共查询到20条相似文献，搜索用时 31 毫秒
1.
Wightman RM 《Science (New York, N.Y.)》2006,311(5767):1570-1574
Over the past 20 years, the technological impediments to fabricating electrodes of micrometer dimensions have been largely overcome. These small electrodes can be readily applied to probe chemical events at the surface of tissues or individual biological cells; they can even be used to monitor concentration changes within intact animals. These measurements can be made on rapid time scales and with minimal perturbation of the system under study. Several recent applications have provided important insights into chemical processes at cells and in tissues. Examples include molecular flux measurements at the surface of single cells and through skin-which can offer insights into oxidative stress, exocytosis, and drug delivery-and real-time brain neurotransmitter monitoring in living rats, which reveals correlations between behavior and molecular events in the brain. Such findings can promote interdisciplinary collaborations and may lead to a broader understanding of the chemical aspects of biology. 相似文献
2.
Wightman RM 《Science (New York, N.Y.)》1988,240(4851):415-420
Voltammetric electrodes of microscopic dimension, termed ultramicroelectrodes, can be used to make measurements that are difficult or impossible with conventional electrochemical techniques. Measurements of chemical concentration can be made with these electrodes on a microsecond time scale and with micrometer spatial resolution. In addition, measurements can be made in highly resistive solutions. 相似文献
3.
The dimensions of the topographical signals for growth orientation and infection structure formation, a cell differentiation event that includes nuclear division, were determined for the stomatal penetrating rust fungus Uromyces appendiculatus. The differentiation signal was found to be a simple ridge on the substrate surface that had a markedly optimum height of 0.5 micrometer. Such ridges were microfabricated on silicon wafers by using electron-beam lithography. A similar ridge, in the form of a stomatal lip, was found associated with the stomatal guard cells of the bean (Phaseolus vulgaris) leaf. Ridge elevations greater than 1.0 micrometer or less than 0.25 micrometer did not serve as effective signals. Germ tubes of the fungus were highly oriented by ridge spacings of 0.5 to 6.7 micrometers. The data indicate that the fungus is able to distinguish uniquely minute differences in leaf surface topography in order to infect the host plant. 相似文献
4.
Carter JL 《Science (New York, N.Y.)》1973,181(4102):841-842
A probable vapor-liquid-solid (VLS) type of growth has been discovered for the first time in nature on the surface of lunar rock 15015. Scanning electron microprobe and energy dispersive x-ray data indicate that the growth occurs as metallic iron stalks from about 0.015 to 0.15 micrometer in diameter, with bulbous tips consisting of a mixture of iron and sulfur and measuring from about 0.03 to 0.2 micrometer in diameter. The stalk length is two to ten times the bulb diameter. 相似文献
5.
《Science (New York, N.Y.)》1980,210(4471):784-786
Twenty spectra of Io (0.26 to 0.33 micrometer), acquired with the International Ultraviolet Explorer spacecraft, have been studied. There is a strong ultraviolet absorption shortward of 0.33 micrometer that is consistent with earlier ground-based spectrophotometry; its strength is strongly dependent on Io's rotational phase angle at the time of observation. This spectral feature and its variation are interpreted as indicative of a longitudinal variation in the distribution of sulfur dioxide frost on Io. The frost is most abundant at orbital longitudes 72 degrees to 137 degrees and least abundant at longitudes 250 degrees to 323 degrees . Variations in spectral reflectivity between 0.4 and 0.5 micrometer, reported in earlier ground-based spectral studies, correlate inversely with variations in reflectivity between 0.26 and 0.33 micrometer. It is concluded that this is because the Io surface component with the highest visible reflectivity (sulfur dioxide frost) has the lowest ultraviolet reflectivity. At least one other component is present and may be sulfur allotropes or alkali sulfides. This model is consistent with ground-based ultraviolet, visible, and infrared spectrophotometry. Comparison with Voyager color photographs indicates that the sulfur dioxide frost is in greatest concentration in the "white" areas on Io and the other sulfurous components are in greatest concentration in the "red" areas. 相似文献
6.
Twelve rock chips and two samples of fines all have electronic absorption bands in diffuse reflected light between 0.32 and 2.5 micrometers. Major bands occur between 0.94 and 1.00 micrometer and at 2.0 micrometers, and arise from Fe(2+) in clinopyroxene and to a lesser extent in olivine. A band at 0.95 micrometer and other details of curve slope and shape for the lunar surface fines match McCord's telescopic curve for an 18-kilometer area that includes the Apollo-il site. Results confirm mineralogical predictions based on telescopic data and support the feasibility of obtaining mineralogical information by remote and in glass content. reflectivity measurements. 相似文献
7.
The role of surface chemistry in filter feeding by zooplankton 总被引：1，自引：0，他引：1
Surface chemistry of both particles and animals is important in filter feeding at low Reynolds number. Daphnia magna, fed mixtures of three sizes of polystyrene particles, retained particles that were smaller than the mesh size of the animals (1.0 micrometer) at greater efficiencies than predicted by a sieving model. Retention efficiency of the smallest particles (0.5 micrometer) was increased when negative surface charge on the particles was neutralized, and retention was decreased when a nonionic surfactant was, added to reduce wettability. 相似文献
8.
