663 research outputs found
Structural Analysis of Boolean Equation Systems
We analyse the problem of solving Boolean equation systems through the use of
structure graphs. The latter are obtained through an elegant set of
Plotkin-style deduction rules. Our main contribution is that we show that
equation systems with bisimilar structure graphs have the same solution. We
show that our work conservatively extends earlier work, conducted by Keiren and
Willemse, in which dependency graphs were used to analyse a subclass of Boolean
equation systems, viz., equation systems in standard recursive form. We
illustrate our approach by a small example, demonstrating the effect of
simplifying an equation system through minimisation of its structure graph
Relaxed Operational Semantics of Concurrent Programming Languages
We propose a novel, operational framework to formally describe the semantics
of concurrent programs running within the context of a relaxed memory model.
Our framework features a "temporary store" where the memory operations issued
by the threads are recorded, in program order. A memory model then specifies
the conditions under which a pending operation from this sequence is allowed to
be globally performed, possibly out of order. The memory model also involves a
"write grain," accounting for architectures where a thread may read a write
that is not yet globally visible. Our formal model is supported by a software
simulator, allowing us to run litmus tests in our semantics.Comment: In Proceedings EXPRESS/SOS 2012, arXiv:1208.244
Improving optimal control of grid-connected lithium-ion batteries through more accurate battery and degradation modelling
The increased deployment of intermittent renewable energy generators opens up
opportunities for grid-connected energy storage. Batteries offer significant
flexibility but are relatively expensive at present. Battery lifetime is a key
factor in the business case, and it depends on usage, but most techno-economic
analyses do not account for this. For the first time, this paper quantifies the
annual benefits of grid-connected batteries including realistic physical
dynamics and nonlinear electrochemical degradation. Three lithium-ion battery
models of increasing realism are formulated, and the predicted degradation of
each is compared with a large-scale experimental degradation data set
(Mat4Bat). A respective improvement in RMS capacity prediction error from 11\%
to 5\% is found by increasing the model accuracy. The three models are then
used within an optimal control algorithm to perform price arbitrage over one
year, including degradation. Results show that the revenue can be increased
substantially while degradation can be reduced by using more realistic models.
The estimated best case profit using a sophisticated model is a 175%
improvement compared with the simplest model. This illustrates that using a
simplistic battery model in a techno-economic assessment of grid-connected
batteries might substantially underestimate the business case and lead to
erroneous conclusions
Особливості емоційного вигорання педагогів із різним стажем роботи
зв'язку з великою емоційною напруженістю професійної
діяльності педагога, нестандартністю педагогічних ситуацій,
відповідальністю і складністю професійної праці вчителя,
збільшується ризик розвитку синдрому «емоційного вигорання». При
цьому дуже мало звертається уваги на діючі ефективні психолого-
педагогічні та медичні технології, які спрямовані на збереження
здоров'я педагога, що знижують ризик формування синдрому
«емоційного вигорання» і появи кризи професії в цілому
Longer-term increased cortisol levels in young people with mental health problems.
Disturbance of hypothalamus-pituitary-adrenal axis activity is commonly reported in a range of mental disorders in blood, saliva and urine samples. This study aimed to look at longer-term cortisol levels and their association with clinical symptoms. Hair strands of 30 young people (16-25 years) presenting with mental health problems (Mage±SD=21±2.4, 26 females) and 28 healthy controls (HC, Mage±SD=20±2.9, 26 females) were analyzed for cortisol concentrations, representing the past 6 months prior to hair sampling. Clinical participants completed an assessment on psychiatric symptoms, functioning and lifestyle factors. All participants completed the Perceived Stress Scale. Hair cortisol concentrations representing the past 3 (but not 3-6) months were significantly increased in clinical participants compared to HC. Perceived stress in the past month was significantly higher in clinical participants compared to HC, but not significantly correlated with hair cortisol. Hair cortisol levels were not significantly associated with any other measures. Hair segment analyses revealed longer-term increased levels of cortisol in the past 3 months in early mental health problems. Further insight into the role of cortisol on the pathogenesis of mental illnesses requires longitudinal studies relating cortisol to psychopathology and progression of illness
Efficiently enforcing mutual state exclusion requirements in symbolic supervisor synthesis
Given a model of an uncontrolled system and a requirement specification, a supervisory controller can be synthesized so that the system under control adheres to the requirements. There are several ways in which informal behavioral safety requirements can be formalized, one of which is using mutual state exclusion requirements. In current implementations of the supervisor synthesis algorithm, synthesis may be inefficient when mutual state exclusion requirements are used. We propose a method to efficiently enforce these requirements in supervisor synthesis. We consider symbolic supervisor synthesis, where Binary Decision Diagrams are used to represent the system. The efficiency of the proposed method is evaluated by means of an industrial and academic case study
Unlocking Extra Value from Grid Batteries Using Advanced Models
Lithium-ion batteries are increasingly being deployed in liberalised
electricity systems, where their use is driven by economic optimisation in a
specific market context. However, battery degradation depends strongly on
operational profile, and this is particularly variable in energy trading
applications. Here, we present results from a year-long experiment where pairs
of batteries were cycled with profiles calculated by solving an economic
optimisation problem for wholesale energy trading, including a
physically-motivated degradation model as a constraint. The results confirm the
conclusions of previous simulations and show that this approach can increase
revenue by 20% whilst simultaneously decreasing degradation by 30% compared to
existing methods. Analysis of the data shows that conventional approaches
cannot increase the number of cycles a battery can manage over its lifetime,
but the physics-based approach increases the lifetime both in terms of years
and number of cycles, as well as the revenue per year, increasing the possible
lifetime revenue by 70%. Finally, the results demonstrate the economic impact
of model inaccuracies, showing that the physics-based model can reduce the
discrepancy in the overall business case from 170% to 13%. There is potential
to unlock significant extra performance using control engineering incorporating
physical models of battery ageing
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