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排序方式: 共有315条查询结果,搜索用时 11 毫秒
31.
Pierre Rabaso Fabrice Dassenoy Fabrice Ville Moussa Diaby Béatrice Vacher Thierry Le Mogne Michel Belin Jérôme Cavoret 《Tribology Letters》2014,55(3):503-516
Inorganic fullerene-like molybdenum disulfide (IF-MoS2) nanoparticles are known to exhibit great friction and wear-reducing abilities in severe boundary lubrication regimes, when added to a base oil alone. Their use in fully formulated lubricants was investigated in this study, and the tribological benefits attributed to the IF-MoS2 nanoparticles were found to be lost in the presence of dispersants. Various experimental techniques were used on three reference oils (base oil containing only IF-MoS2, only dispersants and both IF-MoS2 and dispersants) in order to understand the effect of succinimide-based dispersants on the three phases needed for effective nanoparticle-based lubrication, namely (1) the passing of the nanoparticles through the contact (2) the exfoliation of the IF-MoS2 inside the contact and (3) the adhesion of the released MoS2 platelets on the friction surfaces. The dispersants were shown to improve the dispersion of the nanoparticles in the oil by reducing their agglomeration, but prevented the adhesion of a low-friction MoS2 tribofilm on the steel surfaces. In-situ contact visualization revealed that the well-dispersed nanoparticles passed through the contact and exfoliated nanoparticles were observed after tribological testing. These results imply that nanoparticle dispersion itself does not seem to be an issue concerning nanoparticle effectiveness, even though the reduced agglomerate size and inertia may have affected nanoparticle flow near the contact, as well as entrapment and exfoliation conditions inside the contact. The use of succinimide-based dispersants may, however, have affected the tribochemistry of the contact, by an excessive adsorption on the steel surfaces and/or by encapsulating the released MoS2 platelets, preventing tribofilm adhesion. A balance was finally found between nanoparticle dispersion and friction reduction, but for very low dispersant concentrations and after a running-in period. The role of succinimide-based dispersants and their effect on nanoparticle lubrication were discussed in the light of these results. 相似文献
32.
Juan Li Xuelin Tian Alexander Pyymaki Perros Sami Franssila Ville Jokinen 《Advanced Materials Interfaces》2014,1(3)
A radial pattern with continuous topography gradient is presented, which induces a continuous inward wettability gradient and enables self‐propelling and accurate positioning of droplets to the pattern center. The effect of droplet size and wettability gradient of the pattern on the self‐mobility of droplets is investigated. The wettability gradient is found to increase towards the pattern center, enhancing the self‐motion of droplets at the inner area of the pattern. Moreover, larger droplets give rise to a larger solid‐liquid contact diameter, which helps to satisfy the self‐motion criteria that the advancing contact angle at front edge is smaller than the receding contact angle at rear edge. Consequently, a larger droplet size favors self‐motion initiated from the outer area of the pattern. The continuous topography gradient employed here allows the flexible dispensing of droplets at any place within a certain range, and avoids potential pinning defects to droplets at geometrical discontinuities. An average self‐motion velocity up to 4.0 cm/s for microliter‐sized droplets is achieved on the resultant patterned surface. 相似文献
33.
Tuomas Vallius Konstantins Jefimovs Ville Kettunen Markku Kuittinen Pasi Laakkonen Jari Turunen 《Journal of Modern Optics》2013,60(12):1869-1879
Abstract We introduce an efficient Fourier-domain formulation of an approximate method to model non-paraxial diffractive elements. The method is based on evaluation of local field perturbations caused by abrupt surface-profile transitions. It facilitates fast parametric optimization of binary and four-level diffractive array illuminators in the non-paraxial domain of diffractive optics. Comparison with rigorous electromagnetic theory of gratings shows that optimization with the perturbation method gives accurate results if the smallest feature size in the surface profile is larger than one wavelength. Some binary designs are demonstrated using electron beam lithography. 相似文献
34.
