共查询到20条相似文献，搜索用时 31 毫秒
1.
Rimer JD An Z Zhu Z Lee MH Goldfarb DS Wesson JA Ward MD 《Science (New York, N.Y.)》2010,330(6002):337-341
Crystallization of L-cystine is a critical step in the pathogenesis of cystine kidney stones. Treatments for this disease are somewhat effective but often lead to adverse side effects. Real-time in situ atomic force microscopy (AFM) reveals that L-cystine dimethylester (L-CDME) and L-cystine methylester (L-CME) dramatically reduce the growth velocity of the six symmetry-equivalent {100} steps because of specific binding at the crystal surface, which frustrates the attachment of L-cystine molecules. L-CDME and L-CME produce l-cystine crystals with different habits that reveal distinct binding modes at the crystal surfaces. The AFM observations are mirrored by reduced crystal yield and crystal size in the presence of L-CDME and L-CME, collectively suggesting a new pathway to the prevention of L-cystine stones by rational design of crystal growth inhibitors. 相似文献
2.
In situ atomic force microscopy reveals the morphology, surface topography, and growth and dissolution characteristics of microscopic single crystals of the low-dimensional organic conductor (tetrathiafulvalene)Br(0.76)' which are grown by electrocrystallization on a highly oriented pyrolytic graphite electrode in an atomic force microscope liquid cell. The growth modes and the distribution and orientation of topographic features on specific crystal faces, whose identity was determined by "atomic force microscope goniometry," can be correlated with the strength and direction of anisotropic solid-state intermolecular bonding. Growth on the (011) face of (tetrathiafulvalene)Br(0.76) crystals involves the formation of oriented self-similar triangular islands ranging in size from 200 to 5000 angstroms along a side. These nuclei eventually transform into rectangular rafts at larger length scales, where bulk intermolecular bonding interactions and surface energies dominate over nuclei-substrate interactions. 相似文献
3.
Plagioclase and olivine crystals in the crystalline rocks from the Sea of Tranquillity show little or no evidence of either static or dynamic deformation. The large disorientations in many of the pyroxene crystals are commonly consistent with slip on the system T -(100), t = [001], but these distortions are not due to plastic flow. They are ascribed to rapid growth and quenching phenomena as deduced from studies of chondrules and of quenched natural and experimentally produced melts. Some of the silicates in the breccias and regolith show evidence of shock deformation, from mild to intense, as indicated by pervasive featuring, shock lamallae, and partial transformatiion of pyroxene and plagioclase crystals to glass. 相似文献
4.
将原子力显微镜技术应用于木陶瓷分析,观测了大青杨木材和酚醛树脂炭化前后样品表面的微观形态.结果表明,通过原子力显微镜技术,可以清晰地观察到大青杨木材表面呈波纹状排列有序的纤维物质,波纹峰谷间水平距离390.63nm,垂直距离14.745nm.炭化后该结构消失,样品的粗糙度大大增加,均方根粗糙度由炭化前的4.487nm增加到炭化后的68.147nm.未炭化酚醛树脂因固化时水分的逸出,留下类似火山口状的峰谷,谷宽437.60nm,谷深22.202nm.炭化后该结构完全消失,样品的均方根粗糙度由炭化前的4.612nm增加到50.446nm. 相似文献
5.
Josefowicz JY Maliszewskyj NC Idziak SH Heiney PA McCauley JP Smith AB 《Science (New York, N.Y.)》1993,260(5106):323-326
Monolayer Langmuir-Blodgett films of a discotic mesogen have been studied with atomic force microscopy (AFM). These measurements confirm the "edge on" arrangement for the disk-shaped molecules suggested by surface pressure-area isotherms and show that the molecules form columns that are separated by 17.7 angstroms +/- 10 percent. Column alignment is found to be predominantly along the film deposition direction, with an angular spread of 35 degrees . The AFM images also show that the mean disk separation within the columns is 5.1 +/- 1.3 angstroms, in good agreement with x-ray diffraction (XRD) results. Roomtemperature XRD measurements on bulk samples of the same material indicate a disordered-hexagonal liquid crystalline mesophase, with a column-to-column spacing of 19.9 +/- 0.2 angstroms. 相似文献
6.
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
7.
