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11.
胶体粒子聚集速率常数实验值远低于理论值一直是被普遍关注的问题.聚集速率常数的理论推导是基于粒子的几何半径来考虑的,但决定粒子扩散速率及聚集速率的应该是粒子的流体力学半径(大于几何半径),因而它是使聚集速率常数实验值低于理论值的因素之一.影响流体力学半径的因素很多,其中,带电粒子在溶液中因表面存在双电层,会明显增大流体力学半径,造成聚集速率减慢.而双电层的厚度又随溶液中离子强度的不同而改变.本工作在聚集速率的公式中引入了修正因子,即几何半径与其流体力学半径之比,以修正由于用几何半径代替流体力学半径带来的误差.其中几何半径和流体力学半径可以分别用扫描电镜(SEM)和动态光散射(DLS)来测定.以两种粒径的聚苯乙烯带电微球为例,考察了在不同离子强度下,该误差的大小.结果发现,对于半径为30 nm的微球,用流体力学半径计算的慢聚集速率常数比理论值偏低约8%.该误差随离子强度增加而减少.对于快聚集情况,流体力学半径对聚集速率基本没有影响. 相似文献
12.
During the determination of the constitution of ekersenin isolated from Ekererbegia senegalensis, eight isomeric monomethoxy-monomethylcoumarins were synthesised. These studies proved that ekersenin was 4-methoxy-5-methylcoumarin, a constitution with novel biosynthetic implications. Apparently ekersenin is the first example of natural coumarin biosynthesis involving onlythepolyketide route. Comparative spectral correlations on substituted coumarins are summarised. 相似文献
13.
Amita Gupta Alexei Yu Ganin Parmanand Sharma Vikrant Agnihotri LM Belova KV Rao Mikhail E Kozlov AA Zakhidov RH Baughman 《Pramana》2002,58(5-6):1051-1059
We present studies of novel nanocomposites of BiNi impregnated into the structure of opals as well as inverse opals. Atomic force microscopy and high resolution elemental analyses show
a highly ordered structure and uniform distribution of the BiNi filler in the matrix. These BiNi-based nanocomposites are
found to exhibit distinct ferromagnetic-like ordering with transition temperature of about 675 K. As far as we know there
exists no report in literature on any BiNi compound which is magnetic. 相似文献
14.
Darshan C Kundaliya Reeta Vij AA Tulapurkar U Vaidya R Pinto RG Kulkarni 《Pramana》2002,58(5-6):1041-1044
Electrical resistance (R) measurements of a bulk La0.33Nd0.33Ca0.33MnO3 perovskite in magnetic fields up to 40 kOe have revealed anomalous temperature hysteretic effects both in 0 Oe and 20 kOe
magnetic fields. The sharp peak observed in the R vs. T plot indicates the occurrence of metal-to-insulator (M-I) transition at a temperature of T
MI=110 K and 140 K, for cooling and warming paths, respectively. An applied magnetic field of 20 kOe reduces the resistance
and shifts T
MI to 160 K and 185 K for cooling and warming, respectively. We have observed a much higher resistance in the cooling path than
in the warming path leading to the hysteretic resistance ratio (R
cool/R
warm) of 200 at 110 K and 1.8 at 160 K for 0 Oe and 20 kOe, respectively. Record values of colossal magnetoresistance (CMR) have
been achieved. The CMR value reaches nearly 99% in the temperature ranges of 90 K to 140 K and 90 K to 170 K for 20 kOe and
40 kOe magnetic fields in the cooling mode, respectively. The observed unusual behavior is attributed to the co-existence
of La-rich and Nd-rich domains assumed to be distributed randomly in the compound. 相似文献
15.
We have studied the peak effect (PE) phenomenon in single crystals of weakly pinned superconductors CeRu2 and 2H-NbS2. 2H-NbS2 is iso-structural and iso-electronic to 2H-NbSe2, whose similarity with CeRu2 as regards the PE representing the order-to-disorder transformation of the flux line lattice was claimed some time ago. We
report on the step change in equilibrium magnetization across the peak effect in CeRu2. We also present the vortex phase diagram of 2H-NbS2 obtained from the magnetization data, and compare the PE phenomenon in 2H-NbS2 and 2H-NbSe2. 相似文献
16.
