Sudden Imbalance Research Articles

Active power control design for supporting grid frequency regulation in wind farms

Among renewable energy sources, wind power is expected to contribute a larger and rapidly growing portion of the world's energy portfolio. However, the increased penetration of wind power into the power grid has challenged the reliable and stable operation of the grid. This motivates new opportunities in the design and development of novel control schemes capable of actively maintaining the necessary balance between power generation and load, which in turn regulates the grid frequency when plenty of winds are available. This paper presents two active power control schemes that are developed based on adaptive pole placement control and fuzzy gain-scheduled proportional-integral control approaches. The active power control is conducted collectively across a wind farm to provide rapid power response while maintaining safe structural loading on turbines’ components. The proposed active power control schemes are evaluated and compared by a series of simulations on an advanced wind farm benchmark model in the presence of wind turbulences, measurement noises, and grid load variations. It is further demonstrated that the mentioned schemes are able to tolerate probable occurrence of sudden imbalance between generation and load due to relevant faults/failures in the wind farm or electric grid.

Effect of a Novel Video Game on Stroke Knowledge of 9- to 10-Year-Old, Low-Income Children

Improving actionable stroke knowledge of a witness or bystander, which in some cases are children, may improve response to an acute stroke event. We used a quasiexperimental pre-test post-test design to evaluate actionable stroke knowledge of 210 children aged 9 to 10 years in response to a single, 15-minute exposure to a stroke education video game conducted in the school computer laboratory. After immediate post-test, we provided remote password-protected online video game access and encouraged children to play at their leisure from home. An unannounced delayed post-test occurred 7 weeks later. Two hundred ten children completed pretest, 205 completed immediate post-test, whereas 198 completed delayed post-test. One hundred fifty-six (74%) children had Internet access at home, and 41 (26%), mostly girls, played the video game remotely. There was significant improvement in stroke symptom composite scores, calling 911, and all individual stroke knowledge items, including a distractor across the testing sequence (P<0.05). Children who played the video game remotely demonstrated significant improvement in knowledge of 1 symptom (sudden imbalance) compared with children who did not (P<0.05), although overall composite scores showed no difference. Stroke education video games may represent novel means for improving and sustaining actionable stroke knowledge of children.

Adaptation of muscles of the lumbar spine to sudden imbalance in patients with lower back pain caused by military training

ObjectiveThis study aims to investigate the effects of sudden load changes (expected and unexpected imbalance) on the activity of muscles of the lumbar spine and their central motor control strategy in military personnel with or without chronic low back pain (LBP).DesignBilateral sudden imbalance was examined (2 × 2 factorial design).SettingThe 117th PLA Hospital, Hangzhou, ChinaParticipantsTwenty-one male subjects with lower back pain and 21 male healthy control subjects were active members of the Nanjing Military Region land forces.Outcome measuresIndependent variables: LBP vs. healthy controls and imbalance anticipation (expected and unexpected imbalance). Dependent variables: rapid reaction time (RRT) and intensity of rapid reaction (IRR) of bilateral lumbar (L3–L4) erector spinae (ES), lumbar (L5–S1) multifidus (MF), and abdominal external oblique muscles.ResultsUnder expected or unexpected sudden imbalance conditions, subjects with LBP demonstrated significantly greater IRR than healthy controls in ipsilateral and contralateral ES and MF, respectively (P < 0.05 for all). IRR of contralateral ES was significantly larger than that of the ipsilateral ES. A significant group effect of RRT of both ipsilateral and contralateral ES muscles and a significant time expectation effect on RRT of contralateral MF muscles were also observed. RRT of the contralateral ES muscles was significantly lower than that of the ipsilateral ES muscles (P < 0.001).ConclusionsSudden imbalance prolonged RRT of selected trunk muscles in patients with chronic LBP. The activation amplitude increased. The results may provide a theoretical basis for a study on the pathogenesis of chronic LBP.

Neurobiological Mechanisms of Acute Vertigo

The vestibular system provides us with reflexive responses of eye movements and balance control, as well as with perceptual estimates of self-motion and gravity direction. Crucial to its proper functioning is a bilaterally balanced vestibular signal originating from the vestibular end organs in the inner ears and projecting via vestibular nerve afferents to the brainstem vestibular nuclei. Disturbances of the bilateral vestibular interplay become evident in cases of acute unilateral peripheral vestibular deafferentation. The resultant sudden imbalance of vestibular afferent tone at the level of the vestibular nuclei leads to pronounced ocular–motor and postural impairment, as well as to intensive vertigo and/or dizziness, accompanied by autonomic symptoms, such as nausea and vomiting. Subsequent compensatory mechanisms efficiently diminish these static symptoms (such as spontaneous nystagmus) within days and allow functional recovery of dynamic symptoms (such as blurred vision during fast head turns) to such a degree that most patients return to their normal daily activities within weeks. This article aims to provide an understanding about the pathophysiological changes after unilateral vestibular deafferentation and the current knowledge on the compensatory mechanisms.