Ville Polojärvi Alexander GubanovAndreas Schramm Riku KoskinenJonna Paajaste Joel SalmiSoile Suomalainen Mircea Guina 《Materials Science and Engineering: B》2012,177(13):1103-1107
We report the influence of V/III beam-equivalent-pressure ratios and post-growth annealing on the photoluminescence of GaSb quantum dots grown on GaAs(1 0 0) by molecular beam epitaxy. Increasing the V/III beam-equivalent-pressure ratio from 3 to 5 and then to 7 results in decreased photoluminescence intensity and redshifts the photoluminescence wavelength. The post-growth annealing blueshifts the quantum dot photoluminescence emission and decreases the full-width-at-half-maximum of the photoluminescence peak when annealing temperature is increased above 800 °C. The blueshift behavior is found to be independent on the V/III ratios indicating a similar atomic interdiffusion mechanism for all investigated samples regardless of the quantum dot properties. The photoluminescence intensities of the three samples experience an increase after moderate annealing. Whereas the intensity of the sample with the highest V/III ratio further increases, the intensity of the sample with lower V/III ratios decreases again upon higher annealing steps above 900 °C. Furthermore, temperature- and power dependent photoluminescence measurements are performed on as-grown and 870 °C annealed samples with V/III ratios of 3 and 7 in order to study the reduced quantum dot confinement in more detail. 相似文献
35.
Katja M?enp?? Ville Ell? Jari Mauno Minna Kellom?ki Riitta Suuronen Timo Ylikomi Susanna Miettinen 《Journal of the Royal Society Interface》2010,7(42):177-188
There is currently no suitable replacement for damaged temporomandibular joint (TMJ) discs after discectomy. In the present study, we fabricated bilayer biodegradable polylactide (PLA) discs comprising a non-woven mat of poly(L/D)lactide (P(L/D)LA) 96/4 and a P(L/DL)LA 70/30 membrane plate. The PLA disc was examined in combination with adipose stem cells (ASCs) for tissue engineering of the fibrocartilaginous TMJ disc in vitro. ASCs were cultured in parallel in control and chondrogenic medium for a maximum of six weeks. Relative expression of the genes, aggrecan, type I collagen and type II collagen present in the TMJ disc extracellular matrix increased in the ASC-seeded PLA discs in the chondrogenic medium. The hypertrophic marker, type X collagen, was moderately induced. Alcian blue staining showed accumulation of sulphated glycosaminoglycans. ASC differentiation in the PLA discs was close to that observed in pellet cultures. Comparison of the mRNA levels revealed that the degree of ASC differentiation was lower than that in TMJ disc-derived cells and tissue. The pellet format supported the phenotype of the TMJ disc-derived cells under chondrogenic conditions and also enhanced their hyalinization potential, which is considered part of the TMJ disc degeneration process. Accordingly, the combination of ASCs and PLA discs has potential for the development of a tissue-engineered TMJ disc replacement. 相似文献
36.
37.
Luosujärvi L Arvola V Haapala M Pól J Saarela V Franssila S Kotiaho T Kostiainen R Kauppila TJ 《Analytical chemistry》2008,80(19):7460-7466
The factors influencing desorption and ionization in newly developed desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS) were studied. Redirecting the DAPPI spray was observed to further improve the versatility of the technique: for dilute samples, parallel spray with increased analyte signal was found to be the best suited, while for more concentrated samples, the orthogonal spray with less risk for contamination is recommended. The suitability of various spray solvents and sampling surface materials was tested for a variety of analytes with different polarities and molecular weights. As in atmospheric pressure photoionization, the analytes formed [M + H](+), [M - H](-), M(+*), M(-*), [M - H + O](-), or [M - 2H + 2O](-) ions depending on the analyte, spray solvent, and ionization mode. In positive ion mode, anisole and toluene as spray solvents promoted the formation of M(+*) ions and were therefore best suited for the analysis of nonpolar compounds (anthracene, benzo[a]pyrene, and tetracyclone). Acetone and hexane were optimal spray solvents for polar compounds (MDMA, testosterone, and verapamil) since they produced intensive [M + H](+) ion peaks of the analytes. In negative ion mode, the type of spray solvent affected the signal intensity, but not the ion composition. M(-*) ions were formed from 1,4-dinitrobenzene, and [M - H + O](-) and [M - 2H + 2O](-) ions from 1,4-naphthoquinone, whereas acidic compounds (naphthoic acid and paracetamol) formed [M - H](-) ions. The tested sampling surfaces included various materials with different thermal conductivities. The materials with low thermal conductivity, i.e., polymers like poly(methyl methacrylate) and poly(tetrafluoroethylene) (Teflon) were found to be the best, since they enable localized heating of the sampling surface, which was found to be essential for efficient analyte desorption. Nevertheless, the sampling surface material did not affect the ionization mechanisms. 相似文献
38.
