Mars' volatile and climate history.

There is substantial evidence that the martian volatile inventory and climate have changed markedly throughout the planet's history. Clues come from areas as disparate as the history and properties of the deep interior, the composition of the crust and regolith, the morphology of the surface, composition of the present-day atmosphere, and the nature of the interactions between the upper atmosphere and the solar wind. We piece together the relevant observations into a coherent view of the evolution of the martian climate, focusing in particular on the observations that provide the strongest constraints.     

Biomineralization and magnetism of bacterial magnetosomes

Magnetosomes of magnetotactic bacteria are of great interest in understanding biomiueralizatiou and possible links between organisms and geomagnetic field. Fossil maguetosomes are ubiquitous in marine and lake sediments and may significantly contribute to magnetic signals. In this review, we firstly introduce some characteristics of magnetotactic bacteria, followed by considering recent progress in maguetosome formation, magnetic measurements, and identification of bacterial magnetites in bulk sediments as well as their paleoenviroumeutal implications. Finally, we briefly discuss potential future breakthroughs in magnetosome studies and its applications.     

Fe掺杂TiO2结构和磁性

在退火温度为773K、Fe掺杂量为n(Fe)/n(Fe+Ti)=1∶25的制备条件下,用溶胶-凝胶法在空气氛围中制备Fe掺杂TiO2稀磁半导体纳米粉末;用直流磁控溅射方法并在真空和空气氛围中结合原位退火工艺,在普通玻璃基片上制备Fe掺杂TiO2薄膜.利用X射线衍射仪(XRD)对其结构进行表征,振动样品磁强计(VSM)对磁性进行表征.结果表明,溶胶-凝胶法制备的粉末材料的磁性为室温顺磁性;直流磁控溅射法制备的薄膜样品在空气和真空氛围中均为室温铁磁性,其中真空退火能够产生更强的铁磁性.这说明可能是薄膜和基底的相互作用产生和铁磁性至关重要的氧空位,而真空环境退火能够增加氧空位.     

电与磁在教学中的对称性

在大学物理教学中，相关对称性的教学内容很多，但电与磁间的对称性更为广泛，掌握其内在联系的对称性，对提高教学效率更有意义。     

First-principles studies for magnetism in Cu-doped GaN

Hole carrier mediated magnetization in Cu-doped GaN is investigated by using the first-principles calculations.By studying the sp-d interaction and the direct exchange interaction among the dopants,we obtain an equation to determine the spontaneous magnetization as a function of the Cu dopant concentration and the hole carrier density.It is demonstrated that nonmagnetic Cu doped GaN can be of room-temperature ferromagnetism.The system’s Curie temperature Tc can reach about 345 K with Cu concentration of 1.0% and hole carrier density of 5.0×1019 cm-3.The results are in good agreement with experimental observations and indicate that ferromagnetism in this systems is tunable by controlling the Cu concentration and the hole carrier density.     

Lanthanide contraction and magnetism in the heavy rare earth elements

The heavy rare earth elements crystallize into hexagonally close packed (h.c.p.) structures and share a common outer electronic configuration, differing only in the number of 4f electrons they have. These chemically inert 4f electrons set up localized magnetic moments, which are coupled via an indirect exchange interaction involving the conduction electrons. This leads to the formation of a wide variety of magnetic structures, the periodicities of which are often incommensurate with the underlying crystal lattice. Such incommensurate ordering is associated with a 'webbed' topology of the momentum space surface separating the occupied and unoccupied electron states (the Fermi surface). The shape of this surface-and hence the magnetic structure-for the heavy rare earth elements is known to depend on the ratio of the interplanar spacing c and the interatomic, intraplanar spacing a of the h.c.p. lattice. A theoretical understanding of this problem is, however, far from complete. Here, using gadolinium as a prototype for all the heavy rare earth elements, we generate a unified magnetic phase diagram, which unequivocally links the magnetic structures of the heavy rare earths to their lattice parameters. In addition to verifying the importance of the c/a ratio, we find that the atomic unit cell volume plays a separate, distinct role in determining the magnetic properties: we show that the trend from ferromagnetism to incommensurate ordering as atomic number increases is connected to the concomitant decrease in unit cell volume. This volume decrease occurs because of the so-called lanthanide contraction, where the addition of electrons to the poorly shielding 4f orbitals leads to an increase in effective nuclear charge and, correspondingly, a decrease in ionic radii.     

稀土元素在光、电、磁方面的研究应用进展

综述了稀土元素在光、电、磁方面的应用，并对其应用进展情况作了分析和研究，指出稀土元素及其化合物表现出了许多独特的光、电、磁学性质，使得它在工、农业生产，现代高科技研究及国防现代化建设中有着十分广泛的应用前景．近年来，国内外开展了广泛的研究开发工作，特别是在新型功能材料方面，并取得了一系列的重要成果．     

The electronic structures, magnetism and metastable states of DNA

Molecular devices are the ultimate goal in the miniaturization of the electronic technology. Based on the unique properties of DNA (e.g. self-assembly and molecular recognition), people have made great efforts to develop molecular devices in the last few …     

CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap

The martian polar caps are among the most dynamic regions on Mars, growing substantially in winter as a significant fraction of the atmosphere freezes out in the form of CO2 ice. Unusual dark spots, fans and blotches form as the south-polar seasonal CO2 ice cap retreats during spring and summer. Small radial channel networks are often associated with the location of spots once the ice disappears. The spots have been proposed to be simply bare, defrosted ground; the formation of the channels has remained uncertain. Here we report infrared and visible observations that show that the spots and fans remain at CO2 ice temperatures well into summer, and must be granular materials that have been brought up to the surface of the ice, requiring a complex suite of processes to get them there. We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth.     

No signature of clear CO2 ice from the 'cryptic' regions in Mars' south seasonal polar cap

The seasonal polar ice caps of Mars are composed mainly of CO2 ice. A region of low (< 30%) albedo has been observed within the south seasonal cap during early to mid-spring. The low temperature of this 'cryptic region' has been attributed to a clear slab of nearly pure CO2 ice, with the low albedo resulting from absorption by the underlying surface. Here we report near-infrared imaging spectroscopy of the south seasonal cap. The deep and broad CO2 absorption bands that are expected in the near-infrared with a thick transparent slab of CO2 ice are not observed. Models of the observed spectra indicate that the low albedo results from extensive dust contamination close to the surface of a CO2 ice layer, which could be linked to atmospheric circulation patterns. The strength of the CO2 absorption increases after mid-spring, so part of the dust is either carried away or buried more deeply in the ice layer during the CO2 ice sublimation process.     

Evidence from the Mars Express High Resolution Stereo Camera for a frozen sea close to Mars' equator

It is thought that the Cerberus Fossae fissures on Mars were the source of both lava and water floods two to ten million years ago. Evidence for the resulting lava plains has been identified in eastern Elysium, but seas and lakes from these fissures and previous water flooding events were presumed to have evaporated and sublimed away. Here we present High Resolution Stereo Camera images from the European Space Agency Mars Express spacecraft that indicate that such lakes may still exist. We infer that the evidence is consistent with a frozen body of water, with surface pack-ice, around 5 degrees north latitude and 150 degrees east longitude in southern Elysium. The frozen lake measures about 800 x 900 km in lateral extent and may be up to 45 metres deep--similar in size and depth to the North Sea. From crater counts, we determined its age to be 5 +/- 2 million years old. If our interpretation is confirmed, this is a place that might preserve evidence of primitive life, if it has ever developed on Mars.