Ultra-short Term Research Articles

Grid code for wind power fluctuation in China and particle swarm optimization-based power dispatch solution

The intermittency and variability of wind lead to the fluctuation of wind power, which has an impact on the power grid. With the increasing capacity of wind power, the grid code restrictions for wind farms have become more rigorous than ever. The State Grid Corporation of China proposed standards for the maximal fluctuation in 1- and 10-min time windows, relative to the rated power of a wind farm. This paper presents an approach to calculate the power fluctuation on a certain timescale and find the balance between the generating benefit and fluctuation loss under the limitation standard. A new active power dispatch solution is applied based on the ultra-short term power forecasting result for 10 min. A penalty function and objective function are established and solved by particle swarm optimization to obtain the optimal control instruction to mitigate the power fluctuation. To validate the proposed solution, a wind power acquisition data series is used in both offline and online simulation cases. The results show that the new solution, with its small operating cost, is a valuable approach to avoid “abandoning wind” because of power over-fluctuation, and effectively increases valid production incomes.

Improved Method of High Voltage Switchgear Temperature Prediction Based on WNN

Based on WNN, an improved model of High Voltage Switchgear temperature prediction is built. The model is optimized with hard threshold de-noising with wavelet package analysis, made an ultra-short term prediction loosely combines Elman neural network. However, the characteristics of the original signal are reserved and the noise interference is mostly eliminated. The experiment results show the processed sample as input one improves the prediction accuracy of Elman Network and reduces the root-mean-square error. And the prediction values show good coincidence to the measured ones that improves the reliability of early warning.

A New Algorithm for Ultra-Short Term Wind Prediction Based on Dynamic Relative Turbine Locations

This paper is focusing on ultra-short term wind prediction, using the wind speed of so called “leading turbine” as a reference to calculate the distribution wind speed in a wind farm, where the leading turbine is the first one to contact the wind determined by relative location of every turbine in wind farm. Then wake effect, time-lag effect and dynamic relative locations algorithms are introduced and integrated into the calculation to get every input wind speed of remained wind turbines. The illustrative cases take a wind farm in China as study subject to forecast wind speed of every wind turbine based on actual captured data of “leading turbine”. Then the comparison demonstrates difference of selected turbine's time-varying wind speed and power output in wind farm estimated by wake effect factor and time-lag effect factor. The conclusion reflects feature that wake effect will reduce power output and time-lag effect will smooth power output. At last we transform the integrated wind speed prediction results into the total power output data, and compare it with actual captured output power data of wind farm, the result shows that the accurate and rapid calculation method based on dynamic relative location of turbines in wind farm is authentic and effective.

Improved Data Stream On-Line Segmentation Based Ultra Short-Term Load Forecasting

To improve both realtime performance and accuracy of ultra short-term load forecasting and to cope with the higher requirement of power grid on realtime load forecasting, based on improved data stream on-line segmentation an ultra short-term load forecasting method is proposed. Based on the time trend of load development, the realtime data stream processing is utilized in the proposed method to perform ultra short-term forecasting, then combining with the results of short-term load forecasting, which contain the whether factors and the effect of load cycle property, the realtime forecasting result at the segmentation point is corrected. The fast segmentation and forecasting ability of the proposed method avoid repeat modeling and improve the speed of forecasting; the realtime correction and handling of the segmentation point increase historical information utilization and decrease the error of segmentation point, thus the forecasting accuracy can be maintained at a better level. Actual load data is adopted to validate the effectiveness of the proposed model, and validation results show that both load forecasting accuracy and speed by the proposed model have an advantage over those by several conventional ultra short-term load forecasting algorithms, besides the forecasting error at the inflection point of load can be decreased and the proposed method can also adapt to the sudden change of the weather.

A Multi-Objective Optimization Approach to Active Power Control of Wind Farm

With more and more wind farms integrated into the power grid, the stability and security of the grid can be significantly affected by the wind-farm-generated power, due to the intermittent and volatile nature of the wind-farm-generated power. Therefore, control of the wind-farm power to meet the stability and quality requirements becomes important. Active control of wind-farm power, however, is challenging because the wind-farm output power can only be reliably predicted for a short period of time (i.e., ultrashort term power prediction), and large variations exist in the wind-turbine output power. In this paper, an optimal active power control scheme is proposed to maximize the running time of each wind turbine, and minimize the on-and/or-off switching of wind turbines, resulting in substantial reduction of wind-turbine wear and thereby, maintenance cost, and extension of wind-turbine lifetime, all together, a significant saving of operation cost of the whole wind farm. The proposed approach is illustrated by implementing it to the active power allocation of a wind-farm model in simulation.