Panu Tanninen Ville Leminen Sami Matthews Mika Kainusalmi Juha Varis 《Packaging Technology and Science》2018,31(5):369-376
Three‐dimensional forming of paperboard is commonly done by a press forming process, which has been widely researched. However, the process cycle of the press forming of paperboard trays has not yet been completely optimized due to limited adjustability and unsophisticated mechanical structure of commonly used forming equipment. The object of this study is to optimize the force curve of stroke to improve product quality without compromising the production rate using LUT Adjustable Packaging Line prototype for practical evaluation of formability and multibody dynamics software MSC Adams for simulation. Several process parameters were investigated with different process cycles to study their effect on the quality of the formed products. With optimized male mould speed, acceleration and speed of the blank could be reduced, which led to significantly reduced rupturing tendency without compromising the production speed. It was also found that a constant blank holding force should be used to achieve acceptable tray quality, although this results in a significantly increased surface pressure applied to the formed substrate. It was also discovered that a novel male mould attachment, which included a pressing force adjustment system that utilized a spring set with an adjustable preload, made it possible to control the force distribution between different forming tools during the dwelling phase of the process cycle in an improved way. Utilization of the method used in this paper leads to a better tray quality without compromising the production efficiency. Furthermore, this can increase the number of possible package applications for sustainable materials, such as paperboard. 相似文献
39.
Karvinen J Laitala V Mäkinen ML Mulari O Tamminen J Hermonen J Hurskainen P Hemmilä I 《Analytical chemistry》2004,76(5):1429-1436
We have developed assay technologies to measure hydrolyzing enzymes based on homogeneous time-resolved fluorescence quenching (TruPoint). High sensitivity was obtained using fluorescent europium chelates as labels, internally quenched by suitable quenchers and released upon enzymatic reaction. This approach allows robust and sensitive monitoring of low enzyme activities. The assay technology and the choice of donor-acceptor pairs were evaluated in three different enzymatic assays, a protease related to apoptosis, helicase involved in DNA unwinding, and phosphatase having an important role in cellular signaling cascades. All the assays produced an increasing signal, were sensitive, and had a good dynamic range. There were significant differences in optimized quenchers for each of the assays depending on the size, flexibility, and rigidity of the substrates. Also, clear differences in the energy-transfer reactions, their requirements for spectral overlapping, ionic interactions, and energy-transfer distances were found. Each of the enzymatic assays was briefly tested in a high-throughput screening environment by analyzing signal dynamics and statistical relevance as Z' factors. 相似文献
40.
Pól J Kauppila TJ Haapala M Saarela V Franssila S Ketola RA Kotiaho T Kostiainen R 《Analytical chemistry》2007,79(9):3519-3523
The first microchip version of sonic spray ionization (SSI) as an atmospheric pressure ionization source for mass spectrometry (MS) is presented. The microchip used for SSI has recently been developed in our laboratory, and it has been used before as an atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) source. Now the ionization is achieved simply by applying high (sonic) speed nebulizer gas, without heat, corona discharge, or high voltage. The microchip SSI was applied to the analysis of tetra-N-butylammonium, verapamil, testosterone, angiotensin I, and ibuprofen. The limits of detection were in the range of 15 nM to 4 microM. The technique was found to be highly dependent on the position of the chip toward the mass spectrometer inlet, and on the gas and the sample solution flow rates. The microchip SSI provided dynamic linearity following a pattern similar to that used with electrospray, good quantitative repeatability (RSD=16%), and long-term signal stability. 相似文献