3,028 research outputs found
Accelerated SVD-based initialization for nonnegative matrix factorization
No full textNonnegative matrix factorization (NMF) is a popular dimensionality reduction technique. NMF is typically cast as a non-convex optimization problem solved via standard iterative schemes, such as coordinate descent methods. Hence the choice of the initialization for the variables is crucial as it will influence the factorization quality and the convergence speed. Different strategies have been proposed in the literature, the most popular ones rely on singular value decomposition (SVD). In particular, Atif et al. (Pattern Recognit Lett 122:53-59, 2019) have introduced a very efficient SVD-based initialization, namely NNSVD-LRC, that overcomes the drawbacks of previous methods, namely, it guarantees that (i) the error decreases as the factorization rank increases, (ii) the initial factors are sparse, and (iii) the computational cost is low. In this paper, we improve upon NNSVD-LRC by using the low-rank structure of the residual matrix; this allows us to obtain NMF initializations with similar quality to NNSVD-LRC (in terms of error and sparsity) while reducing the computational load. We evaluate our proposed solution over other NMF initializations on several real dense and sparse datasets
Amido functional phthalocyanines as metal ion sensor; synthesis, characterization, spectroscopy, electrochemistry, in-situ spectroelectrochemistry
No full textTetrasubstituted metal ion sensor amido functional phthalocyanines, PyMA-MPc, {PyMA: [N-1,N-3-bis(pyridin-2-ylmethyl)malonamide], M = Pd(II), Cu(II) and Co(II)} bearing amido functionality on the periphery were synthesized from the corresponding tetrasubstituted diethylmalonate substituted phthalocyanines, DEM-MPc (DEM: diethylmalonate; M = Pd(II), Cu(II) and Co(II)), and 2-aminopyridine in N,N-dimethylaminoethanol (DMAE) solvent. The new complexes have been characterized by elemental analysis, FT-IR, H-1 NMR and mass spectra. Peripheral malonamide groups of the phthalocyanine complexes serve as exocyclic binding sites for metal ion, such as Pd-II and also increase the solubility in protic solvents, i.e MeOH. Protonation of the pyridyl groups with HCl formed quaternized salts of the MPc, N-1, N-3-bis(pyridin-2-ylmethyl) malonamide substituted metallophthalocyanines (PyMA-PdPcx8HCl) which are freely soluble in aqueous media. Methylation of M[ Pc(CH(COOC2H5)(2))(4)] with CH3I gave the octacationic 2(3), 9(10), 16(17), 23(24)-tetrakis-[N-1,N-3-bis(N-methylpyridin-2-ylmethyl)malonamide]-phthlocyaninato Cu(II) salts which are freely soluble in water. Voltammetric and spectroelectrochemical studies show that while PyMA-Pd(II) Pc and PyMA-Cu(II) Pc give ring-based reversible/quasi-reversible redox processes, PyMA-Co(II) Pc give both metal and ring-based, reversible/quasi-reversible electron transfer processes. (C) 2010 Elsevier B. V. All rights reserved
Highly soluble tetra lauryl alcohol substituted phthalocyanines; synthesis, electrochemistry, spectroelectrochemistry
No full textThe tetra peripherally -substituted 2(3),9(10),16(17),23(24)-tetrakis undecyloxy phthalocyanine derivatives, M{Pc[O-(CH2)(11)CH3)](4)} Pc: Phthalocyanine, [M: Zn(II)(2), Ga(III)(3), and Ti(IV)(4)], have been synthesized and characterized using FT-IR, H-1, and (CNMR)-C-13, MS(MALDI-TOF), UV-vis, atomic force microscopy, electro and spectroelectro chemical and elemental analysis. The new synthesized complexes are soluble in both polar solvents and nonpolar solvents, such as THF, DMF, CHCl3, CH2Cl2, benzene, and even hexane. Electrochemical and spectroelectrochemical measurements give common metal-based and/or Pc ring-based redox processes which support the proposed structures of the complexes. While titanium phthalocyanine exhibits metal- and Pc ring-based reduction and/or oxidation couples, gallium and zinc phthalocyanines give only Pc ring-based electron transfer processes
Novel scorpion type phthalocyanine chemosensors for detection of selective-metal ion by inducing H- and J-aggregations in solution; synthesis, characterization and electrochemistry
No full textScorpion type metal(II) and metal(III) phthalocyanine reversible sensors, MPc[beta-[dihydroxypropylthio](8)]X [where M = 2H(2), Cu(II)(3), Co(II)(4), Mn(III)(5) or Pb(II)(6); X = Cl only when M = Mn(III)] have been prepared for detection of selective soft metal ion from the corresponding metal salts and 4,5-bis-(1,2-dihydroxy propylthio)-phthalonitrile compound (1). Upon addition of Ag(I), Pd(II), Zn(II), Ni(II), Na(I) and Mg(II) metal ions into the solution of 2, 3, 4 or 6 in THF, only Pd(II) and Ag(I) metal ions result in particular responses pronounced in the Q- and the B-bands of their UV-Vis spectra as a result of donor acceptor interactions. The novel compounds have been characterized by using MALDI-TOF MS, FT-IR, UV-Vis, H-1 NMR,C-13 NMR, AFM and elemental analysis. In compounds (4) and (5), metal based electron transfer reactions have been observed in addition to the common phthalocyanine ring-based electron transfer processes. In case of compound (6), stable anionic species have been observed without demetallation of the Pb(II). (C) 2014 Elsevier Ltd. All rights reserved
