887 research outputs found
A structuring mechanism for embedded control systems using co-modelling and co-simulation
In most embedded control system (ECS) designs, multiple engineering disciplines and various domain-specific models are involved, such as embedded software models in discrete-event (DE) domain and dynamic plant model in continuous-time (CT) domain. In this paper, we advocate collaborative modelling and co-simulation to verify different aspects of the system as a whole before implementation. This paper proposes a development approach and structuring mechanism for CT-intensive ECS designs using co-modelling and co-simulation techniques. Based on this approach, an integrated co-model can be developed and refined using different domain-specific languages and tools. Influences from one domain to the other can be simulated via co-simulation and analysed in both perspectives. Our structuring and development process has been applied to a mobile robot using this co-simulation technique. We have experienced that structuring the co-modelling process allows us to produce co-models an co-simulations effectively. Future work is on checking for model inconsistencies during collaboration, and provide approaches to deal with this
Collapse of ringlike structures in 2DEGs under tilted magnetic fields
In the quantum Hall regime, the longitudinal resistivity plotted
as a density--magnetic-field () diagram displays ringlike structures
due to the crossings of two sets of spin split Landau levels from different
subbands [e.g., Zhang \textit{et al.}, Phys. Rev. Lett. \textbf{95}, 216801
(2005)]. For tilted magnetic fields, some of these ringlike structures "shrink"
as the tilt angle is increased and fully collapse at . Here we theoretically investigate the topology of these structures
via a non-interacting model for the 2DEG. We account for the inter Landau-level
coupling induced by the tilted magnetic field via perturbation theory. This
coupling results in anti-crossings of Landau levels with parallel spins. With
the new energy spectrum, we calculate the corresponding diagram of
the density of states (DOS) near the Fermi level. We argue that the DOS
displays the same topology as in the diagram. For the
ring with filling factor , we find that the anti-crossings make it
shrink for increasing tilt angles and collapse at a large enough angle. Using
effective parameters to fit the data, we find a collapsing
angle . Despite this factor-of-two discrepancy with
the experimental data, our model captures the essential mechanism underlying
the ring collapse.Comment: 3 pages, 2 figures; Proceedings of the PASPS V Conference Held in
August 2008 in Foz do Igua\c{c}u, Brazi
Dynamic modelling for ecological and economic sustainability in a rapid urbanizing region
AbstractRecently years, most of China's rapidly developed regions are becoming China's large industrial cities and drawing the attention of the world. Consequently, the impacts of rapid urbanization to urban ecosystem will be greatly increased with the increasing economic development. If relationship between economic development and ecological sustainability is not fully realized, urban ecosystem will be degraded at a high rate. Therefore, study on ecological and economic sustainability for this area is of great importance. The objectives of this study are: (1) to find a balance between economic development and ecological protection in these regions; (2) to develop a process-based ecological and economic sustainable development model; (3) to supply the optimal controls for these reigns by conducting a policy analysis. To this end, a system dynamic model for urban sustainable development was constructed. The model was based on the analysis of many index and three subsystems, which are society system, economic system, and environmental system. We also selected typical development policies for a rapidly urbanizing region, Tianjin, in the future
The simulation of magnetorheological elastomers adaptive tuned dynamic vibration absorber for automobile engine vibration control
The aim of this article is to investigate the use of a Dynamic Vibration Absorber to control vibration of engine by using simulation. Traditional means of vibration control have involved the use of passive and more recently, active methods. This study is different in that it involves an adaptive component in the design of vibration absorber using magnetorheological elastomers (MREs) as the adaptive spring.
