Quartzlike carbon dioxide: An optically nonlinear extended solid at high pressures and temperatures

An extended-solid phase, carbon dioxide phase V (CO2-V), was synthesized in a diamond anvil cell by laser heating the molecular orthorhombic phase, carbon dioxide phase III, above 40 gigapascals and 1800 kelvin. This new material can be quenched to ambient temperature above 1 gigapascal. The vibration spectrum of CO2-V is similar to that of the quartz polymorph of silicon dioxide, indicating that it is an extended covalent solid with carbon-oxygen single bonds. This material is also optically nonlinear, generating the second harmonic of a neodymium-yttrium-lithium-fluoride laser at a wavelength of 527 nanometers with a conversion efficiency that is near 0.1 percent.     

The hydride anion in an extended transition metal oxide array: LaSrCoO3H0.7

We present the synthesis and structural characterization of a transition metal oxide hydride, LaSrCoO3H0.7, which adopts an unprecedented structure in which oxide chains are bridged by hydride anions to form a two-dimensional extended network. The metal centers are strongly coupled by their bonding with both oxide and hydride ligands to produce magnetic ordering at temperatures up to at least 350 kelvin. The synthetic route is sufficiently general to allow the prediction of a new class of transition metal--containing electronic and magnetic materials.     

Z-DNA forms without an alternating purine-pyrimidine sequence in solution

Nuclear magnetic resonance spectra (proton and phosphorus-31) and ultraviolet absorption spectra of the DNA decamer d(br5CGbr5CGATbr5CGbr5CG), in which the central two adenine-thymine base pairs are out of order with the rest of the purine-pyrimidine alternation sequence, indicate that under appropriate solvent conditions (high salt and methanol) the molecule undergoes a structural transition from a right-handed B-DNA conformation to a left-handed Z-DNA conformation. Measurements of the two-dimensional nuclear Overhauser effect on the decamer indicate that all of the guanines as well as the two equivalent thymines adopt the syn conformation.     

工业土壤重金属污染修复技术适用性评估

针对目前我国工业土壤重金属污染修复技术的研究和应用案例,对固化/稳定化、土壤淋洗、植物修复、电动修复和微生物修复等5种技术进行阐述和适用性评估。结果表明,固化/稳定化是工业土壤重金属污染最适宜的修复技术,其他4种技术存在局限性。其中淋洗技术成本高,电动技术对土质要求高,植物修复适合低浓度单一重金属污染土壤,微生物修复在实验室研究阶段。     

Stress gradient in solid methane at high pressures

The magnitude of the axial pressure gradient at 77 degrees K (11 percent per centimeter) in solid methane compressed along one axis for applied pressures up to 10 kilobars was determined by comparing the electrical resistance of a pair of doped tellurium pressure gages with that of a set of single-crystal gages made of high-purity bismuth. The existence of the pressure gradient revealed the causes of deformation in metal tensile specimens embedded in solid methane and cycled to high pressure.     

Hemoglobin I mutation encoded at both alpha-globin loci on the same chromosome: concerted evolution in the human genome

Genetic analysis of an individual expressing an unexpectedly high level of hemoglobin I, an alpha-globin structural mutant, reveals that the mutation is present at both the alpha 1- and the alpha 2-globin gene loci. Kindred analysis confirms that the two affected genes are located in cis. The most likely explanation for this finding is that a recent conversion event occurred within the human alpha-globin gene cluster.     

Oscillatory kinetics and spatio-temporal self-organization in reactions at solid surfaces

Chemical reactions far from equilibrium on solid surfaces may exhibit typical phenomena of nonlinear dynamics, as exemplified by the catalytic oxidation of carbon monoxide on a platinum(110) single-crystal surface. Depending on the external parameters (temperature and partial pressures of the reactants), the temporal variation of the reaction rate may become oscillatory or even chaotic. In a parallel way, the concentration distributions of the adsorbed species on the surface form spatio-temporal patterns including propagating and standing waves, rotating spirals, as well as irregular and rapidly changing structures denoted "chemical turbulence."     

