基于二氧化碳工质的回热器振荡流实验与模拟研究

采用二氧化碳气体作为斯特林发动机内部循环工质可以实现机器长时间运行,降低成本。为探究二氧化碳工质在回热器中的流动特性,完善斯特林循环分析方法,更好地设计和优化基于二氧化碳工质的斯特林发动机,本文基于CFD方法建立了有限体积模型和振荡流模型,并搭建了振荡流实验台进行实验验证,获得了二氧化碳在金属丝网回热器中的压降、摩擦特性和流阻关联式。随后发现热吹和冷吹过程中流阻关联式的差异较大,在高雷诺数下（1 733＜Re＜3 587）二氧化碳和空气流阻关联式差异小于10%,在低雷诺数下（Re＜1 733）两者相差超过10%。此外,对二氧化碳工质循环率进行了修正,拟合得到了循环率与频率和目数的定量关系式。该流阻关联式和循环率可为优化回热器设计、完善斯特林循环分析方法提供理论支持。     

Rapid 3-D mapping of hyperpolarized 3He spin-lattice relaxation times using variable flip angle gradient echo imaging with application to alveolar oxygen partial pressure measurement in rat lungs

Objective  

The purpose of this work was to develop a rapid 3-D, variable flip angle (VFA) method for measurement of hyperpolarized ³He T ₁ which accounts for the effects of radiofrequency (RF) pulses without the need for additional flip angle information.     

Separation of carbon dioxide with the use of chemical-looping combustion and gasification of fuels

Matters regarding using new technology for chemical-looping combustion of fuels for solving the problem of separation and disposal of artificial CO₂ (CO₂ sequestration) are discussed. The primary results of investigations and possible schemes for implementing the processes in pilot and commercial installations are presented. Their technical and economic indicators are estimated, and a possibility of disposing CO₂ produced during electricity generation is considered.     

Detection of glioblastoma multiforme using quantitative molecular magnetic resonance imaging based on 5-aminolevulinic acid: in vitro and in vivo studies

Magnetic Resonance Materials in Physics, Biology and Medicine - We demonstrated a novel metabolic method based on sequential administration of 5-aminolevulinic acid (ALA) and iron supplement, and...     

A comparative technical and economic analysis of different alternatives for using coal in a combined-cycle plant with minimal emission of carbon dioxide into the atmosphere

We consider the technical and economic aspects of a problem related to reducing the amount of CO₂ emitted when coal is burned at thermal power stations. The additional costs associated with different technologies for entrapping carbon dioxide produced when coal is burned in steam-turbine units and combined-cycle plants (which are the main types of power-generating installations) are analyzed by way of comparison. The specific cost of removing carbon dioxide using different technologies for its entrapment is estimated.     

A comparative thermodynamic analysis of alternative technologies for using coal in a combined-cycle plant with minimization of emissions of carbon dioxide into the atmosphere

We consider the problem of reducing the amount of carbon dioxide emitted into the atmosphere when using coal at power stations. A comparative thermodynamic analysis of different methods for entrapping carbon dioxide during the combustion of coal in steam-turbine units and combined-cycle plants is carried out. The levels of reducing CO₂ emissions achieved using different technologies for entrapping it are compared, and the resulting loss in the thermal efficiency of power installations is analyzed.     

内燃机余热回收分流式二氧化碳动力循环系统经济性分析

相较于不分流余热回收系统,含有分流设计的CO2跨临界动力循环内燃机余热回收系统可以有效避免各换热器之间的温度干涉,提高烟气余热利用率和回热器效率,进一步提高余热回收系统的做功能力,但更加复杂的系统不可避免地增加了系统各项成本。对此,基于MATLAB平台,建立了该系统的经济性模型,采用单位发电量成本CUEC、换热器面积功率比rAPR和环境回收期tEPP作为评价参数,综合考虑净功率、系统小型化潜力和环境经济性来评估分流系统的经济性潜力。结果表明:分流系统在膨胀机入口温度约505 K、入口压力约13.5 MPa的较大工况范围内CUEC指标存在优势;在膨胀机入口温度高于473 K时,分流系统的rAPR存在明显优势,相较不分流系统最高改善11.6%;tEPP指标在所有工况下均优于不分流系统;当膨胀机入口温度高于480 K时,分流系统在经济性上具有更大优势。最后,针对未来研究方向,给出了对经济性参数进行多目标优化、开展余热回收系统与内燃机耦合的相关研究等建议。     

