Journal articles on the topic 'Transient shunt model'
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Venkataraman, Pranav, Samuel R. Browd, and Barry R. Lutz. "A physical framework for implementing virtual models of intracranial pressure and cerebrospinal fluid dynamics in hydrocephalus shunt testing." Journal of Neurosurgery: Pediatrics 18, no. 3 (September 2016): 296–305. http://dx.doi.org/10.3171/2016.2.peds15478.
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OBJECTIVE The surgical placement of a shunt designed to resolve the brain's impaired ability to drain excess CSF is one of the most common treatments for hydrocephalus. The use of a dynamic testing platform is an important part of shunt testing that can faithfully reproduce the physiological environment of the implanted shunts. METHODS A simulation-based framework that serves as a proof of concept for enabling the application of virtual intracranial pressure (ICP) and CSF models to a physical shunt-testing system was engineered. This was achieved by designing hardware and software that enabled the application of dynamic model-driven inlet and outlet pressures to a shunt and the subsequent measurement of the resulting drainage rate. RESULTS A set of common physiological scenarios was simulated, including oscillations in ICP due to respiratory and cardiac cycles, changes in baseline ICP due to changes in patient posture, and transient ICP spikes caused by activities such as exercise, coughing, sneezing, and the Valsalva maneuver. The behavior of the Strata valve under a few of these physiological conditions is also demonstrated. CONCLUSIONS Testing shunts with dynamic ICP and CSF simulations can facilitate the optimization of shunts to be more failure resistant and better suited to patient physiology.
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Poznanski, Roman R. "Transient response in a tapering cable model with somatic shunt." NeuroReport 7, no. 10 (July 1996): 1700. http://dx.doi.org/10.1097/00001756-199607080-00035.
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Xiong, Jun Jie, Min Sun, Rui Xiang Fan, Tao Ding, and Luo Jiang Qian. "Research of Digital Simulating Model of Assembling Shunt Capacitor." Advanced Materials Research 605-607 (December 2012): 2413–18. http://dx.doi.org/10.4028/www.scientific.net/amr.605-607.2413.
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The paper describes numerical base of user defined component model (UDC) for real time digital simulator (RTDS), gives applied method of UDC technique combined with user defined steps of assembling shunt capacitor (ASC), compares transient simulating results of ASC UDC with models from RTDS library, and demonstrates UDC possess higher simulating efficiency and simulating quality is not decreased.
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Kisielewicz, Tomasz, and Milton Cuenca. "Overview of Transient Simulations of Grounding Systems under Surge Conditions." Energies 15, no. 20 (October 18, 2022): 7694. http://dx.doi.org/10.3390/en15207694.
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The present paper gives an overview of modelling methods of standard grounding systems under surge conditions, using the non-uniform transmission line approach. The model presented considers the soil ionization and the frequency dependence of the soil parameters during the current transients. Furthermore, the representation of the non-linear response of the soil is made using a shunt time-variable resistance to simulate the behavior of the grounding resistance when a surge current flows through the system. The model development and analysis are made using ATP-EMTP/ATPDraw transient software.
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Yang, Guang, Lin Li, Xile Zhang, Qing Jia, and Liqiang Liu. "A Transient Model for Controlled Shunt Reactor Based on Duality Theory." IEEE Transactions on Magnetics 51, no. 3 (March 2015): 1–4. http://dx.doi.org/10.1109/tmag.2014.2359013.
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Hoh, Brian L., Shih-Shan Lang, Michael V. Ortiz, Yueh-Yun Chi, Stephen B. Lewis, and David W. Pincus. "LOWER INCIDENCE OF REOPERATION WITH LONGER SHUNT SURVIVAL WITH ADULT VENTRICULOPERITONEAL SHUNTS PLACED FOR HEMORRHAGE-RELATED HYDROCEPHALUS." Neurosurgery 63, no. 1 (July 1, 2008): 70–75. http://dx.doi.org/10.1227/01.neu.0000335072.32105.38.
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ABSTRACT OBJECTIVE The incidence of reoperation for ventriculoperitoneal shunts (VPS) in adults, although lower than in pediatric patients, is not insignificant. We hypothesize that adult VPS placed for hemorrhage-related hydrocephalus have a lower incidence of reoperation than those placed for other types of hydrocephalus. METHODS We retrospectively reviewed all adult (≥ 20 yr) VPS initially placed from February 2001 to August 2006 at the University of Florida. We determined the incidence and time interval to reoperation. Follow-up was conducted by telephone interview and review of medical records. RESULTS A total of 286 adult VPS were initially placed: 96 (34%) hemorrhage and 190 (66%) nonhemorrhage. A total of 15 (16%) hemorrhage patients underwent 22 shunt reoperations, compared with 50 (27%) nonhemorrhage patients who underwent 82 shunt reoperations (P = 0.0316). A Poisson regression analysis of the number of reoperations, factoring hemorrhage, age, and sex, demonstrated a significantly lower incidence of reoperation in hemorrhage patients (P = 0.0900). A Cox proportional hazards model analysis of time to first reoperation, factoring hemorrhage, age, and sex, demonstrated a significantly longer shunt survival in hemorrhage patients (P = 0.0404). CONCLUSION Adult VPS placed for hemorrhage-related hydrocephalus have a significantly lower incidence of reoperation and significantly longer shunt survival. This result may be related to an incidence of transient shunt dependency in patients with hemorrhage-related hydrocephalus. However, the precise mechanism remains unclear.
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Guo, Xiaomei, Chongyang Jiang, Heng Qian, Zuchao Zhu, and Changquan Zhou. "Effect of Tip Clearance on the Cavitation Flow in a Shunt Blade Inducer." Energies 15, no. 17 (August 30, 2022): 6330. http://dx.doi.org/10.3390/en15176330.
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In order to study the effect of tip clearance on the internal cavitation stability of a shunt blade inducer, an external characteristics experiment of a centrifugal pump with a shunt blade inducer was carried out. Based on the turbulence model and mixture model, the cavitating flow in a centrifugal pump with the inducer was numerically simulated. The influence of tip clearance on the cavitating flow in a shunt inducer was studied and analyzed. Through the research, it was found that tip clearance has a certain influence on the critical cavitation coefficient. The existence of the tip clearance caused a significant leakage vortex near the inducer’s inlet and a strong transient effect was shown. The location and degree of cavitation caused by the tip leakage are clarified in this paper. Tip clearance has a great impact on the pressure distribution on a shunt blade inducer. The influence law of tip clearance on an inducer’s blade load distribution was clarified. The results showed that tip clearance has a significant effect on the cavitation of a shunt blade inducer under low flow rate conditions.
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Van, Chi Nguyen, and Hoang Dang Danh. "Control shunt active filter based on dq frame using current model prediction." IAES International Journal of Robotics and Automation (IJRA) 8, no. 4 (December 1, 2019): 301. http://dx.doi.org/10.11591/ijra.v8i4.pp301-312.
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The nonlinear loads present more in the power systems in the practice today by developing of electronic technology and using the small distributed power sources (solar power, wind power etc.), this causes the increasing the high frequency switch devices etc. in the power network. Nonlinear loads cause non-sinusoidal currents and voltages with harmonic components, increasing the reactive power, overload of power lines and electrical devices, low power factor and affecting badly to the networks. Shunt active filters (SAF) with current controlled voltage source inverters (CCVSI) are used effectively to reduce the harmonics and to balance the phases sinusoidal source currents by generating the currents to compensate the harmonic currents caused by the nonlinear loads. In this paper we suppose a control strategy to generate the compensation currents of SAF by using the current model predictive engineering. This method is better than the control strategy using PI controller in term of transient time. The desired compensation currents can track exactly the reference compensation currents on the dq frame. The simulation results implemented on the nonlinear load, a full bridge rectifier and 3 phase unbalance load, show that the transient period decrease from 0.1s to 0.02s in comparing with PI controller. The experimental results proof that the THD of source currents decrease from 24.8% to 5.4% when using the proposed method.
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Oramus, Piotr, Tomasz Chmielewski, Tomasz Kuczek, Wojciech Piasecki, and Marcin Szewczyk. "Transient recovery voltage analysis for various current breaking mathematical models: shunt reactor and capacitor bank de-energization study." Archives of Electrical Engineering 64, no. 3 (September 1, 2015): 441–58. http://dx.doi.org/10.2478/aee-2015-0034.
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Abstract Electric arc is a complex phenomenon occurring during the current interruption process in the power system. Therefore performing digital simulations is often necessary to analyse transient conditions in power system during switching operations. This paper deals with the electric arc modelling and its implementation in simulation software for transient analyses during switching conditions in power system. Cassie, Cassie-Mayr as well as Schwarz-Avdonin equations describing the behaviour of the electric arc during the current interruption process have been implemented in EMTP-ATP simulation software and presented in this paper. The models developed have been used for transient simulations to analyse impact of the particular model and its parameters on Transient Recovery Voltage in different switching scenarios: during shunt reactor switching-off as well as during capacitor bank current switching-off. The selected simulation cases represent typical practical scenarios for inductive and capacitive currents breaking, respectively.
