Search for: high-yield
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    Change point estimation of high-yield processes with a linear trend disturbance

    , Article International Journal of Advanced Manufacturing Technology ; Volume 69, Issue 1-4 , May , 2013 , Pages 491-497 ; 02683768 (ISSN) Niaki, S. T. A ; Khedmati, M ; Sharif University of Technology
    In this paper, the maximum likelihood estimator (MLE) of the change point in a high-yield process when a linear trend disturbance occurs in the proportion nonconformity of the process is first derived. Then, the performances of the proposed change point estimator in terms of both accuracy and precision are compared to the MLE of the change point designed for step changes. The results of the comparison analysis that is performed using Monte Carlo simulation experiments show that not only the average estimates of the change point estimator designed for linear trends are closer to the real change point, but also its mean square error is smaller than the one of the estimator designed for step... 

    Change point estimation of high-yield processes experiencing monotonic disturbances

    , Article Computers and Industrial Engineering ; Vol. 67, issue. 1 , January , 2014 , p. 82-92 Niaki, S. T. A ; Khedmati, M ; Sharif University of Technology
    In this paper, we first propose a maximum likelihood estimator (MLE) of a change point in high-yield processes, where the only assumption is that the change belongs to a family of monotonic changes. Following a signal from the cumulative count of conforming (CCC) control chart, the performance of the proposed monotonic change-point estimator is next evaluated by comparing its performances to the ones designed for step-changes and linear-trend disturbances through extensive simulation experiments involving different single step-changes, linear-trend disturbances, and multiple-step changes. The results show that when the type of change is not known a priori, using the proposed change-point... 

    Monitoring high-yields processes with defects count in nonconforming items by artificial neural network

    , Article Applied Mathematics and Computation ; Volume 188, Issue 1 , 2007 , Pages 262-270 ; 00963003 (ISSN) Abbasi, B ; Akhavan Niaki, S. T ; Sharif University of Technology
    In high-yields process monitoring, the Geometric distribution is particularly useful to control the cumulative counts of conforming (CCC) items. However, in some instances the number of defects on a nonconforming observation is also of important application and must be monitored. For the latter case, the use of the generalized Poisson distribution and hence simultaneously implementation of two control charts (CCC & C charts) is recommended in the literature. In this paper, we propose an artificial neural network approach to monitor high-yields processes in which not only the cumulative counts of conforming items but also the number of defects on nonconforming items is monitored. In order to... 

    Selective oxidation of sulfides to sulfoxides by a molybdate-based catalyst using 30% hydrogen peroxide

    , Article Catalysis Communications ; Vol. 52, issue , July , 2014 , pp. 16-21 ; ISSN: 15667367 Bayat, A ; Shakourian-Fard, M ; Hashemi, M. M ; Sharif University of Technology
    An efficient method is reported for selective oxidation of various types of sulfides to sulfoxides and sulfones in good to high yields using 30% H 2O2 in the presence of catalytic amounts of molybdate-based catalyst in acetonitrile as solvent at room temperature. The catalyst can be easily recovered and reused for seven reaction cycles without considerable loss of activity  

    Commercial zinc oxide: a facile, efficient, and eco-friendly catalyst for the one-pot three-component synthesis of multisubstituted 2-aminothiophenes via the Gewald reaction

    , Article Industrial and Engineering Chemistry Research ; Volume 51, Issue 44 , October , 2012 , Pages 14577-14582 ; 08885885 (ISSN) Tayebee, R ; Ahmadi, S. J ; Rezaei Seresht, E ; Javadi, F ; Yasemi, M. A ; Hosseinpour, M ; Maleki, B ; Sharif University of Technology
    An eco-friendly, simple, and effective protocol is developed for the synthesis of various multisubstituted 2-aminothiophenes. In the presence of a catalytic amount of ZnO (5 mol), ketones or aldehydes, malononitrile and elemental sulfur were converted to the corresponding 2-aminothiophene derivatives in moderate to high yields (27%-70%) under solvent-free conditions at 100 °C. Zinc oxide as an efficient, readily available, and reusable catalyst, showed very good catalytic activity for the synthesis of 2-aminothiophene derivatives. Thus far, little research has been reported on the Gewald reaction under solvent-free conditions; to the best of our knowledge, this is the first time that it has... 

    Crosslinked poly(ionic liquid) as high loaded dual acidic organocatalyst

    , Article Journal of Molecular Catalysis A: Chemical ; Volume 365 , 2012 , Pages 55-59 ; 13811169 (ISSN) Pourjavadi, A ; Hosseini, S. H ; Soleyman, R ; Sharif University of Technology
    A dual acidic heterogeneous organocatalyst was synthesized by copolymerization of acidic ionic liquid monomer (vinyl-3-(3-sulfopropyl) imidazolium hydrogen sulfate [VSim][HSO 4]) and ionic liquid crosslinker (1,4-butanediyl-3,3′-bis-l-vinyl imidazolium dihydrogen sulfate). The resulting ionic heterogeneous catalyst is shown to be an efficient dual acidic organocatalyst for synthesis of dihydropyrimidines using the Biginelli synthetic route under mild reaction conditions in high yields. Since monomers make the catalyst bed, crosslinked poly(ionic liquid) will have high loading level of acidic groups comparing to other heterogeneous acid catalysts. Despite of conventional heterogeneous ionic... 

