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991.
Two novel noncentrosymmetric borates oxides, MBi2B2O7 or MBi2O(BO3)2 (MCa, Sr), have been synthesized by solid-state reactions in air at temperatures in the 600-700 °C range. Their crystal structures have been determined ab initio and refined using powder neutron diffraction data. CaBi2B2O7 crystallizes in the orthorhombic Pna21 space group with a=8.9371(5) Å, b=5.4771(3) Å, c=12.5912(7) Å, Z=4, Rwp=0.118, χ2=2.30. SrBi2B2O7 crystallizes in the hexagonal P63 space group with a=9.1404(4) Å, c=13.0808(6) Å, Z=6, Rwp=0.115, χ2=4.15. Large displacement parameters suggest the presence of disorder in SrBi2B2O7 as also revealed by diffuse 2×a superstructure reflections in electron diffraction patterns. Both structures are built of identical (001) neutral layers of corner-sharing BO3 triangles and MO6 trigonal prisms forming six-membered rings in which Bi2O groups are located. Adjacent layers are stacked in a staggered configuration and connected through weak Bi-O bonds. A moderate efficiency for second harmonic generation (SHG) has been measured for a powder sample of CaBi2B2O7 (deff=2deff(KDP)). 相似文献
992.
The phase behavior of DOPE/DOTAP-DNA complexes in phase-separated oil(dodecane)/water mixtures was explored using Small Angle
X-Ray Scattering (SAXS) and Fluorescence Correlation Spectroscopy (FCS). Inverse micelles of DNA with cationic-lipid coating
were found in the oil phase. Varying the ratio between cationic and neutral lipids a transition from wormlike to spherical
structures is observed for both long ( ≈ 75000bp) and short (30-1246bp) DNA. In contrast to lipid/DNA complexes in the water
phase, there is no indication of condensed liquid-crystalline structures in the non-polar phase. In fact, FCS measurements
on short DNA oligomers complexed with cationic lipid in alkane give clear evidence for monomeric inverse micelles of DNA.
Dilution series revealed a critical lower concentration of lipids and DNA for observing lipid/DNA micelles. 相似文献
993.
994.
Hasan M. Khan Muhammad Ismail Muhammad Abid Zia Khalid Khan 《Isotopes in environmental and health studies》2013,49(2):295-301
The analysis of gamma-emitting radionuclides in nature, i.e. 226Ra, 232Th, 40K and 137Cs, has been carried out in soil samples collected from Peshawar University Campus and surrounding areas using a high purity germanium detector coupled with a computer-based high-resolution multichannel analyser. The activity concentrations in soil ranged from 30.20±0.65 to 61.90±0.95, 50.10±0.54 to 102.80±1.04, 373.60±4.56 to 1082±11.38 and 9.50±0.11 to 46.60±0.42 Bq kg?1 for 226Ra, 232Th, 40K and 137Cs, with a mean value of 45±7.70, 67±12.50, 878±180 and 19±9.20 Bq kg?1, respectively. The radium equivalent activity, internal and external hazard indices have mean values of 203.40±29.40 Bq kg?1, 0.56 and 0.68, respectively. The mean values of outdoor and indoor absorbed dose rates in air and the annual effective dose equivalents were found to be 106.50 and 128 nGy h?1 and 0.19 and 0.54 mSv y?1, respectively. In the present study, 40K was the major radionuclide present in soil samples. The presence of 137Cs indicates that this area also received some fallout from the nuclear accident of the Chernobyl power plant in 1986. The activity concentrations of radionuclides found in soil samples during the current investigation were nominal. Therefore, they are not associated with any potential source of health hazard to the public. 相似文献
995.
In the framework of the relativistic mean field theory (RMFT), the relativistic energy losses of the direct Urca processes withhyperons (Y-DURCA) for reactionsΛ→p + e +\bar{\nu}_{e} andΞ- →Λ + e +νe arestudied in neutron stars. We calculate the energy gap ofΛ hyperons and investigate the effects of the 1S0superfluidity (SF) ofΛ hyperons on the Y-DURCA processes. The calculated results are in line with the recent experimental data\Delta BΛΛ∽1.01±0.20+0.18-0.11 MeV.The results indicate that the 1S0 SF ofΛ hyperons exists in most density ranges of happening the two reactions. The
theoretical cooling curves are in agreement with observation data. 相似文献
996.
In this Perspective article we review retrospectively the streamline of our work on iron-based superconductors, and reflect on the mechanism of Cooper pairing in conventional and unconventional, such as iron-based superconductors. The main theme of this review is the concept of effective interaction and renormalization group. 相似文献
997.
998.
999.
研究有限域 上一类方程 , , 的解数. 在保持方程系数不变的前提下, 通过对其次数矩阵进行有效降次, 可以改进对原方程解数的各种估计. 若对方程未知变量和系数进行适当限定, 则可将其化为椭圆曲线方程, 从而利用Hasse定理得到原方程解数的一个精确界. 相似文献
1000.
A New Higher Order Shear Deformation Model for Static Behavior of Functionally Graded Plates 下载免费PDF全文
Tahar Hassaine Daouadji Abdelouahed Tounsi & El Abbes Adda Bedia 《advances in applied mathematics and mechanics.》2013,5(3):351-364
In this paper, a new displacement based high-order shear deformation theory is introduced
for the static response of functionally graded plate. Unlike any other theory, the number
of unknown functions involved is only four, as against five in case of other shear deformation
theories. The theory presented is variationally consistent, has strong similarity with
classical plate theory in many aspects, does not require shear correction factor, and
gives rise to transverse shear stress variation such that the transverse shear stresses
vary parabolically across the thickness satisfying shear stress free surface conditions.
The mechanical properties of the plate are assumed to vary continuously in the thickness
direction by a simple power-law distribution in terms of the volume fractions of the
constituents. Numerical illustrations concerned flexural behavior of FG plates with
Metal-Ceramic composition. Parametric studies are performed for varying ceramic volume
fraction, volume fraction profiles, aspect ratios and length to thickness ratios. The
validity of the present theory is investigated by comparing some of the present results
with those of the classical, the first-order and the other higher-order theories. It
can be concluded that the proposed theory is accurate and simple in solving the static
behavior of functionally graded plates. 相似文献