辽西河滩地杨树立地质量代换评价及适地适树的研究

本文采用数量化地位指数方法实现了小青杨、北京杨、小钻杨、健杨等辽西主要适宜杨树种类间的立地质量代换评价，建立了６对树种转换评价的配对方程。在此基础上进行了适地适树分析，将江西河滩地分为５个地力等级，分析了不同立地条件下各树种生长特性，在高地位质量条件下健杨生长最好，在中等立地条件下小钻杨为最优造林树种，在立地条件较差时小青杨、小叶杨较为适宜，北京杨则不作为辽西今后大力发展的树种。最后为不同地力等级内的各立地类型设计了最优造林树种和主要的改土培肥措施。     

不同立地类型火炬树人工林生物量初步研究

测定了生长在渭北黄土高原6个立地类型上的火炬树平均各器官的含水率和生物量。结果表明,各立地类型火炬树全株平均含水率为500.1～521.7g/kg,根的平均含水率为541.4～585.5g/kg,叶的平均含水率为548.3～591.7g/kg,茎枝的平均含水率最低,为410.2～419.7g/kg;不同立地类型火炬树生物量的排序为:阳坡上部(0.4308t/hm2)>峁顶(0.3195t/hm2)>阳坡下部(0.285t/hm2)>沟底(0.1478t/hm2)>阴坡上部(0.0887t/hm2)>阴坡下部(0.0626t/hm2);茎枝是火炬树生物量的主要组成部分,占全株总生物量的41.48%～60.19%,根占24.05%～37.86%,而叶仅占到13.46%～20.74%;6个立地类型上,火炬树各器官生物量以及全株生物量均表现出显著的差异性。     

固体进样在土壤金属元素测定中的应用及展望

准确快速的土壤重金属检测方法能为土壤重金属污染防治提供基础条件。直接固体进样技术因具有能简化样品前处理、缩短分析时间、减少有害化学试剂使用等特点,已被广泛用于农业土壤环境样品中各类金属元素含量的测定。鉴于此,本文首先概述了电热蒸发、激光烧蚀、等离子体进样、中子活化技术等典型土壤固体样品导入技术。其次,根据检测器的不同对固体进样技术进行了分类,并对其工作原理、国内外最新研究进展及标准现状进行了总结。本文进一步从样品的称样量及目数选择、校准方法、基体干扰和消除技术方面对土壤直接固体进样技术存在的问题进行了概述。最后,从土壤固体进样技术的自动化程度、精度提高、成本节约等方面对其未来发展方向进行了展望。     

Nitrogenase MoFe-protein at 1.16 A resolution: a central ligand in the FeMo-cofactor

A high-resolution crystallographic analysis of the nitrogenase MoFe-protein reveals a previously unrecognized ligand coordinated to six iron atoms in the center of the catalytically essential FeMo-cofactor. The electron density for this ligand is masked in structures with resolutions lower than 1.55 angstroms, owing to Fourier series termination ripples from the surrounding iron and sulfur atoms in the cofactor. The central atom completes an approximate tetrahedral coordination for the six iron atoms, instead of the trigonal coordination proposed on the basis of lower resolution structures. The crystallographic refinement at 1.16 angstrom resolution is consistent with this newly detected component being a light element, most plausibly nitrogen. The presence of a nitrogen atom in the cofactor would have important implications for the mechanism of dinitrogen reduction by nitrogenase.     

Lattice images of solid xenon precipitates in aluminum at room temperature

Small solid precipitates (bubbles) of xenon in an aluminum matrix have been formed by ion implantation. Lattice images of this room-temperature inert gas solid were obtained using high-resolution phase-contrast electron microscopy. Many bubbles showed a high degree of crystalline perfection, but regions of defective crystallinity were observed in several cases.     

Fragile sites at 16q22 are not at the breakpoint of the chromosomal rearrangement in AMMoL

There is much speculation about fragile sites on human chromosomes predisposing to specific chromosome rearrangements seen in cancer. Acute myelomonocytic leukemia is characterized by neoplastic chromosome rearrangements involving band 16q22 in patients who carry the rare fragile site at 16q22. This specific leukemic breakpoint is within the metallothionein gene cluster, which is here shown to be proximal to the rare fragile site (FRA16B) and to a common fragile site (FRA16C) in this region. Hence neither of these fragile sites are at the breakpoint in this leukemic chromosomal rearrangement.     

