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81.
Thermal conductivity of YBa2Cu3O7 has been measured on samples of a few mm thickness. AboveT
c thermal conductivity is found to decrease with increase in temperature, pointing towards a contribution to thermal resistivity
from three-phonon Umklapp processes. BelowT
c thermal conductivity increases rapidly before reaching a maximum at about 50 K and then falls towards zero at lower temperatures.
The experimental set up is described and results discussed. 相似文献
82.
83.
A. Antony Muthu Prabhu S. Siva R. K. Sankaranarayanan N. Rajendiran 《Journal of fluorescence》2010,20(1):43-54
The photophysical behaviour of 2,6-diaminopyridine (DAP) has been studied in solvents of different polarity, pH, β-cyclodextrin
(β-CD) and compared with 2-amino pyridine (2AP). The inclusion complex of both molecules with β-CD are analysed by UV-visible,
fluorimetry, FT-IR, 1H NMR, SEM and AM1 methods. The solvent studies shows i) DAP gives more red shifted absorption and emission maxima than 2AP
molecule and ii) addition of amino group in 2AP effectively increase the resonance interaction in the pyridine ring. A regular
red shift observed in acidic pH solutions suggests intramolecular proton transfer (IPT) present in both molecules. β-CD studies
indicates i) in pH ~ 7, a regular red shifted absorption and emission maxima observed in AP molecules suggests pyridine ring
encapsulated in to the β-CD cavity (1:1 inclusion complex formed) and ii) in pH ~ 1, a blue shifted absorption maxima noticed
in 2AP, is due to protonated amino group deeply encapsulated in to the hydrophobic part of the β-CD cavity. 相似文献
84.
Ashok Kumar Baral V. Sankaranarayanan 《Applied Physics A: Materials Science & Processing》2010,98(2):367-373
The nanocrystalline material of 15 mol% Gd-doped ceria (Ce0.85Gd0.15O2−δ
) was prepared by citrate auto ignition method. The electrical study and dielectric relaxation technique were applied to investigate
the ionic transport process in this nanocrystalline material with an average grain size of 13 nm and the dynamic relaxation
parameters are deduced in the temperature range of 300–600°C. The ionic transference number in the material is found to be
0.85 at 500°C at ambient conditions. The oxygen ionic conduction in the nanocrystalline Ce0.85Gd0.15O2−δ
material follows the hopping mechanism. The grain boundary relaxation is found to be associated with migration of charge
carriers. The frequency spectra of modulus M″ exhibited a dielectric relaxation peak corresponding to defect associates
(Gd-Vo\blacksquare \blacksquare)\blacksquare(\mathrm{Gd}\mbox{-}\mathrm{V}_{\mathrm{o}}^{_{_{{\blacksquare\,\blacksquare}}}})^{_{_{{\blacksquare}}}}. The material exhibits very low values of migration energy and association energy of the oxygen vacancies in the long-range
motion, i.e., 0.84 and 0.07 eV, respectively. 相似文献
85.
Jeremy H Toyn Xu-Alan Lin Mark W Thompson Valerie Guss Jere E Meredith Jr Sethu Sankaranarayanan Nestor Barrezueta John Corradi Antara Majumdar Daniel L Small Melissa Hansard Thomas Lanthorn Ryan S Westphal Charles F Albright 《BMC neuroscience》2010,11(1):1-12
Background
The zebrafish visual system is a good research model because the zebrafish retina is very similar to that of humans in terms of the morphologies and functions. Studies of the retina have been facilitated by improvements in imaging techniques. In vitro techniques such as immunohistochemistry and in vivo imaging using transgenic zebrafish have been proven useful for visualizing specific subtypes of retinal cells. In contrast, in vivo imaging using organic fluorescent molecules such as fluorescent sphingolipids allows non-invasive staining and visualization of retinal cells en masse. However, these fluorescent molecules also localize to the interstitial fluid and stain whole larvae.Results
We screened fluorescent coumarin derivatives that might preferentially stain neuronal cells including retinal cells. We identified four coumarin derivatives that could be used for in vivo imaging of zebrafish retinal cells. The retinas of living zebrafish could be stained by simply immersing larvae in water containing 1 μg/ml of a coumarin derivative for 30 min. By using confocal laser scanning microscopy, the lamination of the zebrafish retina was clearly visualized. Using these coumarin derivatives, we were able to assess the development of the zebrafish retina and the morphological abnormalities induced by genetic or chemical interventions. The coumarin derivatives were also suitable for counter-staining of transgenic zebrafish expressing fluorescent proteins in specific subtypes of retinal cells.Conclusions
The coumarin derivatives identified in this study can stain zebrafish retinal cells in a relatively short time and at low concentrations, making them suitable for in vivo imaging of the zebrafish retina. Therefore, they will be useful tools in genetic and chemical screenings using zebrafish to identify genes and chemicals that may have crucial functions in the retina. 相似文献86.
