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1.
M.P. Bakas V.A. Greenhut D.E. Niesz G. D. Quinn J. W. McCauley A. A. Wereszczak J. J. Swab 《International Journal of Applied Ceramic Technology》2004,1(3):211-218
The ballistic performance of state-of-the-art silicon carbide armor material can exhibit a fairly wide variability in certain test configurations, which, it is proposed, may be due to the presence of large (>0.1 mm), rare defects, termed, herein, "anomalous" defects. SiC rubble resulting from ballistic tests was examined, as were quasi-static test samples. Ballistic fragment fracture surfaces revealed large carbonaceous defects that seemed to affect fracture path and mode. Low-strength biaxial flexure samples demonstrated similar defects (>0.1 mm) as failure origins. Carbonaceous defects similar in appearance but smaller in size were also found at the fracture origins of SiC bend bars. Frequently, alumina inclusions were found within the carbonaceous discontinuities. These alumina inclusions may cause the graphitic regions to form during sintering. The random distribution of such large, rare carbonaceous discontinuities from sample-to-sample, as well as batch-to-batch variability, may explain high ballistic variability for SiC armor ceramics. 相似文献
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Processing, Microstructure, and Wear Behavior of Silicon Nitride Hot-Pressed with Alumina and Yttria 总被引:3,自引:0,他引:3
Ajoy Zutshi Richard A. Haber Dale E. Niesz Jane W. Adams John B. Wachtman Mattison K. Ferber Stephen M. Hsu 《Journal of the American Ceramic Society》1994,77(4):883-890
Commercial silicon nitride powder with A12 O3 and Y2 O3 additives was hot-pressed to complete density. The resulting microstructure contained elongated grains with no trace of remaining α-Si3 N4 . The aspect ratio of the elongated grains increased with increasing soak time at a fixed hot-pressing temperature. X-ray diffraction analysis showed that the crystalline phase in the hot-pressed samples was β-sialon (Si6−z Alz Oz N8−z ) with z values that increased with soak time. The fracture strength and fracture toughness of the samples increased as the aspect ratio of the grains increased. The Vickers hardness decreased slightly as the soak time was increased, which was attributed to a grain size effect. Wear tests of silicon nitride against silicon nitride were conducted on a reciprocating pin-on-disk apparatus with paraffin oil as a lubricant. Correlation studies of wear with microstructure and mechanical properties were performed. The wear rate increased rapidly with increasing soak time in spite of the increased strength and toughness. This was attributed to increased third-body wear caused by pullout of pieces from the wear surface. The pullout mechanism was not conclusively identified. However, TEM examination showed clear evidence of dislocation motion under the wear scar. Grain boundary microstresses caused by the anisotropic thermal expansion and elastic properties of the elongated grains may have contributed to the observed pullout. 相似文献
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Many parasitoids are known to use herbivore-induced plant volatiles as cues to locate hosts. However, data are lacking on how much of an advantage a parasitoid can gain from following these plant cues and which factors can limit the value of these cues to the parasitoid. In this study, we simulate the Cotesia rubecula-Pieris rapae-Brassica oleracea system, and ask how many more hosts can a parasitoid attack in a single day of foraging by following plant signals versus randomly foraging. We vary herbivore density, plant response time, parasitoid flight distance, and available host stages to see under which conditions parasitoids benefit from herbivore-induced plant cues. In most of the parameter combinations studied, parasitoids that responded to cues attacked more hosts than those that foraged randomly. Parasitoids following plant cues attacked up to ten times more hosts when they were able to successfully attack herbivores older than first instar; however, if parasitoids were limited to first instar hosts, those following plant cues were at a disadvantage when plants took longer than a day to respond to herbivory. At low herbivore densities, only parasitoids with a larger foraging radius could take advantage of plant cues. Although preference for herbivore-induced volatiles was not always beneficial for a parasitoid, under the most likely natural conditions, the model predicts that C. rubecula gains fitness from following plant cues. 相似文献
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Petra S.Pálvölgyi Daniel Sebők Imre Szenti Eva Bozo Henri Ervasti Olli Pitkänen Jari Hannu Heli Jantunen Marko E.Leinonen Sami Myllymäki Akos Kukovecz Krisztian Kordas 《Nano Research》2021,14(5):1450-1456
