TBIR应用于航空胎侧胶的热氧老化性能

研究了反式-1,4-丁二烯-异戊二烯共聚橡胶(TBIR)应用于航空轮胎胎侧胶[天然橡胶(NR)/顺丁橡胶(BR)/TBIR]的耐热氧老化性能.结果表明,与NR/BR硫化胶相比,10～20份质量的TBIR取代BR后,NR/BR/TBIR硫化胶的交联密度明显提高,压缩温升降低2. 2～3. 4℃,耐屈挠疲劳性能提高约100%,填料分散性改善,填料团聚体体尺寸减小,拉伸性能基本不变.随热氧老化时间延长,硫化胶的交联密度先增加后降低,并用TBIR的硫化胶交联密度在老化48 h后趋于平缓.与NR/BR相比,老化后的NR/BR/TBIR硫化胶生热最低,耐屈挠疲劳性最高.     

江西相山铀矿区与非铀矿区稻谷中天然放射性核素含量对比研究

文章对比分析研究了江西相山铀矿区和非铀矿区稻谷中天然放射性核素U和Th的含量特征。样品分别采自江西省相山铀矿区及远离铀矿区的抚州市郊丘陵水稻种植区。结果表明相山铀矿区稻谷中天然放射性核素U的含量显著高于非铀矿区的稻谷,铀矿区内稻谷中放射性核素U含量平均值是非铀矿区的5.30倍;但铀矿区内稻谷中放射性核素Th的含量却较非铀矿区稻谷含量低,仅为其Th含量的50%。另外,相山铀矿区内稻谷中放射性核素U和Th之间存在较为显著的线性关系,稻谷中放射性核素Th的含量随U含量的增加而升高。铀矿区内稻谷中放射性核素U含量显著高于非铀矿区的原因还有待于进一步深入研究,然而加强该领域的研究对于保证我国区域稻谷质量和食品安全是非常重要和有意义的。     

天然竹红菌素粗品的光物理特性及机理分析

用SP-2558型光谱实验系统测得了天然竹红菌素粗品的三维荧光光谱,给出其随样品浓度变化的规律,进而利用软件和理论分析提出,天然竹红菌素粗品荧光光谱主要是竹红菌甲素（HA）和竹红菌乙素（HB）荧光光谱的贡献,HA的荧光光谱受其他成分影响较大,造成了短波峰的蓝移和长波峰的红移;HA与HB之间的辐射能量转移导致其荧光光谱中长波成分增加,从而形成较宽的谱段;由分子间氢键形成的多聚体会导致天然竹红菌素粗品溶液的发射峰随浓度的增加而红移,因而通过对天然竹红菌素粗品的浓度调控,可以在一定的范围内实现对发射光波段的调控,这对指导临床上的应用具有较高的参考价值。     

Crack detection of a double-beam carrying a concentrated mass

This paper presents the influence of a concentrated mass location on the natural frequencies of a cracked double-beam. The double-beam consists of two different beams connected by an elastic medium. The concentrated mass is located on the main beam. The relationship between the natural frequency and the location of concentrated mass is established and called “Frequency–Mass Location” (FML). The numerical simulations show that when there is a crack, the frequency of the double-beam changes irregularly when the concentrated mass is attacked at the crack position. This irregular change can be amplified by the wavelet transform and this is useful for crack detection: the crack location can be detected by the location of peaks in the wavelet transform of the FML. Finite element model for the cracked double-beam carrying a concentrated mass is presented and numerical simulations are also provided.     

The efect of the couple stress parameter and Prandtl number on the transient natural convection flow over a vertical cylinder

An analysis is performed to study transient free convective boundary layer flow of a couple stress fluid over a vertical cylinder, in the absence of body couples. The solution of the time-dependent non-linear and coupled governing equations is carried out with the aid of an unconditionally stable Crank–Nicolson type of numerical scheme. Numerical results for the steady-state velocity, temperature as well as the time histories of the skin-friction coefcient and Nusselt number are presented graphically and discussed. It is seen that for all flow variables as the couple stress control parameter, Co, is amplified, the time required for reaching the temporal maximum increases but the steady-state decreases.     

Formation of tryptanthrin compounds upon Oxone-induced dimerization of indole-3-carbaldehydes

Tryptanthrin is a natural product with numerous important pharmacological properties. Tryptanthrin and its analogs are commonly prepared by condensation of isatoic anhydride and isatin. In this Letter we investigate the formation of tryptanthrin derivatives upon Oxone-induced oxidative dimerization of indole-3-carbaldehydes.     

Elemental characterization of Suaeda mollis L. (Amaranthaceae) from Algerian rangelands using gamma-ray spectrometry

Present study was performed to measure the chemical status of Suaeda mollis L. (Amaranthaceae) that is widely browsed by livestock (sheep and goats) in Algerian arid rangelands. Gamma-ray spectrometry technique was performed to characterize some major and trace elements, e.g., calcium, potassium, sodium, iron, zinc, cobalt, europium, antimony, and terbium in this fodder-shrub. Results revealed that S. mollis had good levels of calcium, potassium, and cobalt to meet needs of sheep and goats. However, this species had substantial level of sodium above the recommended concentration for livestock. The potential toxins (europium, antimony and terbium) were within the safety-limits suggested by the National Research Council guidelines. The data obtained in the present study can be useful in the ration formulation for grazing livestock.     

Environmental radioactivity of soils and sediments: Egyptian sector of the Nile valley

The activity concentrations of natural ⁴⁰K, ²³²Th, and ²³⁸U in 89 soil and 84 sediment samples collected over the entire Egyptian Nile River basin including the Nile delta are reported based on the results of epithermal neutron activation analysis. The average activity concentrations of ⁴⁰K, ²³²Th, and ²³⁸U equal to 15.3?±?6.6, 15.6?±?11.1 and 220?±?31 Bq/kg, respectively, are significantly lower than those reported for the Upper Continental Crust, World Average Sediments as well as World Average Soils, suggesting the presence of a considerable portion of mafic material, most probably originating from the Ethiopian High Plateau. Their average activity concentrations are statistically the same in soil and sediments, indicating that the Nile sediments and soil material are of the same origin. The main goal of this study was not only to estimate the radiological hazards but also to show the influence of sedimentary material transportable by the Blue Nile from the Ethiopian High Plateau. The different hazard indices like the radium equivalent, gamma index, external hazard as well as the internal hazard show a low radiological exposure either on direct contact or if local mud bricks are used in the construction of dwellings.     

Application of Prins cyclization to the total synthesis of (+)-decytospolides A and B

(+)-Decytospolides A and B, natural products containing the tetrahydropyran skeleton, were synthesized via Prins cyclization as the key step.     

Natural convection heat transfer at reduced pressures

This paper experimentally studies the natural convection heat transfer characteristics on horizontal and vertical plates at pressures lower than atmospheric value. Eight different pressures ranging from 10Pa to 101.325kPa, and three heating loads were used in the experiments. It is found that natural convection heat transfer characteristics at reduced pressures are independent of the plate arrangements and present different behaviors in two pressure ranges, 10Pa < p < 1000Pa and p > 1000Pa. The experimental heat transfer results are correlated into a non-dimensional equation to help the thermal design of stratosphere aircrafts and airborne equipment.