Electrochemomechanical energy conversion efficiency in silica nanochannels

The electrochemomechanical energy conversion efficiency has been investigated using a new theoretical and numerical framework for modeling the multiphysiochemical transport in long silica nanochannels. Both the chemical dissociation effects on surface charge boundary conditions and the bulk concentration enrichment caused by double layer interactions are considered in the framework. The results show that the energy conversion efficiency decreases monotonically with the increasing ionic concentration at pH = 8. For a given ionic concentration, there is an optimal channel height for the highest efficiency. The efficiency does not increase with the pH value monotonically, and there is an optimal pH value for the maximum energy conversion efficiency as the other conditions are given. The energy conversion efficiency increases with the environmental temperature. The present results may guide the design and optimization of nanofluidic devices for energy conversion.     

Electrokinetics in nanochannels grafted with poly-zwitterionic brushes

In this paper, we compute the electrokinetic transport in soft nanochannels grafted with poly-zwitterionic (PZI) brushes. The transport is induced by an external pressure gradient, which drives the ionic cloud (in the form of an electric double layer or EDL) at the brush surfaces to induce an electric field that drives an induced electroosmotic transport. We characterize the overall transport by quantifying this electric field, overall flow velocity, and the energy conversion associated with the development of the electric field and a streaming current. We specially focus on how the ability of the PZI to ionize and demonstrate a significant charge at both large and small pH can be efficiently maneuvered to develop a liquid transport, an electric field, and an electrokinetically induced power across a wide range of pH values.     

State of charge neural computational models for high energy density batteries in electric vehicles

Environmental concerns, increasing gasoline demand together with unpopularity of alternative energy sources to propel vehicles, have pushed on hybrid electric vehicles (HEVs) solutions. The main problem in battery management of HEVs is how to determine the battery state of charge (SOC). Estimation of SOC is an active area of research, and several approaches have been presented in the literature to monitor the SOC of a cell. At the first step, we use an optimized structure multi-layer perceptron (MLP) and an RBF neural network to determine the SOC changes of a high energy density battery in this paper. Then, a hybrid optimized structure neural model is used for SOC prediction considering the aging effect through the state of health (SOH) and discharge efficiency (DE) parameters. In this way, particle swarm optimization (PSO) algorithm is used for determining the optimum number of nodes in hidden layer(s) of MLPs. Experimental results show that the SOC estimation error by the proposed hybrid optimized structure neural model is 1.9% when compared with the real SOC obtained from a discharge test. In addition, monolithic optimized structure MLP and RBF neural models offer a good estimation of differentiated SOC.     

Efficient entanglement concentration for electron-spin W state with the charge detection

We present two entanglement concentration protocols (ECPs) for arbitrary three-electron W state based on their charges and spins. Different from other ECPs, with the help of the electronic polarization beam splitter and charge detection, the less-entangled W state can be concentrated into a maximally entangled state only with some single charge qubits. The second ECP is more optimal than the first one, for by constructing the complete parity check gate, the second ECP can be used repeatedly to further concentrate the less-entangled state and obtain a higher success probability. Therefore, both the ECPs especially the second one may be useful in current quantum information processing.     

谐振频率转换机制振动能采集器研究进展

环境振动能采集器可为低功耗系统提供绿色环保、可再生能源,具有寿命长久、能量密度高、微型、易集成等优势.能量采集环境具有随机振动频率低、频域广、振源幅值小且多方向性等特点,频率转换机制可有效解决采集器与环境振动频率不匹配问题,提高其能量转换效率.发电装置中的拾振结构频变方式主要分为接触式和非接触式,具体操作方法包括直接或间接碰撞拾振体、驱使振动体形变、磁力耦合调频等.综合比较了各类频率转换机制的优缺点及其实用性,指出了低宽频、高效能、智能化是未来振动能采集微电源的研究趋势.     

Electrokinetic energy conversion in micrometer-length nanofluidic channels

In this study, we present a theoretical and numerical investigation of electrokinetic energy conversion in short-length nanofluidic channels, taking into account reservoir resistance and concentration polarization effects. The concentration polarization effect was demonstrated through numerical modeling using the Poisson–Nernst–Planck (PNP) model. In the absence of concentration polarization, the modified Onsager reciprocal relation for the electrokinetic flow through a one-dimensional (1D) nanochannel is derived from both Ohm’s law and Kirchhoff’s current law while considering the reservoir resistance. Based on this modified Onsager reciprocal relation and the Poisson–Boltzmann (PB) model, a theoretical model for electrokinetic energy conversion is proposed to address the importance of the reservoir resistance effect on electrokinetic energy conversion. The applicability of our proposed model is also verified through numerical modeling of the PNP model. The results calculated from our proposed model are shown to be in good agreement with those from the PNP model when the concentration polarization effect does not occur significantly at the reservoirs. The conversion efficiency and generation power are decreased when the channel resistance is not much larger than the reservoir resistance, especially for a shorter-length nanochannel (e.g., a channel several micrometers in length) with a lower electrolyte concentration and a higher surface charge density. After the concentration polarization effect becomes increased as a larger pressure gradient is applied through an ideal ion-selective nanochannel, the conversion efficiency/generation power is further decreased due to the ion depletion at the inlet reservoir, which increases the electrical resistance of the inlet reservoir or the equivalent electrical resistance of the electrokinetic energy conversion system. The onset pressure difference (or gradient) for a significant concentration polarization is identified both theoretically and numerically. In order to avoid decreases in the conversion efficiency/generation power mentioned above, some key factors such as the length of the nanochannel, the position of electrodes at the reservoirs, and the applied pressure gradient were noticed in this study.     

