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171.
An efficient algorithm is derived for solving the quantile regression problem combined with a group sparsity promoting penalty. The group sparsity of the regression parameters is achieved by using a \(\ell _{1,\infty }\) -norm penalty (or constraint) on the regression parameters. The algorithm is efficient in the sense that it obtains the regression parameters for a wide range of penalty parameters, thus enabling easy application of a model selection criteria afterwards. A Matlab implementation of the proposed algorithm is provided and some applications of the methods are studied. 相似文献
172.
新型磺酸功能化吡啶盐酸盐离子液体催化剂用于六氢喹啉合成(英文) 总被引:1,自引:0,他引:1
Ardeshir Khazaei Mohammad Ali Zolfigol Ahmad Reza Moosavi-Zare Javad Afsar Abdolkarim Zare Vahid Khakyzadeh Mohammad Hassan Beyzavi 《催化学报》2013,34(10):1936-1944
Sulfonic acid functionalized pyridinium chloride [pyridine-SO3 H]Cl has been synthesized as a novel Brnsted acidic ionic liquid and characterized on the basis of its FT-IR,1H and 13C NMR,MS,ther-mogravimetry,and derivative thermogravimetry data.The material has also been used as a highly efficient,homogeneous,and reusable catalyst for the preparation of hexahydroquinolines according to the one-pot multi-component condensation of arylaldehydes,dimedone(5,5-dimethylcyclohexane-1,3-dione),β-ketoesters,and ammonium acetate under solvent-free conditions. 相似文献
173.
Vahid Majidi Christian Hassell 《International journal of environmental analytical chemistry》2013,93(14-15):1111-1121
Various aspects of chemical instrument miniaturizing are explored. The limitations imposed by scaling laws are discussed, and the influences of system dynamics on chemical and physical behaviour of molecules in microsystems are presented. The complexity of chemical systems, as defined by intra- and intermolecular forces, influencing minimum device dimensions is illustrated for solution and gas-phase species. The basic concepts for environmental sensor networks are presented for a hypothetical system. 相似文献
174.
We report on an inorganic–organic hybrid nanocomposite that represents a novel kind of fiber coating for solid-phase microextraction (SPME) of polycyclic aromatic hydrocarbons (PAHs). The material is composed of ZnO nanoparticles, polythiophene and hexagonally ordered silica, and displays good extraction capability due to its nanostructure. The nanocomposite was synthesized by an in-situ polymerization technique, and the ZnO nanoparticles were anchored to the pores in the walls. The ZnO/polythiophene/hexagonally ordered silica (ZnO/PT/SBA-15) nanocomposite was then deposited on a stainless steel wire to obtain the fiber for SPME of PAHs. Optimum conditions include an extraction temperature of 85 °C (for 30 min only), a desorption temperature of 260 °C (for 2 min), and a salt concentration (NaCl) of 20 % (w/v). The detection limits are between 8.2 and 20 pg mL?1, and the linear responses extend from 0.1 to 10 ng mL?1. The repeatability for one fiber (for n?=?5), expressed as relative standard deviation, is between 4.3 and 9.1 %. The method offers the advantage of being simple to use, rapid, and low-cost (in terms of equipment). The thermal stability of the fiber and high relative recovery (compared to conventional methods) represent additional attractive features. Figure
We report on an inorganic–organic hybrid nanocomposite that represents a novel kind of fiber coating with thermal stability and high relative recovery for solid-phase microextraction (SPME) of polycyclic aromatic hydrocarbons (PAHs). The method is simple to use, rapid and low-cost. 相似文献
175.
In a previous paper [Nat. Photon. 5, 166 (2011)], we reported on a planar dielectric antenna that achieved 96% efficiency in collecting the photons emitted by a single molecule. In that work, the transition dipole moment of the molecule was set perpendicular to the antenna plane. Here, we present a theoretical extension of that scheme that reaches collection efficiencies beyond 99% for emitters with arbitrarily oriented dipole moments. Our work opens important doors in a wide range of contexts including quantum optics, quantum metrology, nanoanalytics, and biophysics. In particular, we provide antenna parameters to realize ultrabright single-photon sources in high-index materials such as semiconductor quantum dots and color centers in diamond, as well as sensitive detection of single molecules in nanofluidic devices. 相似文献
176.
