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排序方式: 共有487条查询结果,搜索用时 15 毫秒
1.
Low dielectric poly[methylsilsesquioxane‐ran‐trifluoropropylsilsesquioxane‐ran‐(2,4,6,8‐tetramethyl‐2,4,6,8‐tetraethylenecyclotetrasiloxane)silsesquioxane]s {P[M‐ran‐TFP‐ran‐(TCS)]SSQs} having various compositions were synthesized using trifluoropropyl trimethoxysilane, methyl trimethoxysilane and 2,4,6,8‐tetramethyl‐2,4,6,8‐tetra(trimethoxysilylethyl)cyclotetrasiloxane. The chemical composition of the polymers and the content of SiOH end‐groups were controlled by adjusting the reaction conditions, and they were characterized by 1H‐NMR. The thermally decomposable trifluoropropyl groups on the P[M‐ran‐TFP‐ran‐(TCS)]SSQ backbone and heptakis(2,3,6‐tri‐O‐methyl)‐β‐cyclodextrin (CD) were employed as pore generators. The dielectric constants of the porous CD/P[M‐ran‐TFP‐ran‐(TCS)]SSQ films were in the range 2.0–2.7 (at 100 kHz) depending on the concentration of the porogens, and showed no change over 4 days under aqueous conditions. The pore size of the films showed a bimodal distribution, with diameters of ca 0.5–1.0 nm for those originating from the trifluoropropyl groups and 1.7 nm from the CD. The elastic modulus and hardness of the 30 vol% CD‐blended film with a dielectric constant of 2.26 were 2.40 and 0.38 GPa, respectively, as determined by a nanoindenter. Copyright © 2005 Society of Chemical Industry 相似文献
2.
韩国许多城市指定了专项旅游区,通过提供若干激励政策来促进城市旅游.汉城的梨泰院1997年被指定为专项旅游区并成为CBD的一部分.本研究追溯了它作为旅游购物区的变化过程,并通过调查其土地使用找出城市空间结构的变化特征.最后,作者提出了对发展城市旅游的政策性建议,包括减少指定性区域和特殊政策. 相似文献
3.
Kum‐Il Lee Yong‐Sik Yim Sang‐Wook Chung Jiaqiu Wei Jong Il Rhee 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(9):1036-1045
A two‐dimensional (2D) spectrofluorometer was used to monitor various fermentation processes with recombinant E coli for the production of 5‐aminolevulinic acid (ALA). The whole fluorescence spectral data obtained during a process were analyzed using artificial neural networks, ie self‐organizing map (SOM) and feedforward backpropagation neural network (BPNN). The SOM‐based classification of the whole spectral data has made it possible to qualitatively associate some process parameters with the normalized weights and variances, and to select some useful combinations of excitation and emission wavelengths. Based on the classified fluorescence spectra a supervised BPNN algorithm was used to predict some of the process parameters. It was also shown that the BPNN models could elucidate some sections of the process's performance, eg forecasting the process's performance. Copyright © 2005 Society of Chemical Industry 相似文献
4.
The rate of filtration and the water content of cake are influenced by the existence of a dense skin in a highly compressible
cake. The phenomenon of the dense skin has been rarely studied, and its existence has not been verified experimentally. In
this study, the porosity variation in a very compressible cake is measured by using a new experimental apparatus, and with
this the existence of dense skin has been established experimentally. ‘Unified theory on solid-liquid separation’, a recently
developed theory, is utilized for calculating the porosity variation in a very compressible cake. 相似文献
5.