Synthesis, electrochemistry and in situ spectroelectrochemistry of water-soluble phthalocyanines
No full textThe synthesis, characterization and voltammetric and spectroelectrochemical properties of newly synthesized metal-free and metallo phthalocyanines (M = Co, Cu, Zn) containing four dialkylaminophenoxy or trialkylammoniumphenoxy substituents on peripheral positions have been presented in this work. The new compounds have been characterized by using elemental analysis, UV-Vis, FT-IR, H-1 NMR and MS spectroscopic data. Phthalocyanines with trialkylammoniumphenoxy substituents are soluble in aqueous solution over a wide pH range, and these compounds are present as aggregated species in solution as confirmed by the blue shift of Q-bands in their electronic spectra. The electrochemical behavior of the phthalocyanines was investigated by cyclic voltammetry and differential pulse voltammetry on a platinum-working electrode in DCM and DMSO. The voltammetric and spectroelectrochemical measurements of the complexes show that while cobalt phthalocyanine gives both ligand- and metal-based redox processes, metal-free, zinc and copper phthalocyanine complexes give only ligand-based processes in harmony with common phthalocyanine complexes
An electrochemical sensor for the detection of pesticides based on the hybrid of manganese phthalocyanine and polyaniline
No full textA mimic enzymeless electrochemical sensor (M-Eless-ES) based on the terminal alkynyl substituted manganese phthalocyanine (MnPc-TA) and 4-azido polyaniline (N-3-PANI) hybrid was constructed and tested as a selective and sensitive pesticide sensor. A new electrode modification technique, solid state electropolymerization of a film, was developed for the preparation of ITO/MnPc-TA/N-3-PANI electrode as M-Eless-ES for the first time in this study. During construction of ITO/MnPc-TA/N(3-)PANI electrode, MnPc-TA was firstly deposited on indium tin oxide coated glass substrate (ITO) with Langmuir Blodgett (LB) technique. Then 4-azidoaniline (N-3-ANI) was bonded to the terminal alkynyl substituents of MnPc-TA (ITO/MnPc-TA/N-3-ANI) with click chemistry (CC) and finally ANI groups of the solid MnPc-TA/N-3-ANI hybrid film was electropolymerized on ITO surface to form ITO/MnPc-TA/N-3-PANI electrode. The modified electrode was characterized with square wave voltammetry (SWV), X-ray diffraction (XRD), scanning electron microscope (SEM), and fourier transform infrared (FT-IR). Finally, ITO/MnPc-TA/N-3-PANI electrode was tested as potential M-Eless-ES for the fenitrothion, eserine, and diazinon via SWV technique. Different voltammetric responses were observed for each pesticide. Observation of a new redox peak due to the interaction of the electrode with the fenitrothion indicated its distinct selectivity for this pesticide. The limit of detection (LOD) (0.049 mu mol dm(-3) for fenitrothion, 0.088 mu mol dm(-3) for eserine and 0.062 mu mol dm(-3) for diazinon), wide linear ranges, and especially higher selectivity were observed with ITO/MnPc-TA/N-3-PANI which are the basic requirements for the practical applications for the pesticide sensing. Reproducibility, easy of construction, and stability of the electrode are other superior advantages. As a real sample application, ITO/MnPc-TA/N-3-PANI sensor was successfully employed for determining the fenitrothion residue in rosehip sample
Resolving Debt Overhang: Political Constraints in the Aftermath of Financial Crises
No full textDebtors bear the brunt of a decline in asset prices associated with financial crises and policies aimed at partial debt relief may be warranted to boost growth in the midst of crises. Drawing on the US experience during the Great Recession of 2008-09 and historical evidence in a large panel of countries, we explore why the political system may fail to deliver such policies. We find that during the Great Recession creditors were able to use the political system more effectively to protect their interests through bailouts. More generally we show that politically countries become more polarized and fractionalized following financial crises. This results in legislative stalemate, making it less likely that crises lead to meaningful macroeconomic reforms.
