Experimental delineation of the “e” ⇌ I\bar 1 and “e” ⇌ C\bar 1 transformations in intermediate plagioclase feldspars

Approximately 125 hydrothermal annealing experiments have been carried out in an attempt to bracket the stability fields of different ordered structures within the plagioclase feldspar solid solution. Natural crystals were used for the experiments and were subjected to temperatures of ～650°C to ～1,000°C for times of up to 370 days at \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) =600 bars, or \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) =1,200 bars. The structural states of both parent and product materials were characterised by electron diffraction, with special attention being paid to the nature of type e and type b reflections (at h+k=(2n+1), l=(2n+1) positions). Structural changes of the type C \(\bar 1\) → I \(\bar 1\) , C \(\bar 1\) → “e” structure, I \(\bar 1\) → “e” and “e” structure → I \(\bar 1\) have been followed. There are marked differences between the ordering behaviour of crystals with compositions on either side of the C \(\bar 1\) ? I \(\bar 1\) transition line. In the composition range ～ An₅₀ to ～ An₇₀ the e structure appears to have a true field of stability relative to I \(\bar 1\) ordering, and a transformation of the type I \(\bar 1\) ? e has been reversed. It is suggested that the e structure is the more stable ordered state at temperatures of ～ 800°C and below. For compositions more albite-rich than ～ An₅₀ the upper temperature limit for long range e ordering is lower than ～ 750°C, and there is no evidence for any I \(\bar 1\) ordering. The evidence for a true stability field for “e” plagioclase, which is also consistent with calorimetric data, necessitates reanalysis both of the ordering behaviour of plagioclase crystals in nature and of the equilibrium phase diagram for the albite-anorthite system. Igneous crystals with compositions of ～ An₆₅, for example, probably follow a sequence of structural states C \(\bar 1\) → I \(\bar 1\) → e during cooling. The peristerite, Bøggild and Huttenlocher miscibility gaps are clearly associated with breaks in the albite, e and I \(\bar 1\) ordering behaviour but their exact topologies will depend on the thermodynamic character of the order/disorder transformations.     

Phenotypic plasticity of floral traits and pollination adaption in an alpine plant <Emphasis Type="Italic">Pedicularis siphonantha</Emphasis> D. Don when transplanted from higher to lower elevation in Eastern Himalaya

Phenotypic plasticity and/or pollinator-mediated selection may be responsible for the changes in floral traits of plants when they are forced to live in new conditions. Although the two events could be independent, we hypothesized that phenotypic plasticity in floral traits might help to coordinate plant-pollinator interactions and enhance plant reproductive success in changing habitats. To test this hypothesis, we investigated floral traits and pollination on three natural populations of a lousewort (Pedicularis siphonantha) ranging at different elevations, as well as two downward transplanted populations in Shangeri-La County and Deqin County, northwest Yunnan, China. The results indicated that floral traits, i.e. phenology, longevity, display size, corolla tube length and pollen production differed significantly among populations. Moreover, or the two transplanted populations, floral traits diverged from their original populations, but converged to their host populations. Although the phenotypic plasticity in floral traits might be a rapid response to abiotic factor such as warmer environment, the changes in floral traits were found to be well adapted to pollination environment of the host population. Compared with plants of their original habitats in higher elevation, the transplanted individuals advanced flowering time, shortened flower longevity, reduced floral display size and pollen production, received higher visiting frequency and yielded more seeds. These findings suggested that phenotypic plasticity of floral traits might help plants adjust their resource allocation strategy between preand post-pollination stages in response to harsh or temperate conditions, which might correspondingly meet a pollinator-poor or hyphen rich environment. This would be beneficial for the widely-distributed species to adapt to various environmental changes.     