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Poznanski, Roman R. "Transient response in a somatic shunt cable model for synaptic input activated at the terminal." Journal of Theoretical Biology 127, no. 1 (July 1987): 31–50. http://dx.doi.org/10.1016/s0022-5193(87)80159-5.
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Janaki, M., R. Thirumalaivasan, and Nagesh Prabhu. "Design of Robust Current Controller for Two-Level 12-Pulse VSC-based STATCOM." Advances in Power Electronics 2011 (June 16, 2011): 1–7. http://dx.doi.org/10.1155/2011/912749.
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The static synchronous compensator (STATCOM) is a shunt connected voltage source converter (VSC) based FACTS controller using GTOs employed for reactive power control. A typical application of a STATCOM is for voltage regulation at the midpoint of a long transmission line for the enhancement of power transfer capability and/or reactive power control at the load centre. The PI controller-based reactive current controller can cause oscillatory instability in inductive mode of operation of STATCOM and can be overcome by the nonlinear feedback controller. The transient response of the STATCOM depends on the controller parameters selected. This paper presents a systematic method for controller parameter optimization based on genetic algorithm (GA). The performance of the designed controller is evaluated by transient simulation. It is observed that the STATCOM with optimized controller parameters shows excellent transient response for the step change in the reactive current reference. While the eigenvalue analysis and controller design are based on D-Q model, the transient simulation is based on both D-Q and 3-phase models of STATCOM (which considers switching action of VSC).
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Jarupula, Somlal, Narsimha Rao Vutlapalli, and Narsimha Rao Vutlapalli. "Power Quality Improvement in Distribution System using ANN Based Shunt Active Power Filter." International Journal of Power Electronics and Drive Systems (IJPEDS) 5, no. 4 (April 1, 2015): 568. http://dx.doi.org/10.11591/ijpeds.v5.i4.pp568-575.
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<p>This paper focuses on an Artificial Neural Network (ANN) controller based Shunt Active Power Filter (SAPF) for mitigating the harmonics of the distribution system. To increase the performance of the conventional controller and take advantage of smart controllers, a feed forward-type (trained by a back propagation algorithm) ANN-based technique is implemented in shunt active power filters for producing the controlled pulses required for IGBT inverter. The proposed approach mainly work on the principle of capacitor energy to maintain the DC link voltage of a shunt connected filter and thus reduces the transient response time when there is abrupt variation in the load. The entire power system block set model of the proposed scheme has been developed in MATLAB environment. Simulations are carried out by using MATLAB, it is noticed that the %THD is reduced to 2.27% from 29.71% by ANN controlled filter. The simulated experimental results also show that the novel control method is not only easy to be computed and implemented, but also very successful in reducing harmonics.</p><p> </p>
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Alia Jasim Mohammed. "AN APPRAISAL OF THE TRANSIENT RESPONSE OF A D.C. SHUMT MOTOR USING MATLAB/SIMULINK UNDER NO LOADING AND FULL LOADING CONDITIONS." Diyala Journal of Engineering Sciences 4, no. 2 (December 1, 2011): 130–40. http://dx.doi.org/10.24237/djes.2011.04210.
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Electric machines are used to generate electrical power in power plants and provide mechanical work in industries. This paper describes the MATLAB/SIMULINK realization of the performance of a D.C. shunt motor and introduces model power components to use computer simulation as a tool for conducting transient by using Simulink and SimPower System. These simulation models were employed to calculate the speed (N), torque (T), armature current (Ia), input and output power (Pin and Pout), losses (Plosses) and efficiency (η) for the motor at no load and load conditions. The results obtained using MATLAB were compared with the practical results, the ratio of error is about (1-2) % was found. The SIMULINK was written in MATLAB languages version (6.5).
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Stone, Scellig S. D., and Benjamin C. Warf. "Combined endoscopic third ventriculostomy and choroid plexus cauterization as primary treatment for infant hydrocephalus: a prospective North American series." Journal of Neurosurgery: Pediatrics 14, no. 5 (November 2014): 439–46. http://dx.doi.org/10.3171/2014.7.peds14152.
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Object Combined endoscopic third ventriculostomy with choroid plexus cauterization (ETV/CPC) enhances the likelihood of shunt freedom over ETV alone, and thus avoidance of shunt-related morbidity, in hydrocephalic infants. To date, virtually all published reports describe experiences in Africa, thus hampering generalization to other parts of the world. Here, the authors report the first North American prospective series of this combined approach to treat hydrocephalus of various etiologies in infants. Methods A prospective series of 50 boys and 41 girls (mean and median ages 4.7 and 3.2 months, respectively) with hydrocephalus underwent ETV/CPC performed by the senior author at Boston Children's Hospital from August 2009 through March 2014. Success data were analyzed using the Kaplan-Meier method and Cox proportional hazards model. Results The 91 patients treated included those with aqueductal stenosis (23), myelomeningocele (23), posthemorrhagic hydrocephalus (25), Dandy-Walker complex (6), post-infectious hydrocephalus (6), and other conditions (8). Using Kaplan-Meier survival analysis, 57% of patients required no further hydrocephalus treatment at 1 year. Moreover, 65% remained shunt free to the limit of available follow-up (maximum roughly 4 years). A Cox proportional hazards model identified the following independent predictors of ETV/CPC failure: post-infectious etiology, age at treatment younger than 6 months, prepontine cistern scarring, and prior CSF diversion. Of patients with at least 6 months of follow-up, the overall ETV/CPC success at 6 months (59%) exceeded that predicted by the ETV Success Score (45%). Complications included 1 CSF leak and 1 transient syndrome of inappropriate antidiuretic hormone secretion, and there were no deaths. Conclusions ETV/CPC is an effective, safe, and durable treatment for infant hydrocephalus in a North American population, with 1-year success rates similar to those reported in Africa and equivalent to those for primary shunt placement in North America. These findings underscore the need for prospective multicenter studies of the outcomes, quality of life, and economic impact of the procedure compared with primary shunt insertion.
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Wu, Zhensheng, Deling Fan, and Fan Zou. "Traction Load Modeling and Parameter Identification Based on Improved Sparrow Search Algorithm." Energies 15, no. 14 (July 10, 2022): 5034. http://dx.doi.org/10.3390/en15145034.
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In this paper, a traction load model parameter identification method based on the improved sparrow search algorithm (ISSA) is proposed. According to the load characteristics of the AC traction power supply system under transient disturbance, the model structure of the traction load is equated to the composite load model structure of the static load shunt induction motor’s dynamic load. The traditional sparrow search algorithm is improved to enhance its accuracy and convergence. The generalization ability of the model was tested, and the accuracy of the proposed model was verified. Using the ISSA to determine the load model from the measured data, the results can verify the effectiveness of the ISSA for comprehensive load model parameter identification. Comparing the ISSA with the traditional SSA and PSO algorithms, it shows that the ISSA has better accuracy and convergence.
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Xu, Pan, Haiyun Yuan, Jian Zhuang, Neichuan Zhang, Qianjun Jia, Yuhao Dong, Qifei Jian, and Meiping Huang. "The Hemodynamics of Patent Ductus Arteriosus in Patients after Central Shunt Operation." Computational and Mathematical Methods in Medicine 2021 (April 24, 2021): 1–12. http://dx.doi.org/10.1155/2021/6675613.
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A central shunt (CS) was an important surgery of systemic-to-pulmonary shunt (SPS) for the treatment of complex congenital heart diseases with decreased pulmonary blood flow (CCHDs-DPBF). There was no clear conclusion on how to deal with unclosed patent ductus arteriosus (PDA) during CS surgery. This study expanded the knowledge base on PDA by exploring the influence of the closing process of the PDA on the hemodynamic parameters for the CS model. The initial three-dimensional (3D) geometry was reconstructed based on the patient’s computed tomography (CT) data. Then, a CS configuration with three typical pulmonary artery (PA) dysplasia structures and different sizes of PDA was established. The three-element windkessel (3WK) multiscale coupling model was used to define boundary conditions for transient simulation through computational fluid dynamics (CFD). The results showed that the larger size of PDA led to a greater systemic-to-pulmonary shunt ratio ( Q S / A ), and the flow ratio of the left pulmonary artery (LPA) to right pulmonary artery (RPA) ( Q L / R ) was more close to 1, while both the proportion of high wall shear stress (WSS) areas and power loss decreased. The case of PDA nonclosure demonstrates that the aortic oxygen saturation (Sao2) increased, while the systemic oxygen delivery (Do2) decreased. In general, for the CS model with three typical PA dysplasia, the changing trends of hemodynamic parameters during the spontaneous closing process of PDA were roughly identical, and nonclosure of PDA had a series of hemodynamic advantages, but a larger PDA may cause excessive PA perfusion and was not conducive to reducing cyanosis symptoms.
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Xiang, Changyuan, Zutao Xiang, Wenjia Xu, and Weihua Xiang. "Transient Characteristics Analysis of 500kV Parallel Circuit Breaker Based on Highly Coupled Split Reactor." E3S Web of Conferences 118 (2019): 02048. http://dx.doi.org/10.1051/e3sconf/201911802048.