Modeling and optimization of microwave structures using quick space mapping with variable weight coefficients

We describe an improvement of a recent space mapping (SM) modeling approach that uses variable weight coefficients (SM‐VWC). Our modification alleviates the main drawback of SM‐VWC: the computational overhead related to a separate parameter extraction required for each evaluation of the surrogate model. In our new procedure, the output SM parameters of the surrogate model are obtained by solving a linear regression problem instead of being determined in the nonlinear parameter extraction process. This dramatically reduces the evaluation time of the surrogate model. Moreover, the modeling accuracy of the modified technique is even better than the accuracy of the original SM‐VWC approach, which is because—in a practical implementation—the original SM‐VWC technique reduces the computational cost of the parameter extraction at the expense of its quality. Examples demonstrate the robustness of our approach. Applications of the quick SM‐VWC for the parametric design optimization are also presented. Copyright © 2010 John Wiley & Sons, Ltd.     

Feasibility of in vivo three-dimensional T<Stack><Subscript>2</Subscript><Superscript>*</Superscript></Stack> mapping using dicarboxy-PROXYL and CW-EPR-based single-point imaging

Objectives

The aim of this study was to demonstrate the feasibility of in vivo three-dimensional (3D) relaxation time T ₂ ^* mapping of a dicarboxy-PROXYL radical using continuous-wave electron paramagnetic resonance (CW-EPR) imaging.

Materials and methods

Isotopically substituted dicarboxy-PROXYL radicals, 3,4-dicarboxy-2,2,5,5-tetra(²H₃)methylpyrrolidin-(3,4-²H₂)-(1-¹⁵N)-1-oxyl (²H,¹⁵N-DCP) and 3,4-dicarboxy-2,2,5,5-tetra(²H₃)methylpyrrolidin-(3,4-²H₂)-1-oxyl (²H-DCP), were used in the study. A clonogenic cell survival assay was performed with the ²H-DCP radical using squamous cell carcinoma (SCC VII) cells. The time course of EPR signal intensities of intravenously injected ²H,¹⁵N-DCP and ²H-DCP radicals were determined in tumor-bearing hind legs of mice (C3H/HeJ, male, n = 5). CW-EPR-based single-point imaging (SPI) was performed for 3D T ₂ ^* mapping.

Results

²H-DCP radical did not exhibit cytotoxicity at concentrations below 10 mM. The in vivo half-life of ²H,¹⁵N-DCP in tumor tissues was 24.7 ± 2.9 min (mean ± standard deviation [SD], n = 5). The in vivo time course of the EPR signal intensity of the ²H,¹⁵N-DCP radical showed a plateau of 10.2 ± 1.2 min (mean ± SD) where the EPR signal intensity remained at more than 90% of the maximum intensity. During the plateau, in vivo 3D T ₂ ^* maps with ²H,¹⁵N-DCP were obtained from tumor-bearing hind legs, with a total acquisition time of 7.5 min.

Conclusion

EPR signals of ²H,¹⁵N-DCP persisted long enough after bolus intravenous injection to conduct in vivo 3D T ₂ ^* mapping with CW-EPR-based SPI.

     

Quantitative in vivo 23Na MR imaging of the healthy human kidney: determination of physiological ranges at 3.0T with comparison to DWI and BOLD

Objectives

The purpose of this prospective study was to assess the normal physiologic ranges of the renal corticomedullary ²³Na-concentration ([²³Na]) gradient at 3.0T in healthy volunteers. The corticomedullary [²³Na] gradient was correlated with other functional MR imaging parameters—blood oxygenation level dependent (BOLD) and diffusion-weighted imaging (DWI)—and to individual and physiologic parameters—age, gender, estimated glomerular filtration rate (eGFR), body mass index (BMI), and blood serum sodium concentration ([²³Na]_serum).

