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151.
152.
We have studied the temperature dependence of the stacking periodicity, d, of oriented phospholipid multilayers using grazing angle neutron scattering techniques. d is found to increase substantially at higher temperatures, just before the bilayers peel off from the substrate. Although we do not observe thermal unbinding, our results are consistent with the notion that the unbinding transition is driven by steric repulsion arising from thermal fluctuations of the membranes, in contrast to those of a recent study by Vogel et al. [Phys. Rev. Lett. 84, 390 (2000)]. 相似文献
153.
We report the observation of a cholesterol-induced modulated phase (Pbeta) in dipalmitoyl phosphatidylcholine bilayers. It occurs below the main transition of the lipid at cholesterol concentrations of around 15 to 20 mol % and is distinct from the ripple (Pbeta') phase found in between the main and pretransitions at lower cholesterol concentrations. An electron density map of this phase, constructed from x-ray diffraction data from oriented multilayers, shows that the bilayers in this phase have a one-dimensional periodic height modulation with an amplitude of about 2.5 A. A partial phase diagram of the system deduced from diffraction data is in broad agreement with earlier studies. 相似文献
154.
Y Hariharan M P Janawadkar T S Radhakrishnan A L E Terrance G A Dixit V S Raghunathan 《Pramana》1986,26(6):513-524
Titanium-rich transition metal alloys are metastable in their quenched boc β phase. The instability is relieved by low temperature
structural transformations. We have investigated this in a series of Ti-Nb alloys, through the measurements of electrical
resistivity (ρ), superconducting transition temperature and upper critical field. Supporting structural evidence has been
obtained from transmission electron microscopy (tem) and x-ray studies. It is shown that both ρ and dρ/dT can be used as useful indices of this instability. The enhanced value of resistivity on account of the instability results
in the enhancement of upper critical field as shown from dH
c2/dT measurements. 相似文献
155.
N Chandrabhas A K Sood D Sundararaman S Raju V S Raghunathan GVN Rao V S Sastry T S Radhakrishnan Y Hariharan A Bharathi C S Sundar 《Pramana》1994,42(5):375-385
The structure of multilayered carbon tubules has been investigated by electron microscopy and X-ray diffraction. The structure
of tubules is characterized by disorder in the stacking of cylindrical graphene sheets. Raman scattering measurements have
been carried out in tubules and compared with graphite. The observed features in the Raman spectra in tubules can be understood
in terms of the influence of disorder. The additional Raman modes predicted for single layer carbon tubules have not been
observed. 相似文献
156.
S. Selladurai K. Muthukkumaran P. Kuppusami R. Divakar E. Mohandas V. S. Raghunathan 《Ionics》2006,12(6):365-370
Microstructural characterization of thin films of 5 mol% gadolinia doped ceria films deposited by pulsed laser ablation in
the energy range 100–600 mJ/pulse has been investigated, as deposited films were found to be nanocrystalline with preferred
orientation. X-ray diffraction analysis revealed that the size of the nanocrystals of doped ceria does not vary significantly
with increasing laser energy, whereas transmission electron microscopy study showed a uniform distribution of nanocrystal
of 8–10 nm for energies ≤200 mJ/pulse and nanocrystals embedded in a large crystalline matrix of doped ceria for energies
in the range 400–600 mJ/pulse. Although the laser-ablated films were totally free from secondary phases, lattice imaging of
the large grained doped ceria showed growth-induced defects, such as dislocations and ledges. 相似文献
157.
158.
159.
160.
The novel bicyclic pentadentate ligand 5-methyl-1,5,9,24,25-pentaazapentacyclo[7.7.7.5.5]pentacosane11,13,15,18(25),20,22-hexene (L1) has been synthesized. Because of its cross-bridged topology it exhibits a relatively rigid preorganized conformation especially appropriate to complex formation, as shown by the crystal structure of the monoprotonated ligand salt, HL1ClH2O [orthorhombic, P212121, a = 9.4405(5) A, b = 13.3617(5) A, c = 16.710(1) A]. The complexes of L1 with both iron(II) and manganese(II) have been characterized, including the crystal structures of [FeL1CH3CN][FeCL4] and [MnL1Cl][PF6] [monoclinic, P21/n, a = 10.0460(5) A, b = 19.237(9) A, c = 15.6254(8) A, beta = 95.97(2)degrees and a = 7.745(2) A, b = 22.786(4) A, c = 14.639(4) A, beta = 105.074(10)degrees respectively]. The manganese complex is high spin with mueff = 5.96 and theta = 2.5 +/- 0.8 cm(-1), indicating weak ferromagnetic interactions. The reactions of the complexes with tert-butyl hydroperoxide and hydrogen peroxide have been shown by ESR spectroscopy to produce the tert-butyl peroxyl and hydroperoxyl radicals, as evidenced by their spin adducts with the spin traps N,N-dimethyl-1-pyrroline-N-oxide and N-tert-butyl-phenyl-nitrone. 相似文献