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91.
92.
Dr. Lidia Armelao Dr. Franziskus Heigl Dr. Sophie Brunet Dr. Ramaswami Sammynaiken Dr. Tom Regier Dr. Robert I. R. Blyth Dr. Lucia Zuin Dr. Rami Sankari Dr. Johannes Vogt Prof. Tsun‐Kong Sham 《Chemphyschem》2010,11(17):3625-3631
The distinct optical emission from ZnO materials, nanoneedles and microcrystallites synthesized with different sizes and morphologies by a flow deposition technique, is investigated with X‐ray excited optical luminescence (XEOL) and time‐resolved X‐ray excited optical luminescence (TR‐XEOL) from a synchrotron light source at the O K and Zn L3,2 edges. The innovative use of XEOL, allowing site‐specific chemical information and luminescence information at the same time, is fundamental to provide direct evidence for the different behaviour and the crucial role of bulk and surface defects in the origin of ZnO optical emission, including dynamics. XEOL from highly crystalline ZnO nanoneedles is characterized by a sharp band‐gap emission (~380 nm) and a broad red luminescence (~680 nm) related to surface defects. Luminescence from ZnO microcrystallites is mostly dominated by green emission (~510 nm) associated with defects in the core. TR‐XEOL experiments show considerably faster decay dynamics in nanoneedles compared to microcrystallites for both band‐gap emission and visible luminescence. Herein we make a fundamental step forward correlating for the first time the interplay of size, crystallinity, morphology and excitation energy with luminescence from ZnO materials. 相似文献
93.
M. Geetha P. Senthil Kumar K. Vasudevan A. Prakasam G. Meenakshi P.M. Anbarasan 《Journal of Saudi Chemical Society》2010,14(4):399-407
The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 3,4-pyridinedicarbonitrile was studied based on Hartree–Fock (HF) and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet–visible (UV–Vis) spectrum was investigated by time dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands are assigned to π → π1 transitions. Calculated results suggest that the three lowest energy excited states are due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO2 electrode and 3,4-pyridinedicarbonitrile is due to electron injection process from excited dye to the semiconductor’s conduction band. The role of cyanine in 3,4-pyridinedicarbonitrile in geometries, electronic structures, and spectral properties were analyzed. 相似文献
94.
K.V. Geetha 《Journal of Computational and Applied Mathematics》2010,233(10):2492-112
In this paper, Economic Order Quantity (EOQ) based model for non-instantaneous deteriorating items with permissible delay in payments is proposed. This model aids in minimizing the total inventory cost by finding an optimal replenishment policy. In this model shortages are allowed and partially backlogged. The backlogging rate is variable and dependent on the waiting time for the next replenishment. Some useful theorems have been framed to characterize the optimal solutions. The necessary and sufficient conditions of the existence and uniqueness of the optimal solutions are also provided. An algorithm is designed to find the optimal replenishment cycle time and order quantity under various circumstances. Numerical examples are given to demonstrate the theoretical results. Sensitivity analysis of the optimal solution with respect to major parameters of the system has been carried out and the implications are discussed in detail. In the discussions, suggestions are given to minimize the total cost of the inventory system. 相似文献
95.
Dr. Pramodkumar D. Jadhav Dr. Jianheng Shen Dr. Ramaswami Sammynaiken Prof. Martin J. T. Reaney 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(47):17023-17034
Flax cyclic peptides (orbitides, linusorbs (LOs)) [1–8‐NαC],[1‐MetO2]‐linusorb B1 ([MetO2]‐LO1) and [1–9‐NαC],[1‐MetO2]‐linusorb B2 ([MetO2]‐LO2) are biologically active. These LOs lack active nuclei commonly used in peptide modification. We have developed reactions to activate methionine methyl sulphide to produce stable derivatives. In these reactions, LOs are converted to sulfonium intermediates and subsequently to derivatives containing active nuclei while preserving their fundamental structures. The reaction conditions preserved cyclic peptide fundamental structure and organic solvent solubility. [Met]‐LO1 and [Met]‐LO2 analogues containing activated groups (?CN, ?COOEt, and ?NH2) in the form of methionine, methionine (S)‐oxide, and methionine (S,S)‐dioxide amino acids were synthesized and characterized by LCMS and 1D and 2D NMR spectroscopy. Coumarin orbitide complexes produced in this manner bind Eu3+ yielding FRET compounds that absorb energy through coumarin antennae and emit photons at lanthanide wavelengths. 相似文献
96.
