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排序方式: 共有198条查询结果,搜索用时 15 毫秒
91.
92.
Tommi Tervonen Gert van Valkenhoef Nalan Baştürk Douwe Postmus 《European Journal of Operational Research》2013
Models for Multiple Criteria Decision Analysis (MCDA) often separate per-criterion attractiveness evaluation from weighted aggregation of these evaluations across the different criteria. In simulation-based MCDA methods, such as Stochastic Multicriteria Acceptability Analysis, uncertainty in the weights is modeled through a uniform distribution on the feasible weight space defined by a set of linear constraints. Efficient sampling methods have been proposed for special cases, such as the unconstrained weight space or complete ordering of the weights. However, no efficient methods are available for other constraints such as imprecise trade-off ratios, and specialized sampling methods do not allow for flexibility in combining the different constraint types. In this paper, we explore how the Hit-And-Run sampler can be applied as a general approach for sampling from the convex weight space that results from an arbitrary combination of linear weight constraints. We present a technique for transforming the weight space to enable application of Hit-And-Run, and evaluate the sampler’s efficiency through computational tests. Our results show that the thinning factor required to obtain uniform samples can be expressed as a function of the number of criteria n as φ(n) = (n − 1)3. We also find that the technique is reasonably fast with problem sizes encountered in practice and that autocorrelation is an appropriate convergence metric. 相似文献
93.
94.
T.A. Peters W.M. Tucho A. Ramachandran M. Stange J.C. Walmsley R. Holmestad A. Borg R. Bredesen 《Journal of membrane science》2009
The long-term stability of Pd–23%Ag/stainless steel composite membranes has been examined in H2/N2 mixtures as a function of both temperature and feed pressure. During continuous operation, the membrane shows a good stability at 400 °C while the N2 leakage increases very slowly at a temperature of 450 °C (Pfeed = 10 bar). After 100 days of operation (Pfeed = 5–20 bar, T = 350–450 °C), the N2 permeance equals 7.0 × 10−9 mol m−2 s−1 Pa−1, which indicates that the H2/N2 permselectivity still lies around 500, based on a H2 permeance equal to 3.0 × 10−6 mol m−2 s−1 Pa−1. Despite the generation of small pinholes, a membrane life-time of several (2–3) years (T ≤ 425 °C) is estimated for the experimental conditions employed based on long-term stability tests over 100 days. Post-process characterisation shows a considerable grain growth and micro-strain relaxation in the Pd–23%Ag membrane after the prolonged permeation experiment. Changes in surface area are relatively small. In addition, segregation of Ag to the membrane surfaces is observed. The formation of pinholes is identified as the main source for the increased N2 leakage during testing at higher temperature. 相似文献
95.
Raymond E. Borg Maryam Hatamimoslehabadi Stephanie Bellinger Jeffrey La Farha Mithila Chandra Yelleswarapu Jonathan Rochford 《Photochemistry and photobiology》2019,95(1):280-292
The synthesis, photophysical and photoacoustic characterization for a series of nine π‐extended quadrupolar curcumin dyes is presented. A systematic evaluation of the π‐bridging unit including the p‐phenyl, naphth‐4‐yl, thien‐2‐yl and hybrid 4‐naphthathien‐2‐yl groups is presented. Furthermore, evaluation of the strongly donating donor‐π‐acceptor‐π‐donor quadrupolar dimethylamino terminated derivatives is also included. Select dyes exhibit excited state absorption at increased laser fluence which translates to the production of a nonlinear enhanced photoacoustic response. In particular, the bis‐4‐dimethylaminonaphtha‐2‐thien‐5‐yl curcuminBF2 contrast agent DMA‐5 exhibits an excellent molar photoacoustics (PA) emission at both low (9.4 × 103 V M?1) and high (1.47 × 105 V M?1) laser fluence which is confirmed by its strong contrast by photoacoustic tomography (PAT). In summary, the strong absorbance and enhanced photoacoustic properties of naphthyl and thienyl curcuminoids here presented provides great promise for future photoacoustic imaging applications as demonstrated by preliminary PAT studies. 相似文献
96.