不同立地闽粤栲群落药用植物种群数量特征

以封育28 a较好立地、一般立地及封育8 a较差立地闽粤栲群落为对象,分析主要药用植物种群数量特征。在较好立地上,乔木层主要药用植物为山杜英、老鼠刺、幌伞枫等;在灌木层,主要药用植物为山杜英、毛冬青、老鼠刺等;在草本层,主要药用植物为狗脊、杜茎山、菜蕨等。在一般立地上,乔木层主要药用植物为山杜英、南酸枣和山乌桕等;在灌木层,主要药用植物为山杜英、老鼠刺和朱砂根等;在草本层,主要药用植物为狗脊、芒萁及朱砂根等。在较差立地上,乔木层主要药用植物为杉木、杜鹃和山杜英等;在灌木层,主要药用植物为芒萁、白花苦灯笼及朱砂根等;在草本层,主要药用植物为扇叶铁线蕨、毛冬青及芒萁等。     

Interaction of calcitonin and calcitonin gene-related peptide at receptor sites in target tissues

Discrete receptor sites for calcitonin (CT) and calcitonin gene-related peptide (CGRP) were found in the nervous system and in peripheral tissues. Each peptide was capable of cross-reacting with the specific receptor of the other. In contrast to CT receptors, CGRP receptors were not linked to adenylate cyclase. However, CGRP could stimulate adenylate cyclase in CT target tissues apparently by interacting with CT receptors. The relative abilities of CGRP and mammalian CT to inhibit CT binding suggest that CGRP could serve as an endogenous ligand for CT receptors in the central nervous system.     

Transmutation products may influence radiotracer diffusion rates in an ionic solid

An inherent aspect of radiotracer diffusion is that alpha, beta(+), or beta(-) emission produces a daughter element of different ionization state. This process must either cause a change in the vacancy concentrations or create space charge, depending on the effectiveness of the internal sources or sinks. Four coupled equations established to model the kinetics, when solved by numerical methods, predict that the apparent tracer diffusion rate may easily be in error by a factor of 2 or 3 and, under certain conditions, by as much as an order of magnitude.     

Herbicide resistance and cross-resistance: changes at three distinct sites in the herbicide-binding protein

Plants and algae resistant to the commonly used s-triazine herbicides display a wide spectrum of cross-resistance to other herbicides that act in a similar manner. Analysis of uniparental mutants of the green alga Chlamydomonas reinhardi showed that three different amino acid residues in the 32-kilodalton thylakoid membrane protein can be independently altered to produce three different patterns of resistance to s-triazine and urea-type herbicides. These results clarify the molecular basis for herbicide resistance and cross-resistance. Two of the mutations do not alter normal electron transport and thus may have applications of agronomic interest.     

不同生态点播期对小麦籽粒戊聚糖含量的影响

2001至2002年分别在河北保定、江苏徐州和姜堰3个不同的生态点,研究了播期（适播和晚播）对小麦（徐州26、皖麦38和徐州25）籽粒戊聚糖含量的影响。结果表明：晚播能极显著提高小麦籽粒戊聚糖含量。在播期、环境与基因犁凼子中,以环境对籽粒戊聚糖含量的影响最大。保定点和姜堰点的小麦籽粒戊聚糖含量明显高于徐州点。播期与生态点间、生态点与品种间存在显著的互作效应。播期相同,环境对小麦籽粒戊聚糖含量的影响大于基因型。随着纬度的升高,播期对籽粒戊聚糖含量的影响下降。小麦籽粒戊聚糖含量与气象因子密切相关,以花后气象因子的效应大。     

K+ current diversity is produced by an extended gene family conserved in Drosophila and mouse

The Drosophila Shaker gene on the X chromosome has three sister genes, Shal, Shab, and Shaw, which map to the second and third chromosomes. This extended gene family encodes voltage-gated potassium channels with widely varying kinetics (rate of macroscopic current activation and inactivation) and voltage sensitivity of steady-state inactivation. The differences in the currents of the various gene products are greater than the differences produced by alternative splicing of the Shaker gene. In Drosophila, the transient (A current) subtype of the potassium channel (Shaker and Shal) and the delayed-rectifier subtype (Shab and Shaw) are encoded by homologous genes, and there is more than one gene for each subtype of channel. Homologs of Shaker, Shal, Shab, and Shaw are present in mammals; each Drosophila potassium-channel gene may be represented as a multigene subfamily in mammals.