Hassan Rakhshandeh Hamed Rajabi Khasevan Anella Saviano Mohammad Reza Mahdinezhad Vafa Baradaran Rahimi Sajjad Ehtiati Leila Etemad Alireza Ebrahimzadeh-bideskan Francesco Maione Vahid Reza Askari 《Molecules (Basel, Switzerland)》2022,27(18)
Background: Type-one diabetes (T1D), a chronic autoimmune disease with marked inflammatory responses, is associated with infertility complications and implications. Based on the anti-diabetic, antioxidant, and anti-hyperlipidemic potential of Portulaca oleracea (PO), this study aimed to evaluate the protective effect of this plant extract on streptozotocin-induced type-I-diabetes-associated reproductive system dysfunction and inflammation. Methods: Male rats were randomly divided into four experimental groups: control, diabetic, and treatment/s (PO extract at 100 or 300 mg/kg/daily). Then food and water consumption, body, testis and epididymis weights, histopathological evaluation, seminiferous tubules diameter, sperm count and motility, glucose levels, sex hormones, and inflammatory and oxidative stress markers were evaluated. Results: Our results showed that streptozotocin-induced diabetes significantly increased food and water consumption; increased glucose, MDA, TGF-β1, and TNF-α levels; and decreased the seminiferous tubules diameter, sperm count and motility, levels of LH, testosterone, total thiol, VEGF, and SOD activity. Interestingly, PO extract (phytochemically characterized by using liquid chromatography–mass spectrometry to detect bioactive molecules) significantly ameliorated these parameters and histopathological indexes’ damage in rats. Conclusion. Even if more preclinical assessments are needed to better characterize the mechanism/s of action, the results of this study will pave the way for the rational use of PO on diabetic-associated clinical complications and implications. 相似文献
177.
Aisa Sendijarevi Vahid Sendijarevi Kurt C. Frisch Branka Koruga-Lazarevi Enes Torli 《Journal of polymer science. Part A, Polymer chemistry》1990,28(13):3603-3615
The synthesis and properties of thermoplastic urethane-modified polyimides, based on different isocyanates, with different concentrations of hard segments and different ratios of imide and urethane groups, were studied. The effect of catalysts, isocyanates, and temperature was investigated on model reactions leading to formation of monoimides, bisimides, and polyimides. A polymer based on 2,4-TDI, poly(oxytetramethylene) glycol of 1000 molecular weight and pyromellitic dianhydride, with 75% of imide in the hard segments, retained about 50% of the original tensile strength at 120°C and about 30% at 150°C. Increasing the temperature up to 150°C had very little effect on the elongation of this copolymer. In general, increasing the imide concentration in the polymer structure provided better retention of stress-strain properties at elevated temperatures. 相似文献
178.
Givargis T. Vahid F. Henkel J. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2002,10(4):416-422
In this work, we provide a technique for efficiently exploring the power/performance design space of a parameterized system-on-chip (SOC) architecture to find all Pareto-optimal configurations. These Pareto-optimal configurations will represent the range of power and performance tradeoffs that are obtainable by adjusting parameter values for a fixed application that is mapped on the SOC architecture. Our approach extensively prunes the potentially large configuration space by taking advantage of parameter dependencies. We have successfully applied our technique to explore Pareto-optimal configurations of our SOC architecture for a number of applications. 相似文献
179.
Hajrija ehovi Aia Sendijarevi Vahid Sendijarevi Kurt C. Frisch 《Journal of polymer science. Part A, Polymer chemistry》1987,25(10):2729-2736
The reaction of butyl isocyanate with phenylglycidyl ether was selected as a model reaction for the synthesis of aliphatic isocyanate-based poly(2-oxazolidones). The selectivity of different metal halides and aluminum trichloride/triphenylphosphine oxide (AlCl3 TPPO) and aluminum hexamethylphosphoramide (AlCl3 HMPA) complexes were investigated for oxazolidone formation. Both FTIR and mass spectrographic methods were employed for characterization of the reaction products. The kinetics of the model reaction was studied using AlCl3 TPPO in o-dichlorobenzene at 120 and 140°C. 相似文献
180.
Soraia Meghdadi Mehdi Amirnasr Mohammad H. Habibi Ahmad Amiri Vahid Ghodsi Azadeh Rohani Ross W. Harrington William Clegg 《Polyhedron》2008
Two series of complexes of the types trans-[CoIII(Mebpb)(amine)2]ClO4 {Mebpb2− = N,N-bis(pyridine-2-carboxamido)-4-methylbenzene dianion, and amine = pyrrolidine (prldn) (1a), piperidine (pprdn) (2a), morpholine (mrpln) (3a), benzylamine (bzlan) (4a)}, and trans-[CoIII(cbpb)(amine)2]X {cbpb2− = N,N-bis(pyridine-2-carboxamido)-4-chlorobenzene dianion, and amine = pyrrolidine (prldn), X = PF6 (1b), piperidine (pprdn), X = PF6 (2b), morpholine (mrpln), X = ClO4 (3b), benzylamine (bzlan), X = PF6 (4b)} have been synthesized and characterized by elemental analyses, IR, UV–Vis, and 1H NMR spectroscopy. The crystal structure of 1a has been determined by X-ray diffraction. The electrochemical behavior of these complexes, with the goal of evaluating the effect of axial ligation and equatorial substitution on the redox properties, is also reported. The reduction potential of CoIII, ranging from −0.53 V for (1a) to −0.31 V for (3a) and from −0.48 V for (1b) to −0.22 V for (3b) show a relatively good correlation with the σ-donor ability of the axial ligands. The methyl and chloro substituents of the equatorial ligand have a considerable effect on the redox potentials of the central cobalt ion and the ligand-centered redox processes. 相似文献