Schaedler TA Jacobsen AJ Torrents A Sorensen AE Lian J Greer JR Valdevit L Carter WB 《Science (New York, N.Y.)》2011,334(6058):962-965
Ultralight (<10 milligrams per cubic centimeter) cellular materials are desirable for thermal insulation; battery electrodes; catalyst supports; and acoustic, vibration, or shock energy damping. We present ultralight materials based on periodic hollow-tube microlattices. These materials are fabricated by starting with a template formed by self-propagating photopolymer waveguide prototyping, coating the template by electroless nickel plating, and subsequently etching away the template. The resulting metallic microlattices exhibit densities ρ ≥ 0.9 milligram per cubic centimeter, complete recovery after compression exceeding 50% strain, and energy absorption similar to elastomers. Young's modulus E scales with density as E ~ ρ(2), in contrast to the E ~ ρ(3) scaling observed for ultralight aerogels and carbon nanotube foams with stochastic architecture. We attribute these properties to structural hierarchy at the nanometer, micrometer, and millimeter scales. 相似文献
9.
Recent determinations of high production rates (up to 30 percent of primary production in surface waters) implicate free-living marine bacterioplankton as a link in a "microbial loop" that supplements phytoplankton as food for herbivores. An enclosed water column of 300 cubic meters was used to test the microbial loop hypothesis by following the fate of carbon-14-labeled bacterioplankton for over 50 days. Only 2 percent of the label initially fixed from carbon-14-labeled glucose by bacteria was present in larger organisms after 13 days, at which time about 20 percent of the total label added remained in the particulate fraction. Most of the label appeared to pass directly from particles smaller than 1 micrometer (heterotrophic bacterioplankton and some bacteriovores) to respired labeled carbon dioxide or to regenerated dissolved organic carbon-14. Secondary (and, by implication, primary) production by organisms smaller than 1 micrometer may not be an important food source in marine food chains. Bacterioplankton can be a sink for carbon in planktonic food webs and may serve principally as agents of nutrient regeneration rather than as food. 相似文献
10.
An electrooptical memory effect is observed with solid thin films of the photoconductor zinc-octakis(beta-decoxyethyl) porphyrin (ZnODEP) sandwiched between two optically transparent electrodes. Upon irradiation with the simultaneous application of an electric field, electron-hole pairs are generated and separated within the photoconductive layer. These electron-hole pairs become "frozen" within the films when the irradiation is interrupted. These trapped charges can be released by irradiation of the cell, resulting in a transient short-circuit photocurrent. No cross talk between adjacent memory elements separated by approximately 0.2 micrometer (a density of 3 gigabits per square centimeter) was detected. The charge storage system is robust and nonvolatile. The response time for the write-read beam is in the subnanosecond range, and no refreshing is required for long-term retention of trapped charges. 相似文献
11.
Simultaneous measurements of surface force and surface charge demonstrate strong attraction due to the spontaneous transfer of electrical charge from one smooth insulator (mica) to another (silica) as a result of simple, nonsliding contact in dry nitrogen. The measured surface charge densities are 5 to 20 millicoulombs per square meter after contact. The work required to separate the charged surfaces is typically 6 to 9 joules per square meter, comparable to the fracture energies of ionic-covalent materials. Observation of partial gas discharges when the surfaces are approximately 1 micrometer apart gives valuable insight into the charge separation processes underlying static electrical phenomena in general. 相似文献
12.
缓/控释肥料研制和应用已成为提高肥料利用率和降低环境污染风险的重要途径。通过田间小区试验,研究了5种具有代表性的缓释肥料包膜材料纳米-亚微米级水溶性聚合物,即纳米级聚乙烯醇混聚物(CF2)、纳米-亚微米级高岭土-聚酯混聚物(N-KL)、纳米-亚微米级腐植酸混聚物(N-FZ)、纳米-亚微米级丙烯酸酯类混聚物(N-BX)、纳米-亚微米级聚苯乙烯泡沫塑料混聚物(N-PS),在降解释放过程中对土壤主要微生物、主要功能群以及具有代表性土壤动物群落影响。结果表明,不同水溶物聚合物对土壤生物的影响不同,与CK相比,5种水溶性聚合材料处理后细菌、放线菌、氨化细菌、硝化细菌、纤维分解菌种群数量分别增加1.08～2.34倍、0.37～0.96倍、0.3～2.17倍、0.52～1.15倍、0.03～2.45倍,其中腐植酸混聚物处理增加量最大;对真菌、固氮菌种群数量影响不大;对反硝化细菌种群数量有减少的趋势。5种水溶性聚合材料处理对土壤动物的线虫动物门、蜱螨目个体数分别增加15.16%～52.98%、12.33%～200%,其中腐植酸混聚物处理增加数量最多。 相似文献
13.
