Assessment of MR imaging during one-lung flooding in a large animal model

Magnetic Resonance Materials in Physics, Biology and Medicine - Magnetic resonance imaging (MRI) of the lung remains challenging due to the low tissue density, susceptibility artefacts,...     

海勃湾水库库区桥位壅水的冰凌模型试验研究

黄河内蒙古河段海勃湾枢纽是一项防凌、发电综合利用的水利枢纽工程,建成后将对其上下游的防凌安全产生深远的影响.本文通过对冰凌运动模型相似条件的分析,重点以水流条件相似和浮冰运动条件相似为基础,建立了其上游河段约15公里附近的河道模型和冰凌输移模型,按海勃湾水库修建与否、不同流凌密度及不同流量级,对其上游乌达铁路新桥附近开展了多组次冰凌模型试验.试验结果表明,在无水库情况下,小流量级别的流凌相对更容易在桥位处形成卡冰结坝、壅高水位;在有水库的情况下,由于库区回水的影响,不易在库区桥位附近形成严重的冰凌险情,水库的修建,对库区桥位附近的冰情无不利的影响.研究成果对黄河海勃湾河段冰凌运动的模型试验进行了探索性的研究,为分析海勃湾水库的建立对上游库区内桥位附近防凌的影响提供了可供借鉴的参考.     

PD inference for the early detection of electrical treeing in insulation systems

Partial discharge (PD) measurements constitute one of the most promising tools for electrical insulation diagnosis. This paper describes how a procedure based on PD measurements can provide early detection of electrical trees in polymeric insulation systems. Such an application relies upon a new methodology, which provides enhanced tools for the identification of PD generating defects. Tree inference is carried out stepwise. Acquired signals are primarily separated according to their waveform, thus achieving data sets related to a specific PD typology. Then, fuzzy algorithms are applied to PD height and phase derived quantities belonging to these homogeneous data sets, in order to assign a membership degree to specific output categories. If the data set is relevant to an internal defect, a further analysis is performed in order to establish whether or not this defect is a treed region. The algorithm described in this paper was developed resorting to tests performed on artificial test specimens and electrical apparatus. In particular, the rules to detect the presence of electrical trees were derived from experiments carried out on needle-plane objects, constituted by slabs of cross-linked polyethylene (XLPE) where a needle is inserted and partially extracted in order to generate a cavity in front of the needle tip. Tests were also performed on cables having artificial defects., as well as on other insulation systems, such as high frequency transformers. Applications of the proposed approach to MV cables and to HV transformers show that electrical trees can be detected successfully before final breakdown.     

A Bayesian hierarchical model for DCE-MRI to evaluate treatment response in a phase II study in advanced squamous cell carcinoma of the head and neck

Object

Pharmacokinetic parameters from dynamic contrast-enhanced MRI (DCE-MRI) were used to assess the perfusion effects due to treatment response using a tyrosine kinase inhibitor. A Bayesian hierarchical model (BHM) is proposed, as an alternative to voxel-wise estimation procedures, to test for a treatment effect while explicitly modeling known sources of variability.

Materials and methods

Nine subjects from a randomized, blinded, placebo-controlled, multicenter, phase II study of lapatinib were examined before and after treatment. Kinetic parameters were estimated, with an extended compartmental model and subject-specific arterial input function, on a voxel-by-voxel basis.

Results

The group treated with lapatinib had a decrease in median K ^trans of 0.17min^??, when averaged across all voxels in the tumor ROIs, compared with no change in the placebo group based on nonlinear regression. A hypothesis test of equality between pre- and posttreatment K ^trans could not be rejected against a one-sided alternative (P = 0.09). Equality between median K ^trans in placebo and lapatinib groups posttreatment could also not be rejected using the BHM (P = 0.32). Across all scans acquired in the study, estimates of K ^trans at one site were greater on average than those at the other site by including a site effect in the BHM. The inter-voxel variability is of similar order (within 15%) when compared to the inter-patient variability.

Conclusion

Though the study contained a small number of subjects and no significant difference was found, the Bayesian hierarchical model provided estimates of variability from known sources in the study and confidence intervals for all estimated parameters. We believe the BHM provides a straightforward and thorough interrogation of the imaging data at the level of voxels, patients or sites in this multicenter clinical study.     

