Power Deficit Research Articles

Water resources management under future development and climate change impacts in the Upper Srepok River Basin, Central Highlands of Vietnam

This study aimed to assess the impacts of future development and climate change on the water balance in the Upper Srepok River Basin, in the Central Highlands of Vietnam. A hydrological model was calibrated and validated to model the rainfall-runoff process. Estimates of the water demand of different water sectors were based on the functional relationships between water and productive uses. The estimates were input into a calibrated basin management model for simulation. The climate projections were downscaled to the studied basin. Future land use was predicted using a geographic information system (GIS)-based logistic regression approach. The water balance was examined under various developed scenarios. The results show a relatively high current annual irrigation water deficit at a basin scale; some sub-basins suffer from water shortage, especially during dry seasons and dry years. All water use sectors will be affected to some extent under the impacts of future development and water supply policies. When the new water policy is introduced, the deficits of irrigation and environmental flow are reduced while the power deficit is increased. Considering climate change impact, the annual water deficits are reduced. However, the temporal and spatial variations of rainfall make future water deficits more severe during the dry seasons and dry years.

The cognitive profile of type 1 Gaucher disease patients

BackgroundThe absence of neurological symptoms and signs is traditionally considered mandatory for a diagnosis of type 1 Gaucher disease (GD1), but in recent years many reports have emerged on neurological manifestations in GD1 patients. Nevertheless, it has been unclear whether cognitive deficits are part of the disease as well.MethodsCognitive function was assessed in a large cohort of GD1 patients with the use of the CDR system, a set of computerised cognitive tests. Testing was performed at baseline and every 6 months thereafter during a two-year study period.ResultsOur patient cohort (84 patients, median age 40 years, median time from diagnosis 15 years) showed mild deficits relative to healthy age-matched subjects on the composite scores: power of attention (Z-score (mean ± SD) -0.9 ± 1.37) and speed of memory (Z-score (mean ± SD) -1.39 ± 1.49). No decline in cognitive function was seen during the two-year period. Age correlated with the composite scores variability of attention and quality of working memory. Moreover, severely affected patients (Zimran severity score (SSI) ≥ 15) scored more poorly compared to mildly affected patients (SSI ≤ 5) on the composite measure power of attention, reflecting the ability to concentrate.ConclusionsGD1 patients exhibit mild deficits in power of attention and speed of memory, reflecting a decreased ability to focus attention and process information, together with a slowing in the speed of retrieval of items from memory. The clinical relevance of these findings is uncertain.

The assessment of the contribution of short-term wind power predictions to the efficiency of stand-alone hybrid systems

Distribution of electricity to the rural areas, particularly in regions which have rough topography causes high costs and losses. Hybrid systems can provide electricity at a relatively economic price at these regions. This paper designs and tests a stand-alone hybrid system combining variable speed wind turbine (WT), fuel cell (FC) and battery. The main objective is to optimize the hydrogen utilization while guaranteeing the load balance implicitly as well as to achieve proper FC operation. To this end, a wind power prediction based controller is proposed in order to take action according to foreseen amount of power deficit or excess in the system. For the purpose of investigating the effects of predictions on the system efficiency, a case study is carried out on a coastal area with a high wind potential in Izmir, Turkey. The results obtained provide insights about the advantages of utilizing wind power predictions in a hybrid system.

Energy potential of Republic of Serbia as an Investment Opportunity UDK 338.48

Serbia has a big potential to accomplish the goal of making the environment green and comfortable for living. It started with reforms in comprehensive Energy Sector and set up a new Energy Policy in accordance with the EU practice and standards. With new national policy, Serbia became aware of middle-term and long-term strategies for developing of adequate Power Sectors. There were investments into the Network and there are plans for building new and expanding existing transforming stations, building new interconnecting line and making some other investments. Having in mind the cooperation with EU, Service for Electrical Energy Market Development has already prepared wide range of available services related to market and deregulation of network, from requirements for connecting to transmission line to securing balance mechanism, and that makes possible for international Electrical Power market to exist. Since the production system is unable to respond to the demand in certain moments of time and Serbia has to import Electrical Energy, that makes Renewable Energy Sources very attractive for use in Power system. Deficit of electrical power must be covered either by import or by more intensive investments in new production capacities, making Serbian energy sector economically interesting.