Analysis of capillary filling in nanochannels with electroviscous effects

Capillary filling is the key phenomenon in planar chromatography techniques such as paper chromatography and thin layer chromatography. Recent advances in micro/nanotechnologies allow the fabrication of nanoscale structures that can replace the traditional stationary phases such as paper, silica gel, alumina, or cellulose. Thus, understanding capillary filling in a nanochannel helps to advance the development of planar chromatography based on fabricated nanochannels. This paper reports an analysis of the capillary filling process in a nanochannel with consideration of electroviscous effect. In larger scale channels, where the thickness of electrical double layer (EDL) is much smaller than the characteristic length, the formation of the EDL plays an insignificant role in fluid flow. However, in nanochannels, where the EDL thickness is comparable to the characteristic length, its formation contributes to the increase in apparent viscosity of the flow. The results show that the filling process follows the Washburn’s equation, where the filled column is proportional to the square root of time, but with a higher apparent viscosity. It is shown that the electroviscous effect is most significant if the ratio between the channel height (h) and the Debye length (κ ⁻¹) reaches an optimum value (i.e. κh ≈ 4). The apparent viscosity is higher with higher zeta potential and lower ion mobility.     

冲击测试中电荷变换电路的零漂分析与优化设计

压电加速度传感器在进行高g值冲击测量时经常出现零漂现象,严重影响了测试结果的精度和可靠性。为解决这一问题,首先建立压电传感器冲击测量时的数学响应模型,分析了测量电路中RC时间常数对零漂的影响。同时针对传输电缆耦合的共模噪声,设计了一种三运放差动电荷放大电路。测试证明,该电路在抑制共模噪声干扰的同时可进行±20 pC的小电荷的检测放大。最后通过恩德福克冲击台进行改进前后的对比冲击测试,验证改进后的设计对冲击测量中零漂抑制切实有效,为工程使用提供一定的参考价值。     

A new energy harvester using a cross-ply cylindrical membrane shell integrated with PVDF layers

In this paper, we proposed a smart cylindrical membrane shell panel (SCMSP) model for vibration-based energy harvester. The SCMSP is made of an orthotropic elastic core covered by outer PVDF layers with transverse polarization vector. Electrodynamics governing equations of motion are derived by applying extended Hamilton’s principle. The governing equations are based on Donnell’s linear thin shell theory. The SCMSP displacement fields are expanded by means of double Fourier series satisfying immovable edges with free rotation boundary conditions and coupled system of linear partial differential equations are obtained. The discretized linear ordinary differential equations of motion are obtained using Galerkin method. The output power is taken as an indicating criterion for the generator. A parametric study for MEMS applications is conducted to predict the power generated due to radial harmonic ambient vibration. Optimal resistance value is also obtained for the particular electrode distribution that gives maximum output power. A low vibration amplitude (5?Pa), and a low-frequency (471.79?Hz) vibration source is targeted for the resonance operation, in which the output power of 0.4111?μW and peak-to-peak voltage of 0.2952?V are predicted.     

Efficient computation of the coupling matrix in time-dependent density functional theory

We present an efficient implementation of the computation of the coupling matrix arising in time-dependent density functional theory. The two important aspects involved, solution of Poisson's equation and the assembly of the coupling matrix, are investigated in detail and proper approximations are used. Poisson's equation is solved in the reciprocal space and bounded support of the wave functions are exploited in the numerical integration. Experiments show the new implementation is more efficient by an order of magnitude when compared with a standard real-space code. The method is tested to compute optical spectra of realistic systems with hundreds of atoms from first principles. Details of the formalism and implementation are provided and comparisons with a standard real-space code are reported.     

