Qualitative analysis of the dynamics of the time delayed Chua's circuit

IEEE TRANS. CIRCUITS SYST.

On the thermal dynamic behaviour of the helium-cooled DEMO fusion reactor

The EU-DEMO conceptual design is being conducted among research institutions and universities from 26 countries of European Union, Switzerland and Ukraine. Its mission is to realise electricity from nuclear fusion reaction by 2050. As DEMO has been conceived to deliver net electricity to the grid, the choice of the Breeding Blanket (BB) coolant plays a pivotal role in the reactor design having a strong influence on plant operation, safety and maintenance. In particular, due to the pulsed nature of the heat source, the Primary Heat Transfer System (PHTS) becomes a very important actor of the Balance of Plant (BoP) together with the Power Conversion System (PCS). Moreover, aiming to mitigate the potential negative impact of plasma pulsing on BoP equipment, for the DEMO plant is also being investigated a "heat transfer chain" option which envisages an Intermediate Heat Transfer System (IHTS) equipped with an Energy Storage System (ESS) between PHTS and PCS. Within this framework, a preliminary study has been carried out to analyse the thermal dynamic behaviour of the IHTS system for the Helium-Cooled Pebble Bed (HCPB) BB concept during pulse/dwell transition which should be still considered as the normal operating mode of a fusion power plant. Starting from preliminary thermal-hydraulic calculations made in order to size the main BoP components, the global performances of DEMO BoP have been quantitatively assessed focusing the attention on the attitude of the whole IHTS to smooth the sudden power variations which come from the plasma. The paper describes criteria and rationale followed to develop a numerical model which manages to simulate simple transient scenarios of DEMO BoP. Results of numerical simulations are presented and critically discussed in order to point out the main issues that DEMO BoP has to overcome to achieve a viable electricity power output

Differential-difference equations for the transient simulation of lossy MTLs

In this paper, we address the differential representation of the time-domain characteristics of lossy MTLs. This approach is of great interest for the efficient simulation of circuits with long interconnects and nonlinearities. The properties of this characterization method are discussed with particular emphasis on the bandwidth and on the order of the differential operators used. Our discussion is supported by a complete characterization example for a realistic wideband 3-conductor interconnec

Efficient computation of transient responses of frequency-dependent nonlinearly loaded transmission lines

The authors address the combined time and frequency domain analysis of nonlinearly loaded low-loss transmission lines. They show that a variety of interconnects are characterized by transfer functions, whose impulse responses have a fast initial-time structure and a slow long-time component. A piecewise linear approximation of the transient functions with nonuniform sampling is proposed as an effective method to obtain high accuracy with low computational cost

Exploratory study of the EU-DEMO Water-Cooled Lithium Lead breeding blanket behaviour in case of loss of cooling capability

Within the framework of the European Roadmap to the realization of fusion energy, a strong international cooperation is ongoing to develop a Breeding Blanket (BB) system for the EU-DEMO reactor. Although it is still to be decided whether the DEMO in-vessel components should perform any safety function, the pursuing of robust blanket concepts able to handle upset and accidental loading conditions has been always seen as good practice in fusion reactor engineering to enhance the inherent plant safety performances. Amongst the several classes of events that might challenge the BB structural integrity, the large Loss of Coolant Accident is one of the most relevant because it usually leads to a fast loss of cooling capability of the structures. Due to the characteristic of the tokamak assembly, the behaviour of each blanket segment during a sudden loss of cooling capability does not depend only upon distinguishing features of the component itself. In fact, the overall transient can be governed by conditions established in surrounding elements, like adjacent blanket segments and vacuum vessel, as well as by the plasma shutdown strategies adopted to protect the reactor. The scope of the activity herein presented is to make a preliminary assessment of the intrinsic capability of EU-DEMO tokamak architecture to cope with the loss of cooling in the Water-Cooled Lithium Lead (WCLL) BB concept. Evaluation of BB thermal field in short and medium term under simplified, yet conservative, assumptions was carried out for four transient scenarios with the aim of investigating the response of the structure in case of: a) fast or soft plasma shutdown, and b) different blanket cooling schemes. Moreover, the WCLL BB thermo-mechanical response in the most critical time steps has been assessed. The obtained results shall help for future decisions on safety systems/action to be implemented to cope with accidents

Fall risk assessment in elderly with and without history of falls: kinematic gait analysis: a comparative study

Objectives: The objective of this research was to verify if there was a variation in the MFC (Minimum Foot Clearance) value among elderly with and without history of falls and, if there were any, verify which joint of the lower limb was responsible for that variation. It was also a main objective to verify if there was a correlation between the risk of falling, achieved through the Timed Up and Go Test (TUG), and the MFC variation. Material and Methods: The sample consisted of a total of 30 elderly who met the inclusion and exclusion criteria. These were divided into the group without history of falls (n=15) and into the group with history of falls (n=15). The MFC and the joint movement amplitudes of the hip, knee and ankle, of the dominant lower limb, were assessed using the Kinovea programme and for the risk of fall assessment it was used the TUG. Results: There were no statistically significant differences in the MFC and TUG values between the groups with and without history of falls. However, there is a decrease of the MFC value for the group with history of falls, being the ankle the joint that most contributed to the MFC variation in the group without history of falls, and the knee in the group with history of falls. About the relation between MFC and TUG, it was obtained a negative correlation (r=-0,269) but it was not significant (p=0,150). Conclusion: In our sample no significant differences in the MFC value were obtained between the group with history of falls and the group without history of falls. Besides the lack of significant differences in the MFC value it was determined the articulation of the lower limb responsible for its variation, and it has been found, although with a p>0,05, that for the group with no history of falls it was the ankle that more contributed to this variation and the knee to the group with history of falls. Concerning to the TUG and MFC value correlation it wasn’t significant. Thus, it was concluded that the TUG use is more effective and sensitive in predicting the risk of falling when compared with the kinematic analysis to obtain the MFC value and the joints amplitude

