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991.
Jaspreet Sandhu Amit Kumar Singh Chauhan Govind 《Journal of nanoparticle research》2011,13(8):3503-3509
The room temperature growth of gallium atoms on the highly oriented pyrolytic graphite (HOPG) surface has been performed.
The gallium atoms were deposited by thermal evaporation method in an ultra high vacuum system at a base pressure 5 × 10−10 torr. The X-ray photo electron spectroscopy (XPS) studies had been performed to confirm the presence of gallium atoms on
HOPG surface. Scanning tunneling spectroscopy (STM) technique was employed to study the surface morphology of the clean HOPG
surface and gallium covered HOPG surfaces which recognize the formation of gallium induced nanostructures. The deconvoluted
XPS core level spectra of C (1s) and Ga (3d) demonstrate the possible interaction between substrate and the adsorbate atoms.
The STM analysis revealed that the gallium deposition on HOPG led to significant change in the surface morphology. It was
observed that the Ga atoms adsorbed as layer structure on HOPG surface for low coverage while quasi one-dimensional chain
like nanostructure (1 ± 0.2 nm) has been formed for higher Ga coverage. The nanostructured surfaces induced by Ga deposition
are found to be stable and could be used as a template for the growth of metallic nanostructures. 相似文献
992.
含油气的岩层被钻开以后,其中的油气一部分保留在岩样中,另一部分则进入钻井液,岩样中的油、气及钻井液中的气都有相应的录井方法来检测,唯独钻井液中的油一直是录井检测的空白. 随着油气勘探程度的加深及钻井工艺技术的发展,岩屑含油级别低甚至无显示、气测异常幅度低甚至无异常的油井是越来越多,导致油气层的发现与评价变得十分困难. 因此,急需对钻井液中的含油量进行随钻检测. 通过对不同油质、 不同含油量的钻井液进行磁共振试验,结果表明,可以通过核磁共振一维谱(T2谱)实现轻~中质油的含油量分析,通过二维谱(T2-D谱)以实现对重质油的含油量分析. 该项研究对于完善录井技术系列、提高油层发现率和评价准确率具有十分重要的意义. 相似文献
993.
994.
Ethynylated phenothiazine based fluorescent boronic acid probes were prepared. Sonogashira coupling reaction was used to introduce
substituted phenylethynylene fragments to the phenothiazine fluorophore to extend the π-conjugation and to enhance the emission
property. The photophysical properties and the binding properties of these probes with hydroxyl acids were investigated. We
found that the probes with significant ICT effect show emissions which are sensitive to solvent polarity. The phenothiazine
moiety is proved to be electron-donating. We found the substitution profile imparts significant effect on the photophysical
properties of the probes. For example, one of the probes shows d-PeT effect, whereas the regioisomer probe with similar π-conjugation
fragment but different substitution profile shows the a-PeT effect. The easy derivatization of phenothiazine fluorophore,
the structure-photophysical property relation and the novel d-PeT fluorescence transduction profile of the phenothiazine based
probes described herein may inspire more investigation into this fascinating research area. 相似文献
995.
Jung A. Jung Young Baek Kim Young A. Kim Seung Bum Ryu Veronica Kim 《Journal of nanoparticle research》2011,13(6):2361-2374
Functional spherical solid and hollow particles of polysilsesquioxanes (PSQs) containing amine, thiol, and vinyl groups were
prepared by polymerizing organotrialkoxysilanes (OTASs) containing corresponding chemical groups. Fluorescent PSQ particles
were prepared by physically entrapping Rhodamine 6G, Coumarin 7, and Fluoresceine sodium salts. The intensity of fluorescent
light increased initially with increasing amount of entrapped fluorophores and then leveled off or decreased slightly after
reaching a maximum value. PSQ particles containing gold nanoparticles (GNPs), both inside and on the surface, were prepared
by the in situ reduction of gold ions by the PSQ particles. When the reduction reaction was carried out for extended periods
of time, the GNP that had formed inside the poly(3-mercaptopropyl)silsesquioxane (PMPSQ) and polyvinylsilsesequioxane (PVSQ)
particles underwent interesting morphological changes. PSQ particles containing amine and thiol groups fixed the GNPs on the
surface, which could be utilized further in binding amine-modified oligo-DNA strands. The aggregation of PSQ/GNP particles
combined with complementary oligo-DNA strands was examined to demonstrate that these particles could be applied to DNA assays
and isolation. The particles were characterized by scanning electron microscopy, transmission electron microscopy, solid state
nuclear magnetic resonance spectroscopy, ultraviolet/visible spectroscopy, and fluorescence microscopy. 相似文献
996.