The discrepancy between the magnetic hysteresis properties of magnetite crystals that are precipitated from solution (<0.3 micrometer) and of crushed sifted grains (>0.3 micrometer) is not an inherent property of magnetite but is caused by the highly stressed state of crushed material and by adhering finer fragments. The size trends of magnetic properties exhibited by submicrometer-size precipitated grains continue in the size range from 1 micrometer to 1 millimeter in a set of hydrothermally recrystallized magnetite crystals. Coercive forces of these narrowly sized crystals follow a power law over a wide size range (0.1 micrometer to 1 millimeter) as predicted by theory. Dislocation etch pits show similar dislocation densities for hydrothermally grown (3 x 10(10) meter (-2)) and natural (1 x 10(10) meter(-2)) magnetite crystals. Hysteresis parameters of hydrothermally grown crystals are similar to those of natural crystals but are about one-fifth of those for crushed grains. 相似文献
14.
This work demonstrates the practicality of forming two self-assembled monolayers (SAMs), independently but simultaneously, by adsorption of two different adsorbates from a common solution onto a substrate exposing two different materials at its surface. The experimental procedure and the degree of independence achieved in the resulting SAMs are illustrated by examination of monolayers obtained by adsorption of alkanethiols on gold and alkane carboxylic acids on alumina. This procedure provides a method for modifying the surface characteristics of microlithographically generated patterns and offers a versatile technique for controlling solid-vapor and solid-liquid interfacial properties in systems having patterns with dimensions of the order of 1 micrometer. 相似文献
15.
16.
Lane AL Hord CW West RA Esposito LW Simmons KE Nelson RM Wallis BD Buratti BJ Horn LJ Graps AL Pryor WR 《Science (New York, N.Y.)》1986,233(4759):65-70
The Voyager 2 photopolarimeter successfully completed the Uranus encounter, acquiring new data on the planet's atmosphere, its principal satellites, and its ring system. Spatially resolved photometry of the atmosphere at 0.27 micrometer shows no enhancement in absorption toward the pole, unlike the case for Jupiter and Saturn. Stellar occultation measurements indicate the temperature at the 1-millibar level over the north pole is near 90 kelvins. The geometric albedos of the five large satellites of Uranus were measured at 0.27 and 0.75 micrometer and indicate the presence of low albedo, spetrally flat absorbing material. Titania seems to have a fluffy surface, as indicated by its phase curve. The nine ground-based rings were detected, and their internal structure, optical depths, and positions were determined. The sharp edges of the in ring made it possible to measure its edge thickness (less than 150 meters) and particle sizes (less than 30 meters); little or no dust was detcted. New narrow rings and partial rings (arcs) were measured, and the narrow component of the eta ring was found to be discontinuous. 相似文献
17.
Bimetallic electrodes are used in a number of electrochemical processes, but the role of particular arrangements of surface metal atoms (ensembles) has not been studied directly. We have evaluated the electrochemical/catalytic properties of defined atomic ensembles in atomically flat PdAu(111) electrodes with variable surface stoichiometry that were prepared by controlled electrodeposition on Au(111). These properties are derived from infrared spectroscopic and voltammetric data obtained for electrode surfaces for which the concentration and distribution of the respective metal atoms are determined in situ by atomic resolution scanning tunneling microscopy with chemical contrast. Palladium monomers are identified as the smallest ensemble ("critical ensemble") for carbon monoxide adsorption and oxidation, whereas hydrogen adsorption requires at least palladium dimers. 相似文献
18.
Melanin pigmentation: an in vivo model for studies of melanosome kinetics within keratinocytes 总被引：3，自引：0，他引：3
The phagocytosis of latex beads by epidermal cells is proposed as a model for stludies on melanosome kinetics within the epidermis. Large latex beads (0.8 micrometer) are ingested singly, whereas, small beads (0.1 micrometer) are taken up in groups, results showing that the uptake mechanism depends on the size of thze indlividual particles. This size-dependency may explain the different distribution patterns of melanosomes and thus the differences of skin color in the Caucasoid and Negroid races. 相似文献
19.
A method of constructing <30-nanometer structures in close proximity with precise spacings is presented that uses the step-by-step application of organic molecules and metal ions as size-controlled resists on predetermined patterns, such as those formed by electron-beam lithography. The organic molecules serve as a ruler for scaling down a larger "parent" structure. After metal deposition and lift-off of the organic multilayer resist, an isolated smaller structure remains on the surface. This approach is used to form thin parallel wires (15 to 70 nanometers in width and 1 micrometer long) of controlled thickness and spacing. The structures obtained were imaged with field emission scanning electron microscopy. A variety of nanostructures could be scaled down, including structures with hollow patterns. 相似文献
20.
Turkevich AL Patterson JH Franzgrote EJ Sowinski KP Economou TE 《Science (New York, N.Y.)》1970,167(3926):1722-1724
Evidence has been obtained for a radioactive deposit on the lunar surface at Mare Tranquillitatis with a total intensity of 0.09 +/- 0.03 alpha disintegration per second per square centimeter. The presence of polonium-210 in amounts that are close to equilibrium indicates a continuous turnover rate of lunar material at this site of less than 0.1 micrometer per year. The lack of such a deposit at two other lunar sites suggests lower local concentrations of uranium there. 相似文献