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With the continuous expansion of power system capacity, parallel high-voltage circuit breakers with a Highly Coupled Split Reactor (HCSR) have a potential application for limitation of high short-circuit current. However, as the parallel circuit breakers open at different time, the residual voltage of the split reactor on the post-open circuit breaker is higher and the stray capacitors of HCSR form high-order oscillating circuits, which may lead to serious transient recovery voltage (TRV). Therefore, it is necessary to analyze and simulate the transient characteristics of 500kV HCSR. Firstly, the equivalent model of HCSR circuit breakers is built in EMTP simulation plat-form, and its TRV generation is analyzed. Then, the TRV of parallel circuit breakers under different operating conditions and fault types is simulated and calculated. Finally, according to the statistical calculation results, the protection measure of 0.2uF shunt capacitance to limit rise rate of TRV is proposed.
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CHENNAI, Salim. "Shunt Active Power Filter Performances based on Seven-level NPC Inverter using Fuzzy and LS-PWM Control Scheme." Electrotehnica, Electronica, Automatica 70, no. 1 (March 15, 2022): 23–30. http://dx.doi.org/10.46904/eea.22.70.1.1108003.
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This paper presents novel seven-level neutral point clamped (npc) shunt active power filter system based on LS-PWM and fuzzy control approaches which can eliminate current harmonics generated by nonlinear loads. Today, multi-level inverters are strongly used in the medium and high voltage applications; their advantages are low harmonic distortions, low switching losses, low electromagnetic interference, and low acoustic noise. Second, fuzzy logic techniques have been successfully employed in several power electronic applications. Fuzzy controller does not need an accurate mathematical model, can work with imprecise inputs, can handle non-linearity, and are more robust than conventional controllers. To benefit from these advantages a novel control scheme for seven-level (npc) inverter based on Fuzzy and LS-PWM technique is proposed. The reference current signals required to compensate harmonic currents use the synchronous current detection method, this technique is easy to implement and achieves good performances for harmonic compensation. The proposed shunt APF is evaluated using Matlab-Simulink software and SimPowerSystem Toolbox under transient and steady state for various operation conditions. The simulation results show the effectiveness of the proposed shunt active filter based on seven-level (NPC) inverter for improving the power quality and the superiority of combined fuzzy and LS-PWM control scheme to conventional controller in term of harmonics compensation and dynamic performances.
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Velpula, Srikanth, Thirumalaivasan R, and Janaki M. "Stability Enhancement of STATCOM using Flower Pollination Algorithm." International Journal of Engineering & Technology 7, no. 4.10 (October 2, 2018): 206. http://dx.doi.org/10.14419/ijet.v7i4.10.20897.
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The Static Synchronous Compensator (STATCOM) is a Voltage Source Converter (VSC) based shunt connected FACTS device. The key roles of STATCOM are to control the voltage at midpoint of transmission line, enhance power transfer capability and control reactive power at load end. However, the performance of STATCOM depends upon the parameters of the controller. In this paper, we present the tuning of Type-1 controller parameters for STATCOM based on a systematic method using Flower Pollination Algorithm (FPA). The margins for the Type-1 controller parameters are estimated from the movement of eigenvalues for the variation in controller parameters during inductive and capacitive modes of STATCOM. The performance of the STATCOM with FPA optimized Type-1 controller parameters is evaluated by transient simulation. The eigenvalue analysis and transient simulation are done based on D-Q model of STATCOM. It is noticed that, the response of STATCOM follows the step change in reactive current reference with least error.
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Wang, Xiuli, Yonggang Lu, Rongsheng Zhu, Yuanyuan Zhao, and Qiang Fu. "Study on pressure pulsation characteristics of reactor coolant pump during the idling transition process." Journal of Vibration and Control 25, no. 18 (June 21, 2019): 2509–22. http://dx.doi.org/10.1177/1077546319858856.
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The idling characteristic of the reactor coolant pump is one of the important indicators for the safe operation of the nuclear power system. The idling transition process of the reactor coolant pump under the power failure accident condition belongs to the transient flow process. During most of the time of the idling transition process, the parameters of flow, rotating speed, and head are all nonlinear changes, and the study of the idling change law is extremely difficult. This paper introduces the nonlinear inertia transient phase of the reactor coolant pump and the principle of wavelet analysis. Based on the experimental results of the idling transition process, the polynomial fitting of the flow curve and the rotating speed curve is fitted, and the idling transient equation is established which is a boundary condition for computational fluid dynamics simulation of the nonlinear idling transient stage of the reactor coolant pump with different types of guide vanes. The signal fluctuation of pressure pulsation time-domain change at the volute outlet in different sub-bands is analyzed by means of a fast, discrete wavelet transform, and the effects of different vane optimizations in different idling stages are analyzed. It was found that the pressure fluctuation amplitude of each sub-frequency range of pump outlet in the model of the shunt guide vane is significantly smaller than that of the normal guide vane.
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Gonser, M. "P21.01: Transient shunt of low oxygenated blood to the fetal brain: may antenatal steroids trigger decompensation in ARED-fetuses? An explanatory model." Ultrasound in Obstetrics & Gynecology 44, S1 (September 2014): 309. http://dx.doi.org/10.1002/uog.14410.
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Alsuwian, Turki, Abdul Basit, Arslan Ahmed Amin, Muhammad Adnan, and Mansoor Ali. "An Optimal Control Approach for Enhancing Transients Stability and Resilience in Super Smart Grids." Electronics 11, no. 19 (October 8, 2022): 3236. http://dx.doi.org/10.3390/electronics11193236.
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Super smart grids (SSGs) are a wide area transmission network that mainly uses renewable energy resources (RERs), contributing to the reduction of greenhouse gas (GHGs) emissions and supporting the power infrastructure of multiple countries. The SSGs comprise two-way communication between the loads and sources of different countries, and these loads can be mostly served with numerous types of RERs tied with the grids. The RERs will play a pivotal role in the development of future grids and the generation of electricity. However, the main challenge to tackle in these RERs is that they are intermittent in nature. Due to intermittency in these RERs, transient stability issues have become one of the critical research challenges in SSGs. These stability issues are escalated and become more difficult to handle if a network is vulnerable to an arising of different kinds of faults. To address these problems, multiple approaches to enhance transient stability already exist in the current literature. After reviewing the literature, flexible alternating current transmission systems (FACTS) devices proved more promising in improving transient stability. Among FACTSdevices, UPFC is a versatile FACTS device, which provides complete stability to power system networks in the form of series and shunt compensations. Considering this scenario, a hypothetical network for SSGs is designed in this research work based on the interconnection between two countries, i.e., Denmark and Norway, to address the transient stability issues in SSGs. The complete probabilistic model of the system is also designed to enhance the stability of the system. The results clearly showed that the insertion of UPFC is an effective technique to enhance the transient stability and resilience of the power system networks as compared to other purposed techniques in the literature. The main contribution of this paper is that extensive simulation studies employing accurate RERs models are used to analyze and investigate various problems arising due to the integration of many clusters of RERs in SSGs.
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Ohashi, Nobuko, Daisuke Uta, Mika Sasaki, Masayuki Ohashi, Yoshinori Kamiya, and Tatsuro Kohno. "Acetaminophen Metabolite N-Acylphenolamine Induces Analgesia via Transient Receptor Potential Vanilloid 1 Receptors Expressed on the Primary Afferent Terminals of C-fibers in the Spinal Dorsal Horn." Anesthesiology 127, no. 2 (August 1, 2017): 355–71. http://dx.doi.org/10.1097/aln.0000000000001700.
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Abstract Background The widely used analgesic acetaminophen is metabolized to N-acylphenolamine, which induces analgesia by acting directly on transient receptor potential vanilloid 1 or cannabinoid 1 receptors in the brain. Although these receptors are also abundant in the spinal cord, no previous studies have reported analgesic effects of acetaminophen or N-acylphenolamine mediated by the spinal cord dorsal horn. We hypothesized that clinical doses of acetaminophen induce analgesia via these spinal mechanisms. Methods We assessed our hypothesis in a rat model using behavioral measures. We also used in vivo and in vitro whole cell patch-clamp recordings of dorsal horn neurons to assess excitatory synaptic transmission. Results Intravenous acetaminophen decreased peripheral pinch-induced excitatory responses in the dorsal horn (53.1 ± 20.7% of control; n = 10; P < 0.01), while direct application of acetaminophen to the dorsal horn did not reduce these responses. Direct application of N-acylphenolamine decreased the amplitudes of monosynaptic excitatory postsynaptic currents evoked by C-fiber stimulation (control, 462.5 ± 197.5 pA; N-acylphenolamine, 272.5 ± 134.5 pA; n = 10; P = 0.022) but not those evoked by stimulation of Aδ-fibers. These phenomena were mediated by transient receptor potential vanilloid 1 receptors, but not cannabinoid 1 receptors. The analgesic effects of acetaminophen and N-acylphenolamine were stronger in rats experiencing an inflammatory pain model compared to naïve rats. Conclusions Our results suggest that the acetaminophen metabolite N-acylphenolamine induces analgesia directly via transient receptor potential vanilloid 1 receptors expressed on central terminals of C-fibers in the spinal dorsal horn and leads to conduction block, shunt currents, and desensitization of these fibers.