形态小波在低压系统短路故障早期检测中的DSP实现

本文将具有多结构元素的广义形态开滤波器作为三次B样条二进小波变换的前置滤波单元,形成一种新型的形态小波滤波器,并应用于低压系统短路故障早期检测中.该滤波器可以较好地抑制各种噪声、保护故障特征,并从整体上降低了算法的复杂程度,使之在硬件上实时实现成为可能.本文研制了以美国TI公司新近推出的TMS320F2812 DSP为核心的短路故障早期检测系统,在此系统上实时实现了上述形态小波滤波算法.计算机仿真及实验结果均证实了该算法能够有效滤除低压系统中常见的白噪声及脉冲噪声,同时也证实了该算法在低压系统短路故障早期检测应用中的有效性.     

Development of partial discharge detection method using an autoregressive model in gas-insulated switchgears (GIS)

Gas-insulated switchgears (GIS) are important equipment in electric-supply stations where advanced techniques for safety and maintenance are required. As a result, a system is being developed that can automatically monitor and diagnose a GIS in service. This article focuses on some problems concerning insulating functions of GIS to discuss a method of signal processing for partial discharge detection and position identification. For sensors, potential detectors were installed on flanges of the GIS. Focusing on the potential fluctuations measured by these detectors, an autoregressive model is designed for potential fluctuation in a state without any partial discharge. This model is called a normal state model. The difference was found between potential fluctuations measured during partial discharge and those of the normal state model. The index of whiteness test method of the residual random process is a useful parameter for representing this difference, and the use of this method allowed detection of partial discharge that could not be found at normal potential levels. These results indicate bright prospects for manufacturing a monitoring system that can detect deterioration in GIS insulation with a high sensitivity in an early stage and that also operates on-line.     

Magnetic resonance imaging detection of multiple ischemic injury produced in an adult rat model of minor stroke followed by mild transient cerebral ischemia

Objectives

To determine whether cumulative brain damage produced adjacent to a minor stroke that is followed by a mild transient ischemia is detectable with MRI and histology, and whether acute or chronic recovery between insults influences this damage.

Materials and methods

A minor photothrombotic (PT) stroke was followed acutely (1–2 days) or chronically (7 days) by a mild transient middle cerebral artery occlusion (tMCAO). MRI was performed after each insult, followed by final histology.

Results

The initial PT produced small hyperintense T₂ and DW infarct lesions and peri-lesion regions of scattered necrosis and modestly increased T₂. Following tMCAO, in a slice and a region adjacent to the PT, a region of T₂ augmentation was observed when recovery between insults was acute but not chronic. Within the PT slice, a modest region of exacerbated T₂ change proximate to the PT was also observed in the chronic group. Corresponding histological changes within regions of augmented T₂ included increased vacuolation and cell death.

Conclusion

Within regions adjacent to an experimental minor stroke, a recurrence of a mild transient cerebral ischemia augmented T₂ above increases produced by tMCAO alone, reflecting increased damage in this region. Exacerbation appeared broader with acute versus chronic recovery between insults.

     

Evaluation of a suture electrode for direct bladder stimulation in a lower motor neuron lesioned animal model.

The purpose of this study was to evaluate a "suture" type electrode for direct bladder stimulation in an animal model of a lower motor neuron lesion. During an initial surgery, five male cats were instrumented under anesthesia using multistranded, 316 LVM, stainless-steel, wire electrodes implanted on the bladder wall serosa above the trigone area. Electrodes were constructed with a needle attached to the end that was removed after suturing the electrode in place. Additional instrumentation included urinary bladder catheters (tubes) for pressure recording and filling, and hook type electrodes for leg and pelvic floor electromyography recording. Chronic bladder filling and stimulation studies were conducted in tethered animals three to four weeks following surgery. To test these electrodes in a spinal cord injury model, a lower motor neuron lesion was performed including the sacral cord and complete nerve roots at L6 and below. These animals were evaluated during weeks 3 and 10 after injury. Direct bladder stimulation induced active contractions and voiding both before and after spinal cord injury. Effective stimulation parameters consisted of 40 pulses per s, 300 micros to 1 ms pulse duration, a stimulation period from 3 to 4 s, and a stimulation current from 10 to 40 mA. Fluoroscopy revealed an open membranous urethra during stimulation and following stimulation. A small diameter penile urethra was observed to limit flow. Postmortem evaluation of the suture electrode revealed no abnormalities such as corrosion, migration into the bladder lumen or displacement. These findings indicate that suture electrodes are suitable and effective for short-term implantation in the lower motor neuron animal model.     