Evaluation of Liver Preservation Solutions by Using Rats Transgenic for Luciferase

IntroductionThe solution in which graft tissue is stored (that is, preservation solution) is an important component of liver transplantation technology. Its protective effect is induced by substances in the solution, including radical scavengers, buffers, and energy-giving substances. New preservation solutions have proven to be effective in preventing organ damage during cold ischemia and in extending the time limits for storage. AimThis study determined the relationship between luminescence intensity and content of adenosine triphosphate (ATP) in liver tissue and proposes a new ex vivo screening system that uses Lewis rats transgenic for luciferase for evaluating the effectiveness of preservation solutions. MethodsSamples (diameter, 2 mm) of liver were obtained from transgenic rats. The viability of these tissues after storage for as long as 6 hours in University of Wisconsin (UW) solution, extracellular trehalose solution of Kyoto, Euro-Collins (EC) solution, histidine–tryptophan–ketoflutarate solution, low potassium dextran solution, or normal saline was assessed by determining ATP content and luminescence intensity. ResultsLuminescence had a linear relationship (R = 0.88) with ATP levels. Regardless of the preservation solution used, the luminescence intensities of the liver tissue chips decreased linearly with time especially through a short span of time (0 to 2 hours; R2 = 0.58–1.0). The luminescence of liver chip tissues maintained long term (2 to 6 hours) in UW solution tended to be higher than those of tissues stored in other solutions (P < .05; 6 hours). On the basis of luminescence intensity, EC might be preferable to the other solutions tested for ultra-short–term storage (0.5 to 2 hours). ConclusionOur model, which combines the use of the bioimaging system and Lewis rats transgenic for luciferase, effectively assessed the viability of liver tissue samples. We believe that this ex vivo screening system will be an effective tool for evaluating preservation solutions for liver grafts.

A three-stage birandom program for unit commitment with wind power uncertainty.

The integration of large-scale wind power adds a significant uncertainty to power system planning and operating. The wind forecast error is decreased with the forecast horizon, particularly when it is from one day to several hours ahead. Integrating intraday unit commitment (UC) adjustment process based on updated ultra-short term wind forecast information is one way to improve the dispatching results. A novel three-stage UC decision method, in which the day-ahead UC decisions are determined in the first stage, the intraday UC adjustment decisions of subfast start units are determined in the second stage, and the UC decisions of fast-start units and dispatching decisions are determined in the third stage is presented. Accordingly, a three-stage birandom UC model is presented, in which the intraday hours-ahead forecasted wind power is formulated as a birandom variable, and the intraday UC adjustment event is formulated as a birandom event. The equilibrium chance constraint is employed to ensure the reliability requirement. A birandom simulation based hybrid genetic algorithm is designed to solve the proposed model. Some computational results indicate that the proposed model provides UC decisions with lower expected total costs.

Ultra-short term clomiphene citrate in high responder women with polycystic ovary syndrome: a case series

ObjectiveTo evaluate a new trial of short-term clomiphene citrate (CC) in high responder women with polycystic ovary syndrome (PCOS). Study designThis case series was conducted in the infertility outpatient clinics of two centres. Ovulation induction was performed with CC 50–100mg a day in six high-responder women with PCOS who had a history of cancellation of treatment because of ≥3 mature follicles between March 2010 and June 2013. Induction was initiated on the third day of their cycles and the duration of induction was only two days. Demographic data of the patients, number of mature follicles on hCG day, ovulation rate, luteal phase length, pregnancy rate, and type of pregnancy were recorded. All data were analysed by SPSS packet programme (SPSS, 17.0, SPSS Inc., Chicago, IL, USA). Result(s)The median number of mature follicles and duration of the follicular phase were 1.3 (1–2) and 11.9 (11–14) days, respectively. The ovulation rate was 80% (12/15) and pregnancy rate per cycle was 26.6%. Conclusion(s)If this hypothesis is supported by large prospective randomised controlled studies, ultra-short term ovulation induction with CC may provide an alternative approach for high-responder women with PCOS who have a history of treatment cycle cancellations.