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Piecha, Felix, Daniel Paech, Janina Sollors, Helmut-Karl Seitz, Martin Rössle, Vanessa Rausch, and Sebastian Mueller. "Rapid change of liver stiffness after variceal ligation and TIPS implantation." American Journal of Physiology-Gastrointestinal and Liver Physiology 314, no. 2 (February 1, 2018): G179—G187. http://dx.doi.org/10.1152/ajpgi.00239.2017.
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Liver stiffness (LS) as measured by transient elastography is widely used to screen for liver fibrosis. However, LS also increases in response to pressure changes like congestion but no data on portal pressure are available. We study here the effect of rapid portal pressure changes on LS. Therefore, LS was assessed directly prior and after ligation of esophageal varices ( n = 11) as well as transjugular intrahepatic portosystemic shunt (TIPS) implantation in patients with established cirrhosis ( n = 14). Additionally, we retrospectively analyzed changes in LS and variceal size in patients with sequential gastroscopic monitoring and LS measurements ( n = 14). To study LS and portal pressure in healthy livers, LS (µFibroscan; Echosens, Paris, France) and invasive pressures (Powerlab, AD Instruments, New Zealand) were assessed in male Wistar rats after ligation of single liver lobes. Ligation of esophageal varices caused an immediate and significant increase of LS from 40.3 ± 19.0 to 56.1 ± 21.5 kPa. Likewise, LS decreased significantly from 53.1 ± 16.6 to 43.8 ± 17.3 kPa after TIPS placement, which correlated significantly with portal pressure ( r = 0.558). In the retrospective cohort, the significant LS decrease from 54.9 ± 23.5 to 47.9 ± 23.8 kPa over a mean observation interval of 4.3 ± 3 mo was significantly correlated with a concomitant increase of variceal size ( r = −0.605). In the animal model, LS and portal pressure increased significantly after single lobe ligation without changes of arterial or central venous pressure. In conclusion, rapid changes of portal pressure are a strong modulator of LS in healthy and cirrhotic organs. In patients with stable cirrhosis according to the model for end-stage liver disease (MELD), a decrease of LS may be indicative for enlarging varices. NEW & NOTEWORTHY Liver stiffness (LS) immediately increases after variceal ligation while it decreases after transjugular intrahepatic portosystemic shunt (TIPS) implantation due to portal pressure changes. LS and portal pressure rapidly increase after single lobe ligation in Wistar rats without changes of arterial or central venous pressure. Collateral formation may be one cause for a transient decrease in LS in the absence of other confounders. Such pressure changes should be considered when interpreting LS in clinical practice.
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Glantz, Raymon M., and John P. Schroeter. "Encoder Adaptation Modulates the Visual Responses of Crayfish Interneurons." Journal of Neurophysiology 92, no. 1 (July 2004): 327–40. http://dx.doi.org/10.1152/jn.00035.2004.
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The responses of sustaining and dimming fibers were characterized by the time varying firing rates elicited by extrinsic current and flashes of light. These data were simulated by an adaptive integrate-and-fire model. A postimpulse shunt conductance simulated spike-frequency adaptation. The correlation between observed and model current-elicited impulse rates was 0.94–0.98. However, except for a difference in input resistance (both measured and simulated), the voltage to impulse encoders of the two cell groups was similar and exhibited comparable degrees of spike-frequency adaptation (40 to 45%). The encoder model derived from current-elicited responses (with fixed parameters) was used to simulate visual responses elicited by light flashes. These simulations included a synaptic current derived from the time course of the postsynaptic potential (PSP). The sustaining fiber visual response consisted of a large excitatory PSP and high-frequency transient burst that adapted (by ∼80%) to a low-frequency plateau discharge. The simulations indicated that spike-frequency adaptation had no effect on the transient discharge but reduced the plateau firing rate by ∼60%. Encoder adaptation enhances the sustaining fiber response to the time derivative of the stimulus. In dimming fibers, the light flash elicits an inhibitory PSP that interrupts the “dark discharge” and an off response following the end of the flash. The simulations indicated that spike-frequency adaptation reduces the firing rate of both the dark discharge and the off response. Thus the model suggests that different effects of encoder adaptation on the two cell types arise from the same encoder mechanisms, but different actions are determined by differences in impulse rate and the time course of the discharge.
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Knabb, Robert M., Charles A. Kettner, Pieter B. M. W. M. Timmermans, and Thomas M. Reilly. "In Vivo Characterization of a New Synthetic Thrombin Inhibitor." Thrombosis and Haemostasis 67, no. 01 (1992): 056–59. http://dx.doi.org/10.1055/s-0038-1648379.
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SummaryWe have examined the in vivo pharmacology of DuP 714 (Ac-[D]-Phe-Pro-boroArginine), a representative of a new series of synthetic thrombin inhibitors which contain a boronic acid derivative of arginine. Intravenous bolus injections of DuP 714 in anesthetized rats and conscious rabbits produced transient elevations of clotting times. Clinically relevant prolongations of the APTT were also observed in rabbits after i. v. infusion of less than 0.1 mg kg-1 h-1. Efficacy against venous thrombosis was demonstrated in a rabbit model of stasis induced thrombosis. Clots formed in 100% of control animals and only 33% of animals treated with 0.5 mg/kg DuP 714, and were less severe in treated animals. In a rabbit arterial-venous shunt model mimicking arterial thrombosis, occlusion occurred within 30 min in 72% of control animals vs. 11% of animals treated with 0.1 mg kg-1 h-1 DuP 714. Results indicate that DuP 714 is a highly effective anticoagulant which should be useful for the prevention of both venous and arterial thrombotic diseases.
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Agasthi, Pradyumna, Kantha Ratnam Kolla, Charan Yerasi, Sibghat Tullah, Venkata Siva Pulivarthi, Boshra Louka, Reza Arsanjani, Eric H. Yang, Farouk Mookadam, and F. David Fortuin. "Are we there yet with patent foramen ovale closure for secondary prevention in cryptogenic stroke? A systematic review and meta-analysis of randomized trials." SAGE Open Medicine 7 (January 2019): 205031211982826. http://dx.doi.org/10.1177/2050312119828261.
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Background: We performed a meta-analysis to evaluate the benefit of patent foramen ovale closure in stroke prevention. Methods: We searched Medline/PubMed, EMBASE, Web of Science and Cochrane central database for randomized control trials assessing the incidence of recurrent stroke after patent foramen ovale closure when compared to medical therapy. Pooled odds ratio and 95% confidence intervals were calculated using a random effects model. The heterogeneity among studies was tested using the χ2 test and inconsistency was quantified using the I2 statistic. Results: Our search strategy yielded 71 articles. We included five studies with a total of 3440 patients. Median age in the device group was 45 (43, 5.5) years and in the medical group was 45 (44.5, 46) years; 52% were male, 27.7% of patients had an atrial septal aneurysm, 25% had hypertension, and 20.5% had diabetes mellitus. The median follow-up time was 44 (34.5–50) months. The pooled odds ratio of recurrent stroke, transient ischemic attack and composite end point of stroke + transient ischemic attack + peripheral embolism in the patent foramen ovale closure versus medical therapy group were 0.4 (95% confidence interval 0.25–0.63, I2 = 57.5%), 0.93 (95% confidence interval 0.61–1.42, I2 = 0%), and 0.6 (95% confidence interval 0.44–0.82, I2 = 0%), respectively. The incidence of atrial fibrillation was found to be significantly higher in the patent foramen ovale closure group with odds ratio of 6 (95% confidence interval 3.13–11.4, I2 = 33.5%). On subgroup analysis, patent foramen ovale closure appeared to benefit males and patients with a large shunt. Number needed to treat to prevent one recurrent stroke with patent foramen ovale closure is 42. Number needed to harm to cause one atrial fibrillation with patent foramen ovale closure is 39. Conclusion: This meta-analysis of randomized trials concludes that percutaneous patent foramen ovale closure is effective in recurrent stroke prevention especially in males and in those with a large shunt.
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Cotton, R. B., D. P. Lindstrom, H. W. Sundell, J. W. Hammon, A. Silberberg, and T. Olsson. "Origin of cardiac-related thoracic electrical impedance variations in lambs." Journal of Applied Physiology 71, no. 3 (September 1, 1991): 1025–31. http://dx.doi.org/10.1152/jappl.1991.71.3.1025.