New Local Adaptive Load-shedding Methods to Mitigate Power System Blackouts

Under-frequency load shedding is a globally accepted remedial measure against a severe drop of power system frequency. With the ever-increasing size of power systems, severe frequency drops are usually caused by combinational severe disturbances. For such disturbances, the active power deficit is usually accompanied by a reactive power deficit presenting some challenges to the load-shedding protection schemes. In this article, two adaptive combinational load-shedding methods are proposed that enhance the frequency and voltage security of power systems for such disturbances. In the proposed algorithms, the under-frequency load-shedding scheme is modified so that the load shedding is adaptively started from locations that have a lower voltage stability margin. Besides, the speed of load shedding is changed adaptively depending on the voltage stability status of the system and the rate of frequency decline. The proposed methods use locally measured frequency and voltage signals and are, therefore, easily applicable. Performance of the proposed load-shedding methods has been compared to that of the conventional method for various disturbances in two different systems. Obtained simulation results confirm that by using the proposed algorithms the power system becomes more robust against large disturbances and the probability of the power system instability is decreased.

Optimizing muscle power after stroke: a cross-sectional study

BackgroundStroke remains a leading cause of disability worldwide and results in muscle performance deficits and limitations in activity performance. Rehabilitation aims to address muscle dysfunction in an effort to improve activity and participation. While muscle strength has an impact on activity performance, muscle power has recently been acknowledged as contributing significantly to activity performance in this population. Therefore, rehabilitation efforts should include training of muscle power. However, little is known about what training parameters, or load, optimize muscle power performance in people with stroke. The purpose of this study was to investigate lower limb muscle power performance at differing loads in people with and without stroke.MethodsA cross-sectional study design investigated muscle power performance in 58 hemiplegic and age matched control participants. Lower limb muscle power was measured using a modified leg press machine at 30, 50 and 70% of one repetition maximum (1-RM) strength.ResultsThere were significant differences in peak power between involved and uninvolved limbs of stroke participants and between uninvolved and control limbs. Peak power was greatest when pushing against a load of 30% of 1RM for involved, uninvolved and control limbs. Involved limb peak power irrespective of load (Mean:220 ± SD:134 W) was significantly lower (p < 0.05) than the uninvolved limb (Mean:466 ± SD:220 W). Both the involved and uninvolved limbs generated significantly lower peak power (p < 0.05) than the control limb (Mean:708 ± SD:289 W).ConclusionsSignificant power deficits were seen in both the involved and uninvolved limbs after stroke. Maximal muscle power was produced when pushing against lighter loads. Further intervention studies are needed to determine whether training of both limbs at lighter loads (and higher velocities) are preferable to improve both power and activity performance after stroke.

The impact of turbulence intensity and atmospheric stability on power deficits due to wind turbine wakes at Horns Rev wind farm

ABSTRACTThe wind turbine operational characteristics, power measurements and meteorological measurements from Horns Rev offshore wind farm have been identified, synchronized, quality screened and stored in a common database as 10 min statistical data. A number of flow cases have been identified to describe the flow inside the wind farm, and the power deficits along rows of wind turbines have been determined for different inflow directions and wind speed intervals. A method to classify the atmospheric stability based on the Bulk‐Ri number has been implemented. Long‐term stability conditions have been established, which confirms, in line with previous results, that conditions tend towards near neutral as wind speeds increase but that both stable and unstable conditions are present at wind speeds up to 15 m s −1. Moreover, there is a strong stability directional dependence with southerly winds having fewer unstable conditions, whereas northerly winds have fewer observations in the stable classes. Stable conditions also tend to be associated with lower levels of turbulence intensity, and this relationship persists as wind speeds increase. Power deficit is a function of ambient turbulence intensity. The level of power deficit is strongly dependent on the wind turbine spacing; as turbulence intensity increases, the power deficit decreases. The power deficit is determined for four different wind turbine spacing distances and for stability classified as very stable, stable and others (near neutral to very unstable). The more stable the conditions are, the larger the power deficit. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Isokinetic strength and power deficits in the hand following stroke