Enyenihi AA Yang H Ytterberg AJ Lyutvinskiy Y Zubarev RA 《Journal of the American Society for Mass Spectrometry》2011,22(10):1763-1770
His64 and His93 are the two well-known sites of heme binding in water-dissolved holo-myoglobin, with His93 being a proximal,
strongly binding partner, while the distal His64 weakly coordinates to the heme through a small-molecule ligand, e.g., water
or O2. The heme bonding scheme in a water-free environment is as yet unclear. Here we employed electron transfer dissociation tandem
mass spectrometry to study the preferential attachment site of the ferri-heme (Fe3+) in electrospray-produced 12+, 14+, and 16+ holo-myoglobin ions. Contrary to expectations, in lower-charge complexes that
should have a structure resembling that in solution, the heme seems to be preferentially attached to the “distal” histidine.
In contrast, in the highest studied charge state, the “proximal” histidine is the site of preferential attachment; the 14+
charge state is an intermediate case. This surprising finding raises a question of heme coordination in proteins transferred
to water-free environment, as well as the effect of the protonation sites on heme bonding. 相似文献
17.
Olav Vahtras Hans rgren Hans Jrgen AA. Jensen 《Journal of computational chemistry》1994,15(6):573-579
The evaluation of gradient vectors of a general operator with one-index, double-one-index, or higher-order one-index transformed integrals is a key operation in multiconfiguration response theory calculations. We describe an integral-driven direct algorithm that carries out this operation efficiently without pretransforming the integrals. The use of this algorithm leads to a considerable reduction in disk space and timing. © 1994 by John Wiley & Sons, Inc. 相似文献
18.
A new series of 6,8-dibromo-2-(4-chlorophenyl)quinazolin-4(3H)-one derivatives VI–XIII were synthesized. Their chemical structures were confirmed by spectral and elemental analysis. The cytotoxic effect of the newly synthesized compounds was tested in vitro against human breast cancer cell line (MCF-7). Most of the tested compounds have shown promising cytotoxic activity. Compounds X and XIIIb exerted a powerful cytotoxic effect against MCF-7 with a very low IC50 (0.0015 and 0.0047 µmol/ml), while compounds VI, VII, VIII, XIIb, XI, XIIIc and IX exerted a moderate cytotoxic effect (IC50 0.01523, 0.0213, 0.031, 0.0478, 0.049, 0.068 and 0.079 µmol/ml respectively), compared to doxorubicin (0.0025 µmol/ml). Exploring their apoptotic effect; interestingly,all compounds activated apoptotic cascade in MCF-7. Compounds VI, XIIIb, XIIb, XI, XIIa, VII, V and VIII showed potent effect even much more than doxorubicin by 12.87–5.91 folds, while compounds XIIIc, IX, XIIIa, XIIc and X showed moderate increase in CASP3 activity by 4.96–3.22 folds relative to untreated cells more or less similar to doxorubicin (5.57 folds). 相似文献
19.
Obliquely propagating altra-low-frequency dust-electromagnetic waves in a self-gravitating, warm, magnetized, two fluid dusty
plasma system have been investigated. Two special cases, namely, dust-Alfvén mode propagating parallel to the external magnetic
field and dustmagnetosonic mode propagating perpendicular to the external magnetic field have also been considered. It has
been shown that effects of self-gravitational field, dust fluid temperature, and obliqueness significantly modify the dispersion
properties of these ultra-low-frequency dust-electromagnetic modes. It is also found that in parallel propagating dust-Alfvén
mode these effects play no role, but in obliquely propagating dust-Alfvén mode or perpendicular propagating dust-magnetosonic
mode the effect of self-gravitational field plays destabilizing role whereas the effect of dust/ion fluid temperature plays
stabilizing role. 相似文献
20.
It is shown how one can transform scalar first-order ordinarydifferential equations which admit non-local symmetries of theexponential type to integrable equations admitting canonicalexponential non-local symmetries. As examples we invoke theAbel equation of the second kind, the Riccati equation and naturalgeneralizations of these. Moreover, our method describes howa double reduction of order for a second-order ordinary differentialequation which admits a two-dimensional Lie algebra of generatorsof point symmetries can be affected if the second-order equationis first reduced in order once by a symmetry which does notspan an ideal of the two-dimensional Lie algebra. 相似文献