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Cardiac-related deflections in thoracic electrical impedance have been thought to correlate sufficiently well with cardiac stroke volume to be used as the basis for a noninvasive estimation of cardiac output. To determine more precisely the physiological origin of the impedance deflection (DZ), we regarded right ventricular stroke volume (SVa) as the sum of two components: 1) that part of SVa responsible for the transient increment in pulmonary blood volume within a cardiac cycle, SVa-v and 2) the remaining part of SVa, (SVa-SVa-v). SVa-v was measured in lambs by integration of the difference between pulmonary arterial and pulmonary venous flow. SVa and its components were varied experimentally by opening and closing an aorticocaval shunt or by inflating and deflating a cuff implanted around the pulmonary artery. DZ was measured using a tetrapolar disk electrode system. Multivariate linear regression analysis revealed that SVa-v had a significant positive effect on DZ, and, at the same time, (SVa-SVa-v) had a significant negative effect on DZ. In the pulmonary artery occluder model, the positive effect of SVa-v dominated the opposing negative effect of (SVa - SVa-v) so that the net effect of SVa on DZ was positive and significant. In the aorticocaval shunt model, these effects opposed each other to the extent that there was no significant correlation between SVa and DZ. These results shed new light on the physiological origin of DZ. They also demonstrate that use of DZ to measure acute changes in cardiac output may yield misleading results. Changes or the lack of changes in thoracic electrical impedance do not necessarily reflect cardiac output status.
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Atabay, Orhan, Murat Ötkür, and İsmail M. Ereke. "Model based predictive engine torque control for improved drivability." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 232, no. 12 (October 27, 2017): 1654–66. http://dx.doi.org/10.1177/0954407017733867.
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Elasticity of the various driveline components and backlash originating from gear reduction mechanisms and fasteners may cause torsional vibrations resulting in unintended shunt and shuffle behaviours, when a vehicle is subjected to an acceleration change request. As a result of recent improvements to engine control structures and computational capability developments during the last few decades, the idea of using generated brake torque control has been considered a state of the art research topic among academic researchers and original equipment manufacturers (OEMs). In order to improve transient vehicle response to an acceleration change manoeuvre, a novel engine generated brake torque based model predictive control (MPC) algorithm with an additional anti-shuffle control element has been developed to manipulate the pedal map oriented torque demand signal in an automotive powertrain application. A four mass powertrain model was built and model validation considering longitudinal vehicle dynamics was performed with vehicle level tests using a tip-in followed by a tip out acceleration pedal signal input manoeuvre. Comparison of simulation results and vehicle test data shows that the proposed model is capable of capturing the vehicle acceleration profile revealing unintended error states for the specified input signals. MPC structures based on three mass vehicle models (derived from the four mass model via subtracting tyre dynamics due to high order nonlinearities at the tyre model) was developed in a “MATLAB/Simulink” environment to obtain a smooth and responsive acceleration profile. The MPC controller delivers signal states with the expected performance metrics without error states such as excessive jerks and shuffles. An additional engine to wheel speed difference based proportional controller is employed in order to further reduce powertrain oscillations without compromising from overall system response speed resulting in a comfortable drive.
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Zhang, Jianwu, Benben Chai, and Xingyang Lu. "Active oscillation control of electric vehicles with two-speed transmission considering nonlinear backlash." Proceedings of the Institution of Mechanical Engineers, Part K: Journal of Multi-body Dynamics 234, no. 1 (October 1, 2019): 116–33. http://dx.doi.org/10.1177/1464419319877332.
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The nonlinear backlash can influence the driveability of the electric driveline due to the lack of the traditional clutches and torsional damper devices. During the stand-start, regenerative braking and gear shift process of the electric drive system equipped with two-speed transmission, the request of transient traction motor change will transverse the powertrain backlash, which will excite the driveline oscillations coupled to the first rigid mode of the entire powertrain, referred as shuffle or shunt. These vibrations are transmitted to the chassis, causing deterioration in passenger comfort. In this paper, the nonlinear driveline model including the traction motor, half shaft, driveline backlash, and car wheel are developed. Then, dual extended Kalman filter method is employed to estimate vehicle mass and half shaft torsional angle of the proposed driveline. Based on the estimated information, a hierarchical architecture of the active oscillation compensation is proposed to alleviate the vibration in both contact and backlash mode. The experimental results show that the estimation method is effective and the vehicle shuffle can be significantly decreased by the developed control algorithm.
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Roy, Rajib Baran, Sanath Alahakoon, and Shantha Jayasinghe Arachchillage. "Grid Impacts of Uncoordinated Fast Charging of Electric Ferry." Batteries 7, no. 1 (February 17, 2021): 13. http://dx.doi.org/10.3390/batteries7010013.
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The battery energy storage system (BESS) is an indispensable part of an electric fleet (EF) which needs to be charged by electricity from local grid when the fleet is in the dockyard. The uncoordinated fast charging of BESS in Grid to Ferry (G2F) mode imposes sudden increments of load in the power grid, which is analyzed by a simulated model of grid connected marine load. The probable impact on system stability is examined by MATLAB Simulink and Power World Simulator based models. According to simulation results for IEEE 5 bus system, voltage unbalance factors are 0.01% and 200% for all buses at fundamental and third harmonics frequencies, respectively. The total harmonic distortion (THD) at fundamental frequency becomes 0.16%, 0.16%, and 0.18%, respectively, for three cases. The transient, voltage reactive power (V-Q), and voltage real power (V-P) sensitivity analysis are performed for 7 bus system with load increment contingencies. According to simulation results, the V-Q sensitivity for the assigned contingency is increased by the addition of a shunt generator to the load bus with lowest bus voltage. In case of V-P sensitivity for the selected contingency, the load buses share power among them, and the nose point is attained at maximum shift of power with high V-Q sensitivity.
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Kadrian, David, James van Gelder, Danielle Florida, Robert Jones, Marianne Vonau, Charles Teo, Warwick Stening, and Bernard Kwok. "Long-term Reliability of Endoscopic Third Ventriculostomy." Neurosurgery 56, no. 6 (June 1, 2005): 1271–78. http://dx.doi.org/10.1227/01.neu.0000159712.48093.ad.
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Abstract OBJECTIVE: To describe the short-term operative success and the long-term reliability of endoscopic third ventriculostomy (ETV) for treatment of hydrocephalus and to examine the influence of diagnosis, age, and previous shunt history on these outcomes. METHODS: We retrospectively analyzed 203 consecutive patients from a single institution who had ETV as long as 22.6 years earlier. Patients with hydrocephalus from aqueduct stenosis, myelomeningocele, tumors, arachnoid cysts, previous infection, or hemorrhage were included. RESULTS: The overall probability of successfully performing an ETV was 89% (84–93%). There was support for an association between the surgical success and the individual operating surgeon (odds ratios for success, 0.44–1.47 relative to the mean of 1.0, P = 0.08). We observed infections in 4.9%, transient major complications in 7.2%, and major and permanent complications in 1.1% of 203 procedures. Age was strongly associated with long-term reliability. The longest observed reliability for the 13 patients 0 to 1 month old was 3.5 years. The statistical model predicted the following reliability at 1 year after insertion: at 0 to 1 month of age, 31% (14–53%); at 1 to 6 months of age, 50% (32–68%); at 6 to 24 months of age, 71% (55–85%); and more than 24 months of age, 84% (79–89%). There was no support for an association between reliability and the diagnostic group (n = 181, P = 0.168) or a previous shunt. Sixteen patients had ETV repeated, but only 9 were repeated after at least 6 months. Of these, 4 procedures failed within a few weeks, and 2 patients were available for long-term follow-up. CONCLUSION: Age was the only factor statistically associated with the long-term reliability of ETV. Patients less than 6 months old had poor reliability.
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Rahman Fahim, Shahriar, Subrata K. Sarker, S. M. Muyeen, Md Rafiqul Islam Sheikh, and Sajal K. Das. "Microgrid Fault Detection and Classification: Machine Learning Based Approach, Comparison, and Reviews." Energies 13, no. 13 (July 4, 2020): 3460. http://dx.doi.org/10.3390/en13133460.
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Accurate fault classification and detection for the microgrid (MG) becomes a concern among the researchers from the state-of-art of fault diagnosis as it increases the chance to increase the transient response. The MG frequently experiences a number of shunt faults during the distribution of power from the generation end to user premises, which affects the system reliability, damages the load, and increases the fault line restoration cost. Therefore, a noise-immune and precise fault diagnosis model is required to perform the fast recovery of the unhealthy phases. This paper presents a review on the MG fault diagnosis techniques with their limitations and proposes a novel discrete-wavelet transform (DWT) based probabilistic generative model to explore the precise solution for fault diagnosis of MG. The proposed model is made of multiple layers with a restricted Boltzmann machine (RBM), which enables the model to make the probability reconstruction over its inputs. The individual RBM layer is trained with an unsupervised learning approach where an artificial neural network (ANN) algorithm tunes the model for minimizing the error between the true and predicted class. The effectiveness of the proposed model is studied by varying the input signal and sampling frequencies. A level of considered noise is added with the sample data to test the robustness of the studied model. Results prove that the proposed fault detection and classification model has the ability to perform the precise diagnosis of MG faults. A comparative study among the proposed, kernel extreme learning machine (KELM), multi KELM, and support vector machine (SVM) approaches is studied to confirm the robust superior performance of the proposed model.
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Medouce, Houssam Eddine, and Hocine Benalla. "Predictive Approach for Power Quality Improvement Based Direct Power Control." International Journal of Power Electronics and Drive Systems (IJPEDS) 9, no. 2 (June 1, 2018): 668. http://dx.doi.org/10.11591/ijpeds.v9.i2.pp668-678.