Dorothy L. Sayers, the Great War, and Shell Shock

Dorothy L. Sayers, the Great War, and Shell Shock

Epileptic seizures in critically ill patients

THE AIM OF THIS ARTICLE: To review the causes, clinical signs, pathophysiology, consequences, and treatment of seizures and status epilepticus in critically ill patients. Only 25% of people, who have seizures and status epilepticus, have epilepsy as well. In the intensive care settings, seizures and status epilepticus are a common neurologic complication, which is attributable to primary neurologic pathology (stroke, hemorrhage, tumor, central nervous system infection, head trauma) or secondary to critical illness (anoxic brain damage, intoxications, metabolic abnormalities) and clinical management. There are three main subtypes of status epilepticus in intensive care units: generalized convulsive status epilepticus, focal motor status epilepticus, and nonconvulsive status epilepticus. A seizure is a consequence of electrical neurological derangement because of sudden imbalance between the inhibitory and excitatory forces within the network of cortical neurons. The main inhibiting neurotransmitter in the brain is gamma-aminobutyric acid (GABA), which binds to GABA-A and GABA-B receptors. The main excitatory neurotransmitter is glutamate, which binds to N-methyl-D-aspartate receptors. Different ions (Cl(-), K(+), Na(+), Ca(2+)) also play a role in the pathophysiology of seizures. Prolonged status epilepticus may lead to different systemic and neurologic consequences. Generalized convulsive status epilepticus is one of the most common emergencies encountered in clinical practice, which requires immediate treatment. The first-line drugs are benzodiazepines (lorazepam, diazepam), the second-line ones - phenytoin and fosphenytoin. For the treatment of refractory status epilepticus, barbiturates (phenobarbital, pentobarbital, thiopental), valproate, midazolam, propofol, and isoflurane are used. The dosage of drugs and parameters to monitor are referred in the article. The mortality from generalized convulsive status epilepticus is 15-50%; the main factors, influencing prognosis, are the cause and the duration of status epilepticus and age of a patient.

CONSTRAINED QUADRATIC PROGRAMMING, ACTIVE CONTROL OF ROTATING MASS IMBALANCE

Jet engines may experience severe vibration due to the sudden imbalance caused by blade failure. The current research investigates employment of piezoelectric actuators to suppress this using active vibration control. This requires identification of the source of the vibrations via an expert system, determination of the required phase angles and amplitudes for the correction forces, and application of the desired control signals to the piezoelectric actuators. Correction forces may exceed the physical limitations of the actuators; hence results of “constrained force” quadratic programming, least squares and multi-point correction algorithms will be compared. It is demonstrated that simply scaling down the least squares predicted correction forces to satisfy the actuator saturation constraints does not necessarily yield optimal reductions in vibration. In this paper test results are shown for sudden imbalance, and the computational time requirements and balancing effectiveness for the various approaches are compared.

Apparent absence of stroke and ischaemic heart disease in a traditional Melanesian island: a clinical study in Kitava.

On the island of Kitava, Trobriand Islands, Papua New Guinea, a subsistence lifestyle, uninfluenced by western dietary habits, is still maintained. Tubers, fruit, fish and coconut are dietary staples. Of the total population, 1816 subjects were estimated to be older than 3 years and 125 to be 60-96 years old. The frequencies of spontaneous sudden death, exertion-related chest pain, hemiparesis, aphasia and sudden imbalance were assessed by semi-structured interviews in 213 adults aged 20-96. Resting electrocardiograms (ECG's) were recorded in 119 males and 52 females. No case corresponding to stroke, sudden death or angina pectoris was described by the interviewed subjects. Minnesota Code (MC) items 1-5 occurred in 14 ECG's with no significant relation to age, gender or smoking. ST items (MC 4.2 and 4.3) were found in two females and Q items (MC 1.1.2, 1.3.2 and 1.3.3) in three males. Stroke and ischaemic heart disease appear to be absent in this population.

Electronic sectionalizer control methodology for improved distribution system reliability

A new methodology for sectionalizer control has been developed that provides more security for applications where system transient currents may cause actuate pickup. Actuate pickup, particularly on ground sensing, may occur during upline ground faults when the sudden load current imbalance is compounded by the unfaulted phase voltage rise causing magnetizing current inrush into a large amount of distribution transformers downline from the sectionalizer. Also, motor backfeed and nonsimultaneous fault clearing may cause actuate pickup if the load is sufficiently large. The control has five automatic restraint features: inrush restraint, count restraint, time-integrated threshold restraint, response restraint, and ground restraint. The last three are new features. The control logic was tested by connecting a prototype to the transient network analyzer and simulating conditions that were suspected of causing problems. >

Constrained output feedback control of flexible rotor-bearing systems

The design of an optimal constrained output feedback controller for a rotor-bearing system is described, based on a reduced order model. The aims are to stabilize the unstable or marginally stable motion and to control the large build-up of periodic disturbances occurring during operation. The reduced order model is constructed on the basis of a modal model and singular perturbation, retaining the advantages of the two methods. The onset of instability due to spillover is prevented by the constrained optimization, and the robustness and pole assignability are improved by designing not merely a static output feedback but a dynamic compensator. The periodic disturbances, usually caused by rotation, are reduced by using the disturbance observer and feed-forward compensation. The efficiency of the proposed method is demonstrated through two simulation models, a rigid shaft supported by soft bearings at its ends and an overhung rotor system with a tip disk, under both transient vibration and sudden imbalance situations.