Comparison between standard short-term, very-short and ultra-short-term heart rate variability analysis in healthy subjects during exercise testing

Purpose: Stepwise exercise testing, with workload increasing every two minutes, determines progressive changes of autonomic nervous system (ANS) adaptations that might affect stationarity during the intervals sampled for Standard Short term (SST) heart rate variability analysis (HRVa) according to ESC guidelines. To quantify such transients short-lasting changes very-short (VST) and ultra-short term (UST) analysis (HRVa) might be more appropriate, but have not been validated so far. The study aimed to evaluate, in healthy subjects (HS), the information provided by VST and UST HRVa in comparison with SSTHRVa, during exercise testing. Methods: 12-lead ECG recorded in 25 HS, before, at each workload step and during recovery after maximal exercise testing with a bicycle ergometer (workload increasing by 25 watts, every two minutes). The coefficients of variation (CV) and of reproducibility (CR) and the Pearson correlation (R2) of the same linear [time-domain (TD) and frequency-domain (FD)] and nonlinear (NL) HRV parameters, computed from SST (5-minutes), VST (60-seconds) and UST (30-seconds) intervals with Kubios HRV 2.1, (Biosignal Analysis and Medical Imaging Group, Department of Physics, University of Kuopio, Finland), were evaluated. VST and UST intervals were selected at the end of each step. Results: SSTHRVa was appropriate only at rest, before exercise and in the recovery phase. A significant correlation was found among parameters estimated from 5-minutes, 60- and 30-seconds time intervals (Pearson R2 range: 0.42 -0.98, p< 0.05 – 0.000001), except for a certain degree of variability of frequency peaks estimated with the Fast Fourier transform. At peak workload only VST and USTHRVa parameters were significantly correlated (R2 range: 0.6 -0.99, p< 0.01 – 0.000001), whereas the 5-minute interval was too long and averaged ther consecutive workload steps. At peak exercise, the CV and the CR of LF/HF, estimated from 60- and 30-seconds time-intervals were 9.3 and 0.54, respectively, thus almost optimal. Among NL methods, only the Poincare plot was calculable in all conditions. Instead recurrence plot, detrended fluctuation, approximate entropy, sample entropy and correlation dimension parameters required at least 40-seconds intervals, unless heart rate exceeded 100 bpm. Discussion: The good correlation among HRV parameters estimated at rest from 5-minutes, 60- and 30-seconds time intervals proves that VST or UST HRVa are a feasible option to evaluate changes of cardiac autonomic modulation induced by stepwise exercise testing when time-variant HRVa is unavailable.

Sliding mode control-based active power control for wind farm with variable speed wind generation system

Active power control in wind farm, implemented with hierarchical structure (including the central wind farm active power control system and the control system of variable speed wind generation system), has significantly improved the wind-farm-generated power. However, the interaction between the control system of variable speed wind generation system and the central wind farm active power control system has not been considered in the control system design of both sides. The wind generation system with active power control in wind farm, as a high-order nonlinear large-scale system, will not only autonomous operating with maximum power capture, but also being demanded to regulate power output according to the power set points ordered by the central wind farm active power control system. Therefore, robust active power control of wind farm is clearly necessary. In this article, sliding mode is used to design the active power control system for wind farm, which makes the output power of wind farm track the active power order from the power grid operator asymptotically. Particularly, the control system of the variable speed wind generation system is designed with cascaded structure: the input of the internal rotational speed control loop of the wind generation system is controlled by the external power loop which tracks the specified power set point. Then, based on the dynamic model of wind farm, the central wind farm active power control system is designed to control the total output power of wind farm by using the sliding mode control method. Furthermore, in order to ensure the given power set point is within the regulation capability of the wind generation system, the proportional distribution strategy is utilized to specify the power set point according to the available output power of each wind generation system, which is quantified by ultra-short term power prediction model. The proposed approach is illustrated by implementing it to the active power control of a wind-farm model in simulation. The simulation results demonstrate that the proposed method outperforms the method based on proportional-integral control.

The Ultra-short Term Prediction of Wind Power Based on Chaotic Time Series

In this paper, we propose a method to predict ultra-short term wind power production with chaotic time series. Through analysis of the data measured from real wind farm, the ultra-short term prediction model of wind power is established based on the space theory of chaotic time series phase. The wind power of a real wind farm in northeast China in some future time including 15 m, 30 m and 1h are predicted by the prediction model finally. Test results are presented in the paper.