Construction of Modified Electrodes with Click Electrochemistry Based on the Hybrid of 4-Azido Aniline and Manganese Phthalocyanine and Electrochemical Pesticide Sensor Applications
No full textTerminal alkynyl substituted manganese phthalocyanine (TA-MnPc) was bounded to 4-azido polyaniline (PANI-N-3) on an indium thin oxide coated glass (ITO) electrode by using click electrochemistry (CEC) method in order to prepare PANI-N-3/TA-MnPc hybrid. Constructed ITO/PANI-N-3/TA-MnPc electrode was characterized with square wave voltammetry (SWV), scanning electron microscope (SEM), and Fourier transform infrared (FT-IR) spectra and then it was investigated as a mimic enzymeless electrochemical sensor (M-Eless-ES) for the pesticide detection. During construction of ITO/PANI-N-3/TA-MnPc electrode, 4-azidoaniline (ANI-N-3) was firstly coated on the ITO surface with the electropolymerization of ANI-N-3 and hereby ITO/PANI-N-3 electrode bearing functional azide groups was prepared. Then TA-MnPc was bounded to the azide groups of ITO/PANI-N-3 electrode with CEC by forming threeazole ring between the azide and terminal alkynyl groups with the catalytic assist of Cu-I ions generated electrochemically on the surface of the electrode. Finally, ITO/PANI-N-3/TA-MnPc electrode was tested as a potential M-Eless-ES for various pesticides. While PANI-N-3/TA-MnPc hybrid interacted with all pesticides, the interaction with the fenitrothion showed completely different voltammetric results than the others. Observation of a new characteristic peak for the fenitrothion sensing illustrated selectivity of the electrode for this pesticide. In addition to the better selectivity, good stability, reproducibility, small detection limit (LOD), high sensitivity, and wide linear range of the electrode indicated possible application of ITO/PANI-N-3/TA-MnPc electrode as a practical pesticide sensor. (C) 2018 The Electrochemical Society
Alcohol-soluble functional vic-dioxime bearing alcoholhexylsulfanyl moieties: preparation, spectroscopy and electrochemistry
No full textA new alcohol soluble functionalized vic-dioxime, bis-[(1-hydroxyhexyl)-(8,9-hydroxyimino)-7,10-dithiahexacosane (LH2), and its alcohol-soluble mono and dinuclear complexes (Ni-II, Cu-II, Co-II, Mn-II, Pd-II and UO2II) have been prepared from 6-mercapto-1-hexanol and (E,E)-dichloroglyoxime under high dilution basic conditions. Reactive polyalcohol moieties appended at the periphery of the oxime containing two different heteroatoms (S-, O-), serve as a weak exocyclic binding sites for Pd (II) and Ag (I) metal ions and also provide solubility for the vic-dioxime complexes in low molecular-weight alcohols. Both mono-nuclear (LH)(2)M and homodinuclear (LH)(2)(UO2)(2)(OH)(2) and heterotrinuclear (LH)(2)MM(2)(')Xn, where M = Co-II M' = Pd-II, X = Cl-, n = 4 and Ag-I X = NO3-, n = 2) complexes have been obtained with a 1:2, 2:2, 3:2 metal/ligand ratio, respectively. Electronic spectra of the modified vic-dioximes exhibit monitorable changes in UV. All mono and dinuclear-complexes are soluble in common organic solvents. The elemental analysis, H-1-n.m.r, i.r., u.v-vis, and f.a.b.-m.s data and by cyclic and differential pulse voltammetry measurements are presented
Selective metal sensor phthalocyanines bearing non-peripheral functionalities: Synthesis, spectroscopy, electrochemistry and spectroelectrochemistry
No full textA novel alcohol-soluble ionophore ligand and its non-peripherally tetrasubstituted functional 1,8,15,22-tetrakis(6-hydroxyhexylsulfanyl) metallophthalocyanines M[Pc(alpha-SC(6)H(12)OH)(4)] (M = Cu(II), Zn(II), Co(II); Pc=phthalocyanine) are reported. The aggregation and cation binding behaviors of the phthalocyanine compounds in the presence of soft Ag(I) and Pd(II) metal ions were investigated by using UV-Vis spectroscopy. The new compounds have been characterized by elemental analysis, IR, (1)H, (13)C NMR, UV/Vis spectroscopy, ESI and MALDI-TOF-MS mass spectra. Voltammetric and in-situ spectroelectrochemical studies show that while copper and zinc phthalocyanine complexes give well-defined ring-based reduction and oxidation processes, the cobalt phthalocyanine gives both metal-based and ring-based redox processes which have reversible and diffusion controlled character. (c) 2008 Elsevier Ltd. All rights reserved
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