Transient vibration of lightweight rotor due to sudden imbalance.

The transient vibration due to imbalance of a lightweight rotor that comprises flexible blades, disk, shaft, and rigid bearings is analyzed by a finite element method. The dimensions of matrices used in the computation are reduced by representing the shaft and blades by beam elements, and the disk by annular elements. The computed results are compared with the experimental data obtained by a test conducted on a small model rotor with a blade loss simulator. A fairly good agreement was obtained between the computed and experimental results.

Active Control of Transient Rotordynamic Vibration by Optimal Control Methods

Although considerable effort has been put into the study of steady-state vibration control, there are few methods applicable to transient vibration control of rotor-bearing systems. In this paper optimal control theory has been adopted to minimize rotor vibration due to sudden imbalance, e.g., blade loss. The system gain matrix is obtained by choosing the weighting matrices and solving the Riccati equation. Control forces are applied to the system via a feedback loop. A seven mass rotor system is simulated for illustration. A relationshp between the number of sensors and the number of modes used in the optimal control model is investigated. Comparisons of responses are made for various configurations of modes, sensors, and actuators. Furthermore, spillover effect is examined by comparing results from collocated and noncollocated sensor configurations. Results show that shaft vibration is significantly attenuated in the closed-loop system.

Novel frequency-factor method for power-frequency measurement and estimation of load shedding

The paper defines a new term called ‘frequency factor’ and develops a method which utilises this factor to detect change in fundamental components of power-system frequency. A straight-line fit algorithm then optimally computes the average frequency deviation and average rate of change of frequency from the oscillatory response of any generator busbar caused by a sudden imbalance in generation and load demand in the system and predicts the amount of load to be shed. Results of computer simulation with a sample power system were also given in the paper.

Transient Vibration of High-Speed, Lightweight Rotors Due to Sudden Imbalance

In the field of rotor dynamics, increased attention is being given to the transient response analysis of the rotor, since the effects of impact loading and vibrations of the rotor arising from blade loss can be studied by a time transient solution of the rotor system. As recent trends in rotating machinery have been directed towards lightweight, high-speed flexible rotors, the effect of flexibility on transient response analysis is becoming of increasing importance. In the present paper, a transient vibration analysis is carried out on a flexible-disk/flexible-shaft system or rigid-disk flexible-shaft system subjected to a sudden imbalance that is assumed to represent the effect of blade loss. To solve the basic equation governing a rotating flexible disk the Galerkin’s method is used, and the equation of motion of the rotor system is numerically solved by employing the Runge-Kutta-Gill’s method. Experiments were conducted on a model rotor having a blade loss simulator; the shaft vibrations were also measured. The validity of the anaytical results was demonstrated by comparison with the experimental results.

Intratumoral Hemorrhage after a Ventriculoperitoneal Shunting Procedure

Ventriculoperitoneal shunting has been accepted as a safe and useful preliminary procedure that lowers the mortality and morbidity of definitive surgery for tumors causing obstructive hydrocephalus. We are reporting four patients with intratumoral hemorrhage as a complication of shunting. The hemorrhage was massive and fatal in two patients, one with an unverified pineal tumor and the other with a malignant astrocytoma of the thalamus. The hemorrhage was small and limited in the other two patients, one with a glioblastoma of the thalamus and the other with a cerebellar astrocytoma. On the basis of this experience, we conclude that the possibility of intratumoral hemorrhage should be taken into consideration when planning the preoperative management of obstructive hydrocephalus caused by brain tumors. It is possible that ventricular decompression may result in rapid motion and distortion of the intracranial structures and a sudden imbalance between intracranial and intratumoral pressures, leading to vascular insufficiency, congestion, and then hemorrhage within the tumor.

Crisis and Reform in the World's Economy

There are several crucial reasons for the need to reform the world economy. First, the worldwide inflation, a terrible cancerous disease which, if uncontrolled, might destroy the roots of economic development. Second (a direct consequence of inflation), a sudden imbalance in our international monetary system: capital flight in monstrous dimensions, devaluation of important reserve currencies, the United States dollar, the English pound, followed by the Japanese yen and a number of European currencies. Third, growing unemployment all over the world, again as a consequence of inflation and of a worldwide lack of confidence. Finally, but not least, the growing conflict of the developing countries, mainly in the Southern Hemisphere, with the industrialized world mainly in the Northern. This north-south struggle, brewing for long years, has reached the dimensions of what we might call an “economic cold war” on a worldwide level. Thus far, efforts to find new solutions which would be satisfactory to both consumers and producers have failed.