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201.
IA Simpson R Bol ID Bull RP Evershed K Petzke SJ Dockrill 《Rapid communications in mass spectrometry : RCM》1999,13(13):1315-1319
Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
202.
Ayushi Rastogi Kaushlendra Agrahari Govind Pathak Atul Srivastava Jakub Herman 《Liquid crystals》2019,46(5):725-735
The present study is based on effect of dispersing Cd1?xZnxS/ZnS core/shell quantum dots (QDs) on the memory behaviour of nematic liquid crystal 2020 with the variation of dopant concentration and applied voltage. Around 26% and 45% memory storage in QDs dispersed nematic matrix (MIX 1 and MIX 2) has been the core finding. The presence of ionic charges at low-frequency regime along with their reduction in QDs dispersed nematic matrix has been confirmed from tan δ curve. Pure nematic LC as well as nematic/QD mixtures depict volatile memory effect that depends upon concentration of QDs. The existence of memory due to storage of charge on QDs has been further confirmed from the dielectric, polarising optical micrographs and electro optical study under the influence of bias voltage. The observation of memory effect is attributed to the ion capturing and ion releasing phenomenon. The dispersion of QDs in nematic material plays an important role to enhance memory parameter by capturing and releasing the ionic charges under the application of bias voltage which has been confirmed from capacitance-voltage curve. 相似文献
203.
Shiva K. Rastogi Benjamin D. Denn A. Larry Branen 《Journal of nanoparticle research》2012,14(1):673-12
This study demonstrates a one versus two-step synthesis of fluorescent gold quantum dots (F-AuQDs) and nano clusters (F-AuNCs)
functionalized with thiolated organic linkers using reduction of gold precursor in N,N′-dimethylformamide in 1 h of reaction. The F-AuQDs and F-AuNCs show fluorescence emission at 425 ± 5 nm upon excitation at
345 ± 5 nm of wavelength, with good water solubility and stability. Five different thiolated organic binary linkers consisting
of various functional groups including: carboxylic acid, hydroxyl, and aromatic amine, were conjugated with the F-AuQDs and
F-AuNCs. The formation mechanism and functionalization of the F-AuQDs and F-AuNCs was characterized using UV–vis absorption
spectra, UV–vis light, fluorescent emission spectra, pH, TEM, and FTIR. The fluorescence emission of the F-AuQDs and F-AuNCs
is greatly dependent on the thio-linker. This novel one-step approach provides facile and fast synthesis of F-AuQDs and F-AuNCs
over the two-step method, with less than 5 h of reaction and workup compared to more than 28 h of reaction for the two-step
approach. These thio-linker functionalized F-AuQDs and F-AuNCs have a wide application in fluorescent labeling of biomolecules,
optical devices, imaging, energy transfer, and biosensing. 相似文献
204.
The kinetics of ligand substitution between aquapentacyanoruthenate(II) ion, [Ru(CN)5H2O]3− and 4-cyanopyridine (4-CNpy) has been investigated spectrophotometrically in the presence of anionic surfactant micelle,
namely sodium dodecylsulphate (SDS) at 400 nm (λmax of the intense yellow product [Ru(CN)54-CNpy]3−) under pseudo-first-order conditions using at least 10% excess of 4-CNpy over [Ru(CN)5H2O]3−. The reaction was studied as a function of [Ru(CN)5H2O3−], [4-CNpy], [SDS], pH, ionic strength and temperature, by varying each of these variables one at a time. The reaction exhibited
overall second-order kinetics, being first order each in [4-CNpy] and [Ru(CN)5H2O3−] over a wide concentration range. Variation of ionic strength of the medium had a significant negative effect on the rate.
The SDS micelle, being negatively charged, does not reveal any regular effect except at or near its critical micelle concentration
(c.m.c). The rate of reaction was measured at different temperatures, and the activation parameters were computed using Arrhenius
and Eyring plots. A plausible mechanism consistent with the experimental results has been proposed. 相似文献
205.
Fringe projection techniques are popular tools for three-dimensional shape measurement in optical metrology. In these techniques, the information about the shape or the surface profile of an object is usually encoded in the phase of a recorded fringe pattern. The paper presents a high-order instantaneous moments based method for phase estimation in fringe projection. The method employs a piecewise polynomial phase approximation approach and uses high-order instantaneous moments to determine the polynomial phase coefficients to estimate the phase. The method's working is demonstrated using simulation examples and its practical applicability is validated through a shape measurement experiment. 相似文献
206.
We present a large-core planar optical waveguide design showing high group velocity dispersion (GVD). The design is based
on a coupled asymmetric dual-core structure with an additional layer of over cladding. The resonance between the two dissimilar
cores, namely, core-1 and core-2, has been utilized to achieve high GVD. The core separation controls the magnitude of the
GVD. The resonance wavelength can be fine tuned by varying the parameters of the core-2. The over-cladding helps in maintaining
high GVD even with large core-1. We show a GVD of 7.8×10−25 s2/mm with the core-1 size as large as 6 μm. Such a structure should find applications in the design of high-power integrated-optic
dispersion compensators for optical telecommunication and ultrafast waveguide lasers. 相似文献
207.
208.
The photophysical properties of a series of 3-(1′H-Indol-3′-yl)-1-phenylprop-2-en-1-one and its derivatives (indole chalcones) were studied in different solvents. Solvent effects
on the absorption and fluorescence spectra were quantified using Reichardt’s and bulk solvent polarity parameters and were
complemented by the results of the Kamlet-Taft treatment. The observed excited state dipole moment was found to be larger
than the ground state dipole moment of these chalcones. The correlation of the solvatochromic Stokes-shifts with the microscopic
solvent polarity parameter (ETN E_T^N ) was found to be superior to that obtained using bulk solvent polarity functions. 相似文献
209.
Kumar S Jain SK Sharma N Rastogi RC 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2001,57(2):299-308
The absorption and fluorescence spectra of some biologically active flavones have been studied as a function of the acidity (pH/H0) of the solution. Dissociation constants have been determined for the ground and first excited singlet states. The results are compared with those obtained from Forster-Weller calculations. The acidity constants obtained by fluorimetric titration method are in complete agreement (in most of the systems) with ground state data indicating a excited state deactivation prior to prototropic equilibration. Compared to umbelliferones, flavones are only weakly fluorescent in alkaline solution. This behaviour is explained by the small energy difference between the singlet excited state and triplet excited state giving rise to more efficient intersystem crossing. Most of the flavones studied here undergo adiabatic photodissociation in the singlet excited state indicating the formation of an exciplex or a phototautomer. 相似文献
210.
Quantum chemical predictions of the vibrational spectra of polyatomic molecules. The uracil molecule and two derivatives 总被引:1,自引:0,他引:1
Palafox MA Rastogi VK 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(3):411-440
This work describes the different scaling procedures used to correct the quantum-chemical theoretical predictions of the IR and Raman vibrational wavenumbers. Examples of each case are shown, with special attention to the uracil molecule and some derivatives. The results obtained with different semiempirical and ab initio methods, and basis sets, are compared and discussed. A comprehensive compendium of the main scale factors and scaling equations available to obtain the scaled wavenumbers is also shown. 相似文献