Oh SH Chisholm MF Kauffmann Y Kaplan WD Luo W Rühle M Scheu C 《Science (New York, N.Y.)》2010,330(6003):489-493
In vapor-liquid-solid (VLS) growth, the liquid phase plays a pivotal role in mediating mass transport from the vapor source to the growth front of a nanowire. Such transport often takes place through the liquid phase. However, we observed by in situ transmission electron microscopy a different behavior for self-catalytic VLS growth of sapphire nanowires. The growth occurs in a layer-by-layer fashion and is accomplished by interfacial diffusion of oxygen through the ordered liquid aluminum atoms. Oscillatory growth and dissolution reactions at the top rim of the nanowires occur and supply the oxygen required to grow a new (0006) sapphire layer. A periodic modulation of the VLS triple-junction configuration accompanies these oscillatory reactions. 相似文献
8.
Rates of hydrothermal reactions 总被引：1，自引：0，他引：1
The rates of reactions of silicates and aqueous fluids follow zero-order kinetics controlled by the reacting surface area with the rate constant given by the equation: log k[unknown] -2900/T -6.85, where T is temperature and where k has the unit's gram-atoms of oxygen per square centimeter per second. This expression appears to hold for all silicates and for reactions involving dissolution, fluid production, or solid-solid transformations in the presence of a fluid of moderate to high pH. 相似文献
9.
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
10.
Falub CV von Känel H Isa F Bergamaschini R Marzegalli A Chrastina D Isella G Müller E Niedermann P Miglio L 《Science (New York, N.Y.)》2012,335(6074):1330-1334
Quantum structures made from epitaxial semiconductor layers have revolutionized our understanding of low-dimensional systems and are used for ultrafast transistors, semiconductor lasers, and detectors. Strain induced by different lattice parameters and thermal properties offers additional degrees of freedom for tailoring materials, but often at the expense of dislocation generation, wafer bowing, and cracks. We eliminated these drawbacks by fast, low-temperature epitaxial growth of Ge and SiGe crystals onto micrometer-scale tall pillars etched into Si(001) substrates. Faceted crystals were shown to be strain- and defect-free by x-ray diffraction, electron microscopy, and defect etching. They formed space-filling arrays up to tens of micrometers in height by a mechanism of self-limited lateral growth. The mechanism is explained by reduced surface diffusion and flux shielding by nearest-neighbor crystals. 相似文献
11.
The surface morphology of a diarylethene single crystal [1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene] determined by atomic force microscopy changed reversibly upon photoirradiation. The crystal underwent a thermally irreversible but photochemically reversible color change (colorless to blue) upon alternate irradiation with ultraviolet (wavelength lambda = 366 nm) and visible (lambda > 500 nm) light that drove reversible photocyclization reactions. Upon irradiation with 366-nm light, new steps appeared on the (100) single-crystalline surface that disappeared upon irradiation with visible light (lambda > 500 nm). The step height, about 1 nm, corresponds to one molecular layer. Irradiation with 366-nm light formed valleys on the (010) surface that also disappeared by bleaching upon irradiation with visible light (lambda > 500 nm). The surface morphological changes can be explained by the molecular structural changes of diarylethenes regularly packed in the single crystal. These crystals could potentially be used as photodriven nanometer-scale actuators. 相似文献
12.
The atomic force microscope (AFM) was used to image an electrode surface at atomic resolution while the electrode was under potential control in a fluid electrolyte. A new level of subtlety was observed for each step of a complete electrochemical cycle that started with an Au(111) surface onto which bulk Cu was electrodeposited. The Cu was stripped down to an underpotential-deposited monolayer and finally returned to a bare Au(111) surface. The images revealed that the underpotential-deposited monolayer has different structures in different electrolytes. Specifically, for a perchloric acid electrolyte the Cu atoms are in a close-packed lattice with a spacing of 0.29 +/- 0.02 nanometer (nm). For a sulfate electrolyte they are in a more open lattice with a spacing of 0.49 +/- 0.02 nm. As the deposited Cu layer grew thicker, the Cu atoms converged to a (111)-oriented layer with a lattice spacing of 0.26 +/- 0.02 nm for both electrolytes. A terrace pattern was observed during dissolution of bulk Cu. Images were obtained of an atomically resolved Cu monolayer in one region and an atomically resolved Au substrate in another in which a 30 degrees rotation of the Cu monolayer lattice from the Au lattice is clearly visible. 相似文献
13.