    Permeation of single gases through TEG liquid membranes modified by Na-Y nano-zeolite particles

    , Article Separation and Purification Technology ; Volume 76, Issue 2 , 2010 , Pages 120-125 ; 13835866 (ISSN) Asadollahi, M ; Bastani, D ; Kazemian, H ; Sharif University of Technology
    In this research, a triethylene glycol (TEG)/nano-zeolite Na-Y liquid membrane was developed in order to investigate the effect of zeolite nanoparticles on separation performance of a liquid membrane. To do this, a high yield nano-zeolite Na-Y was synthesized using mid-synthesis addition method. The synthesized samples were characterized by XRD, FT-IR, and SEM (EDX) instrumental techniques. A supported liquid membrane was prepared by impregnating a porous hydrophilic PVDF support with TEG and nano-zeolite Na-Y. The permeation tests of single gas components of O2, N2 and CO2 were carried out at pressure differences of 0.8 and 1.8 bar. The permeances of the single gases were found to be: CO2 >... 

    Synthesis, structural characterization and alcohol oxidation activity of a new mononuclear manganese(II) complex

    , Article Transition Metal Chemistry ; Volume 35, Issue 3 , 2010 , Pages 297-303 ; 03404285 (ISSN) Najafpour, M. M ; Amini, M ; Bagherzadeh, M ; Boghaei, D. M ; McKee, V ; Sharif University of Technology
    A manganese(II) complex of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) has been synthesized and characterized by single-crystal X-ray diffraction, elemental analyses, IR, and UV-Vis spectroscopic techniques. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted by this catalyst using oxone (2KHSO5KH-SO4K2SO4) as an oxidant under biphasic reaction conditions (CH2Cl2/H 2O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature. Easy preparation, mild reaction conditions, high yields of the products, short reaction times, no further oxidation to the corresponding carboxylic acids, high selectivity and inexpensive reagents make this... 

    Microwave-assisted synthesis of 3-substituted coumarins using ZrOCl 2.8H2O as an effective catalyst

    , Article Scientia Iranica ; Volume 16, Issue 1 C , 2009 , Pages 12-16 ; 10263098 (ISSN) Matloubi Moghaddam, F ; Mirjafary, Z ; Saeidian, H ; Sharif University of Technology
    An efficient route for the synthesis of 3-substituted coumarins via Knoevenagel condensation, using ZrOCl2.8H2O (10 mol %) as the. catalyst under microwave heating and solvent-free conditions, is described. This procedure offers several advantages, including the low loading of catalysts, high yields, clean reactions, short reaction times and the. use of various substrates, which make it a useful and attractive strategy for the. synthesis of 3-substituted coumarins. © Sharif University of Technology, June 2009  

    A novel magnetic polyacrylonotrile-based palladium core−shell complex: a highly efficient catalyst for synthesis of Diaryl ethers

    , Article Journal of Organometallic Chemistry ; Volume 916 , 14 June , 2020 Matloubi Moghaddam, F ; Jarahiyan, A ; Eslami, M ; Pourjavadi, A ; Sharif University of Technology
    Elsevier B.V  2020
    The present article describes the synthesis of a new magnetic polyacrylonitrile-based Pd catalyst involving polyacrylonitrile modified via 2-aminopyridine as an efficient support to immobilize Pd nanoparticles. The simple reusability, easy separation and high stability of this Pd complex make it an excellent candidate to generate a C–O bond via Ph-X activation which is a really important subject in achieving biologically active compounds. It is worth to note access to good and high yields as well as broad substrate scope have resulted from superior reactivity of this catalyst complex. Furthermore, the structure of the magnetic polyacrylonitrile-based heterogeneous catalyst was characterized... 

    Thorough tuning of the aspect ratio of gold nanorods using response surface methodology

    , Article Analytica Chimica Acta ; Volume 779 , 2013 , Pages 14-21 ; 00032670 (ISSN) Hormozi Nezhad, M. R ; Robatjazi, H ; Jalali Heravi, M ; Sharif University of Technology
    In the present work a central composite design based on response surface methodology (RSM) is employed for fine tuning of the aspect ratios of seed-mediated synthesized gold nanorods (GNRs). The relations between the affecting parameters, including ratio of l-ascorbic acid to Au3+ ions, concentrations of silver nitrate, CTAB, and CTAB-capped gold seeds, were explored using a RSM model. It is observed that the effect of each parameter on the aspect ratio of developing nanorods highly depends on the value of the other parameters. The concentrations of silver ions, ascorbic acid and seeds are found to have a high contribution in controlling the aspect ratios of NRs. The optimized parameters led... 

    Synthesis, X-ray structure, characterization and catalytic activity of a polymeric manganese(II) complex with iminodiacetate

    , Article Applied Organometallic Chemistry ; Volume 25, Issue 7 , 2011 , Pages 559-563 ; 02682605 (ISSN) Bagherzadeh, M ; Amini, M ; Boghaei, D. M ; Najafpour, M. M ; McKee, V ; Sharif University of Technology
    A polymeric manganese(II) complex with the general formula [Mn(O 2CCH2NH2CH2CO2) 2(H2O)2]n from reaction of iminodiacetatic acid and manganese(II) perchlorate under nitrogen in water, was synthesized and characterized. The structure of the complex was determined using single-crystal X-ray diffraction, elemental analysis, IR and UV-vis spectra. This complex exhibited excellent catalytic activity and selectivity for oxidation of various alcohols and sulfides to the corresponding aldehydes/ketone and sulfoxides using urea hydrogen peroxide and oxone (2KHSO 5·KHSO4·K2SO4), respectively, as oxidants under air at room temperature. The easy preparation, mild reaction conditions, high yields of the...