Two-Micron All-Sky Survey J01542930+0053266: a new eclipsing M dwarf binary system

We report on Two-Micron All-Sky Survey (2MASS) J01542930+0053266, a faint eclipsing system composed of two M dwarfs. The variability of this system was originally discovered during a pilot study of the 2MASS Calibration Point Source Working Data base. Additional photometry from the Sloan Digital Sky Survey yields an eight-passband light curve from which we derive an orbital period of  2.639 0157 ± 0.000 0016  d. Spectroscopic followup confirms our photometric classification of the system, which is likely composed of M0 and M1 dwarfs. Radial velocity measurements allow us to derive the masses  (M₁= 0.66 ± 0.03 M_⊙; M₂= 0.62 ± 0.03 M_⊙)  and radii  (R₁= 0.64 ± 0.08 R_⊙; R₂= 0.61 ± 0.09 R_⊙)  of the components, which are consistent with empirical mass–radius relationships for low-mass stars in binary systems. We perform Monte Carlo simulations of the light curves which allow us to uncover complicated degeneracies between the system parameters. Both stars show evidence of Hα emission, something not common in early-type M dwarfs. This suggests that binarity may influence the magnetic activity properties of low-mass stars; activity in the binary may persist long after the dynamos in their isolated counterparts have decayed, yielding a new potential foreground of flaring activity for next generation variability surveys.     

Sedimentation cycles in a river-mouth tidal freshwater marsh

Tidal freshwater marshes are critical buffers that exist at the interface between watersheds and estuaries. Little is known about the physical dynamics of tidal freshwater marsh evolution. Over a 21-mo period, July 1995 to March 1997, measurements were made of biweekly sediment deposition at 23 locations in a 3.8-ha tidal freshwater marsh in the Bush River subestuary of the upper Chesapeake Bay. Biweekly accumulation showed high spatial and temporal variability, ranging from ?0.28 g cm^?2 to 1.15 g cm^?2. Spatial variability is accounted for by habitat differences including plant associations, elevation, and hydrology. Temporal variability is accounted for by interannual climate variability, the growth cycles of marsh plants, stream-marsh interactions, forest-marsh interactions, and animal activity.     

Gradients,Property Templates,and Land Use Change

The scarcity of historical individual-level data makes understanding historic land use decisions and the influence of physiochemical gradients on these decisions difficult. Here, we present several measures of early property agricultural quality based on commonly available data, including elevation and soil type. These analyses demonstrate the influence of physiochemical gradients on initial land division patterns in the Gywnns Falls watershed (Baltimore, Maryland). Moreover, we examine the influence of the template created by early property decisions on continuing human-driven landscape dynamics. This influence is illustrated by 1900-era forest cover patterns, park locations, and modern transportation networks.     

环雷州半岛近海表层沉积物有机碳分布及其控制因素分析

对环雷州半岛近海43个海底表层沉积物的总有机碳(TOC)、总氮(TN)、沉积介质条件(包括沉积物粒度)进行了分析,探讨了沉积物TOC、TN的区域分布特征以及影响有机碳分布的主要因素。结果表明,环雷州半岛近海海域海底表层沉积物有机碳含量在0～0.79%之间,平均值为0.26%。与中国其它近海海域相比,环雷州半岛大部分近海区域海底表层沉积物有机碳含量明显偏低,为有机质贫乏区,仅雷州半岛西南部流沙湾近海海域为TOC相对高值区。总氮含量也不高,在0.011%到0.100%之间,TOC与TN存在较强的正相关性,且平面上TOC与TN分布高度重合,显示氮元素主要以有机化合物形式存在。TOC/TN比值在5.1～14.3之间,表明沉积有机质具有陆源输入和海洋自生来源的混合特征,但以雷州半岛西侧北部及东侧中部海域受陆源有机质输入影响更大。大多数站位海底沉积物粒度构成以粉砂为主、粘土次之,少数站位以砂质沉积为主。沉积物有机碳含量与粘土及粉砂含量呈弱正相关性,与沉积物pH值、Eh值及砂含量呈弱负相关性,这表明海底沉积物有机质丰度受有机质来源输入、海底氧化还原状态和沉积水动力条件(沉积物粒度)等因素综合控制。