共查询到20条相似文献，搜索用时 15 毫秒
1.
R C Thompson 《Science (New York, N.Y.)》1970,167(924):1494-1497
The distribution of enriched uranium on individual hydroxyapatite crystals after an exchange reaction has been investigated by means of thermal neutron irradiation followed by electron microscopic analysis of fission fragment tracks in plastic support films. One uranyl ion for every two to three surface calcium ions became associated with the mineral but in a nonuniform distribution that strongly favors crystal end regions. 相似文献
2.
Fifty different mineral samples were tested as potential heterogeneous or epitaxial nucleants for four commonly crystallized proteins. It was found, by conventional protein crystallization techniques, that for each protein there was a set of mineral substrates that promoted nucleation of crystals at lower critical levels of supersaturation than required for spontaneous growth. Numerous examples, involving all four proteins, were observed of modification of crystal habit and, in some cases, unit cell properties promoted by the presence of the mineral nucleants. In at least one case, the growth of lysozyme on the mineral apophyllite, it was shown by lattice analysis and x-ray diffraction that the nucleation and growth of the protein crystal on the mineral was likely to involve a direct lattice match. 相似文献
3.
Single-domain magnetite crystals have been isolated and characterized from tissue located in a sinus within the dermethmoid bone of the skull of the yellowfin tuna, Thunnus albacares. Their chemical composition, narrow size distribution, and distinctive crystal morphology indicate that these crystals are biochemical precipitates. Experiments on the interaction between particles reveal the organization of the particles in situ and suggest a possible form for candidate magnetoreceptor organelles. The consistent localization of such particles with similar arrangement within the dermethmoids of this and other pelagic fishes suggests that the ethmoid region is a possible location for a vertebrate magnetic sense organ. 相似文献
4.
Nucleation, growth, and dissolution of crystals have been studied by stereochemical approach involving molecular recognition at interfaces. A methodology is described for using ;;tailor-made' additives designed to interact stereospecifically with crystal surfaces during growth and dissolution. This procedure was instrumental in controlling crystal morphology and in revising the concept of the structure and symmetry of solid solutions. Consequently, it was applied to the transformation of centrosymmetric single crystals into solid solutions with polar arrangement displaying second-harmonic generation and to the performance of asymmetric synthesis of guest molecules inside centrosymmetric host crystals. The method has led to a discovery of a new ;;relay' mechanism explaining the effect of solvent on crystal growth. Finally, it allowed for the design of auxiliary molecules that act as promoters or inhibitors of crystal nucleation that can be used to resolve enantiomers and crystallize desired polymorphs. 相似文献
5.
Rare crystal phases that expand in one or more dimensions when hydrostatically compressed are identified and shown to have negative Poisson's ratios. Some of these crystals (i) decrease volume and expand in two dimensions when stretched in a particular direction and (ii) increase surface area when hydrostatically compressed. Possible mechanisms for achieving such negative linear and area compressibilities are described for single crystals and composites, and sensor applications are proposed. Materials with these properties may be used to fabricate porous solids that either expand in all directions when hydrostatically compressed with a penetrating fluid or behave as if they are incompressible. 相似文献
6.
Hemocyte-mediated shell mineralization in the eastern oyster 总被引：1，自引：0，他引：1
The growth of molluscan shell crystals is usually thought to be initiated from solution by extracellular organic matrix. We report a class of granulocytic hemocytes that may be directly involved in shell crystal production for oysters. On the basis of scanning electron microscopy (SEM) and x-ray microanalysis, these granulocytes contain calcium carbonate crystals, and they increase in abundance relative to other hemocytes following experimentally induced shell regeneration. Hemocytes are observed at the mineralization front using vital fluorescent staining and SEM. Some cells are observed releasing crystals that are subsequently remodeled, thereby at least augmenting matrix-mediated crystal-forming processes in this system. 相似文献
7.
[目的]研究鳗鱼骨矿物质的脱除工艺。[方法]以料液比、温度、盐酸浓度、换液频率、搅拌与否为因素,鳗鱼骨浸酸过程中矿物质钙的溶出速率为指标,研究各因素对鳗鱼骨矿物质脱除的影响,确定鳗鱼骨矿物质的脱除工艺。[结果]鳗鱼骨胶原蛋白提取过程中用盐酸溶液脱除其中的矿物质,可提高胶原蛋白质量。料液比为1∶8(g/ml)时,鳗鱼骨浸酸过程中钙离子可充分溶出。随着盐酸浓度的增加,鳗鱼骨浸酸过程中钙离子的溶出量增加。鳗鱼骨矿物质的最佳脱除工艺为:盐酸浓度0.5 mol/L,料液比1∶8(g/ml),温度15℃,静置,每1 h换液1次,共换3次。[结论]脱除矿物质后,鳗鱼骨的灰分含量由41.22%降低至0.03%,蛋白质含量由40.54%提高至81.47%。 相似文献
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9.