AlF3-coating is attempted to improve the performance of LiNi0.5Mn1.5O4 cathode materials for Li-ion batteries. The prepared powders are characterized by scanning electron microscope, powder X-ray
diffraction, charge/discharge, and impedance. The coated LiNi0.5Mn1.5O4 samples show higher discharge capacity, better rate capability, and higher capacity retention than the uncoated samples.
Among the coated samples, 1.0 mol% AlF3-coated sample shows highest capacity after charge–discharged at 30 mA/g for 3 cycles, but 4.0 mol% coated sample exhibits
the highest capacity and cycling stability when cycled at high rate of 150 and 300 mA/g. The 40th cycle discharge capacity
at 300 mA/g current still remains 114.8 mAh/g for 4.0 mol% AlF3-coated LiNi0.5Mn1.5O4, while only 84.3 mAh/g for the uncoated sample. 相似文献
997.
A dusty multi-ion plasma system consisting of non-isothermal (trapped) electrons, Maxwellian (isothermal) light positive ions,
warm heavy negative ions and extremely massive charge fluctuating stationary dust have been considered. The dust-ion-acoustic
solitary and shock waves associated with negative ion dynamics, Maxwellian (isothermal) positive ions, trapped electrons and
charge fluctuating stationary dust have been investigated by employing the reductive perturbation method. The basic features
of such dust-ion-acoustic solitary and shock waves have been identified. The implications of our findings in space and laboratory
dusty multi-ion plasmas are discussed. 相似文献
998.
We find sufficient conditions for the absence of harmonic L 2 spinors on spin manifolds constructed as cone bundles over a compact Kähler base. These conditions are fulfilled for certain perturbations of the Euclidean metric, and also for the generalized Taub-NUT metrics of Iwai-Katayama, thus proving a conjecture of Vi?inescu and the second author. 相似文献
999.
Dobek K 《Journal of fluorescence》2011,21(4):1547-1557
The influence of temperature varied in the range 183 K–323 K on the fluorescence quantum yield, fluorescence lifetime, absorption
and emission transition moments and non-radiative deactivation rate was determined for the well known and largely used dye
Coumarin 153, dissolved in 1-chloropropane. The Kennard-Stepanov relation connecting the absorption and emission spectra was
used to check for the presence of more than one absorbing/emitting species and to investigate whether intramolecular vibrational
redistribution completes in the C153 excited S
1 state before the emission takes place. The emission spectrum corresponding to S
1→S
0 transition, was fitted at each temperature to the model function including the information on the dye vibrational modes coupling.
In this way the displacement in equilibrium distance for the most active vibrational mode was determined for C153 in S
1 and in S
0. Using the temperature dependence of the fluorescence decay time and quantum yield, the non-radiative deactivation rate was
determined. Its temperature dependence was compared to that calculated using the theoretical model with the most active vibrational
mode displacement values taken from steady-state spectra analysis. The somewhat surprising dependence of the fluorescence
decay time and quantum yield on temperature was related to non-trivial coupling between low-frequency vibrational modes of
C153 in the excited and ground states. 相似文献
1000.
Performance of the backward wave oscillator (BWO) is greatly enhanced with the introduction of plasma. Linear theory of the
dispersion relation and the growth rate have been derived and analysed numerically for plasma-filled rippled wall rectangular
waveguide driven by sheet electron beam. To see the effect of plasma on the TM01 cold wave structure mode and on the generated frequency, the parameters used are: relativistic factor γ = 1.5 (i.e. v/c = 0.741), average waveguide height y
0 = 1.445 cm, axial corrugation period z
0 = 1.67 cm, and corrugation amplitude ε = 0.225 cm. The plasma density is varied from zero to 2 ×1012 cm − 3. The presence of plasma tends to raise the TM01 mode cut-off frequency (14 GHz at 2 ×1012 cm − 3 plasma density) relative to the vacuum cut-off frequency (5 GHz) which also causes a decrease in the group velocity everywhere,
resulting in a flattening of the dispersion relation. With the introduction of plasma, an enhancement in absolute instability
was observed. 相似文献