Ultra-Short Term Wind Power Prediction Model Based on Modified Grey Model Method for Power Control in Wind Farm

With the increasing significance of the power control in wind farms for modern power system, the precise ultra-short term wind power prediction are necessary for achieving the integrated active power control of practical wind farms. This paper focus on the wind power online prediction using the relationship between the wind speed and the wind power generation by ultra-term wind speed forecasting. An improved GM (Grey Model) rolling model is developed in the paper for the ultra-short term wind speed prediction. The simulation results have verified that the developed GM rolling model with the weaken buffer operator for the variable wind data preparation has better prediction performance over the traditional GM rolling model and adaptive alpha-based GM rolling model. This result will obviously optimize the wind power control in the wind farm by predicting the precise wind power generation in real time.

Pathophysiology of Intraocular Pressure Increase and Glaucoma Prevalence in Thyroid Eye Disease: A Mini-Review

The aim of this study was to assess the pathophysiological mechanisms leading to intraocular pressure (IOP) increase and to review the prevalence of glaucoma in thyroid eye disease (TED), an autoimmune reaction affecting extra-ocular muscles and intra-orbital content in thyrotoxicosis (Grave's disease, hyperthyroidism). We applied the modified Friedenswald's and Goldmann's equations to explain the mechanisms by which IOP increases in TED and gave a brief review of the literature. In TED, Friedenswald's equation explains the ultra-short term IOP increase observed when eyes deviate from their primary gaze position (eyeball compression by enlarged and infiltrated extra-ocular muscles). Goldmann's equation explains the long-term IOP increase seen in TED (episcleral venous pressure elevation secondary to intraorbital content and pressure increase). Most studies did not find a significant increase in glaucoma prevalence in patients with TED. In TED, glaucoma prevalence does not seem to be significantly increased and, from a pathophysiological standpoint, the long-term IOP increase is essentially due to episcleral venous pressure elevation.

Intraday momentum and contrarian effects on the JSE

ABSTRACTWe study ultra short term return predictability based on intraday momentum and contrarian effects on the JSE. Statistically significant return predictability is found to be present to some extent when returns are calculated from mid-quote prices. However, when returns are calculated under bid-ask pricing assumptions which are more realistic from a trading point of view, intraday momentum and contrarian effects largely disappear and cannot be exploited profitably.

Antimicrobial Prophylaxis in Vaginal Gynecologic Surgery: A Prospective Randomized Study Comparing Amoxicillin-Clavulanic Acid with Cefazolin

The aim of this prospective, randomized study was to compare amoxicillin-clavulanic acid with cefazolin as ultra-short term prophylaxis in vaginal gynecologic surgery. It was conducted at the Department of Obstetrics and Gynecology, University of Bari. Patients were randomly allocated to receive amoxicillin-clavulanic acid (2.2 g) [Group A] or cefazolin (2 g) [Group B] as a single dose 30 minutes before surgery. Each patient was assessed daily until discharge to evidence febrile status and the presence of infections at the operative site, urinary tract and respiratory tract.In the amoxicillin-clavulanic acid (Group A) and cefazolin (Group B) groups, overall 88 and 90 patients, respectively, were evaluable for prophylactic efficacy at hospital discharge. Infectious complications were infrequent in both arms, with febrile morbidity occurring in 4 (4.5%) and 16 (8.9%) patients respectively in the amoxicillin-clavulanic acid and cefazolin groups (p=0.016). Urinary tract infections were higher but not significantly in the amoxicillin-clavulanic acid group (6.8% versus 4.4 %), whereas asymptomatic bacteriuria was detected in 2.2% of the patients in both groups. There was no respiratory tract infection or septic death in either group. It is concluded that ultra-short term prophylaxis with both amoxicillin-clavulanic acid and cefazolin is safe and effective in elective vaginal gynecologic surgery.

Immediate Loaded Implants in Edentulous Patients: Clinical and Technical Aspects using Biotec Tre and Korum SP Implants

ABSTRACTToday a lot of patients ask to the clinicians how to achieve implant-supported fixed prosthesis rehabilitation in an ultra short term therapy. The answer comes from analysis of the diagnostic phase that represents the most important role in this kind of therapy, especially in the fully edentulous patients. Starting from the diagnostic wax to plan the final rehabilitation, through the right choice of implants, in this article will be represented the surgical applied principles and the prosthodontically-driven implants position. An immediate loading technique in the treatment of edentulous patients with screw-retained provisional restoration, without intrasurgical impression it will be presented, both, for the upper and lower jaws, using internal and external hex Biotec Implants (Povolaro di Dueville, Vicenza-Italy).

