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991.
Dislocation processes in the deformation of nanocrystalline aluminium by molecular-dynamics simulation 总被引:1,自引:0,他引:1
The mechanical behaviour of nanocrystalline materials (that is, polycrystals with a grain size of less than 100 nm) remains controversial. Although it is commonly accepted that the intrinsic deformation behaviour of these materials arises from the interplay between dislocation and grain-boundary processes, little is known about the specific deformation mechanisms. Here we use large-scale molecular-dynamics simulations to elucidate this intricate interplay during room-temperature plastic deformation of model nanocrystalline Al microstructures. We demonstrate that, in contrast to coarse-grained Al, mechanical twinning may play an important role in the deformation behaviour of nanocrystalline Al. Our results illustrate that this type of simulation has now advanced to a level where it provides a powerful new tool for elucidating and quantifying--in a degree of detail not possible experimentally--the atomic-level mechanisms controlling the complex dislocation and grain-boundary processes in heavily deformed materials with a submicrometre grain size. 相似文献
992.
Ferreira M Zucolotto V Huguenin F Torresi RM Oliveira ON 《Journal of nanoscience and nanotechnology》2002,2(1):29-32
Supramolecular structures of polyaniline (PANI) and vanadium oxide (V2O5) have been assembled via the electrostatic layer-by-layer (ELBL) technique. Strong ionic interactions and H-bonding impart unique features to the ELBL films, which are distinct from cast films obtained with the same materials. The interactions were manifested in UV-vis and Fourier transform infrared spectroscopy data. They are enhanced by the intimate contact between the components, as the films are molecularly thin, with 25 A per PANI/V2O5 bilayer. 相似文献
993.
Klocke V 《Journal of nanoscience and nanotechnology》2002,2(3-4):435-440
In recent years Klocke Nanotechnik and partners have developed a new Nanorobotics system that builds a bridge between nanotechnology and classical mechanical engineering. These products combine the advantages of the two technologies: the backlash-free movement of up to 2 kg of load over a stroke of up to 70 mm with a resolution of a few nanometers. This series of positioning modules offers numerous degrees of freedom in the smallest volume for microassembly, interconnection technology, analysis, and reliability testing. Integrated position sensors allow automatic usage, also in rough production technology applications. The repeatability of classical assembly lines is limited to a few microns. Nanorobotics modules allow absolute positioning within 50 nm. 相似文献
994.
Weise W Wilken V Koch C 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2002,49(7):937-945
The frequency response of a fiber-optic hydrophone that uses a dielectric multilayer system as the sensing element for ultrasound detection is investigated. A primary interferometric calibration technique is applied to determine by experiment the frequency-dependent pressure-voltage transfer function up to 45 MHz. The interaction between an incident pressure wave and the fiber end is analyzed by finite element methods. The simulation yields the response of the sensor to a short Gaussian impulse in the time domain from which the transfer function is calculated. The results of the model simulations allowed the transfer function obtained to be interpreted as the result of the superposition of longitudinal, edge diffraction and lateral waves with a resonant vibration mode of the fiber body representing an elastic rod 相似文献
995.
Hydroxypatite-polysaccharide granules for drug delivery 总被引:1,自引:0,他引:1
Krylova E Ivanov A Orlovski V El-Registan G Barinov S 《Journal of materials science. Materials in medicine》2002,13(1):87-90
The formation of hydroxyapatite by co-precipitation from sodium alginate and sodium carboxymethylcellulose aqueous solutions with the use of dibasic calcium phosphate dihydrate and calcium hydroxide as starting reagents is studied. A technique to prepare the hydroxyapatite/polysaccharide (micro)granules is developed. An introduction of an antimicrobial Biocide 1 agent in proper amount into the granules is provided, and the behavior of the granules is evaluated. 相似文献
996.