ObjectiveThe purpose of this study was to compare the torque production in the paretic and non-paretic hands during isokinetic tasks following stroke. MethodsWe compared torque and power production at the MCP joint of chronic stroke survivors during isometric and isokinetic tasks. We also recorded surface electromyography (EMG) activity in the forearm muscles. ResultsIsokinetic torque production at all velocities was less than that produced during isometric trials. Both torque and power produced by the paretic hand was substantially impaired. Deficits were substantially greater in extension than flexion trials. EMG data suggests that excessive co-contraction of agonist and antagonist muscles does not greatly affect isokinetic torque production at the MCP joint. ConclusionsThe fact that movement velocity produces larger deficits in torque and power production may explain why patients who have limited strength impairments still experience functional deficits. SignificanceThis study demonstrates that strength testing of stroke survivors under isometric conditions may underestimate the overall level of impairment.

Muscle power failure in mobility-limited older adults: preserved single fiber function despite lower whole muscle size, quality and rate of neuromuscular activation

This study investigated the physiological and gender determinants of the age-related loss of muscle power in 31 healthy middle-aged adults (aged 40-55 years), 28 healthy older adults (70-85 years) and 34 mobility-limited older adults (70-85 years). We hypothesized that leg extensor muscle power would be significantly lower in mobility-limited elders relative to both healthy groups and sought to characterize the physiological mechanisms associated with the reduction of muscle power with aging. Computed tomography was utilized to assess mid-thigh body composition and calculate specific muscle power and strength. Surface electromyography was used to assess rate of neuromuscular activation and muscle biopsies were taken to evaluate single muscle fiber contractile properties. Peak muscle power, strength, muscle cross-sectional area, specific muscle power and rate of neuromuscular activation were significantly lower among mobility-limited elders compared to both healthy groups (P ≤ 0.05). Mobility-limited older participants had greater deposits of intermuscular adipose tissue (P < 0.001). Single fiber contractile properties of type I and type IIA muscle fibers were preserved in mobility-limited elders relative to both healthy groups. Male gender was associated with greater decrements in peak and specific muscle power among mobility-limited participants. Impairments in the rate of neuromuscular activation and concomitant reductions in muscle quality are important physiological mechanisms contributing to muscle power deficits and mobility limitations. The dissociation between age-related changes at the whole muscle and single fiber level suggest that, even among older adults with overt mobility problems, contractile properties of surviving muscle fibers are preserved in an attempt to maintain overall muscle function.

Smart Management of HVDC Interface Flow for Jeju Island System with High Penetration of Wind Energy

The recent concerns over the threat of global climate change and the requirements of national reduction of CO2 emission have led to the diversification of energy resources and a large scale integration of renewable resources. For island systems, however, the penetration level of renewable energy should be limited to maintain the power system security perspectives to frequency and voltage stability. The main interest of this paper is the operation of Jeju island system with a high penetration level of wind energy. As an option to make a breakthrough against the technical constraints, this paper presents a smart algorithm to set the active power of HVDC (High Voltage Direct Current) interties, which are to supply the power deficit and to regulate the frequency of the system.

Beta band oscillations as a correlate of alertness — Changes in aging

Older adults (>60years) show attentional deficits in comparison to younger people (18–30years). As beta-band EEG activity has been previously postulated to indicate attentional modulation in the visual system, we searched for possible deficits in beta power in elderly subjects performing an attentional task with spatial differentiation between visual stimuli. We found that in older adults a lower level of beta activity correlated with decreased behavioral performance. As compared to young subjects, older adults expressed decreased activation in beta band during an attentional task, which displayed two different dynamics during the anticipatory period. Those dynamics were accompanied by one of two different behavioral pattern deficits. We hypothesize that one group of elderly participants suffered from difficulty in the activation of attentional processes (alertness deficits), while the other — from difficulty in sustaining those processes (vigilance deficits).

