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921.
We present a theoretical analysis of the noise performance of phase measuring feedback interferometers. We first analyse the operation of this kind of instrument and note that under certain circumstances bistability can occur. The bistable region should be avoided if possible when using feedback interferometry for high-accuracy measurement with low-input powers, as it can give rise to very high-noise levels. We then go on to investigate the effects of shot noise (on the interferometer output signal) and thermal noise (in the feedback loop), and relate these to the phase measurement accuracy of the interferometer. A ‘best-case’ calculation indicates that phase noise of about 0.005λ is possible at input powers in the nanowatt region. In practice, we expect that noise levels will be higher than predicted (particularly at high-input powers) due to the effects of vibration and air turbulence. 相似文献
922.
923.
924.
L.R.S. Araújo F.C. Montenegro D.R. Cornejo 《Journal of magnetism and magnetic materials》2008,320(14):e343-e346
The hysteretic behavior of mechanically alloyed nanocomposites FeCo+MnO was studied at high temperatures. These composites present an unusual high and thermally stable coercivity, compared to FeCo milled at equal conditions. Coercivity enhancement was observed in hysteresis loops obtained between room temperature and 750 K. It is attributed to the isolation of the FeCo ferromagnetic particles by the paramagnetic MnO (TN=120 K). The Mrev(Mirr)H curves are clearly linear for the composite, indicating that coherent rotation is the reversal mechanism in these materials. 相似文献
925.
Scott W. Lefevre Heungyeal Choi Taihyun Chang Chang Y. Ryu 《Journal of polymer science. Part A, Polymer chemistry》2009,47(24):2547-2555
In this article, we have investigated a temperature-rise fractionation procedure for poly(3-hexyl thophene) (P3HT) and poly(3-octyl thophene) (P3OT) that provides well-defined molecular weight (MW) fractions with improved molecular weight distributions (MWD) when compared with Soxhlet extraction. This process involves dispersing the material over C18-boned silica stationary phase in a jacketed column and using incremental rises in column temperature (Tcol) to gradually improve solvent quality and selectively dissolve higher molecular weight samples with a narrow polydispersity (PDI). Fractionation of P3HT with ΔTcol = 5 °C in methylene chloride (MC) yielded 7 fractions ranging from Mp of 20 to 53 kg/mol with an average PDI of 1.80 compared with a mother sample of 3.10. Predominant recovery of P3HT was acquired for fractions with Tcol > 20 °C (30 wt %). Subsequent separation of P3OT in methylene chloride, with a reduced ΔTcol of 3 °C per fraction, due to increased solubility from the longer alkyl chain, generated 8 fractions with a weight range of Mn = 22 to 57 kg/mol with an mean PDI of 1.23 with the mother sample having PDI = 2.34, demonstrating the tunability of this method. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2547–2555, 2009 相似文献
926.
Banjong Boonchom Chanaiporn Danvirutai 《Journal of Thermal Analysis and Calorimetry》2009,96(3):771-775
Cumene hydroperoxide (CHP) and its derivatives have caused many serious explosions and fires in Taiwan as a consequence of
thermal instability, chemical contamination, and even mechanical shock. It has been employed in polymerization for producing
phenol and dicumyl peroxide (DCPO). Differential scanning calorimetry (DSC) was used to analyze the thermal hazard of CHP
in the presence of sodium hydroxide (NaOH), sulfuric acid (H2SO4), and sodium bisulfite (Na2SO3). Thermokinetic parameters for decomposition, such as exothermic onset temperature (T
0
), maximum temperature (T
max
), and enthalpy (ΔH), were obtained from the thermal curves. Isothermal microcalorimetry (thermal activity monitor, TAM) was employed to investigate
the thermal hazards during CHP storage and CHP mixed with NaOH, H2SO4, and Na2SO3 under isothermal conditions in a reactor or container. Tests by TAM indicated that from 70 to 90 °C an autocatalytic reaction
was apparent in the thermal curves. According to the results from the TAM test, high performance liquid chromatography (HPLC)
was, in turn, adopted to analyze the result of concentration versus time. By the Arrhenius equation, the activation energy
(E
a
) and rate constant (k) were calculated. Depending on the process conditions, NaOH was one of the incompatible chemicals or catalysts for CHP. When
CHP is mixed with NaOH, the T
0
is induced earlier and the reactions become more complex than for pure CHP, and the E
a
is lower than for pure CHP. 相似文献
927.
Zhi Hui Zhou Jian Hua Yang* Li Feng Chang Yan Zhang Wei Guo Sun Jin Qu Wang* State Key Laboratory of Fine Chemicals Institute of Adsorption Inorganic Membrane Dalian University of Technology Dalian PR China 《中国化学快报》2007,18(4):455-457
Novel NaA/carbon nanocomposite thin films were successfully prepared on a porous a-Al2O3 substrate by incorporatingnanosized NaA zeolite into novolak-type phenolic resin.The prepared films were characterized by XRD,SEM and single gaspermeation tests.The NaA zeolite/carbon nanocomposite thin films exhibited that the ideal separation factor of CO2/CH4 was 28.4and the carbon dioxide flux was 3.39*10-7mol/(Pa m2s)at room temperature and under a pressure difference of 100 kPa,whichwas two orders of magnitude higher than that of pure carbon membrane prepared at the same procedures and conditions as those ofcomposite films.From the SEM images,the films were continuous and highly intergrown.Compared with carbon membranes,thethickness of nanocomposite films was drastically decreased,which was helpful to reduce the diffusion resistance and increase theflux of gas permeance. 相似文献
928.
929.
Daniel Chiew Judy Qiu Sirimon Treepongkaruna Jiping Yang Chenxiao Shi 《Entropy (Basel, Switzerland)》2021,23(4)
Yang and Qiu proposed and reframed an expected utility–entropy (EU-E) based decision model. Later on, a similar numerical representation for a risky choice was axiomatically developed by Luce et al. under the condition of segregation. Recently, we established a fund rating approach based on the EU-E decision model and Morningstar ratings. In this paper, we apply the approach to US mutual funds and construct portfolios using the best rating funds. Furthermore, we evaluate the performance of the fund ratings based on the EU-E decision model against Morningstar ratings by examining the performance of the three models in portfolio selection. The conclusions show that portfolios constructed using the ratings based on the EU-E models with moderate tradeoff coefficients perform better than those constructed using Morningstar. The conclusion is robust to different rebalancing intervals. 相似文献
930.
本文发现了Zn(II)离子掺杂可以加快聚乳酸的结晶过程. 测试了三种Zn(II)盐(ZnCl2、ZnSt和ZnOAc),并与其它离子Mg(II)和Ca(II)进行对照. FT-IR以及变温拉曼光谱分析发现,经Zn(II)离子掺杂后,聚乳酸的结晶度和结晶速率均增加,差示扫描量热技术以及X射线衍射分析也进一步证实. 差示扫描量热技术测定PLA/ZnSt-0.4 wt%材料的结晶率达到22.46%,PLA/ZnOAc-0.4 wt%材料的结晶率达到24.83%. 相似文献