In the next generation wireless communication systems operating at near terahertz frequencies, dielectric substrates with the lowest possible permittivity and loss factor are becoming essential. In this work, highly porous (98.9% ± 0.1%) and lightweight silica foams (0.025 ± 0.005 g/cm3), that have extremely low relative permittivity (εr = 1.018 ± 0.003 at 300 GHz) and corresponding loss factor (tan δ< 3 × 10?4 at 300 GHz) are synthetized by a template-assisted sol-gel method. After dip-coating the slabs of foams with a thin film of cellulose nanofibers, sufficiently smooth surfaces are obtained, on which it is convenient to deposit electrically conductive planar thin films of metals important for applications in electronics and telecommunication devices. Here, micropatterns of Ag thin films are sputtered on the substrates through a shadow mask to demonstrate double split-ring resonator metamaterial structures as radio frequency filters operating in the sub-THz band. 相似文献
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Anjana?SarkarEmail author Eduardo?Gracia-Espino Thomas?W?gberg Andrey?Shchukarev Melinda?Mohl Anne-Riikka?Rautio Olli?Pitk?nen Tiva?Sharifi Krisztian?Kordas Jyri-Pekka?MikkolaEmail author 《Nano Research》2016,9(7):1956-1968
Nanosized metal (Pt or Pd)-decorated TiO2 nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO2 NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO2 under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO2 NFs were found to exhibit enhanced performance compared to Pt-decorated TiO2 NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO2 NFs exhibited higher selectivity for methanol, typically producing ~90 ppmg?1·h?1 methanol. The CO2 photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations. 相似文献
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Lorite Gabriela S. Ylä-Outinen Laura Janssen Lauriane Pitkänen Olli Joki Tiina Koivisto Janne T. Kellomäki Minna Vajtai Robert Narkilahti Susanna Kordas Krisztian 《Nano Research》2019,12(11):2894-2899
Nano Research - New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries. While topography cues are known... 相似文献
8.
Krisztian Niesz Istvan Hornyak Bernadett Borcsek Ferenc Darvas 《Microfluidics and nanofluidics》2008,5(3):411-416
The present communication reports a three-way strategy on utilizing a newly developed continuous high-pressure, high-temperature
micro-fluidic reactor to synthesize and modify nanoparticles (NPs) and produce catalytically relevant materials in one flow.
Well-defined platinum nanoparticles have been synthesized within a few seconds and in a highly controlled fashion. By changing
the applied temperature, flow rate and the type of solvent, the size and the surface morphology of the resulting nanoparticles
was changed and tuned on-the-fly. It was also shown that the primarily synthesized NPs can be successfully modified further
by using them as seeds in the same flow from where they were formed, by applying the seeded growth method, which resulted
in increased particle size and the formation of well-defined but randomly distributed shapes. Furthermore, after synthesizing,
the Pt nanoparticles were adsorbed onto the surface of well-known support materials in the same flow to provide in situ production
of commercially relevant Pt/SiO2 catalysts. The in situ prepared catalytically active materials were tested in the hydrogenation of cinnamaldehyde and showed
high activity. 相似文献
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In this contribution, we report the synthesis of rhodium multipods that result from a homogeneous seeded growth mechanism. Small Rh nanocrystal seeds were synthesized by the reduction of RhCl3 in ethylene glycol in the presence of PVP. These seed particles could be subsequently used, without isolation, to form larger rhodium nanoparticles. A reaction temperature of 190 degrees C led to isotropic cubic Rh particles. Lowering the reaction temperature resulted in more anisotropic growth, which gave Rh cubes with horns at 140 degrees C, and Rh multipods at 90 degrees C. The anisotropic growth occurred in the (111) direction, as determined by high-resolution TEM (HRTEM). Anisotropic growth proceeds via a seeded growth mechanism, and not by oriented attachment. 相似文献
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Krisztian BuzaAuthor Vitae Alexandros Nanopoulos Author VitaeTomáš Horváth Author Vitae Lars Schmidt-Thieme Author Vitae 《Neurocomputing》2012,75(1):163-170
Ensembles constitute one of the most prominent class of hybrid prediction models. One basically assumes that different models compensate each other's errors if one combines them in an appropriate way. Often, a large number of various prediction models are available. However, many of them may share similar error characteristics, which highly depress the error compensation effect. Thus the selection of an appropriate subset of models is crucial. In this paper, we address this issue. As major contribution, for the case if large number of models is present, we propose a network-based framework for model selection while paying special attention to the interaction effect of models. In this framework, we introduce four ensemble techniques and compare them to the state-of-the-art in experiments on publicly available real-world data. 相似文献