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The extensive use of non-linear loads in industry becomes increasingly a serious problem that affects the quality of energy delivered to customers. Therefore, the shunt active power filter (SAPF) has emerged as an important industrial tool to eliminate induced harmonic currents and compensating of reactive power. This paper proposes an improved control configuration for SAPF based on a modern technique called predictive direct power control (Predictive-DPC). The principle of this control is based on the direct regulation of the instantaneous active and reactive powers to guarantee a good energy quality on the grid side. For this purpose the appropriate average voltage vector which cancels power tracking errors is calculated by a simple predictive model at the bigining of each control period. This type of control includes various features such as the lack of look up table (LUTs) and closed current loops and the constant switching frequency is achieved through the use of PWM modulation. The results of the simulation process show a high performance in the steady and transient state function for predictive-DPC control that might be a reasonable alternative to conventional DPC in the field of active power filtering.
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Martinek, Radek, Jaroslav Rzidky, Rene Jaros, Petr Bilik, and Martina Ladrova. "Least Mean Squares and Recursive Least Squares Algorithms for Total Harmonic Distortion Reduction Using Shunt Active Power Filter Control." Energies 12, no. 8 (April 24, 2019): 1545. http://dx.doi.org/10.3390/en12081545.
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This paper deals with the use of least mean squares (LMS, NLMS) and recursive least squares (RLS) algorithms for total harmonic distortion (THD) reduction using shunt active power filter (SAPF) control. The article presents a pilot study necessary for the construction of our own controlled adaptive modular inverter. The objective of the study is to find an optimal algorithm for the implementation. The introduction contains a survey of the literature and summarizes contemporary methods. According to this research, only adaptive filtration fulfills our requirements (adaptability, real-time processing, etc.). The primary benefit of the paper is the study of the efficiency of two basic approaches to adaptation ((N)LMS and RLS) in the application area of SAPF control. The study examines the impact of parameter settings (filter length, convergence constant, forgetting factor) on THD, signal-to-noise ratio (SNR), root mean square error (RMSE), percentage root mean square difference (PRD), speed, and stability. The experiments are realized with real current and voltage recordings (consumer electronics such as PC source without power factor correction (PFC), HI-FI amplifier, etc.), which contain fast dynamic transient phenomena. The realized model takes into account a delay caused by digital signal processing (DSP) (the implementation of algorithms on field programmable gate array (FPGA), approximately 1–5 μs) and a delay caused by the reaction time of the proper inverter (approximately 100 μs). The pilot study clearly showed that the RLS algorithm is the most suitable for the implementation of an adaptive modular inverter because it achieved the best results for all analyzed parameters.
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Denisenko, K. I., V. O. Lesyk, and T. V. Mysak. "INFLUENCE OF THE FILTER IN THE CONTROL CHANNEL CONTOURS OF THE STORAGE CAPACITOR VOLTAGE STABILIZATION ON THE DYNAMICS IN THREE-PHASE SHUNT ACTIVE POWER FILTER." Praci Institutu elektrodinamiki Nacionalanoi akademii nauk Ukraini 2021, no. 58 (May 19, 2021): 55–65. http://dx.doi.org/10.15407/publishing2021.58.055.
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The object of research is a three-phase shunt active power filter, which consists of a semiconductor voltage inverter on fully controllable switches, capacitive storage, and an RL-link. The carried-out decomposition of the research object according to the rate of motion of the dynamic system makes it possible to divide this dynamic system into two subsystems, interconnected by control. The role and influence of the communication subsystem between the voltage stabilization circuit on the storage capacitor of the three-phase shunt active power filter and the circuits for the formation of the compensation current, which is injected by this filter into the distributed power supply network, is considered. The presence of a non-linear load in this network is a source of distortion of the parameters of electrical energy. The formation of the compensation current by the forced introduction of the first order sliding modes along some sliding surfaces was carried out. The two-dimensional sliding surface is a linear combination of the components of the two-dimensional error vectors of the compensation current and the first derivative of the error of this current. The introduced communication subsystem makes it possible to reduce the influence of the disturbance in the form of harmonic components of the rectified voltage on the parameters of the compensating current. The influence of the dynamic characteristics of a communication subsystem with filtering properties on the performance indicators of a parallel active filter and the current distortion factor in the power supply network to which this filter is connected was analyzed. To confirm the theoretical assumptions, a simulation model was built and the results of digital modeling were analyzed. Comparison of different types of filters as a communication subsystem according to the criteria of the duration of the transient process and the harmonic distortion in the current that consumed from the network was carried out. References 26, figures 4, tables 3.
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Mu, Dong Jie, and Chang Chun Li. "Numerical Simulation of Fluid Transients in Servo-Controlled Hydraulic Piping." Advanced Materials Research 383-390 (November 2011): 2262–68. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.2262.
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His analytical model is carried out based on the one-dimensional fluid transient theory. In view of the micro-compression of the fluid can change its momentum in the transient process, an improved fluid dynamic model of pipeline is proposed. The characteristic method and the finite difference method are adopted for this simulation. In this paper, The fluid transients of the pipes after servo valve shut down are analyzed. The correctness of the simulation is approved by the comparison of calculation data with experiment data .The results showed that these models give more reasonable descriptions for water hammer and flow oscillation during servo valve starting process and could provide guidance for designs and experiments of the hydraulic pipe system
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Saad, W. E., W. Bleibel, N. Adenaw, C. E. Wagner, C. Anderson, J. F. Angle, A. M. Al-Osaimi, M. G. Davies, and S. Caldwell. "Thrombocytopenia in Patients with Gastric Varices and the Effect of Balloon-occluded Retrograde Transvenous Obliteration on the Platelet Count." Journal of Clinical Imaging Science 4 (April 30, 2014): 24. http://dx.doi.org/10.4103/2156-7514.131743.
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Objectives: Gastric varices primarily occur in cirrhotic patients with portal hypertension and splenomegaly and thus are probably associated with thrombocytopenia. However, the prevalence and severity of thrombocytopenia are unknown in this clinical setting. Moreover, one-third of patients after balloon-occluded retrograde transvenous obliteration (BRTO) have aggravated splenomegaly, which potentially may cause worsening thrombocytopenia. The aim of the study is to determine the prevalence and degree of thrombocytopenia in patients with gastric varices associated with gastrorenal shunts undergoing BRTO, to determine the prognostic factors of survival after BRTO (platelet count included), and to assess the effect of BRTO on platelet count over a 1-year period. Materials and Methods: This is a retrospective review of 35 patients who underwent BRTO (March 2008–August 2011). Pre- and post-BRTO platelet counts were noted. Potential predictors of bleeding and survival (age, gender, liver disease etiology, platelet count, model for end stage liver disease [MELD]-score, presence of ascites or hepatocellular carcinoma) were analyzed (multivariate analysis). A total of 91% (n = 32/35) of patients had thrombocytopenia (<150,000 platelet/cm3) pre-BRTO. Platelet counts at within 48-h, within 2 weeks and at 30-60 days intervals (up to 6 months) after BRTO were compared with the baseline pre-BRTO values. Results: 35 Patients with adequate platelet follow-up were found. A total of 92% and 17% of patients had a platelet count of <150,000/cm3 and <50,000/cm3, respectively. There was a trend for transient worsening of thrombocytopenia immediately (<48 h) after BRTO, however, this was not statistically significant. Platelet count was not a predictor of post-BRTO rebleeding or patient survival. However, MELD-score, albumin, international normalized ratio (INR), and etiology were predictors of rebleeding. Conclusion: Thrombocytopenia is very common (>90% of patients) in patients undergoing BRTO. However, BRTO (with occlusion of the gastrorenal shunt) has little effect on the platelet count. Long-term outcomes of BRTO for bleeding gastric varices using sodium tetradecyl sulfate in the USA are impressive with a 4-year variceal rebleed rate and transplant-free survival rate of 9% and 76%, respectively. Platelet count is not a predictor of higher rebleeding or patient survival after BRTO.
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Kravtsov, S., N. Sugiyama, and A. A. Tsonis. "Transient behavior in the Lorenz model." Nonlinear Processes in Geophysics Discussions 1, no. 2 (December 9, 2014): 1905–17. http://dx.doi.org/10.5194/npgd-1-1905-2014.
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Abstract. Dynamical systems like the one described by the three-variable Lorenz model may serve as metaphors for complexity in nature. When natural systems are perturbed by external forcing factors, they tend to relax back to their equilibrium conditions after the forcing has shut off. Here we investigate the behavior of such transients in the Lorenz model by studying its trajectories initialized far away from the asymptotic attractor. Perhaps somewhat surprisingly, these transient trajectories exhibit complex routes and, among other things, sensitivity to initial conditions akin to that of the asymptotic behavior on the attractor. Thus, similar extreme events may lead to widely different variations before the perturbed system returns back to its statistical equilibrium.
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Moller, Per W., Bernhard Winkler, Samuel Hurni, Paul Philipp Heinisch, Andreas Bloch, Soren Sondergaard, Stephan M. Jakob, Jukka Takala, and David Berger. "Right atrial pressure and venous return during cardiopulmonary bypass." American Journal of Physiology-Heart and Circulatory Physiology 313, no. 2 (August 1, 2017): H408—H420. http://dx.doi.org/10.1152/ajpheart.00081.2017.