Construction of an in vitro model system for the anatomical reentry phenomenon of cardiac tissues by using microfabrication techniques

Anatomical reentry has been identified as a major cause of clinical cardiac arrhythmia. The probability for anatomical reentry is strongly dependent on the structures and cell characteristics of the causal cardiac regions. In this paper, we propose a simple in vitro model system for analyzing and simulating the anatomical reentry phenomenon in cardiac tissues. Rat ventricular myocytes were cultured and aligned in predesigned structures by using a microcontact printing method. Excitation propagation in the cultures was visualized and evaluated by applying electrical stimulation and the calcium imaging technique. We confirmed that differences between passage times along the two excitation pathways were modulated by changing the structures of cultured myocytes. This simple in vitro model system will be useful for studying the anatomical reentry phenomenon. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

电流回路隐性缺陷在线检测装置的研制与应用

为保证电流二次回路隐性缺陷检测的有效性和快速性,本文设计了一种基于负载阻抗测量的二次电流回路隐性缺陷在线检测装置。装置能够在线采集电流二次回路的电压和电流,然后自动计算出电流二次回路的负载阻抗值,当电流二次回路存在虚接、端子排裂痕等隐性缺陷时,回路负载阻抗值异常,装置能够进行自动判断,并显示回路存在隐性缺陷的具体相别。现场应用实践表明,装置可快速判别出电流二次回路的隐性缺陷,为检修人员准确判断故障点提供依据,提高变电站二次设备运行的可靠性和安全性。     

Using a genetic algorithm for detection and magnitude determination of turn faults in an induction motor

This paper presents a novel scheme for the detection and magnitude determination of turn faults, based on parameter identification of a model in which the turn fault is considered. A genetic algorithm does parameter identification. Insensitivity of the technique to load variation, supply voltage variation, temperature variation, and unbalanced supply voltage is shown by many experimental tests.     

Accurate simulation of commutation overlap effects in an HVDC terminal model for power flow studies

This paper presents a simple algorithm for accurately including the effects of the converter commutation overlap angle in an existing DC model for power flow studies of integrated DC/AC power system networks. The algorithm described provides accurate results during normal DC operating conditions with little additional computation. It can be used for both point-to-point (two-terminal) and multi-terminal DC (MTDC) schemes.A flexible six-variable per DC terminal model is used for the MTDC schemes and an eleven-variable DC link model is used for the point-to-point schemes. The DC equations are combined in each iteration with the AC equations in a simultaneous solution of the power flow problem by using the fast decoupled method.     

Two-stage stochastic-robust model for the self-scheduling problem of an aggregator participating in energy and reserve markets

This paper addresses a two-stage stochastic-robust model for the day-ahead self-scheduling problem of an aggregator considering uncertainties. The aggregator, which integrates power and capacity of small-scale prosumers and fexible community-owned devices, trades electric energy in the day-ahead (DAM) and real-time energy markets (RTM), and trades reserve capacity and deployment in the reserve capacity (RCM) and reserve deployment markets (RDM). The ability of the aggregator providing reserve service is constrained by the regulations of reserve market rules, including minimum ofer/bid size and minimum delivery duration. A combination approach of stochastic programming (SP) and robust optimization (RO) is used to model diferent kinds of uncertainties, including those of market price, power/demand and reserve deployment. The risk management of the aggregator is considered through conditional value at risk (CVaR) and fuctuation intervals of the uncertain parameters. Case studies numerically show the economic revenue and the energy-reserve schedule of the aggregator with participation in diferent markets, reserve regulations, and risk preferences.     