Two-dimensional molecular dynamic simulations on accommodation coefficients in nanochannels with various wall configurations

The accommodation coefficients are often utilized in slip boundary conditions to characterize gas-wall interactions. Due to the insufficient transport of momentum and energy in nanochannels, the accommodation coefficients are always less than unity and greatly influenced by temperature and surface structures. In the present paper, a statistical algorithm of the accommodation coefficients was described in molecular dynamic method. The accommodation coefficients were calculated for various wall configurations in two-dimensional nanochannels. The channels were constituted by several layers of platinum atoms, which vibrated and attached to face centered cubic (FCC) lattice sites. The results revealed that the NMAC and EAC are sensitive with the spring constant and wall atom layers. Subtle distinctions in FCC lattice and nanoscale roughness had strong effects. On FCC (1 1 1) lattice plane, the TMAC in isothermal flows was larger, while the NMAC and EAC in thermal conductions are smaller, than those on FCC (1 1 0) lattice plane. Moreover, larger roughness induced more normal momentum transferred into tangential momentum so that the NMAC decreases while the TMAC and EAC increases for larger roughness. In addition, the accommodation coefficients are also affected by rarefaction that the TMAC and EAC decrease as the Knudsen number increases.     

无线传感器网络中基于能量密度的路由算法

在无线传感器网络中,由于传感器节点分布密度不均衡,造成网络中不同区域的能量资源分布差别很大,使得此能耗分布成为影响网络寿命的主要因素.从能量密度的角度出发,提出基于能量密度和能耗调节的路由算法,选择能量密度高的节点承担更多的通信任务,同时,用调节传输能耗的方法节约能量密度低的节点能耗.模拟结果显示:该算法能改善能耗分布,提高网络寿命和能量利用率.     

Efficient kernel density estimation using the fast gauss transform with applications to color modeling and tracking

Many vision algorithms depend on the estimation of a probability density function from observations. Kernel density estimation techniques are quite general and powerful methods for this problem, but have a significant disadvantage in that they are computationally intensive. In this paper, we explore the use of kernel density estimation with the fast Gauss transform (FGT) for problems in vision. The FGT allows the summation of a mixture of ill Gaussians at N evaluation points in O(M+N) time, as opposed to O(MN) time for a naive evaluation and can be used to considerably speed up kernel density estimation. We present applications of the technique to problems from image segmentation and tracking and show that the algorithm allows application of advanced statistical techniques to solve practical vision problems in real-time with today's computers.     

Heat pipe-based radiator for low grade geothermal energy conversion in domestic space heating

A severe technical drawback of geothermal heat pumps (GHPs) is the fact that the nominal operating temperature available for domestic space heating is typically in the region of 50 °C. This is 25–40 °C less than conventional boiler settings used in hydronic central heating applications. As a result, GHPs are not generally ideal for direct replacement of conventional hydronic central heating systems because of the low relative distribution temperatures unless extreme measures are taken to improve the thermal insulation of the buildings. A preferable option for GHPs is underfloor heating. In terms of retrofitting existing buildings neither the re-insulating nor the underfloor heating options are attractive due to the large added cost and disruptive nature of the installation. As such, very high performance low temperature radiators that are pluggable into existing hydronic central heating systems are a major enabling technology for this sustainable energy source. In this investigation a Simulation Driven Design technique was utilized to develop a novel low water content and high thermal throughput heat pipe-based radiator. The radiator was subsequently fabricated and tested and showed an exceptionally high power density and very fast response time compared with conventional wet radiators.     

Design and experimental study of broadband hybrid energy harvester with frequency-up conversion and nonlinear magnetic force

In this paper, a novel broadband hybrid piezoelectric and electromagnetic energy harvester using in the low frequency vibration environment is proposed, which combines nonlinear magnet force and frequency-up conversion mechanism simultaneously. Performances are studied by theoretical analysis and experimental test. Electromechanical governed equations of harvester are established, and analytical solutions of vibration response, output voltage and power are derived. Then, effects of nonlinear force, spacing between low frequency vibration beam and piezoelectric beam, load resistance and input excitation on harvester performances are investigated by experimental test. It can be concluded that the harvester can be used to work at the low-frequency environment efficiently, and the resonant frequency and harvesting bandwidth can be tuned by the nonlinear force between the magnets and the spacing between beams. Moreover, the larger the nonlinear magnetic force and the smaller the distance between two beams, the lower working frequency and the larger bandwidth. Compared with the corresponding linear apartment, output power and bandwidth of proposed harvester are improved 90% and 125% respectively.

     

Accurate initial conditions for the direct numerical simulation of temporal compressible binary shear layers with high density ratio

Accurate initial conditions based on a 2D temporal self-similarity hypothesis are developed for the direct numerical simulation of compressible binary free shear layers with high density ratio. Sample results illustrate effects of density ratio, convective Mach number and free streams temperature on the similarity solution. Direct numerical simulation of a stiff test case (density ratio ∼ 32) shows how the amplitude of early acoustic waves is strongly reduced, with regards to those generated by classical analytical distributions of velocity, temperature and mass fractions. Hence, stable simulations using higher order centered schemes can be achieved for a reasonable number of grid points, even at moderate Reynolds number.     

Optimization of energy management and conversion in the water systems based on evolutionary algorithms

Neural Computing and Applications - In this article, an application of weed optimization algorithm (WOA) for reservoir operation was proposed. In addition, genetic algorithm (GA) and particle swarm...