Sandford SA 《Science (New York, N.Y.)》1986,231(4745):1540-1541
A chemical dissolution experiment on an interplanetary dust particle (IDP) showed that carbonates, not acid-insoluble organic compounds, were responsible for virtually all the absorption at 6.8 micrometers seen in the infrared spectra of this particle. The IDP examined had an infrared spectrum characteristic of layer-lattice silicates and belongs to a class of IDP's whose spectra resemble those of protostellar objects like W33 A, which also exhibit a band at 6.8 micrometers. 相似文献
14.
E F Rogers R D Brown J E Brown D M Kazazis W J Leanza J R Nichols D A Ostlind T M Rodino 《Science (New York, N.Y.)》1983,222(4624):630-632
Nicarbazin, a drug used to control the protozoal disease coccidiosis in poultry, is a complex of the highly insoluble drug 4,4'-dinitrocarbanilide with 2-hydroxy-4,6-dimethylpyrimidine. The structures of this and other 4,4'-dinitrocarbanilide complexes have not been determined, but an analogous 2:1 complex of 4,4'-dinitrodiphenylamine with 1,4-diacetylpiperazine has been prepared in which the only possible bonds are hydrogen bonds between the amide carbonyls and amino hydrogens. Scanning electron microscopy revealed that micron-size crystals of nicarbazin disintegrate in water to form much smaller dinitrocarbanilide crystals. Similar complex dissolution in the gut of poultry may account for the greater effectiveness of dinitrocarbanilide when administered as complexed rather than uncomplexed drug. Particle size problems associated with other highly insoluble drugs and pesticides may be resolved by the use of nicarbazin-like complexes. 相似文献
15.
We introduce a method for the bottom-up assembly of biomolecular structures that combines the precision of the atomic force microscope (AFM) with the selectivity of DNA hybridization. Functional units coupled to DNA oligomers were picked up from a depot area by means of a complementary DNA strand bound to an AFM tip. These units were transferred to and deposited on a target area to create basic geometrical structures, assembled from units with different functions. Each of these cut-and-paste events was characterized by single-molecule force spectroscopy and single-molecule fluorescence microscopy. Transport and deposition of more than 5000 units were achieved, with less than 10% loss in transfer efficiency. 相似文献
16.
Ottaviani G Sigurd D Marrello V McCaldin JO Mayer JW 《Science (New York, N.Y.)》1973,180(4089):948-949
Amorphous silicon in contact with silver films and amorphous germanium in contact with aluminum films form crystalline precipitates when heated to temperatures well below those at which any liquid phase is present. Crystallization occurs by an initial dissolution of the semiconductor into the metal filmsolvent followed by the growth of crystals out of the solvent. 相似文献
17.
18.