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The relevance of right atrial pressure (RAP) as the backpressure for venous return (QVR) and mean systemic filling pressure as upstream pressure is controversial during dynamic changes of circulation. To examine the immediate response of QVR (sum of caval vein flows) to changes in RAP and pump function, we used a closed-chest, central cannulation, heart bypass porcine preparation ( n = 10) with venoarterial extracorporeal membrane oxygenation. Mean systemic filling pressure was determined by clamping extracorporeal membrane oxygenation tubing with open or closed arteriovenous shunt at euvolemia, volume expansion (9.75 ml/kg hydroxyethyl starch), and hypovolemia (bleeding 19.5 ml/kg after volume expansion). The responses of RAP and QVR were studied using variable pump speed at constant airway pressure (PAW) and constant pump speed at variable PAW. Within each volume state, the immediate changes in QVR and RAP could be described with a single linear regression, regardless of whether RAP was altered by pump speed or PAW ( r2 = 0.586–0.984). RAP was inversely proportional to pump speed from zero to maximum flow ( r2 = 0.859–0.999). Changing PAW caused immediate, transient, directionally opposite changes in RAP and QVR (RAP: P ≤ 0.002 and QVR: P ≤ 0.001), where the initial response was proportional to the change in QVR driving pressure. Changes in PAW generated volume shifts into and out of the right atrium, but their effect on upstream pressure was negligible. Our findings support the concept that RAP acts as backpressure to QVR and that Guyton’s model of circulatory equilibrium qualitatively predicts the dynamic response from changing RAP. NEW & NOTEWORTHY Venous return responds immediately to changes in right atrial pressure. Concomitant volume shifts within the systemic circulation due to an imbalance between cardiac output and venous return have negligible effects on mean systemic filling pressure. Guyton’s model of circulatory equilibrium can qualitatively predict the resulting changes in dynamic conditions with right atrial pressure as backpressure to venous return.
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Li, Yifei, Kaiyu Zhou, Yimin Hua, Chuan Wang, Liang Xie, Jie Fang, Xin Rong, and Jiantong Shen. "Amplatzer occluder versus CardioSEAL/STARFlex occluder: a meta-analysis of the efficacy and safety of transcatheter occlusion for patent foramen ovale and atrial septal defect." Cardiology in the Young 23, no. 4 (December 3, 2012): 582–96. http://dx.doi.org/10.1017/s1047951112001424.
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AbstractObjectivePercutaneous transcatheter occlusion has benefited thousands of patients suffering from patent foramen ovale and atrial septal defect. However, no general agreement has been reached on the superiority among occluders. Thus, a meta-analysis between the two most commonly adopted types of occluders was conducted.MethodsThe literature review has identified relevant studies up to May, 2011 in the databases of PubMed, EMBASE, the Cochrane Central Register of Controlled Trials, and World Health Organization clinical trials registry centre. Meta-analysis was performed in a fixed/random effects model using Revman 5.1.1. Information on complications and outcomes was extracted.ResultsAnalysis from included studies reports an outcome in favour of the Amplatzer. The Amplatzer has proven its superiority in efficacy with a significantly lower risk of early (95% confidence interval = 0.09–0.34) and long-term (95% confidence interval = 0.14–0.97) residual shunt rate for atrial septal defect occlusion, although no significant difference in performance has been reported for patent foramen ovale. In addition, the Amplatzer has also remarkably reduced the risk of embolisation by the device (95% confidence interval = 0.07–0.45) for atrial septal defect and new-set atrial fibrillation (95% confidence interval = 0.18–0.48) for patent foramen ovale. On evaluation of recurrent thrombotic events, it was found that the Amplatzer greatly lowered the rate of thrombus formation on the device (95% confidence interval = 0.02–0.21) for patent foramen ovale; however, no statistical difference was found on atrial septal defect evaluation. However, the result indicated no statistically significant difference between the two kinds of occluders in stroke and transient ischaemic attack of patent foramen ovale.ConclusionThe meta-analysis has proven the Amplatzer to be the superior occluder, serving better prognosis with more fluent procedure and less complications.
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Kravtsov, Sergey, and Anastasios A. Tsonis. "Lorenz-63 Model as a Metaphor for Transient Complexity in Climate." Entropy 23, no. 8 (July 25, 2021): 951. http://dx.doi.org/10.3390/e23080951.
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Dynamical systems like the one described by the three-variable Lorenz-63 model may serve as metaphors for complex natural systems such as climate systems. When these systems are perturbed by external forcing factors, they tend to relax back to their equilibrium conditions after the forcing has shut off. Here we investigate the behavior of such transients in the Lorenz-63 model by studying its trajectories initialized far away from the asymptotic attractor. Counterintuitively, these transient trajectories exhibit complex routes and, in particular, the sensitivity to initial conditions is akin to that of the asymptotic behavior on the attractor. Thus, similar extreme events may lead to widely different variations before the perturbed system returns back to its statistical equilibrium.
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Zirka, Sergey E., Yuriy I. Moroz, and Ebrahim Rahimpour. "Towards a transformer transient model as a lumped-distributed parameter system." COMPEL - The international journal for computation and mathematics in electrical and electronic engineering 36, no. 3 (May 2, 2017): 741–50. http://dx.doi.org/10.1108/compel-09-2016-0389.
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Purpose The purpose of this study is to develop a topological model of a three-phase, three-limb transformer for low-frequency transients. The processes in the core limbs and yokes are reproduced individually by means of a dynamic hysteresis model (DHM). A method of accounting for the transformer tank with vertical magnetic shunts at the tank walls is proposed and tested on a 120 MVA power transformer. Design/methodology/approach The model proposed has been implemented independently in a dedicated Fortran program and in the graphical pre-processor ATPDraw to the ATP version of the electromagnetic transient program. Findings It was found that the loss prediction in a wide range of terminal voltages can only be achieved using a DHM with variable excess field component. The zero sequence properties of the transformer can be accurately reproduced by a duality-derived model with Cauer circuits representing tank wall sections (belts). Research limitations/implications In its present form, the model proposed is suitable for low-frequency studies. Its usage in the case when transformer capacitances are involved should be studied additionally. Practical/implications The presented model can be used either as an independent tool or serve as a reference for subsequent simplifications. Social/implications The model proposed is aimed at meeting the needs of electrical engineering and ecology-minded customers. Originality/value Till date, there were no experimental data on zero-sequence behavior of three-phase, three-limb transformer with vertical magnetic shunts, so no verified transient model existed. The model proposed is probably the first that matched this behavior and reproduced measured no-load losses for a wide voltage range.
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Tucker, Erik I., Ulla M. Marzec, Sawan Hurst, András Gruber, and Stephen R. Hanson. "Moderate Pharmacological Platelet Count Reduction Limits Thrombus Formation without Hemostatic Impairment in Primates." Blood 112, no. 11 (November 16, 2008): 1033. http://dx.doi.org/10.1182/blood.v112.11.1033.1033.
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Abstract Despite the established contribution of platelets to thrombotic cardiovascular disorders, documented in part by the effectiveness of platelet function inhibitors and the increased risk of thrombosis associated with high normal and supranormal platelet counts, relationships between circulating platelet count and thrombotic events remain largely undefined. Since the initiation and propagation of arterial, platelet-dependent thrombus must depend upon platelet count, albeit in a manner that could be nonlinear, we hypothesized that reducing platelet count within the normal range would produce an anti-thrombotic benefit with minimal effects on hemostasis. To test this hypothesis, we reduced the platelet count in baboons (n=4) by targeting the megakaryocyte growth and development factor thrombopoietin (TPO). A polyclonal anti-TPO autoantibody (anti-TPOab) was purified from the serum of a baboon that developed thrombocytopenia following recombinant TPO injections. The IC50 of the purified IgG fraction was found to be 0.76 μg/ml, determined using a proliferation assay with a TPO-dependent cell line. An i.v. bolus of the anti-TPO antiserum, 30–35 ml infused into baboons, resulted in a transient, >60% decrease in the circulating platelet count after 2–3 weeks. Other blood cell counts were unaffected vs. baseline values. The effect of platelet count reduction on thrombogenesis was evaluated using an established baboon arteriovenous (AV) shunt thrombosis model. Accumulation of 111-Indium-labeled platelets and 125-Iodine-labeled fibrinogen were measured within a 4 mm i.d. thrombogenic vascular graft segment that was deployed into a chronic AV shunt for 60 min. Blood flow was maintained at 100 ml/min, producing an arterial wall shear rate of 265 sec−1. Standard template bleeding times (BTs) were used to assess hemostatic impairment at various platelet counts. Platelet count reductions, ranging from 46–61% (normal levels averaging 352,000 ± 61,000 platelets/μl), reduced platelet deposition onto the graft surface by 46–68% (vs. control values of 4.1 ± 0.9 x 109 platelets deposited, n=9). Similarly, thrombus fibrin accumulation was reduced by 14–39% (vs. control values of 2.2 ± 0.4 mgs of deposited fibrin). Thrombus formation was not affected acutely by anti-TPOab administration, but correlated directly with circulating platelet numbers. As expected, BTs were not significantly prolonged until platelet counts fell below ~100,000 cells/μl. In contrast, single dose aspirin (32 mg/kg) at normal platelet counts did not significantly reduce graft associated platelet deposition in this model but doubled the BTs to 6.8 ± 2.6 min (vs. control values of 3.4 ± 0.9 min). With further reduction in platelet counts to 90,000 ± 30,000 platelets/μL, BTs were only slightly prolonged (5.6 ± 1.7 min, n=5). When platelet counts averaged 74,000 ± 20,000 platelets/μl in animals given ASA, BTs averaged only 9.4 ± 2.7 min (n=5). Thus ASA produced a hemostatic impairment that was approximately fixed (i.e., a BT prolongation of 3–4 min) and not disproportionately prolonged at reduced platelet counts. Thus specific lowering of the platelet count by pharmacologic inhibition of megakaryocytopoiesis may be an effective anti-thrombotic strategy in populations currently treated with conventional anti-platelet agents. Since direct inhibitors of platelet function produce a significant risk of bleeding, inhibition of platelet production may represent a safer approach for reducing the pro-thrombotic capacity of the circulating platelet pool.