Optimisation of a sensor for onsite detection of partial discharges in power transformers by the UHF method

Among the different solutions which allow onsite Partial Discharge measurement in energized power transformers, the UHF technique is gaining general interest. In order to apply this method in existing transformers, it is considered advantageous to design a UHF sensor to be fitted inside the transformer tank. This paper describes the constraints affecting the development of such sensor and the process followed to optimize its design. During this process, different solutions for broadband UHF antennas were analysed. The selection was based on computer simulation and experimental results. Computer simulation was used to evaluate differences in radiation pattern, antenna impedance, gain and effective area. Measurements of the antenna response to different partial discharge sources in oil were performed using an oil dielectric breakdown test set in an electromagnetic shielded laboratory. A group of selected antennas were then tested in a power transformer simulating the broadband signals generated by partial discharges by injecting controlled voltage pulses in the transformer. Finally, a sensor based on a conical monopole antenna structure was built and attached to a specially designed housing to be fitted inside the transformer tank through the drain valve. This final prototype was benchmarked during a high voltage factory test of a power transformer which showed a significant partial discharge activity.     

Challenges for labeling and longitudinal tracking of adoptively transferred autoreactive T lymphocytes in an experimental type-1 diabetes model

Magnetic Resonance Materials in Physics, Biology and Medicine - Tracking the autoreactive T-cell migration in the pancreatic region after labeling with fluorinated nanoparticles...     

Chemotherapy response of pancreatic cancer by diffusion-weighted imaging (DWI) and intravoxel incoherent motion DWI (IVIM-DWI) in an orthotopic mouse model

Magnetic Resonance Materials in Physics, Biology and Medicine - To investigate the value of using diffusion-weighted imaging (DWI) and intravoxel incoherent motion DWI (IVIM-DWI) to assess the...     

悬挂式防渗墙控制堤基渗透变形发展模型试验

在室内比例为1∶40的钢化玻璃模型槽中进行堤基渗透变形模型试验。模拟二元结构堤基在不同防渗墙深度、位置条件下渗透变形的发生、发展过程。测试得到随着渗透变形的发展,堤基内部水头的变化、流量变化以及预留出口出砂面积的变化情况。通过理论分析并结合数值计算,合理的解释了在各个阶段渗透变形通道的发展模式,并评估了当防渗墙处于不同位置时对于抑制渗透变形发展所起到的作用。     

Development of an analytical model for generation expansion planning as a tool to provide guidelines for preventing instability in the long‐term electricity market

This paper considers the problem of deciding multiperiod investments for generation expansion planning (GEP) in restructured power systems. This problem has presented a challenge for both market managers and suppliers regarding the stability in the electricity market and minimum income for suppliers over the planning period. In this paper, an analytical model for studying the GEP problem from the viewpoint of a central management entity is presented. The aim of this method is to establish a dynamic balance between energy supply and demand by adjustment of GEP over the horizon of planning so that not only the expected profit is provided for all new generating plants but the long‐term stability in the electricity market is also improved. This analytical model can be utilized by regulatory bodies to obtain some guidelines and thereby to set their policies for improving GEP and preventing instability in the long‐term electricity market. To do so, in this study, the uncertainties of demand and supply have been modeled through two stochastic processes. Furthermore, the market price dynamics and their mutual effects on the GEP's results have been considered. Finally, this nonlinear dynamic optimization problem is solved using a modified genetic algorithm (GA). The efficiency and ability of the proposed method are examined on a test power system. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A model for numerical evaluation of the global stability region in power systems determined by a nonlinear limit cycle

A power system is a large dynamic system, which includes many nonlinear elements. According to the nonlinear analyses using Hopf bifurcation theory, it can be detected that a limit cycle exists around an operating point, which may affect the global stability of a power system significantly. The authors have presented a numerical method to analyze the nonlinear characteristics in power systems by observing the power swing after some perturbation where the coefficients of nonlinear terms are determined by the least squares method. In this paper the method is modified for the application to a longitudinally interconnected power system including an excitation system, and the influence of the excitation voltage limiter on the nonlinear phenomena of the whole power system can be detected by some numerical analyses. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(3): 17–27, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10193     

Use of a graphical user interface approach for digital and physicalsimulation in power systems control education: application to an HVDCtransmission system model

The authors present the design of a laboratory with software and hardware structures for digital and physical simulation in the area of power systems control education. The hardware structure includes a physically based model of the power system. The software structure includes a special man-machine interface designed with a graphical user interface approach. This interface allows the user full control over the simulation and provides facilities for the study of the response of the simulated system. This approach is illustrated with the design of a control system for a physically based high-voltage DC transmission system model