Fall risk assessment in elderly with and without history of falls: strength analysis of lower limb: a comparative study

Objectives: The objective of this research was to analyse muscle performance criteria of the knee joints and ankle flexor and extensor muscles among elderly with and without history of falls. Material and methods: The sample was non-probabilistic, of convenience, comprising a total of 30 elderly (15 with history of falls and 15 without history of falls) who met the inclusion and exclusion criteria. Data were collected through a characterization questionnaire and through the Biodex System Isokinetic Dynamometer. The isokinetic assessment consisted in collecting the Peak Torque per unit of mass (N.m/BW) and ratio FlexorsCon/ExtensorsCon (%) of the knee joints and ankle flexor and extensor muscles, with 5 repetitions and the 60º/s angular speed. This collection has been made in both lower limbs. Results: The sample consisted of 30 individuals, 15 from the group without history of falls and 15 from the group with history of falls with average age of (69,17±4,77) years old. The muscle performance parameters were not significantly different between the groups (p>0,05). Conclusion: The group of elderly with history of falls showed lower Peak Torque numbers per unit of mass (N.m/BW) for the knee and ankle joint comparing with the group without history of falls. In present research also the values of the ratio flexorsCon/ExtensorsCon was analyzed weren't differences found in the knee and ankle joint. Although there are no statistically significant differences between results obtained, approach we believe it will be beneficial to include strengthening exercises for the flexors and extensors muscles of these joints, thereby contributing to the prevention of falls

Fall risk assessment in elderly with and without history of falls: relationship between disorders of balance, fear of falling and gait changes: a comparative study

Objectives: The aim of this study was to assess the changes that occur in the balance, fear of falling and kinematic parameters such as stride length, velocity and time support in elderly with and without a history of falling. Main objective was also to verify whether a relationship exists between changes in gait parameters evaluated, balance and fear of falling. Methods: The sample comprised 30 patients (15 with history of falls and 15 without a history of falls), which met the criteria for inclusion and exclusion. The kinematic evaluation was performed in the dominant leg, which was right in this sample. The stride length, speed and duration of support were assessed using the program Kinovea and for assessment of balance and fear of falling were assessed using the Berg Balance Scale and the Falls Efficacy Scale. Statistical analysis was performed with SPSS version 20. Results: There were no significant differences in the parameters analyzed, except for scores on the Berg Balance Scale (p=0.000) between groups with and without history of falls. However, there is a decrease in the length of the stride and duration of left leg support and the increased length of right leg support, the speed and the fear of falling. The relationship between the parameters obtained, there is only statistically significant result between speed and stride length (r=0.507, p=0.004) and between the score of the Berg Balance Scale and the stride length (r=0.393, p=0,032). Conclusion: Although not having obtained statistically significant results we can conclude that in elderly with a history of falls have changes in speed and stride length that can be related to balance disorders and the aging process itself. However, it is concluded that the use of the Berg Balance Scale is more responsive and effective in the detection of changes occurring in the individual after a fall, and subsequent evaluation of the risk of falling that performing a kinematic analysis

Fall risk assessment in elderly with and without history of falls: gait electromyographic analysis: a comparative study

Objectives: To determinate if there were differences in electromyography parameters of rectus anterior, biceps femoris, gluteus medius, soleus, gastrocnemius medialis and tibialis anterior muscles between group with and without history of falls during. Was analized the relationship between the levels of muscle activation and score in POMA (Performance-Oriented Mobility Assessment). Materials and Methods: This is a transversal, not experimental and comparative study. The sample was composed by 30 older adults, 15 with and 15 without history of falls. To collect the data of electromyography was used BIOPAC systems and followed the SENIAM guidelines. For the collection of kinematic data was used Kinovea program and for assess the risk of falling was applied POMA. Results: Individuals with history of falls present levels of muscle activity relatively to maximum voluntary contraction (MVC) higher in the dominant lower limb (right) compared to subjects without a history of falls, however these differences aren´t statistically significant (p>0,05). There is enormous variation between the sample in relation to phases of gait in which the muscles are more actives. The group with history of falls shows values lower than group without history of falls in POMA score, the difference is significant (p=0.001). The relationship between percentage of muscle activation and the values obtained in POMA not proved statistically significant (p>0,05). Conclusion: Although results obtained weren´t statistically significants, we can conclude that individuals with falls have higher levels of muscle activation relative to MVC that individuals without history of falls, it is believed that the changes are related to the development of strategies for increased stability during gait. There is considerable variability in phases in which the subjects engaged higher levels of muscle activation, which might occur due to task compensatory strategies or by the task have been made at speed of comfort for the individual. It follows that POMA is an instrument more sensitive and effective to identify the risk of falling in these individuals that the electromyographic analysis