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Prikler, L., G. Bán, and G. Bánfai. "EMTP models for simulation of shunt reactor switching transients." International Journal of Electrical Power & Energy Systems 19, no. 4 (May 1997): 235–40. http://dx.doi.org/10.1016/s0142-0615(96)00050-6.
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Korelstein, Leonid, Vladimir Tarasevich, and Elena Yudovina. "Centrifugal pump dynamic simulation experience for waterhammer calculation." E3S Web of Conferences 219 (2020): 01006. http://dx.doi.org/10.1051/e3sconf/202021901006.
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Dynamic model of centrifugal pump with induction motor on the base of Suter curves is described. The model is implemented in surge model of PASS/Hydrosystem software. The ways to provide consistency between transient and steady state flow models are proposed. A rule of thumb is described to preliminarily estimate if pump start-up and shut down can produce significant pressure picks that require detailed simulation.
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Liu, Xin Dong, Rong Guo, and Rui Ming Zeng. "Fault Location for Transmission Line with Shunt Reactors." Advanced Materials Research 605-607 (December 2012): 815–18. http://dx.doi.org/10.4028/www.scientific.net/amr.605-607.815.
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Taking the influence caused by shunt reactors into account, proposes a new fault location algorithm. Based on distributed modal, the algorithm constructs frequency spectrum equations of the faulty network with line parameters to identify, extracts fundamental wave and harmonics of transient signal to solve equations to obtain fault position and exact parameters.
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Yokote, Ryosuke, Mohammad Albarzanji, Yohan Suhardiman, Andrew Tran, Erni Dharma Putra, and Nelson Jose Rodriguez Gonzalez. "Fully integrated dynamic reservoir and well simulation model: Blacktip gas field case study." APPEA Journal 58, no. 1 (2018): 412. http://dx.doi.org/10.1071/aj17052.
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This paper describes an experience of integrating a dynamic reservoir simulation model with a dynamic well simulation model, resulting in an integrated dynamic model from the reservoir to the surface that enhances reservoir and well surveillance capability for the Blacktip gas field. Multiphase transient flow simulation is used to support daily well and pipeline operations for the project. The limitation of the standalone well model using a multiphase transient simulation software was its inability to reproduce pressure build up response during shut-ins, and pressure drawdown during start-ups. The fluid inflow from the reservoir to the well bore is modelled using the Inflow Performance Relationship (IPR) and accordingly the transient pressure behaviour near the well bore is not captured. This makes it difficult to estimate an accurate static reservoir pressure during shut-ins, as the predicted pressure instantaneously builds up to reservoir pressure specified in the IPR. The integrated dynamic model overcomes this limitation. The history matching of production intervals including shut-ins and start-ups using the integrated dynamic model along with high frequency data demonstrates that this integrated modelling approach can be used as a reliable surveillance tool to understand dynamic flow conditions from the reservoir to the surface, including liquid loading and unloading scenarios. The evolution of the history match and subsequent outcomes are discussed in the paper, along with the lessons learnt. Results of a liquid loading and unloading scenario for a gas well are also discussed in the paper.
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Yoshida, Nozomu, A. D. Hill, and Ding Zhu. "Comprehensive Modeling of Downhole Temperature in a Horizontal Well With Multiple Fractures." SPE Journal 23, no. 05 (July 2, 2018): 1580–602. http://dx.doi.org/10.2118/181812-pa.
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Summary Downhole temperature data obtained by either temperature logging or fiber-optic cables have been used to evaluate stimulation treatments and post-stimulation performance of horizontal wells with multiple fractures. Field cases qualitatively show capabilities of detecting creation of transverse fractures, poor zonal isolation, and inflow locations, although downhole temperature behavior in those wells is not fully understood from the theoretical modeling perspective. In this study, we present comprehensive numerical flow and thermal models for a horizontal well with multiple fractures. The well experiences single-phase water flow during injection and shut-in, and gas/water two-phase flow during production. These models are formulated for reservoir and wellbore domains with consideration of their coupling. The reservoir models are formulated in 3D space using mass conservation of each component and thermal energy conservation with Darcy's law in transient conditions. The wellbore models are also transient, and formulated for 1D space using mass conservation of each component, conservation of combined-phase momentum, and total energy conservation. The wellbore- and sandface-temperature profiles are obtained as solutions of these models. These models enable us to simulate field operations in multistage-fracturing treatment; injection and shut-in occur alternately for each stage from toe to heel with zonal isolation. After the stimulation treatments, these models are used to simulate temperature behavior during production in gas/water two-phase flow. We show an example of a single fracture in which the developed model simulates temperature behavior during injection, shut-in, and production to show capabilities of the developed model. This study shows that injected fluid makes the fluid temperature in the fracture lower than the geothermal temperature even after 1 month of shut-in. This affects the temperature interpretation during production because the initial temperature is different from the geothermal temperature assumed as the initial temperature by most studies published previously. A synthetic case with five fractures demonstrates capabilities of detection of created-fracture locations from the shut-in temperature profile. In addition, we apply the model to a field case of distributed-temperature-sensor (DTS) temperature profiles during warmback after multistage hydraulic fracturing, and 30 days after the start of the production in this well. The good match obtained between this model and the DTS data from this well indicates how this modeling approach can be used to estimate the production from individual perforation clusters. The case studies illustrate qualitative interpretations in situations occurring in fields, such as warm-up behavior with multiple clusters during the shut-in period. This paper provides insights from the theoretical modeling perspective for downhole temperature interpretation qualitatively performed at the current time. It also discusses the validity of the assumptions made in previous studies and precautions relevant to those assumptions.
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Holmes, W. R., and W. Rall. "Electrotonic length estimates in neurons with dendritic tapering or somatic shunt." Journal of Neurophysiology 68, no. 4 (October 1, 1992): 1421–37. http://dx.doi.org/10.1152/jn.1992.68.4.1421.
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1. Compartmental models were used to compute the time constants and coefficients of voltage and current transients in hypothetical neurons having tapering dendrites or soma shunt and in a serially reconstructed motoneuron with soma shunt. These time constants and coefficients were used in equivalent cylinder formulas for the electrotonic length, L, of a cell to assess the magnitude of the errors that result when the equivalent cylinder formulas are applied to neurons with dendritic tapering or soma shunt. 2. Of all the formulas for a cylinder (with sealed ends), the most commonly used formula, which we call L tau 0/tau 1 (the formula uses the current-clamp time constants tau 0 and tau 1), was the most robust estimator of L in structures that tapered linearly. When the diameter at the end of the cylinder was no less than 20% of the initial diameter, L tau 0/tau 1 underestimated the actual L by at most 10%. 3. The equivalent cylinder formulas for a cylinder were applied to neurons modeled as a cylinder with a shunted soma at one end. The formula for L based solely on voltage-clamp time constants gave an exact estimate of L. However, the second voltage-clamp time constant cannot be reliably obtained experimentally for neurons studied thus far. Of the remaining formulas, L tau 0/tau 1 was again the most robust estimator of L. This formula overestimated L with the size of the overestimates depending on beta, rho beta = 1, and the actual L of the cylinder, where beta is the soma shunt factor, and rho beta = 1 is the dendritic-to-somatic conductance ratio when beta = 1 (no shunt). When the actual L was 0.5 and the soma shunt was large, this formula overestimated L by two- to threefold, but when the actual L was 1.5, the overestimate was only 10-15% regardless of the size of the shunt. 4. In neurons modeled as two cylinders with soma shunt, the L tau 0/tau 1 value computed with the actual tau 0 and tau 1 values overestimated the average L by two to six times when soma shunt was large. However, the L tau 0/tau 1 estimates computed with tau 0 and tau 1 values estimated with the exponential fitting program DISCRETE from voltage transients computed for these neuron models were never this large because of inherent problems in estimating closely spaced time constants from data.(ABSTRACT TRUNCATED AT 400 WORDS)