Low-temperature study of natural melilite (Ca1.89Sr0.01Na0.08K0.02) (Mg0.92Al0.08)(Si1.97Al0.03)O7: towards a commensurate value of the q vector

As is usual for peculiar chemical compositions, melilite-type compounds exhibit a two-dimensional incommensurately modulated structure which can be described with two wave vectors: q ₁ =(a* + b*) and q ₂ =(–a* + b*), where a* and b* are the tetragonal reciprocal axes of the basic cell. The low-temperature dependence of the modulation wave vector of a natural melilite crystal with chemical composition (Ca_1.89Sr_0.01 Na_0.08K_0.02)(Mg_0.92Al_0.08)(Si_1.97Al_0.03)O₇ has been studied by X-ray single-crystal diffraction methods in the temperature range 298–100 K. The value of the coefficient shows a continuous linear increase, ranging from 0.281(1) at 298 K to 0.299(1) at 100 K. No plateau-like temperature dependence was observed throughout the temperature studied, thus indicating that no independent phase with a specific q stabilizes in this natural crystal. A comparison with the low-temperature behaviour of synthetic Ca₂MgSi₂O₇ is given.     

金刚石优化钻进的新途径

选择了优化钻进的衡量参数（ｈ／ｐ）／ｑ，并以此多数对具体岩石优选了钻头，对具体岩石和钻头优选了合理的钻头每转进尺范围。     

On the red coloration of saltern crystallizer ponds. II. Additional evidence for the contribution of halobacterial pigments

In a previous paper we attempted to assess the contribution of red bacteria of theHalobacterium — Haloferax — Haloarcula group and of the q0v2w85h824348mk/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-carotene-rich green algaDunaliella salina to the red colour of saltern crystallizer ponds. By means of light absorption measurements, we showed that bacterioruberin contained in the bacteria was mainly responsible for the colour of the brines, in spite of the fact that q0v2w85h824348mk/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-carotene derived fromDunaliella was the pigment present in the greatest amount. This apparent discrepancy was explained by the very smallin vivo optical cross-section of q0v2w85h824348mk/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-carotene, which is densely packed in globules inside theD. salina cells. We recently observed that the centrifugation technique used in the previous study to collect biomass from the ponds was unsuitable for this type of measurements, as a substantial part of theDunaliella cells present did not sediment upon centrifugation due to the low specific gravity caused by the high q0v2w85h824348mk/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-carotene content. Therefore similar measurements were performed with biomass collected by filtration. Again,in vivo absorption spectra were dominated by the absorption peaks of bacterioruberin. The results reported here show that, in spite of the methodological problem associated with the earlier study, all views and conclusions expressed in our earlier paper retain their validity.     

Field azimuth disambiguation using ambiguity-free currents

Using the ambiguity-free vertical current defined by Semel and Skumanich (1995) we derive a minimum-current azimuth disambiguation for the observed magnetic field in the active region NOAA 7201. A comparison of such a minimum-current azimuth resolution with those from other extant methods indicates that the resulting resolution, even though found to be limited by noise, is a useful first approximation. A comparison of our minimum current distribution with the currents we derive from an extant disambiguation (Lites et al., 1995) indicates the presence of current discontinuities in the form of linear features near the magnetic neutral line of the associated qtp4138271q83820/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">-spot.The National Center for Atmospheric Research is funded by the National Science Foundation     

GrADS在数值产品分析中的开发应用

介绍了ＧｒＡＤＳ图形分析系统的编程方法,应用ＧｒＡＤＳ软件对数值模式的输出结果进行了编程处理,并结合实例介绍了它在实际中的多种程序设计和图形分析方法。     

Tests for quasi-independence of embedded markov chains

This paper introduces the concept of quasi-independence into embedded Markov chains and identifies the maximum likelihood frequency estimates to be used with q7042801xk322416/xxlarge967.gif" alt="chi" align="MIDDLE" BORDER="0"> ² tests of the null hypothesis of quasi-independence within an embedded Markov chain.     

Low-temperature studies on the two-dimensional modulations in åkermanite-type crystals: Ca2MgSi2O7 and Ca2ZnSi2O7

Two-dimensional modulation in synthetic åkermanite (Ca₂MgSi₂O₇) and hardystonite (Ca₂ZnSi₂O₇) has been studied by the single-crystal X-ray diffraction methods in the temperature range between 18 and 297 K. It is found that change of the modulation wavelength Ca₂MgSi₂O₇ is slight, but that in Ca₂ZnSi₂O₇ it is noticeable and indicates a plateau-like temperature dependence. The plateau-like region may be regarded as an independent phase with a specific q [～0.2924(3)].     

The physical and chemical properties of circumstellar envelopes

An overview is given of recent results on some basic properties of the circumstellar envelopes of evolved stars. The focus is on well studied examples which illustrate envelopes of different types and at different stages of evolution. The close connection between the physical and chemical properties of the envelopes is emphasized.     

A method for determining the reversibility of a Markov sequence

This paper describes, given a tally matrix with strictly positive entries, a method to determine whether the associated Markov process is reversible, and (for reversible Markov processes) methods to compute the reversibility matrix from the tally matrix. If the tally matrixN is symmetric, then it is shown that the Markov process must be reversible and the reversibility matrixC equalss (R ^–1NR^–1), whereR is the diagonal matrix whosei ^th diagonal entry is the sum of the entries of thei ^th row ofN (for everyi) ands denotes the sum of all the entries ofN. Because a symmetric tally matrix is of special importance in applications, a q283/xxlarge967.gif" alt="chi" align="MIDDLE" BORDER="0">² test is proposed for determining, in the presence of experimental errors, whether such a matrix is symmetric.     

城乡过渡带社会经济空间演化特征与机理

城市空间具有市场、规划双向驱动的特点,但中国学界对两者空间影响尺度的研究却相对较少。本文以1980—2010年浙江10个城市的城乡过渡带为案例,以其兼有市场、规划驱动的院落组级、街坊级、小区级、居住区级约60 m至约800 m的空间尺度为研究对象,利用5年期数据对这一微中观空间进行了广义空间多重分形分析。整体分析显示,规律化、趋势化和无序化土地斑块演变组分的耦合,在城乡过渡带形成了3个基本尺度区间：市场驱动为主的院落组级空间,规划驱动为主的居住区级空间,两者过渡的街坊级、小区级空间。空间拓展的主导性分析表明,因市场、规划在各尺度上引领作用的不同,院落组级、小区级、居住区级空间演变的趋势化与规律化相复合的特征明显,街坊级则偏于趋势化与无序化复合下的空间演变。主体性分析进一步显示,各尺度区间在相应驱动力的作用下,院落组级空间以趋势化的集聚、小区级、居住区级空间以趋势化的扩散为主;街坊级则突出表现为无序化的空间拓展。本文的贡献在于通过f(a)-a(q)曲线上规律化、趋势化、无序化区间的组合及时序变化,量化地认识了城乡过渡带常为趋势化与规律化相复合的空间拓展所主导、但却以趋势化的空间拓展为主体的客观现象,为国土空间规划中市场、规划的空间影响尺度划分、“多层级特征的系统辨识”提供具体的科学依据。