【目的】利用生物多糖合成银纳米颗粒,并解析其对烟草赤星病菌（Alternaria alternata）的抑制活性及机理,探索生物多糖合成银纳米颗粒的农业应用前景,为开发安全、高效的抗菌剂提供理论依据。【方法】采用海藻酸钠作为还原剂与表面活性剂在水浴锅中（65℃）一步合成银纳米颗粒（S-AgNPs）。利用透射电镜（TEM）、扫描电镜（SEM）、原子力显微镜（AFM）、紫外分光光度计（UV-vis）、Zeta电位-粒径仪和X射线光电子能谱分析（XPS）分别对S-AgNPs粒径、分散性、稳定性及化学组成进行表征分析。应用Nano Measure软件统计TEM与AFM图像中S-AgNPs的平均粒径。采用平板生长速率法探究S-AgNPs在PDA培养基中浓度为0.0625、0.125、0.25、0.5、1.0 μg·mL-1时对赤星病菌菌丝生长的影响。赤星病菌在S-AgNPs浓度为1.0 μg·mL-1的液态PDA培养基（PDB）中培养后,分别通过测定菌丝的鲜重与干重、SEM观察、电导率测定和考马斯亮蓝G250染色,分析S-AgNPs对菌丝生长量、形态、细胞膜通透性和菌丝可溶性蛋白含量的影响。用孢子悬浮液注射接种法测试S-AgNPs在离体烟草叶片上对赤星病的防治效果。最后通过测定S-AgNPs对鲫鱼生长的影响分析海藻酸钠合成的银纳米颗粒的安全性。【结果】S-AgNPs的TEM、SEM、AFM图像分析表明该方法所合成的S-AgNPs具有分散性好,粒径统一,稳定性强等特点,平均粒径为9.83 nm。生测结果显示S-AgNPs在1.0 μg·mL-1时对烟草赤星病菌菌丝生长抑制率为83.9%。S-AgNPs处理组的菌丝鲜重与菌丝干重明显低于清水对照组,S-AgNPs可以明显破坏菌丝表面结构。进一步抑菌机制研究表明S-AgNPs主要通过抑制赤星病菌可溶性总蛋白合成而破坏其生物膜结构,降低生物膜保水能力,快速破坏菌丝细胞膜通透性,造成大量细胞质渗漏而抑制菌丝生长发育。最终,离体试验证实S-AgNPs能够有效地抑制烟草赤星病菌侵染烟草叶片,且S-AgNPs在有效浓度（1.0 μg·mL-1）内对鲫鱼无明显毒害作用,不影响其正常生命活动。【结论】建立的方法能够稳定合成分散性好,粒径统一,稳定性强的银纳米颗粒。该银纳米颗粒对烟草赤星病菌具有较强的抑制作用,可有效防治烟草赤星病,具有潜在的田间应用前景。 相似文献
19.
[目的]研究pH值对纳米羟基磷灰石吸附水体中稀土离子的影响。[方法]用热分解法合成羟基磷灰石(HAP),并研究合成样品的组成、粒径和形状,进行HAP的溶解和修复试验。[结果]结果表明,样品为纯相HAP,形状为球形,粒径为60~80 nm。当溶液pH≤3时,HAP可迅速溶解,且在60 min内将REEs3+全部转化为沉淀;当溶液pH≥4时,HAP的溶解速度和REEs的去除率均明显下降。HAP修复受到稀土离子污染水体的产物主要是稀土磷酸盐,溶液pH值为4、P/REEs为15/5是最佳修复条件。[结论]HAP对水溶液中稀土离子的去除受诸多因素影响。 相似文献
20.
A. Elvanidi N. Katsoulas T. Bartzanas K. P. Ferentinos C. Kittas 《Precision Agriculture》2017,18(3):332-349
Crop water status is an important parameter for plant growth and yield performance in greenhouses. Thus, early detection of water stress is essential for efficient crop management. The dynamic response of plants to changes of their environment is called ‘speaking plant’ and multisensory platforms for remote sensing measurements offer the possibility to monitor in real-time the crop health status without affecting the crop and environmental conditions. Therefore, aim of this work was to use crop reflectance and temperature measurements acquired remotely for crop water status assessment. Two different irrigation treatments were imposed in tomato plants grown in slabs filed with perlite, namely tomato plants under no irrigation for a certain period; and well-watered plants. The plants were grown in a controlled growth chamber and measurements were carried out during August and September of 2014. Crop reflectance measurements were carried out by two types of sensors: (i) a multispectral camera measuring the radiation reflected in three spectral bands centred between 590–680, 690–830 and 830–1000 nm regions, and (ii) a spectroradiometer measuring the leaf reflected radiation from 350 to 2500 nm. Based on the above measurements several crop indices were calculated. The results showed that crop reflectance increased due to water deficit with the detected reflectance increase being significant about 8 h following irrigation withholding. The results of a first derivative analysis on the reflectance data showed that the spectral regions centred at 490–510, 530–560, 660–670 and 730–760 nm could be used for crop status monitoring. In addition, the results of the present study point out that sphotochemical reflectance index, modified red simple ratio index and modified ratio normalized difference vegetation index could be used as an indicator of plant water stress, since their values were correlated well with the substrate water content and the crop water stress index; the last being extensively used for crop water status assessment in greenhouses and open field. Thus, it could be concluded that reflectance and crop temperature measurements might be combined to provide alarm signals when crop water status reaches critical levels for optimal plant growth. 相似文献