Gaspar LJ Baskar G Reddy BS Ranganathan R Peric M 《Langmuir : the ACS journal of surfaces and colloids》2004,20(21):9029-9035
The cosurfactant activity of N-glycinylmaleamic acid (NGMA) in sodium dodecyl sulfate (SDS) micelles has been demonstrated. The complementary techniques of electron spin resonance (ESR) and fluorescence spectroscopy have been used to draw information on hydration index (H), microviscosity (eta), and aggregation number (N) of micellar assemblies. The estimate of the critical micelle concentration of SDS in the presence of NGMA suggests a synergistic effect of NGMA. The enhanced solubilization of butyl propionate in the presence of NGMA in SDS micelles is explained on the basis of availability of larger interfacial area calculated from a simple spherical geometric model, combined with a low hydrophilicity index as estimated from ESR. Thus, addition of NGMA contributes to an increase of about 50% in ratio of area of polar shell (AP)/volume of hydration (Vh) ratio. The decrease in H accompanied by a decrease in eta with the incorporation of butyl propionate probably arises from solubilization of a butyl component inside the core with the adsorption of propionate ester on the interface. 相似文献
97.
R. Malathi S. S. Rajan Geetha Gopalakrishnan G. Suresh 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(11):o681-o682
The title compound, methyl (2aS,3R,5R,5aS,6S,6aS,8R,9aS,10aR,10bR,10cS)‐8‐(3‐furyl)‐2a,4,5,5a,6,6a,8,9,9a,10a,10b,10c‐dodecahydro‐3‐hydroxy‐2a,5a,6a,7‐tetramethyl‐5‐(3‐methylbut‐2‐enoyloxy)‐2H,3H‐cyclopenta[4′,5′]furo[2′,3′:6,5]benzo[cd]isobenzofuran‐6‐acetate, C32H42O8, was isolated from uncrushed green leaves of Azadirachta indica A. Juss (neem) and has been found to possess antifeedant activity against Spodptera litura. The conformations of the functional groups are similar to those of 3‐desacetylsalannin, which was isolated from neem kernels. The molecules are linked into chains by intermolecular O—H?O hydrogen bonds. 相似文献
98.
Awadhesh Mani J. Janaki T. Geetha Kumary N. Thirumurugan S. Kalavathi A. Bharathi 《Solid State Communications》2011,151(18):1210-1213
Specific heat studies carried out on Fe1.1Te and oxygenated Fe1.1Te and FeTe2 in the range 77-300 K exhibit interesting behavior. The specific heat of the pristine sample reveals a well known structural transition associated with antiferromagnetic ordering near 67 K with a small thermal hysteresis of ∼1 K. Contrastingly, the oxygenated samples exhibit a phase transition with a very large thermal hysteresis of ∼100 K. The specific heat transition observed at the 150 and 260 K regions in the oxygenated Fe1.1Te sample could not be captured by the magnetization measurements indicating that specific heat transitions seen in oxygenated samples may not be of magnetic origin. 相似文献
99.
Geetha Balakrishnan 《Pramana》2008,71(4):721-727
To make headway on any problem in physics, high-quality single crystals are required. In this talk, special emphasis will
be placed on the crystal growth of various oxides (superconductors and magnetic materials), borides and carbides using the
image furnaces at Warwick. The floating zone method of crystal growth used in these furnaces produces crystals of superior
quality, circumventing many of the problems associated with, for example, flux growth from the melt. This method enables the
growth of large volumes of crystal, a prerequisite especially for experiments using neutron beams. Some examples of experimental
results from crystals grown at Warwick, selected from numerous in-house studies and our collaborative research projects with
other UK and international groups will be discussed.
相似文献
100.
Angayarkanny S Vijay R Baskar G Mandal AB 《Journal of colloid and interface science》2012,367(1):319-326
The cationic surfactant, dioctyl ester of cystine hydrochloride (DOEC), was characterized for interfacial adsorption and aggregation behavior in water. The cmc of DOEC was measured as 1.42±0.27×10(-5) mol dm(-3) using the techniques of tensiometry, conductivity and fluorimetry. From specific conductivity measurements, the degree of dissociation (α) of the amine hydrochloride was measured as 0.612. The standard free energy change of micellization (ΔG(m)(°)) and adsorption (ΔG(a)(°)) were calculated to be -25.07 and -44.37 kJ mol(-1), respectively. The aggregated structures provide non-polar microdomains as inferred from the I(3)/I(1) emission intensity ratio of 1.05 of pyrene fluoroprobe and also a blue shift of fluorescence emission wave length (λ(emi.)) maximum down to 470 nm with enhanced intensity of ANS probe in micellar solutions. From Langmuir film balance experiments, it is shown that DOEC forms stable viscoelastic films at the interface with A(0) at 0.69 nm(2)molecule(-1) that agree with the result from surface tension measurements. Molecular modeling suggests the tilted orientation of DOEC at the interface. A large packing parameter (P) of 0.58 and the fibril structures as observed from microscopy studies demonstrate that DOEC favors one-dimensional growth to form elongated micelles. 相似文献