V. K.?Sankaranarayanan D. Y.?Kim S. M.?Yoon C. O.?Kim C. G.?KimEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,45(2):203-206
Effect of low energy ion beam etching on exchange bias in NiFe/FeMn/NiFe
trilayer is investigated in multilayers prepared by rf magnetron sputtering.
Stepwise etching and magnetization measurement of FeMn layer in an NiFe/FeMn
bilayer show increase of bias as etching proceeds and FeMn thickness
decreases. The bias show a maximum around 7 nm FeMn thickness and then fall
sharply below 5 nm, broadly in line with the exchange bias variation at
increasing FeMn thickness but in reverse order, particularly at low FeMn
thickness. Progressive etching of top NiFe layer in the NiFe/FeMn/NiFe
trilayer shows an initial gradual increase in bias followed by a sharp
increase below 7 nm thickness of top NiFe layer, with a maximum at 2 nm
thickness for both NiFe layers and greater bias for seed NiFe layer. 相似文献
87.
C. Krishnamoorthy K. Sethupathi V. Sankaranarayanan R. Nirmala S. K. Malik 《Journal of nanoparticle research》2007,9(5):765-776
Nanocrystalline samples with an average particle size of 40 and 52 nm have been synthesized by citrate-complex auto-ignition
method. Magnetic properties of the samples show para- to ferromagnetic transition at around 135 K. The electron magnetic resonance
(EMR) study on these samples indicates the presence of coexistence of two magnetic phases below 290 K. Electrical resistivity
follows variable range hopping (VRH) mechanism in the paramagnetic regime. The magnetoresistance (MR) data has been analysed
by spin dependent hopping between the localized spin clusters together with the phase-separation phenomenon. These clusters
are assumed to be formed by distribution of canted spins and defects all over the nanoparticle. In addition, the hopping barrier
depends on the magnetic moment orientation of the clusters. The magnetic moments of the clusters are narrowly oriented in
ferro- and are randomly oriented in paramagnetic phase. The ferromagnetic phase contributes to the total MR at low applied
magnetic fields whereas the paramagnetic phase contributes at relatively high fields in both the samples. The average cluster
size in ferromagnetic phase is bigger than that in paramagnetic phase. It is also observed that the cluster size, in ferromagnetic
phase, in 52 nm sample is bigger than that in the 40 nm sample. However, the average cluster size in paramagnetic phase is
almost same in both the samples. 相似文献
88.
Fabrication of polystyrene hollow microspheres as laser fusion targets by optimized density-matched emulsion technique and characterization 总被引:3,自引:0,他引:3
Inertial confinement fusion, frequently referred to as ICF, inertial fusion, or laser fusion, is a means of producing energy
by imploding small hollow microspheres containing thermonuclear fusion fuel. Polymer microspheres, which are used as fuel
containers, can be produced by solution-based micro-encapsulation technique better known as density-matched emulsion technique. The specifications of these microspheres are very rigorous, and various aspects of the emulsion hydrodynamics associated
with their production are important in controlling the final product. This paper describes about the optimization of various
parameters associated with density-matched emulsion method in order to improve the surface smoothness, wall thickness uniformity
and sphericity of hollow polymer microspheres. These polymer microshells have been successfully fabricated in our lab, with
3–30 μm wall thickness and 50–1600 μm diameters. The sphericity and wall thickness uniformity are better than 99%. Elimination
of vacuoles and high yield rate has been achieved by adopting the step-wise heating of W1/O/W2 emulsion for solvent removal. 相似文献
89.
N. Sankaranarayanan K. Chandrasekaran G. Ramaiyan 《Journal of sound and vibration》1985,99(3):351-360
Free vibrations of laminated annular plates with a linear variation in thickness in the radial direction are analyzed. An energy method based on the Rayleigh-Ritz technique is used for the analysis. Displacement functions which are polynomials in the radial co-ordinate are assumed. The resulting generalized eigenvalue problem is solved by a simultaneous iteration technique. Comparison of the results are made with available results in the literature. Extensive parametric studies are undertaken to provide an insight into the interaction and influence of the various geometric and material parameters on the frequencies and mode shapes. 相似文献
90.
The conventional type of magnetic well is formed by superposition of two types of magnetic field, axial bumpy field and radial
multipole field. It is used to contain plasma that consists of neutrals, ions and electrons. These particles are in constant
motion in the well and energetic electrons create plasma by violent collisions with neutrals and ions. The confined electrons
are constantly heated by ECR technique in the presence of magnetic field. In this paper it has been shown theoretically that
how the electron motion is influenced in terms of heating, containment and azimuthal uniformity of plasma, by the axial rotation
of the multipole magnetic field [1,2]. Afterwards, the feasibility of achieving a rotating magnetic multipole field is discussed
to some extent. And it is seen that it is not beyond the capability of the scientific community in the present scenario of
the advanced technology. Presently, it can be achieved for lesser field and slightly larger size of the multipole electromagnet
and can be used for improvement of the ECR ion source (ECRIS). 相似文献