Impact of gamma radiation and salinity on growth and K+/Na+balance in two populations of Medicago sativa(L.)cultivar Gabès

The perennial Medicago sativa cv.Gabès is widely grown on saline soils in Tunisian oases.Morphological and physiological analyses of two populations(Mareth and Gannouch)were conducted in order to study the effect of salinity and gamma radiation(350 Gy)inter-action on two populations of this species.It has been shown that the two irradiated populations of Medicago sativa are fairly tolerant to salt at growth phase compared to the non-irradiated.Exposure to gamma irradiation(350 Gy),alone or in combination with salt stress,increased significantly (p<0.00 1)shoot number,stem height and chlorophyll b pigment especially for the Gannouch population,while no change occurred for the Mareth population.The presence of salt to 9 g/1 affected significantly the root biomass and induced a reduc-tion of shoot development of both control and irradiated alfalfa populations.For all treatments,plants of two populations remained able to produce and to allocate dry matter to the different organs.The survey of Na+/K+ratio showed that the growth of the aerial organs of two non-irradiated populations was at least determined by a selectivity in favour of the K+ions r2=0.97 and r2=0.59 for Mareth and Gannouch non-irradiated populations,respectively).However,the rather weak correlation detected for the irradiated populations,par-ticularly for the irradiated Gannouch.seems to be the consequence of the effect of irradiation that improved potassium availability.essential element for growth and development.Results also showed that the two irradiated populations,especially the Mareth,accumu-lated Na+ions in its photosynthetic organs.This accumulation was associated with an improvement of foliar water content at a level of salinity around 5 g/1.Such a mechanism reflects probably an inclusive behaviour of the plants and a good aptitude to use the dominant ions(Na+)for the osmotic adjustment.However,the non-irradiated populations are unable to adjust their internal osmotic potential.Consequently,irradiated plants have probably adapted to the osmotic stress by either closing their stomata or increasing the osmotic pressure of the leaf cells.     

一种克服机械共振的功率放大电路

许多驱动机械装置的马达的功放电路，由于受到机械共振频率的限制，不能高速运行．本电路采用陷波器，对于机械共振频率进行限制，保证驱动系统在高速运行时的稳定性．     

Isolation of alkaloids fromAthrotaxis selaginoides

Summary A novel series of alkaloids has been obtained from the Tasmanian plantAthrotaxis selaginoides, the first to be isolated from the plant family Taxodiaceae.     

Degradation of phenylalanine in the presence of hydrogen peroxide.

UV-irradiation of phenylalanine by 253.7 nm light in the presence of hydrogen peroxide formed 5 ninhydrin reactive products and ammonia. Four of them were identified as aspartic acid, serine, alanine and lysine.     

低秩矩阵恢复模型改进及其在石油测井中的应用

传统的低秩矩阵恢复模型在去噪过程中通过将观测矩阵分解为低秩部分和稀疏部分达到噪声去除的目的,但该模型要求噪声矩阵必须是稀疏的。然而石油测井所获得的数据中噪声来源复杂,并不能完全保证噪声分布满足稀疏性的要求,使该模型在去噪时表现出一定的局限性,去噪效果不稳定,进而导致后续的数据处理准确率降低。为此,提出将加权范数的思想应用于传统的低秩矩阵恢复模型中,并在惩罚项中将F范数与待恢复矩阵的核范数相结合,构造改进的低秩矩阵恢复模型,使其能够在保证解的稳定性的同时,可以更好地挖掘观测矩阵的低秩性以及增强稀疏矩阵的稀疏性。通过非精确的拉格朗日乘子法分别对改进前后的模型进行求解,并对两种模型去噪后的测井数据分别采用支持向量机(SVM)和相关向量机(RVM)进行油气层识别,结果表明经改进的低秩矩阵恢复模型去噪后的测井数据在保证了油气层识别效率的同时,识别准确率上有了明显提升。     

Aluminium control of argon solubility in silicate melts under pressure

Understanding of the crystal chemistry of the Earth's deep mantle has evolved rapidly recently with the gradual acceptance of the importance of the effect of minor elements such as aluminium on the properties of major phases such as perovskite. In the early Earth, during its formation and segregation into rocky mantle and iron-rich core, it is likely that silicate liquids played a large part in the transport of volatiles to or from the deep interior. The importance of aluminium on solubility mechanisms at high pressure has so far received little attention, even though aluminium has long been recognized as exerting strong control on liquid structures at ambient conditions. Here we present constraints on the solubility of argon in aluminosilicate melt compositions up to 25 GPa and 3,000 K, using a laser-heated diamond-anvil cell. The argon contents reach a maximum that persists to pressures as high as 17 GPa (up to 500 km deep in an early magma ocean), well above that expected on the basis of Al-free melt experiments. A distinct drop in argon solubility observed over a narrow pressure range correlates well with the expected void loss in the melt structure predicted by recent molecular dynamics simulations. These results provide a process for noble gas sequestration in the mantle at various depths in a cooling magma ocean. The concept of shallow partial melting as a unique process for extracting noble gases from the early Earth, thereby defining the initial atmospheric abundance, may therefore be oversimplified.     

Atom-by-atom substitution of Mn in GaAs and visualization of their hole-mediated interactions

The discovery of ferromagnetism in Mn-doped GaAs has ignited interest in the development of semiconductor technologies based on electron spin and has led to several proof-of-concept spintronic devices. A major hurdle for realistic applications of Ga(1-x)Mn(x)As, or other dilute magnetic semiconductors, remains that their ferromagnetic transition temperature is below room temperature. Enhancing ferromagnetism in semiconductors requires us to understand the mechanisms for interaction between magnetic dopants, such as Mn, and identify the circumstances in which ferromagnetic interactions are maximized. Here we describe an atom-by-atom substitution technique using a scanning tunnelling microscope (STM) and apply it to perform a controlled study at the atomic scale of the interactions between isolated Mn acceptors, which are mediated by holes in GaAs. High-resolution STM measurements are used to visualize the GaAs electronic states that participate in the Mn-Mn interaction and to quantify the interaction strengths as a function of relative position and orientation. Our experimental findings, which can be explained using tight-binding model calculations, reveal a strong dependence of ferromagnetic interaction on crystallographic orientation. This anisotropic interaction can potentially be exploited by growing oriented Ga(1-x)Mn(x)As structures to enhance the ferromagnetic transition temperature beyond that achieved in randomly doped samples.     

玉米抗大斑病菌单基因系的建立及其在Exserohilum turcicum生理小种鉴定中的应用

利用美国A632,B37,B73,B68,C103,Va26等30个Ht单基因鉴别寄主, 按美国伊利诺伊大学的大田接种方案与鉴定方法, 建立了适合中国的监测玉米
大斑病菌生理小种鉴定的21个Ht单基因系. 从吉林省15个地区的不同玉米品种中采集玉米大斑病样本, 采用单孢分离获得了32个玉米大斑病菌菌株, 利用已建立的上述21个Ht单基因鉴别寄主, 通过美国的大田鉴定方案进行生理小种鉴定. 结果表明, 这32个菌株均为0号小种, 并未出现生理小种分化现象.