Baran ET Ozer N Hasirci V 《Journal of materials science. Materials in medicine》2002,13(12):1113-1121
In the present study, antileukemic enzyme L-asparaginase (ASNase) was encapsulated into poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanocapsules in order to decrease the immunogenicity and toxicity of the enzyme and to increase its in vivo half life in mice. Nanocapsules were prepared by water-in-oil-in-water approach and each phase was changed systematically. By changing the pH of the w2 phase to the isolelectric point of L-ASNase, the encapsulation efficiency was increased from 23.7% to 28.0%. Also, modification of ASNase with PEG2 increased the encapsulation efficiency from 23.7% to 27.9% and protected the enzyme against denaturation. Combination of the various optima enabled a substantial increase in the activity (0.074–0.429 U/mg nanocapsule). The enzyme activity in the blood due to unmodified PHBV nanocapsules dropped to 38% of its initial value 4 h after injection. When the same sample was tested for the enzyme content in the circulation by using the radio-labeled enzyme a much lower enzyme (30% of initial) could be detected after a shorter time (3 h). The PHBV nanocapsules with heparin conjugated on their surface had a longer presence in the circulation than unmodified PHBV nanocapsules. After 6 h, around 50% of the enzyme was still present in the blood. Radioactivity measurements using the same sample showed a sharp decrease in enzyme amount in the circulation in the early stages. However, radioactivity was still detectable at the eighth hour. No adverse effects and symptoms of anaphylaxis were observed upon injection of encapsulated ASNase-PHBV nanocapsules to mice i.v. through the tail vein. 相似文献
997.
We introduced recently phase measurements usually performed in interferometry to the domain of image processing and intelligent vision [IEEE Trans. Instrum. Meas. 49, 867 (2000)]. Our purpose is to sense with a high accuracy the position, orientation, and displacement of two-dimensional (2D) surfaces observed by a static vision system. We report on significant improvements of the method. Experimental measurements reveal a peak-valley noise of approximately 10(-2) CCD pixel, corresponding approximately to a 10(-3) period of the phase reference pattern. Then the observation of 10 microm scaled features enables an accuracy of a few nm in the position sensing of the phase reference pattern for the extended 2D measurement range. 相似文献
998.
A dipole model is used to simulate incoherent Raman and fluorescent scattering by microspheres. The use of the addition theorem for spherical harmonics circumvents the need to evaluate double sums in the final formulas, thereby drastically reducing computational effort. Special attention is paid to consideration of backscattering geometry, which is important for lidar applications. The formulas derived for backscattering geometry decrease the computation time for size parameter x approdximately 100 by a factor of 200 compared with the time for calculations performed at other angles. 相似文献
999.
The effect of periodic loss on the performance of refractive-index gratings has been studied in detail. It is shown that the loss periodicity and relative phase strongly affects the symmetry of the reflection, transmission, and loss spectra. This asymmetry is explained successfully through consideration of the overlap between the standing-wave intensity distribution and the periodic loss pattern. 相似文献
1000.
Egelhofer V Gobom J Seitz H Giavalisco P Lehrach H Nordhoff E 《Analytical chemistry》2002,74(8):1760-1771
A new strategy for identifying proteins by MALDI-TOF-MS peptide mapping is reported. In contrast to current approaches, the strategy does not rely on a good relative or absolute mass accuracy as the criterion that discriminates false positive results. The protein sequence database is first searched for all proteins that match a minimum five of the submitted masses within the maximum expected relative errors when the default or externally determined calibration constants are used, for instance, +/-500 ppm. Typically, this search retrieves many thousand candidate sequences. Assuming initially that each of these is the correct protein, the relative errors of the matching peptide masses are calculated for each candidate sequence. Linear regression analysis is then performed of the calculated relative errors as a function of m/z for each candidate sequence, and the standard deviation to the regression is used to distinguish the correct sequence among the candidates. We show that this parameter is independent of whether the mass spectrometric data were internally or externally calibrated. The result is a search engine that renders internal spectrum calibration unnecessary and adapts to the quality of the raw data without user interference. This is made possible by a dynamic scoring algorithm, which takes into account the number of matching peptide masses, the percentage of the protein's sequence covered by these peptides and, as new parameter, the determined standard deviation. The lower the standard deviation, the less cleavage peptides are required for identification and vice versa. Performance of the new strategy is demonstrated and discussed. All necessary computing has been implemented in a computer program, free access to which is provided in the Internet. 相似文献