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991.
S. D. Gopal?Ram M. Anbu?Kulandainathan G. Ravi 《Applied Physics A: Materials Science & Processing》2010,99(1):197-203
The rapid synthesis of ZnO nanostructures by microwave treatment of aqueous solutions of different pH values is reported for
the first time. Microwave in various wattages was used as the source of heating or energy feeding the aqueous precursors.
The pH of the zinc metal source was altered by a suitable amount of mineralisers. The considered pH values are 8, 10, 12 and
13.5. Microwave dielectric heating is dependent on the ability of the material to absorb microwave. This is responsible for
molecular friction and dielectric loss, which as a result produce internal heating of the dielectric medium, in this case
the solution. In typical microwave assisted synthesis, the total exposure to the microwave treatment was near about 25 to
35 minutes. The ZnO nanostructures obtained were studied by XRD, SEM and TEM characterisations. From the XRD pattern and the
full width half maximum of the dominant reflections, microstructural parameters of the nanostructures are calculated and compared
for the different pH values. Flower petal like flakes and hexagonal nanorods are formed for the lower and higher pH solutions,
respectively. From the SEM images, the size distributions for the pH 12 and 13.5 cases are compared by drawing a histogram. 相似文献
992.
Moti Ram 《Solid State Sciences》2009,11(7):1206-1210
LiCo3/5Fe2/5VO4 has been synthesized by solution-based chemical method. X-ray diffraction study at room temperature reveals an orthorhombic phase of the compound. Electrical properties are studied using complex impedance spectroscopy (CIS) technique in a range of frequency and temperature. The complex impedance plots identify the grain interior, grain boundary and electrode–material interface contributions to electrical response in the material. Temperature dependence of a.c. and d.c. conductivity indicates that electrical conduction in the material is a thermally activated process. The value of activation energy computed from the Arrhenius plot of σdc with 103/T is ~(0.356 ± 0.012) eV (25–275 °C). Frequency dependence of a.c. conductivity at different temperatures is found to obey Jonscher's universal law. 相似文献
993.
Moti Ram 《Solid State Sciences》2009,11(8):1423-1426
Dielectric and a.c. conductivity properties of LiCo3/5Mn2/5VO4 ceramic are investigated. This compound is prepared by solution-based chemical method and the formation is checked by X-ray diffraction (XRD) study. XRD analysis at room temperature shows an orthorhombic phase. Frequency dependence of dielectric constant (?r) at different temperatures shows a dispersive behavior at low frequencies. Temperature dependence of ?r at different frequencies indicates the transition temperature (Tc) = 235 °C, 245 °C, 257 °C and 265 °C with (?r)max. ~3689, 1373, 750 and 386 for 10, 50, 100 and 200 kHz respectively. A.c. conductivity analysis indicates that electrical conduction in the material is a thermally activated process. 相似文献
994.
Nandini Sharma Upendra K. Sharma Ajai P. Gupta Devla Arun K. Sinha Brij Lal Paramvir S. Ahuja 《Journal of separation science》2009,32(18):3239-3245
A simple, precise, and rapid high‐performance thin‐layer chromatographic (HPTLC) method for the simultaneous quantification of pharmacologically important naphthoquinone shikonin ( 1 ) together with its derivatives acetylshikonin ( 2 ), and β‐acetoxyisovalerylshikonin ( 3 ) in four species of genus Arnebia (A. euchroma, A. guttata, A. benthamii, and A. hispidissima) from the Indian subcontinent has been developed. In addition, the effect of solvents with varying polarity (hexane, chloroform, ethyl acetate, and methanol) for the extraction of these compounds was studied. HPTLC was performed on precoated RP‐18 F254S TLC plates. For achieving good separation, mobile phase consisting of ACN/methanol/5% formic acid in water (40:02:08 v/v/v) was used. The densitometric determination of shikonin derivatives was carried out at 520 nm in reflection/absorption mode. The method was validated in terms of linearity, accuracy, precision, robustness, and specificity. The calibration curves were linear in the range of 100–600 ng for shikonin and acetylshikonin, and 100–1800 ng for β‐acetoxyisovalerylshikonin. Lower LOD obtained for compounds 1 – 3 were 18, 15, and 12 ng, respectively, while the LOQ obtained were 60, 45, and 40 ng, respectively. 相似文献
995.
M. Carmen Sampedro M. Aranzazu Goicolea Nora Unceta Alicia Sánchez‐Ortega Ramón J. Barrio 《Journal of separation science》2009,32(20):3449-3456
A method based on sequential stir bar sorptive extraction followed by automated thermal desorption–GC–MS for the determination of pesticides in underground and superficial water samples has been developed. Retention time locked GC–MS and deconvolution Automated Mass Spectral Deconvolution and Identification System software allows the use of pesticide databases for identification and quantification in routine applications. Quantitation limits and repetitivity using full scan mass spectrometric determination guarantee the applicability of the method, which enables considerable savings to be made in total analysis time, with data processing times of around 2 min/sample. 相似文献
996.
Ramūnas Garunkštis 《Archiv der Mathematik》2009,93(2):143-145
We correct constants in asymptotic formulas of our paper “Note on zeros of the derivative of the Selberg zeta-function”, Arch.
Math. 91 (2008), 238–246.
The online version of the original article can be found under doi:. 相似文献
997.
In 1997, Serre proved an equidistribution theorem for eigenvalues of Hecke operators on the space S(N,k) of cusp forms of weight k and level N. In this paper, we derive an effective version of Serre's theorem. As a consequence, we estimate, for a given d and prime p coprime to N, the number of eigenvalues of the pth Hecke operator Tp acting on S(N,k) of degree less than or equal to d. This allows us to determine an effectively computable constant Bd such that if J0(N) is isogenous to a product of Q-simple abelian varieties of dimensions less than or equal to d, then N?Bd. We also study the effective equidistribution of eigenvalues of Frobenius acting on a family of curves over a fixed finite field as well as the eigenvalue distribution of adjacency matrices of families of regular graphs. These results are derived from a general “all-purpose” equidistribution theorem. 相似文献
998.
Let ψ(x) denote the digamma function. We study the linear independence of ψ(x) at rational arguments over algebraic number fields. We also formulate a variant of a conjecture of Rohrlich concerning linear independence of the log gamma function at rational arguments and report on some progress. We relate these conjectures to non-vanishing of certain L-series. 相似文献
999.
Ram U. Verma 《Positivity》2009,13(4):771-782
First, based on η-maximal accretiveness, a generalization to Rockafellar’s theorem (1976) in the context of approximating a solution to a general
inclusion problem involving a multivalued η-maximal accretive mapping using the proximal point algorithm in a q-uniformly smooth Banach space setting is considered.
Then an application to a minimization problem of a functional is examined. The general framework for η-maximal accretiveness generalizes the general theory of multivalued maximal monotone mappings.
相似文献
1000.
A novel synthesis of highly functionalized alkylsulfanylmethyl arenes 8a-m through the ring transformation of 6-aryl-4-methyl/ethylsulfanyl-2H-pyran-2-one-3-carbonitriles 1a-j, by reaction with methyl vinyl ketone 2, is delineated and illustrated. To ascertain the course of reaction, 3-arylsulfanylmethyl-2-methyl-6-methylsulfanyl-4-phenylbenzonitriles 8k-m were also prepared from the reaction of 1 with 4-arylsulfanyl-butan-2-ones 7c,d. 相似文献