Methods and materials

50 healthy volunteers (30 m, 20 w; mean age: 29.2 years) were included in this IRB-approved study, without a specific a priori preparation in regard to water or food intake. For ²³Na-imaging a 3D density adapted, radial gradient echo (GRE)-sequence (spatial resolution = 5 × 5 × 5 mm³) was used in combination with a dedicated ²³Na-coil and ²³Na-reference phantoms. [²³Na] values of the corticomedullary [²³Na] gradient were measured by placement of a linear region of interest (20 × 1 mm²) from the renal cortex in the direction of the renal medulla. By using external standard reference phantoms, [²³Na] was calculated in mmol/L of wet tissue volume (mmol/l WTV). Axial diffusion-weighted images (spatial resolution = 1.7 × 1.7 × 5.0 mm³) and 2D GRE BOLD images (spatial resolution = 1.2 × 1.2 × 4.0 mm³) were acquired. Mean values ± standard deviations for [²³Na], apparent diffusion coefficient (ADC) values, and R2* values were computed for each volunteer. The corticomedullary ²³Na-concentration gradient (in mmol/l/mm) was calculated along the area of linear concentration increase from the cortex in the direction of the medulla. Correlations between the [²³Na] and DWI, BOLD, and the physiologic parameters were assessed with Pearson correlation coefficients.

Results

The mean corticomedullary [²³Na] for all healthy volunteers increased from the renal cortex (58 ± 17 mmol/l WTV) in the direction of the medulla (99 ± 18 mmol/l WTV). The inter-individual differences ranged from respective cortical and medullary values of 27 and 63 mmol/L WTV to 126 and 187 mmol/L WTV. No statistically significant differences in renal [²³Na] were found based on differences in individual or physiologic parameters (age, gender, [²³Na]_serum, BMI, GFR). No ADC or R2* gradients were identified, and [²³Na] did not correlate with these parameters.

Conclusion

Renal corticomedullary [²³Na] values increase from the cortex in the direction of the medullary pyramid, demonstrating wide inter-individual ranges and no significant correlations with age, gender, [²³Na]_serum, BMI, GFR, ADC, or R2* values. For future clinical evaluations, an approach relying on renal stimulation (e.g. pharmacologically induced diuresis) may be applicable to account for wide inter-individual ranges of normal [²³Na].     

考虑阶梯碳交易和需求响应的含氢储能的并网型微电网优化配置

针对低碳背景下并网型微电网的优化配置问题,提出了一种考虑阶梯碳交易和需求响应的含氢储能的并网型微电网优化配置方法。通过在规划模型中引入阶梯碳交易机制,降低微电网的碳排放;以可再生能源发电功率与负荷功率的差值绝对值之和最小为目标,利用负荷需求响应引导用户改变用能策略,促进可再生能源消纳,减少储能配置容量,进一步降低微电网的碳排放和经济成本;建立包含风力发电机、光伏阵列、柴油发电机、电解槽、储氢罐、燃料电池的并网型微电网的双层优化配置模型,上层模型以微电网等年值综合成本最小为优化目标,下层模型以微电网年运行成本和年碳交易成本之和最小为优化目标;采用遗传算法与混合整数线性规划相结合的方法对双层优化配置模型进行求解。算例结果验证了所建模型的合理性和有效性,能够为含氢储能的并网型微电网的容量配置提供参考。     

双碳目标下含P2G与需求响应的综合能源系统双层优化

在“双碳”目标背景下,对能源系统节能与减排提出了更高的要求。综合能源系统(IES)作为能源系统节能减排的主要载体,为深度发挥IES中用户侧与社区运营商的减排能力,文中提出将用户侧参与需求响应的负荷分为刚性负荷、价格型敏感负荷与碳价型敏感负荷,并在社区运营商中增设P2G设备。在此基础上,建立了用户与IES运营商参与的双主体阶梯碳交易机制,并建立双层优化模型。上层模型为IES运营商运营收益最大,下层模型为用户侧受到园区内碳价与分时能源价格下的用能费用最小。与传统优化模型相比,用户侧行为不仅受到能源价格影响,还受到碳交易价格的影响。此外分析敏感型负荷对需求响应的影响,需求响应及P2G联合优化在IES上的节能减排优势。最后通过4种情境下的仿真,验证了所提模型的有效性。     

基于低碳需求响应的含煤制氢与碳捕集电厂的综合能源系统优化调度

为了提高综合能源系统的低碳性与经济性,提出了煤制氢与碳捕集电厂联合运行模式下考虑低碳需求响应机制的综合能源系统优化调度。对煤制氢与富氧燃烧类型碳捕集电厂进行建模,并引入储碳罐、电转气装置以提高捕碳灵活性,降低制氧、制氢成本;将低碳需求响应机制引入综合能源系统调度模型中,并分析其减排能力;以运行成本最小为目标函数建立了综合能源系统的低碳经济调度模型。通过算例对所提策略进行验证,结果表明该策略能够提高风电消纳水平,降低整体系统的碳排放量,提升系统经济性。     

Small field of view imaging using wavelet encoding with 2 dimensional RF pulses and gradient echo: phantom results

Object  

The objective of this work is to propose an imaging sequence based upon the wavelet encoding approach to provide MRI images free from folding artifacts, in the small field of view (FOV) regime, such as dynamic magnetic resonance imaging (MRI) studies.     

