu18H7L10I] (L=?S(C6H4)PPh2) shows unprecedented features in its 28‐atom framework (18 Cu and 10 S atoms). Seven hydrogen atoms, in hydride form, are needed for charge balance and were located by density functional theory methods. H2 was released from the copper hydride nanoparticles by thermolysis and visible light irradiation. 相似文献
28.
A Soibel SS Banerjee Y Myasoedov ML Rapparort E Zeldov S Ooi T Tamegai 《Pramana》2002,58(5-6):893-898
Using a novel differential magneto-optical imaging technique we investigate the phenomenon of vortex lattice melting in crystals
of Bi2Sr2CaCu2O8 (BSCCO). The images of melting reveal complex patterns in the formation and evolution of the vortex solid-liquid interface
with varying field (H)/temperature (T). We believe that the complex melting patterns are due to a random distribution of material disorder/inhomogeneities across
the sample, which create fluctuations in the local melting temperature or field value. To study the fluctuations in the local
melting temperature/field, we have constructed maps of the melting landscape T
m(H, r), viz., the melting temperature (T
m) at a given location (r) in the sample at a given field (H). A study of these melting landscapes reveals an unexpected feature: the melting landscape is not fixed, but changes rather
dramatically with varying field and temperature along the melting line. It is concluded that the changes in both the scale
and shape of the landscape result from the competing contributions of different types of quenched disorder which have opposite
effects on the local melting transition. 相似文献
29.
A Gurtu P K Malhotra I S Mittra P M Sood SC Gupta VK Gupta GL Kaul LK Mangotra Y Prakash NK Rao ML Sharma 《Pramana》1974,3(5):311-322
This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR em = 〈n s〉/〈n ch〉, where 〈n ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R em = 1·71 implies an effectiveA-dependence ofR A =A 0.18,i.e., a very weak dependence. Predictions ofR em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production. 相似文献
30.
Polynuclear Gold [AuI]4, [AuI]8, and Bimetallic [AuI4AgI] Complexes: C−H Functionalization of Carbonyl Compounds and Homogeneous Carbonylation of Amines 下载免费PDF全文
Ekaterina S. Smirnova Dr. José M. Muñoz Molina Alice Johnson Dr. Nuno A. G. Bandeira Prof. Carles Bo Prof. Antonio M. Echavarren 《Angewandte Chemie (International ed. in English)》2016,55(26):7487-7491
The synthesis of tetranuclear gold complexes, a structurally unprecedented octanuclear complex with a planar [AuI8] core, and pentanuclear [AuI4MI] (M=Cu, Ag) complexes is presented. The linear [AuI4] complex undergoes C?H functionalization of carbonyl compounds under mild reaction conditions. In addition, [AuI4AgI] catalyzes the carbonylation of primary amines to form ureas under homogeneous conditions with efficiencies higher than those achieved by gold nanoparticles. 相似文献