Transient information flow in a network of excitatory and inhibitory model neurons: Role of noise and signal autocorrelation

We investigate the performance of sparsely-connected networks of integrate-and-fire neurons for ultra-short term information processing. We exploit the fact that the population activity of networks with balanced excitation and inhibition can switch from an oscillatory firing regime to a state of asynchronous irregular firing or quiescence depending on the rate of external background spikes. We find that in terms of information buffering the network performs best for a moderate, non-zero, amount of noise. Analogous to the phenomenon of stochastic resonance the performance decreases for higher and lower noise levels. The optimal amount of noise corresponds to the transition zone between a quiescent state and a regime of stochastic dynamics. This provides a potential explanation of the role of non-oscillatory population activity in a simplified model of cortical micro-circuits.

Repeatability of heart rate variability measures

Due to the sparse data on the repeatability of short and ultra-short term heart rate variability (HRV) measures, we measured the repeatability of common HRV measures derived from 10-second, 2-minute, and 6-minute recordings in 63 healthy men and women, aged 45-64, in Chapel Hill, North Carolina. Three 10-second and 2 six-minute heart rate recordings were obtained during each of 2 visits, separated by 1 to 2 weeks. We partitioned the measurement error into components and computed intraclass correlation coefficients using nested, random effects models. Repeatability improved with the length of recording: intraclass correlation coefficients were greater than 0.7 for 6-minute measures and 2-minute time domain measures and greater than 0.5 for 2-minute frequency domain measures. Repeatability of measures from 10-second records was lower, but improved considerably when the mean from 2 or 3 records was used. Correlations between the same measures from different length recordings were quite high. Our findings support the use of records of at least 5 minutes in length in epidemiological studies, in accordance with previous guidelines. Researchers using 10-second records should consider taking the mean of several recordings, when possible, or using statistical methods to correct for measurement error.

Antimicrobial Prophylaxis in Laparoscopic Gynecologic Surgery: A Prospective Randomized Study Comparing Amoxicillin-Clavulanic Acid with Cefazolin

Numerous studies have been published in recent years about antimicrobial prophylaxis in gynecologic surgery, but the optimal drug and schedule for the different surgical procedures is still a matter of debate. The aim of the present study was to compare two ultra-short term antimicrobial prophylaxis regimens (amoxicillin-clavulanic acid and cefazolin) in preventing infections following laparoscopic gynecologic operations. Three hundred sixty women hospitalized for a laparoscopic gynecologic surgery procedure were included in the study between January 1999, and December 2001. Patients were randomly allocated to receive amoxicillin-clavulanic acid (2.2 g) [Group A] or cefazolin (2 g) [Group B] as a single dose 30 minutes before surgery. Each patient was assessed daily until discharge to evidence febrile status and the presence of infections at the operative site, urinary tract and respiratory tract. In the amoxicillin-clavulanic acid (Group A) and cefazolin (Group B) groups, overall 164 and 172 patients, respectively, were evaluable for prophylactic efficacy at hospital discharge. Infectious complications were infrequent in both groups with febrile morbidity occurring in only one patient (0.6%) in the amoxicillin- clavulanic group. No sign of infections at the surgical site, urinary tract and respiratory tract was observed in either group. No death due to sepsis was recorded. It is concluded that ultra-short term prophylaxis with both amoxicillin-clavulanic acid and cefazolin is safe and effective in elective laparoscopic gynecologic surgery.

Low efficacy of an ultra-short term, once-daily dose triple therapy with omeprazole, azithromycin, and secnidazole for Helicobacter pylori eradication in peptic ulcer.

To determine the eradication rate of an ultra-short treatment schedule for Helicobacter pylori infection in a population with peptic ulcers, using omeprazole, secnidazole, and azithromycin in a once-daily dose for 3 days. Thirty patients with peptic ulcer diagnosed by upper endoscopy and for Helicobacter pylori infection by rapid urease test and histologic examination received omeprazole 40 mg, secnidazole 1000 mg, and azithromycin 500 mg, administered once daily for 3 days. A follow-up exam was performed 12 weeks after the end of the treatment. Patients who were negative for Helicobacter pylori infection by rapid urease test and histologic examination were considered cured. Patients were predominantly female, and the mean age was 50 years. Duodenal peptic ulcer was found in 73% of the patients. Eradication was achieved in 9 of the 28 (32%) patients as determined from the follow-up endoscopic exam. The eradication rate by intention to treat was 30%. Side effects were present in 3% of the patients, and compliance to treatment was total. In spite of the low rate of side effects and good compliance, the eradication index was low. A possible drawback of this therapy is that it reduces the efficacy of macrolide and nitroimidazole compounds in subsequent treatments.