Enhancement of Power System Stability Using Adaptive Combinational Load Shedding Methods

In the modern power systems operating at lower stability margins, conventional non-adaptive schemes cannot offer adequate protection for securing the power system, especially against combinational events. For major disturbances, the active power deficit is usually accompanied by reactive power deficit and frequency stability and voltage stability of the system are jeopardized simultaneously. In this paper, three adaptive combinational load shedding methods are proposed to improve operation of the conventional underfrequency load shedding scheme in order to enhance power system stability following severe disturbances. The proposed methods use locally measured frequency and voltage signals to counteract such events. In the proposed algorithms, load shedding is started from the locations which have higher voltage decay for longer period of time. The speed, location, and amount of load shedding are changed adaptively depending on the disturbance location, voltage status of the system, and the rate of frequency decline. Operation of the conventional and the proposed load shedding methods have been simulated in an actual large network. Obtained simulation results confirm that the proposed methods provide considerable enhancement in the power system voltage stability margin, and by using the proposed algorithms, various power system blackouts could be prevented.

Experimental Investigation of Endwall and Suction Side Blowing in a Highly Loaded Compressor Stator Cascade

The following paper describes an experimental investigation of a highly loaded stator cascade with a pitch to chord ratio of t/l=0.6. Experiments without as well as with active flow control by means of endwall and suction side blowing were conducted. Five-hole-probe measurements in pitchwise and spanwise directions as well as endwall oil flow visualizations were carried out in order to determine the performance of the cascade and to analyze the flow phenomena occurring. To quantify the effectivity of the active flow control method, taking the additional energy input into account, corrected losses and an efficiency, which relates the difference of flow power deficit with and without active flow control to the flow power of the blowing jet itself, were evaluated. Even though an increase of static pressure rise could be achieved, a decrease of the total pressure losses was possible for a few operating points only.

Return to Sport: When Should an Athlete Return to Sport After an ACL Surgery?

A torn anterior cruciate ligament (ACL), followed by reconstruction surgery, can be devastating for an athlete. Advances in physical therapy now help athletes improve rapidly during the early period after surgery. However, guidelines on how to determine if it is safe to return to sport are more general and vary widely. Athletes and the people who care about and for them need reliable and valid methods to determine when they are ready to return to sport. A study published in the June 2011 issue of JOSPT provides new insight and evidence-based tools to help answer this question.

The Kazan Leviathan: Russian Street Gangs as Agents of Social Order

This article discusses the evolution of street gangs in the Russian city of Kazan. Using historic and interview data, it shows that the changes in the social organization of these gangs were a reaction to a series of systemic crises in the Soviet and post-Soviet social order. As a result of power deficits, emerging in the space of the streets and in the larger society, the gangs moved through several stages: a) youth peer groups acting out traditional prescriptions of masculine socialisation; (b) territorial ‘elite’ formations; (c) ‘violent entrepreneurs’ and (d) autonomous ruling regimes. The article demonstrates that the gangs, while utilising violence to achieve their projects of social and economic domination, may also regulate its use. It argues that the gangs can be seen as historic agents participating in ground-level social regulation, and not simply products and producers of social disorder.

Power crisis in Rajasthan: Strategies to attain sustainable development

In the past hundred years development has been witnessed in the economy. Human beings have moved from carts driven by horses to space flight. All these have become possible only because of energy. And this is the reason why energy has been considered as the life blood of modern economy. No doubt the development of any economy depends on availability of energy, as development is positively correlated with the demand for it. Since industrial revolution, the use of more and more of energy has led to the path of prosperity and human welfare. In the modern era, energy is considered as inevitable and prime indicator of welfare. Energy is available in many forms but among all the sources electricity is considered as one of the important requisites for all economic and social activities. India is one of the fastest growing country in the world. But the development has resulted in many serious problems, and one among this is the growing power crisis. Power sector an important part of country's infrastructure is going through the process of churning. The power sector of our economy is confronted with the major problem of growing demand-supply gap. The per capita consumption of power has been continuously increasing in the past few decades but the increment in the production rate could not keep pace with the growing demand which has ultimately resulted in the widening of demand supply gap of electricity. The policy of the government in order to overcome the power deficit has been oriented towards increasing the supply of electricity, to bring a balance between demand and supply. But this would in fact have an adverse effect on the environment, since a major portion of installed capacity is based on thermal power resulting in climate change. The present paper would focus on the electrical power crisis in India with special reference to Rajasthan, the reasons for power crisis and the strategies to be adopted in order to overcome the crisis.