The mineral content of bone can be determined by measuring the absorption by bone of a monochromatic, low-energy photon beam which originates in a radioactive source (iodine-125 at 27.3 kev or americium 241 at 59.6 kev). The intensity of the beam transmitted by the bone is measured by counting with a scintillation detector. Since the photon source and detector are well collimated, errors resulting from scattered radiation are reduced. From measurements of the intensity of the transmitted beam, made at intervals across the bone, the total mineral content of the bone can be determined. The results are accurate and reproducible to within about 3 percent. 相似文献
10.
针对设施农田土壤重金属污染与农产品累积风险日趋严重的问题,以设施农田镉污染土壤(0.4~0.8 mg·kg-1)为研究对象,在室内钝化剂筛选实验的基础上,通过田间效果验证,重点探究炭基、磷基、硅酸盐、黏土矿物等钝化材料施加浓度和磷基-炭基钝化材料复合配施对土壤镉修复效果及对植物生长的影响。结果表明:施加生物质炭、羟基磷灰石、蒙脱石等钝化剂可明显降低土壤有效态镉含量,其中羟基磷灰石+生物质炭配施效果最好,土壤有效态镉含量降低46.52%~58.11%。与对照相比,施加钝化剂均能抑制油菜对镉的吸收和根部向地上可食部分转移,使油菜地上部镉的含量较CK降低3.9%~51.2%,全部低于《食品安全国家标准》(GB 2762—2016)食品中污染物限量。考虑生产成本、材料来源等因素,推荐羟基磷灰石(225 kg·hm-2)与0.6%生物炭复合添加配施为优选钝化剂组合。田间效果分析也表明,土壤EC与土壤有效态镉含量呈显著正相关,进一步证明污染设施菜地中施加钝化剂降低土壤镉的生物有效性,是实现设施菜地安全生产的可行措施。 相似文献
11.
Effect of dietary calcium or phosphorus deficiency on bone development and related calcium or phosphorus metabolic utilization parameters of broilers from 22 to 42 days of age 
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下载免费PDF全文 YANG Yun-feng XING Guan-zhong LI su-fen SHAO Yu-xin ZHANG Li-yang LU Lin LUO Xu-gang LIAO Xiu-dong 《农业科学学报》2020,19(11):2775-2783
This experiment was conducted to investigate the effect of dietary calcium (Ca) or phosphorus (P) deficiency on bone development and related Ca or P metabolic utilization parameters of broilers from 22 to 42 days of age based on our previous study, which indicated that dietary Ca or P deficiency impaired the bone development by regulating related Ca or P metabolic utilization parameters of broilers from 1 to 21 days of age. A total of 504 one-day-old Arbor Acres male broilers were randomly assigned to 1 of 4 treatments with 7 replicates in a completely randomized design, and fed the normal control and Ca- or P-deficient diets from 1 to 21 days of age. At 22 days of age, the broilers were further fed the normal control diet (0.90% Ca+0.35% non-phytate P (NPP)), the P-deficient diet (0.90% Ca+0.18% NPP), the Ca-deficient diet (0.30% Ca+0.35% NPP) or the Ca and P-deficient diet (0.30% Ca+0.18% NPP), respectively. The results showed that dietary Ca or P deficiency decreased (P<0.05) tibia bone mineral density (BMD), bone breaking strength (BBS), ash content, tibia ash Ca content and serum P content on days 28 and 42, but increased (P<0.05) tibia alkaline phosphatase (ALP) activity of broilers on day 42 compared with the control group. Furthermore, the broilers fed the P-deficient diet had the lowest (P<0.05) tibia BMD, BBS, ash content, serum P content and the highest (P<0.05) serum Ca content on day 28 compared with those fed the Ca-deficient or Ca and P-deficient diets. The results from the present study indicated that the bone development and related Ca or P metabolic utilization parameters of broilers were the most sensitive to dietary P deficiency, followed by dietary Ca deficiency or Ca and P-deficiency; dietary Ca or P deficiency impaired the bone development possibly by regulating serum Ca and P contents as well as tibia Ca content and ALP activity of broilers from 22 to 42 days of age. 相似文献
12.
Molluscan bivalve hinge ligaments are composed of long needle-shaped aragonite crystals embedded in a protein matrix. These crystals are twinned and, in general, the twin forms a thin lamella through the center of the crystal. 相似文献
13.
土壤中的钙质结核可分为软结核、硬结核和钙质硬盘３种形态，其化学组成以ＣａＣＯ３为主，矿质全量组成的各氧化物平均含量水平的顺序为：ＣａＯ〉ＳｉＯ２〉Ａｌ２Ｏ３〉Ｆｅ２Ｏ３〉ＭｇＯ〉Ｋ２Ｏ〉Ｎａ２Ｏ〉ＴｉＯ２〉ＭｎＯ〉Ｐ２Ｏ５。但在某些软结核中，ＳｉＯ２含量仍大于ＣａＯ含量。微形态分析结果表明，软结核为碳酸盐颗粒的胶结体，常嵌埋较多的土壤基质、石英、长石等粗颗粒；硬结核多为碳酸盐和方解石的胶结体，许多 相似文献
14.