MREs are kind of novel smart material whose shear modulus can be controlled by applied magnetic field. In this paper, the vibration mode of a simple model of automobile engine is simulated by Finite Element Method (FEM) analysis. Based on the analysis, the MREs Adaptive Tuned Dynamic Vibration Absorber (ATDVA) is presented to reduce the vibration of the engine. Simulation result indicate that the control frequency of ATDVA can be changed by modifing the shear modulus of MREs and the vibraion reduction efficiency of ATDVA are also evaluated by FEM analysis
Hund's Rule for Composite Fermions
We consider the ``fractional quantum Hall atom" in the vanishing Zeeman
energy limit, and investigate the validity of Hund's maximum-spin rule for
interacting electrons in various Landau levels. While it is not valid for {\em
electrons} in the lowest Landau level, there are regions of filling factors
where it predicts the ground state spin correctly {\em provided it is applied
to composite fermions}. The composite fermion theory also reveals a
``self-similar" structure in the filling factor range .Comment: 10 pages, revte
Ginkgo biloba extract for essential hypertension: A systemic review
AbstractBackgroundGinkgo biloba extract (GBE), a traditional natural herbal product, is often used in the treatment of essential hypertension (EH) as complementary therapy in China and European countries.AimTo critically assess the current clinical evidence of efficacy and safety of GBE for EH.Methods7 electronic databases (Cochrane Library, PubMed, EMBASE, VIP, CBM, Wanfang data, and CNKI) were searched to identify randomized controlled trials (RCTs) of GBE for EH. Methodological quality was assessed independently using the Cochrane Handbook for Systematic Reviews of Interventions.ResultsA total of 9 RCTs with 1012 hypertensive patients were identified and reviewed. Most RCTs were of high risk of bias with flawed study design and poor methodological quality. 6 trials demonstrated potential positive effect of GBE as complementary therapy on BP reduction when compared with antihypertensive drug therapy; however, it was not associated with a statistically significant effect on both SBP and DBP reduction in 3 other trials. Despite the positive findings, there were so many methodological limitations and significant clinical heterogeneity. Most of the trials did not report adverse effects, and the safety of GBE is still uncertain.ConclusionNo confirmative conclusions on the efficacy and safety of GBE for EH could be drawn. More rigorous trials are warranted to support their clinical use
Spike Timing-Dependent Plasticity in the CA1 Pyramidal Neuron in a Modeled Hippocampal Circuit
Spike timing-dependent plasticity (STDP) plays an important role in sculpting informationstoring circuits in the hippocampus, since motor learning and memory are thought to be
closely linked with this classical plasticity. To further understand the information delivery in
a hippocampus circuit, we build a computational model to study the potential role of linear
changes in the synaptic weight and synaptic number. Several key results have been obtained:
(i) Changes in the synaptic weight and numbers lead to different long-term modification; (ii)
the first paired spiking from two neurons significantly influences the adjusted subsequent
paired spiking; the pre-post spiking pair strengthens the following paired spiking; however,
the post-pre spiking pair depresses the subsequent spiking; (iii) when the synaptic weight and
synaptic numbers are changed, the interval of the first spiking pair may undergo reduction,
and (iv) when we stimulate a stellate neuron weakly or decrease the capacitance of CA1
pyramidal neuron, LTP is more easily produced than LTD; on the contrary, LTD is more easily
produced in an opposite situation; increase in the synaptic numbers can promote activation of
the CA1 pyramidal neuron.Пластичність, залежна від часу генерування піків (spike
timing-dependent plasticity – STDP), відіграє важливу роль
у формуванні нейромереж, що накопичують інформацію
в гіпокампі; вважається, що моторне навчання та пам’ять
тісно пов’язані з пластичністю цього типу. Для глибшого
розуміння процесів передачі інформації в гіпокампальній
нейромережі ми створили комп’ютерну модель, щоб
вивчити потенціальну роль лінійних змін синаптичної ваги
та числа синапсів у таких мережах. Було отримано чотири
основні результати: 1) зміни ваги та числа синапсів можуть
призводити до появи різних феноменів довготривалої
модифікації; 2) перша пара потенціалів дії, генерована
двома нейронами, істотно впливає на характеристики другої
пари піків; генерація пари піків у пре-пост-послідовності
полегшує генерацію наступної пари, тоді як пост-прегенерація пари пригнічує генерацію наступної пари; 3) коли
вага синапсів та їх кількість змінюються, інтервал у першій
парі піків зменшується; 4) коли стимулювати зірчастий
нейрон з невеликою інтенсивністю або зменшити ємність
пірамідного нейрона CA1, легше індукується довготривала
потенціація; у протилежній ситуації легше виникає
довготривала депресія; збільшення числа синапсів полегшує
активацію пірамідного нейрона CA1
Dimensional Crossover in the Effective Second Harmonic Generation of Films of Random Dielectrics
The effective nonlinear response of films of random composites consisting of
a binary composite with nonlinear particles randomly embedded in a linear host
is theoretically and numerically studied. A theoretical expression for the
effective second harmonic generation susceptibility, incorporating the
thickness of the film, is obtained by combining a modified effective-medium
approximation with the general expression for the effective second harmonic
generation susceptibility in a composite. The validity of the thoretical
results is tested against results obtained by numerical simulations on random
resistor networks. Numerical results are found to be well described by our
theory. The result implies that the effective-medium approximation provides a
convenient way for the estimation of the nonlinear response in films of random
dielectrics.Comment: 9 pages, 2 figures; accepted for publication in Phys. Rev.
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