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11.
We consider the temporal homogenization of linear ODEs of the form \({\dot{x}=Ax+\epsilon P(t)x+f(t)}\), where P(t) is periodic and \({\epsilon}\) is small. Using a 2-scale expansion approach, we obtain the long-time approximation \({x(t)\approx {\rm exp}(At) \left( \Omega(t)+\int_0^t {\rm exp}(-A \tau) f(\tau) {\rm d}\tau \right)}\), where \({\Omega}\) solves the cell problem \({\dot{\Omega}=\epsilon B \Omega + \epsilon F(t)}\) with an effective matrix B and an explicitly-known F(t). We provide necessary and sufficient conditions for the accuracy of the approximation (over a \({{\mathcal{O}}(\epsilon^{-1})}\) time-scale), and show how B can be computed (at a cost independent of \({\epsilon}\)). As a direct application, we investigate the possibility of using RLC circuits to harvest the energy contained in small scale oscillations of ambient electromagnetic fields (such as Schumann resonances). Although a RLC circuit parametrically coupled to the field may achieve such energy extraction via parametric resonance, its resistance R needs to be smaller than a threshold \({\kappa}\) proportional to the fluctuations of the field, thereby limiting practical applications. We show that if n RLC circuits are appropriately coupled via mutual capacitances or inductances, then energy extraction can be achieved when the resistance of each circuit is smaller than \({n\kappa}\). Hence, if the resistance of each circuit has a non-zero fixed value, energy extraction can be made possible through the coupling of a sufficiently large number n of circuits (\({n\approx 1000}\) for the first mode of Schumann resonances and contemporary values of capacitances, inductances and resistances). The theory is also applied to the control of the oscillation amplitude of a (damped) oscillator. 相似文献
12.
Tong R Hemmati HD Langer R Kohane DS 《Journal of the American Chemical Society》2012,134(21):8848-8855
We report a novel nanoparticulate drug delivery system that undergoes reversible volume change from 150 to 40 nm upon phototriggering with UV light. The volume change of these monodisperse nanoparticles comprising spiropyran, which undergoes reversible photoisomerization, and PEGylated lipid enables repetitive dosing from a single administration and enhances tissue penetration. The photoswitching allows particles to fluoresce and release drugs inside cells when illuminated with UV light. The mechanism of the light-induced size switching and triggered-release is studied. These particles provide spatiotemporal control of drug release and enhanced tissue penetration, useful properties in many disease states including cancer. 相似文献
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为了考察切向强迫气流对激光辐照下树脂基复合材料热响应的影响,基于边界层换热理论,研究了切向气流与靶面的对流换热系数和热分解气体对表面热交换的覆盖效应,并用有限差分法对激光辐照下树脂基复合材料的1维热响应模型进行数值求解。数值计算表明:高速切向气流的存在会加速靶材表面与外部环境的热交换,从而明显降低激光对靶材的加热效率;边界层换热理论给出的对流换热系数和覆盖因子是合理有效的,适用于数值模拟切向气流对激光辐照下树脂基复合材料热响应的影响;向靶材表面溢出的热分解气体对靶材表面与外部环境的热交换有一定的抑制作用,但影响较小,基本可以忽略不计。 相似文献
15.
水母雪莲化学成分研究(Ⅰ) 总被引:5,自引:0,他引:5
从水母雪莲3地上部分分离出四种黄酮甙,经鉴定为柯伊利素7-O一β-D-葡萄糖甙、洋芹素7-O-β-D葡萄糖甙、木樨草素7-O-β-D-葡萄糖甙,芦丁。 相似文献
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We study the quantum melting of the two-dimensional Wigner crystal using a fixed node quantum Monte Carlo approach. In addition to the two already known phases (Fermi liquid at large density and Wigner crystal at low density), we find a third stable phase at intermediate values of the density. The third phase has hybrid behaviors in between a liquid and a solid. This hybrid phase has the nodal structure of a Slater determinant constructed out of the bands of a triangular lattice. 相似文献
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This paper is concerned with the asymptotic behavior solutions of stochastic differential equations dy
t
=dω
t
−∇Γ(y
t
) dt, y
0=0 and d=2. Γ is a 2 &\times; 2 skew-symmetric matrix associated to a shear flow characterized by an infinite number of spatial scales
Γ12=−Γ21=h(x
1), with h(x
1)=∑
n
=0
∞γ
n
h
n
(x
1/R
n
), where h
n
are smooth functions of period 1, h
n
(0)=0, γ
n
and
R
n
grow exponentially fast with n. We can show that y
t
has an anomalous fast behavior (?[|y
t
|2]∼t
1+ν with ν > 0) and obtain quantitative estimates on the anomaly using and developing the tools of homogenization.
Received: 1 June 2001 / Accepted: 11 January 2002 相似文献
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In cartography, the geographic regions are usually represented using regular dense maps corresponding to heights values associated with the nodes of a regular grid of R2. The simplification of such maps is an absolute requirement in order to make storage, simulation and display possible. In this Note, we propose a new simplification method based on a measure of the local deformation of the surface. The latter allows, in particular, minimization of the approximation error during the simplification. A numerical example is provided to emphasize the efficiency of this approach. To cite this article: P.J. Frey, H. Borouchaki, C. R. Acad. Sci. Paris, Ser. I 334 (2002) 227–232. 相似文献
19.
Shafee Ahmad Sheikholeslami M. Jafaryar M. Babazadeh Houman 《Journal of Thermal Analysis and Calorimetry》2021,144(3):983-991
Journal of Thermal Analysis and Calorimetry - The goal of the current attempt is to offer a new effective turbulator for increasing performance of a thermal system. Incorporating hybrid nanopowders... 相似文献
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