Wise SW 《Science (New York, N.Y.)》1970,167(3924):1486-1488
The microarchitecture of gastropod nacre reveals deposition of aragonite in the form of crystal stacks and differs markedly from the characteristic microstructure of pelecypod nacre. The structure permits direct observation of both organic and mineral phases of deposition on a growth surface topography that is ideal for the study of processes of mollusk shell calcification. The stack mode of deposition is functionally useful to the animal because it increases the number of crystals which can form and develop on the growth surface at one time. 相似文献
15.
The existence of a monoclinic phase of hydroxyapatite, Ca(2)(PO(4))(4)OH, has been confirmed, by single-crystal structure analysis (weighted "reliability" factor = 3.9 percent on |F|(2)). The structure has space group P21/b, a = 9.4214(8) angstroms, b = 2a, c = 6.8814(7) angstroms, and gamma = 120 degrees , and is analogous to that of chlorapatite. The distortions from the hexagonal structure with which the monoclinic structure is pseudosymmetric are similar to those in chlorapatite, including enlargement of that triangular array of oxygen atoms in which the chlorine ion or, in hydroxyapatite, the hydroxyl hydrogen ion is approximately centered. The hydroxyapatite specimen was prepared by the conversion of a single crystal of chlorapatite in steam at 1200 degrees C, was mimetically twinned, and was approximately 37 percent monoclinic. 相似文献
16.
香料烟叶结晶细胞最早可在叶长1cm左右时产生,发生于从下表皮往上数第3层细胞处,叶长2-4cm左右时,结晶细胞含量迅速增加,之后随着叶长增加其含量逐渐下降,并处于栅栏组织和海绵组织之间,呈不连续的条带状.结晶细胞随着叶片的生长逐渐增大,成熟的叶片有一些结晶细胞破裂,结晶颗粒散出.结晶细胞在香料烟根、茎、叶中均有分布,以叶中较多,并随叶位的升高含量增加.新疆碱性土壤下生长的香料烟叶中结晶细胞的含量稍高于云南酸性土壤生长的香料烟.雨水较少年份结晶细胞含量较高.灌水对香料烟叶片结晶细胞含量有明显的影响,不灌水处理叶片结晶细胞含量较高,灌水越多,结晶细胞含量越低. 相似文献
17.
Soft tissues are preserved within hindlimb elements of Tyrannosaurus rex (Museum of the Rockies specimen 1125). Removal of the mineral phase reveals transparent, flexible, hollow blood vessels containing small round microstructures that can be expressed from the vessels into solution. Some regions of the demineralized bone matrix are highly fibrous, and the matrix possesses elasticity and resilience. Three populations of microstructures have cell-like morphology. Thus, some dinosaurian soft tissues may retain some of their original flexibility, elasticity, and resilience. 相似文献
18.
选择58周龄高产期伊莎笼养蛋鸡90羽,应用PCR扩增鸡IGF-I启动子上游7 kb处基因片段,用PstI消化产生限制性片段长度多态性,分析IGF-I多态性与胫骨、股骨、肱骨骨密度之间的关系。结果表明,伊莎蛋鸡PP、Pp、pp基因型频率分别为0.256、0.311、0.433,P和p等位基因频率分别为0.411 1和0.588 9。方差分析显示,肱骨的骨密度与IGF-I基因多态性相关,PP基因型组的骨密度和骨矿含量均显著大于pp基因型(P<0.05),股骨、胫骨基因型间无显著差异。PP基因型体质量显著大于Pp基因型。表明伊莎笼养蛋鸡IGF-I基因多态性和肱骨骨密度显著相关,P等位基因具有一定的优良骨质指针作用。 相似文献
19.
Discs of finite size are a very rare form of stable surfactant self-assembly. It is shown that mixing of two oppositely charged single-chain surfactants can produce rigid nanodiscs as well as swollen lamellar liquid crystals with frozen bilayers. The crucial requirement for obtaining nanodisc self-assembly is the use of H+ and OH- as counterions. These counterions then form water and lower the conductivity to 10 microsiemens per centimeter. In the case of cationic component excess, a dilute solution of nanodiscs is in thermodynamic equilibrium with a lamellar phase. The diameter of the cationic nanodiscs is continuously adjustable from a few micrometers to 30 nanometers, with the positive charge located mainly around the edges. 相似文献
20.
Ice crystals in the form of right hexagonal prisms have faces that form 90 degrees prisms. Light rays were traced through these prism faces by computer calculation, and the light patterns that would be produced in the sky for a particular distribution of crystal orientations were simulated. Crystals with random orientations produce a 46 degrees halo. Hexagonal plate crystals with nearly horizontal end faces produce circumzenithal and circumhorizontal arcs. Hexagonal column crystals with horizontal axes produce supralateral and infralateral arcs. Plate crystals spinning about a horizontal axis that is a face diagonal of the crystal produce a series of arcs touching the 46 degrees halo. Each of these effects was simulated for several elevations of the sun. 相似文献