Pharmacologic profile of survivors of acute myocardial infarction at United States academic hospitals 总被引:1,自引:0,他引:1
BG Phillips JM Yim EJ Brown N Bittar TJ Hoon C Celestin PH Vlasses JL Bauman 《Canadian Metallurgical Quarterly》1996,131(5):872-878
Optimal drug therapy for patients with acute myocardial infarction (AMI) is well described in the medical literature. However, data on the actual pharmacologic management of patients surviving AMI at academic hospitals is unavailable. The purpose of this study was to document treatment profiles in 500 patients surviving AMI at 12 academic hospitals in the United States. These profiles were compared with established guidelines and were evaluated for trends. Overall, thrombolytics (streptokinase > or = tissue-type plasminogen activator) were administered in 29% of the patients, with a greater proportion of patients receiving beta-blockers than calcium channel antagonists in the initial 72 hours (61% vs 40%; p < 0.005) and at discharge (51% vs 35%; p < 0.005). Further, women were less likely than men to receive thrombolytic therapy (odds ratio [OR] = 0.61; confidence interval [CI], 0.54 to 0.69) or beta-blocker therapy within the first 72 hours (OR = 0.61; CI, 0.55 to 0.67) or at hospital discharge (OR = 0.53; CI, 0.48 to 0.58). Overall, improvements could still be made in the number of patients who receive thrombolytic and acute and chronic beta-blocker therapies after AMI, particularly in women. Changes in treatment profiles may be a reflection of the publication of large clinical trials. 相似文献
6.
7.
An investigation into vehicle rollover prevention by coordinated control of active anti-roll bar and electronic stability program 总被引:1,自引:0,他引:1
Seongjin Yim Kwangki Jeon Kyongsu Yi 《International Journal of Control, Automation and Systems》2012,10(2):275-287
This paper presents a method for designing a controller that uses an active anti-roll bar (AARB) and an electronic stability program (ESP) for rollover prevention. ESP with longitudinal speed control (LSC) can carry out active braking to reduce vehicle speed and lateral acceleration to prevent a rollover. To enhance the rollover prevention capability of the ESP, an AARB is adopted. The controller for the AARB was designed based on linear quadratic (LQ) static output feedback (SOF) control methodology, which attenuates the effect of lateral acceleration on the roll angle and roll rate by control of the suspension stroke and the tire deflection of the vehicle. Although this AARB significantly increases ride comfort and rollover prevention, it has a drawback — the vehicle loses its maneuverability. Therefore, the ESP with LSC is used to overcome this drawback. Simulations showed that the proposed method was effective in preventing a rollover. 相似文献
8.
Baik Joon Hyun Yim Sung Dae Nam In-Sik Mok Young Sun Lee Jong-Hwan Cho Byong K. Oh Se H. 《Topics in Catalysis》2004,30(1-4):37-41
Topics in Catalysis - Among the catalysts screened, Cu-ion exchanged ZSM5 zeolite exhibited the highest NO removal activity, particularly at low reaction temperatures below 200 °C,... 相似文献
9.
Based upon a new conception that the solid compressive pressure on a cake surface is not null, almost of all solid-liquid
separation operations have been re-examined. For cake filtration, the phenomenon caused by the solid compressive pressure
on a cake surface is discussed for thin cake. New expression and hindered sed-imentation theories are developed by above new
conception using Darcy’s equation. Application of the new conception to centrifugal filtration and tangential filtration is
also discussed. Above results lead to the conclusion that cake filtration, expression, hindered sedimentation, centrifugal
filtration and tangential filtration can be described with a unified theory, and the main difference between the operations
is only the boundary condition of cake. 相似文献
10.
An Yong Lee Jongguk Yim Youngjin Choi 《International Journal of Control, Automation and Systems》2014,12(5):1102-1109
This paper presents a scaled Jacobian transpose based control method for robotic manipulators as a modification of a conventional Jacobian transpose based method. The proposed method has several advantages such as it shows faster convergence and better tracking performance than the conventional method, furthermore, it does not have any singularity problem similar to the conventional method. The scaled Jacobian transpose is obtained by collecting each pseudoinverse of the column vector of the Jacobian matrix. The proposed method performs a given task well under singular configurations while minimizing the task error. Finally, a few comparative studies with the conventional method are provided to show the effectiveness of the proposed method through simulations. 相似文献