Spatially resolved kinetics of skeletal muscle exercise response and recovery with multiple echo diffusion tensor imaging (MEDITI): a feasibility study

Objectives

We describe measurement of skeletal muscle kinetics with multiple echo diffusion tensor imaging (MEDITI). This approach allows characterization of the microstructural dynamics in healthy and pathologic muscle.

Materials and methods

In a Siemens 3-T Skyra scanner, MEDITI was used to collect dynamic DTI with a combination of rapid diffusion encoding, radial imaging, and compressed sensing reconstruction in a multi-compartment agarose gel rotation phantom and within in vivo calf muscle. An MR-compatible ergometer (Ergospect Trispect) was employed to enable in-scanner plantar flexion exercise. In a HIPAA-compliant study with written informed consent, post-exercise recovery of DTI metrics was quantified in eight volunteers. Exercise response of DTI metrics was compared with that of T2-weighted imaging and characterized by a gamma variate model.

Results

Phantom results show quantification of diffusivities in each compartment over its full dynamic rotation. In vivo calf imaging results indicate larger radial than axial exercise response and recovery in the plantar flexion-challenged gastrocnemius medialis (fractional response: nT2w?=?0.385?±?0.244, nMD?=?0.163?±?0.130, nλ₁?=?0.110?±?0.093, nλ_rad?=?0.303?±?0.185). Diffusion and T2-weighted response magnitudes were correlated (e.g., r?=?0.792, p?=?0.019 for nMD vs. nT2w).

Conclusion

We have demonstrated the feasibility of MEDITI for capturing spatially resolved diffusion tensor data in dynamic systems including post-exercise skeletal muscle recovery following in-scanner plantar flexion.

     

On frequency response and stability of an optical front–end with variable‐gain current amplifier using a bipolar junction transistor translinear loop

A comparative analysis of implementations of an optical front–end with variable transimpedance intended for optical storage systems in two different BiCMOS technologies is given in this article. The variable‐gain current amplifier within the optical front–end is designed by using a modified balanced type of the bipolar junction transistors translinear loop. The predictions of the optical front–end mathematical models are confirmed by the measured results. They show that a 0.6‐µm BiCMOS silicon technology implementation with worse bipolar junction transistor parameters (unity‐gain frequency, current gain β, and the Early voltage) gives much better stability than a 0.35‐µm BiCMOS silicon‐germanium technology implementation. As a consequence, the useful measured transimpedance dynamic range of the proposed optical front–end is 17.5 times larger in the 0.6‐µm BiCMOS silicon technology than that in the 0.35‐µm BiCMOS silicon‐germanium technology. Copyright © 2012 John Wiley & Sons, Ltd.     

Estimation of metabolite <Emphasis Type="Italic">T</Emphasis><Subscript>1</Subscript> relaxation times using tissue specific analysis,signal averaging and bootstrapping from magnetic resonance spectroscopic imaging data

Object A novel method of estimating metabolite T ₁ relaxation times using MR spectroscopic imaging (MRSI) is proposed. As opposed to conventional single-voxel metabolite T ₁ estimation methods, this method investigates regional and gray matter (GM)/white matter (WM) differences in metabolite T ₁ by taking advantage of the spatial distribution information provided by MRSI. Material and methods The method, validated by Monte Carlo studies, involves a voxel averaging to preserve the GM/WM distribution, a non-linear least squares fit of the metabolite T ₁ and an estimation of its standard error by bootstrapping. It was applied in vivo to estimate the T ₁ of N-acetyl compounds (NAA), choline, creatine and myo-inositol in eight normal volunteers, at 1.5 T, using a short echo time 2D-MRSI slice located above the ventricles. Results WM-T _1,NAA was significantly (P < 0.05) longer in anterior regions compared to posterior regions of the brain. The anterior region showed a trend of a longer WM T ₁ compared to GM for NAA, creatine and myo-Inositol. Lastly, accounting for the bootstrapped standard error estimate in a group mean T ₁ calculation yielded a more accurate T ₁ estimation. Conclusion The method successfully measured in vivo metabolite T ₁ using MRSI and can now be applied to diseased brain.