Malcolm Fairbairn Tommi Markkanen David Rodriguez Roman 《The European Physical Journal C - Particles and Fields》2018,78(4):347
We consider the effect of the Gibbons–Hawking radiation on the inflaton in the situation where it is coupled to a large number of spectator fields. We argue that this will lead to two important effects – a thermal contribution to the potential and a gradual change in parameters in the Lagrangian which results from thermodynamic and energy conservation arguments. We present a scenario of hilltop inflation where the field starts trapped at the origin before slowly experiencing a phase transition during which the field extremely slowly moves towards its zero temperature expectation value. We show that it is possible to obtain enough e-folds of expansion as well as the correct spectrum of perturbations without hugely fine-tuned parameters in the potential (albeit with many spectator fields). We also comment on how initial conditions for inflation can arise naturally in this situation. 相似文献
97.
F. Hubenthal D. Blázquez Sánchez N. Borg H. Schmidt H.-D. Kronfeldt F. Tr?ger 《Applied physics. B, Lasers and optics》2009,95(2):351-359
In this contribution we summarize recent experiments with the objective to generate optimized substrates for surface-enhanced
Raman spectroscopy (SERS). For this purpose, the well-established laser-assisted growth technique has been applied, which
relies on a precise control of the growth kinetics of supported metal nanoparticles. With this method reproducible and stable
SERS substrates with tailor-made optical properties possing best field enhancements were produced for specific excitation
wavelengths and detection ranges. Optimization of the SERS substrates has been achieved by stabilizing the localized surface
plasmon polariton resonance (SPR) of gold nanoparticles in the vicinity of the laser wavelength of λ=647 nm and λ=785 nm used for SERS excitation. After nanoparticle preparation, SERS spectra of pyrene were obtained using naturally grown
nanoparticles and nanoparticles prepared by laser-assisted growth.
The most important result is that the optimized substrates prepared by laser-assisted growth exhibit a significantly higher
signal-to-noise ratio as compared to naturally grown nanoparticles. They are even better than substrates whose SPR has been
tuned to the excitation wavelength by an elevated temperature during preparation. Another important observation is that all
SERS spectra exhibit excellent reproducibility and the substrates do not show degradation during the measurements. Finally,
the SERS enhancement factors due to the optimized substrates have been estimated and are on the order of 105 to 106. 相似文献
98.
The structures and relative stabilities of (MgCl(2))(n)() sheetlike clusters and nanoballs were studied by quantum chemical methods. The sheets as discrete molecules were studied up to Mg(100)Cl(200). Their stabilities increase systematically as a function of the size of the sheet. Periodic ab initio calculations were performed for (001) monolayer sheets of alpha- and beta-MgCl(2), beta-sheet being slightly favored. Nanoballs were constructed from Archimedean polyhedra, producing tetrahedral, octahedral, and icosahedral symmetries, and were studied up to Mg(60)Cl(120). Nanoballs prefer to take the shape of truncated cuboctahedron (Mg(48)Cl(96)). Comparisons to sheetlike clusters and periodic calculations suggest that magnesium dichloride nanoballs are stable. 相似文献
99.
Lehtonen JV Still DJ Rantanen VV Ekholm J Björklund D Iftikhar Z Huhtala M Repo S Jussila A Jaakkola J Pentikäinen O Nyrönen T Salminen T Gyllenberg M Johnson MS 《Journal of computer-aided molecular design》2004,18(6):401-419
BODIL is a molecular modeling environment geared to help the user to quickly identify key features of proteins critical to molecular recognition, especially (1) in drug discovery applications, and (2) to understand the structural basis for function. The program incorporates state-of-the-art graphics, sequence and structural alignment methods, among other capabilities needed in modern structure–function–drug target research. BODIL has a flexible design that allows on-the-fly incorporation of new modules, has intelligent memory management, and fast multi-view graphics. A beta version of BODIL and an accompanying tutorial are available at http://www.abo.fi/fak/mnf/bkf/research/johnson/bodil.html 相似文献
100.
The fatiguability of the acoustic stapedius muscle reflex in an actual noisy industrial environment was investigated in normal-hearing subjects. In a laboratory situation a small depression was found with a considerable individual variability. The stapedius reflex recovered slowly, approximately as a linear function of time. In a field study on an entire day of exposure in a ship-building yard the reflex depression was on the average 4 dB in response to a stimulation of 2000 Hz 10 min after the end of the workday. This corresponds to less than 8 dB immediately at the end of the exposure. 相似文献