Power crisis in Rajasthan: Strategies to attain sustainable development

In the past hundred years development has been witnessed in the economy. Human beings have moved from carts driven by horses to space flight. All these have become possible only because of energy. And this is the reason why energy has been considered as the life blood of modern economy. No doubt the development of any economy depends on availability of energy, as development is positively correlated with the demand for it. Since industrial revolution, the use of more and more of energy has led to the path of prosperity and human welfare. In the modern era, energy is considered as inevitable and prime indicator of welfare. Energy is available in many forms but among all the sources electricity is considered as one of the important requisites for all economic and social activities. India is one of the fastest growing country in the world. But the development has resulted in many serious problems, and one among this is the growing power crisis. Power sector an important part of country's infrastructure is going through the process of churning. The power sector of our economy is confronted with the major problem of growing demand-supply gap. The per capita consumption of power has been continuously increasing in the past few decades but the increment in the production rate could not keep pace with the growing demand which has ultimately resulted in the widening of demand supply gap of electricity. The policy of the government in order to overcome the power deficit has been oriented towards increasing the supply of electricity, to bring a balance between demand and supply. But this would in fact have an adverse effect on the environment, since a major portion of installed capacity is based on thermal power resulting in climate change. The present paper would focus on the electrical power crisis in India with special reference to Rajasthan, the reasons for power crisis and the strategies to be adopted in order to overcome the crisis.

Coordination of multilateral trades in electricity markets via power vectors

A transmission restructure model is presented, which resolves line abuse, conflict of incentives and information asymmetry in electricity markets. It uses market compatible game theory, graph theory, market mechanism, multilateral trade structure, etc. rather than conventional tools. The model is useful to emulate any active, competitive transmission sector. It has more relevance in countries like India with high T&D loss and power deficit problems. Cooperative game theory (CGT) is holistically applied in organizational, operational, commercial and planning aspects of restructure. A three phase CGT environment to model entity interactions, an elastic transmission service charge (TSC) to penalize abuse and a powerful power vector to resolve information asymmetry are some proposals developed in this context. In the scheme, Discos use power vectors to play the game and negotiate for agreeable TSC share and engineer fruitful mergers. A stable set of coalitions contracting optimal trades at lowest TSC is finally obtained. The method is illustrated on a 5 bus and successfully tested on a 24 bus Indian power system. The outcome is that agents aggregate sequentially, to safeguard network security as a common agenda, despite market activities starting at diverse locations. These results are important because transmission is the most difficult zone to model in electricity markets due to several issues and this model addresses most of them. Copyright © 2011 John Wiley & Sons, Ltd.

Power system stability enhancement using a new combinational load-shedding algorithm

In the recent years, operation of power systems at lower stability margins has increased the importance of system protection methods that protect the system stability against various disturbances. Among these methods, the load shedding serves as an effective and last-resort tool to prevent system frequency/voltage instability. For major combinational disturbances, the active power deficit is usually accompanied by reactive power deficit. Therefore frequency stability and voltage stability of the system are jeopardised simultaneously. For such cases, the conventional non-adaptive underfrequency load-shedding scheme cannot offer adequate protection to prevent system collapse. In this study a new combinational load shedding method is proposed to increase the security of power system during large disturbances. The proposed method uses locally measured frequency and voltage signals and does not need any communication link. Performance of the conventional scheme and the proposed load-shedding method using different load shedding criterions have been simulated in two test systems: an actual large network and a standard test system. Obtained simulation results confirm that the proposed schemes provide considerable enhancement in the power system voltage stability margin and by using the proposed method various power system blackouts could be prevented.

PV Fluctuation Balancing Using Hydrogen Storage – a Smoothing Method for Integration of PV Generation into the Utility Grid

This paper presents a method for using hydrogen storage to assist in integration of large scale photovoltaic (PV) generation system into the utility grid. An algorithm based on the simple exponential smoothing is used to suppress short term power fluctuations in PV generation. To facilitate economic dispatch by the system operator, the output of the exponential smoothing is held constant for a given dispatch interval. The more stable, step-wise constant power then acts as the power reference to be sent to the utility grid. The resulting power ripple (from the smoothing) and power error (from the step-wise forecast) is then absorbed by the hydrogen storage such that any PV power above the scheduled grid power curve is used to produce hydrogen using an electrolyzer and any power deficit is produced by a fuel cell. Simulation studies based on realistic irradiance data conducted in SIMULINK/SIMPOWER verifies the effectiveness of the developed method.