15 research outputs found
Brownian Carnot engine
The Carnot cycle imposes a fundamental upper limit to the efficiency of a
macroscopic motor operating between two thermal baths. However, this bound
needs to be reinterpreted at microscopic scales, where molecular bio-motors and
some artificial micro-engines operate. As described by stochastic
thermodynamics, energy transfers in microscopic systems are random and thermal
fluctuations induce transient decreases of entropy, allowing for possible
violations of the Carnot limit. Despite its potential relevance for the
development of a thermodynamics of small systems, an experimental study of
microscopic Carnot engines is still lacking. Here we report on an experimental
realization of a Carnot engine with a single optically trapped Brownian
particle as working substance. We present an exhaustive study of the energetics
of the engine and analyze the fluctuations of the finite-time efficiency,
showing that the Carnot bound can be surpassed for a small number of
non-equilibrium cycles. As its macroscopic counterpart, the energetics of our
Carnot device exhibits basic properties that one would expect to observe in any
microscopic energy transducer operating with baths at different temperatures.
Our results characterize the sources of irreversibility in the engine and the
statistical properties of the efficiency -an insight that could inspire novel
strategies in the design of efficient nano-motors.Comment: 7 pages, 7 figure
Selection on Alleles Affecting Human Longevity and Late-Life Disease: The Example of Apolipoprotein E
It is often claimed that genes affecting health in old age, such as cardiovascular and Alzheimer diseases, are beyond the reach of natural selection. We show in a simulation study based on known genetic (apolipoprotein E) and non-genetic risk factors (gender, diet, smoking, alcohol, exercise) that, because there is a statistical distribution of ages at which these genes exert their influence on morbidity and mortality, the effects of selection are in fact non-negligible. A gradual increase with each generation of the ε2 and ε3 alleles of the gene at the expense of the ε4 allele was predicted from the model. The ε2 allele frequency was found to increase slightly more rapidly than that for ε3, although there was no statistically significant difference between the two. Our result may explain the recent evolutionary history of the epsilon 2, 3 and 4 alleles of the apolipoprotein E gene and has wider relevance for genes affecting human longevity
DFT-inspired methods for quantum thermodynamics
In the framework of quantum thermodynamics, we propose a method to
quantitatively describe thermodynamic quantities for out-of-equilibrium
interacting many-body systems. The method is articulated in various
approximation protocols which allow to achieve increasing levels of accuracy,
it is relatively simple to implement even for medium and large number of
interactive particles, and uses tools and concepts from density functional
theory. We test the method on the driven Hubbard dimer at half filling, and
compare exact and approximate results. We show that the proposed method
reproduces the average quantum work to high accuracy: for a very large region
of parameter space (which cuts across all dynamical regimes) estimates are
within 10% of the exact results
Transcriptional repression of Plxnc1 by Lmx1a and Lmx1b directs topographic dopaminergic circuit formation
Measuring Success Factors of Quality Management in the Shipping Industry
It is generally accepted that quality management is considered a valuable competitive factor for firms that confers them competitive advantages and enables them to achieve superior performance. Although there have been numerous studies examining general quality management practices and implementation, industry-specific studies on quality management practices and factors that influence their success in the shipping industry are rather few. This study seeks to identify the factors that are critical to successful quality management, and attempts to develop a reliable, empirically tested, and rigorously validated measurement instrument for quality management, for the shipping industry. We conducted a large-scale survey of shipping industry executives and applied a rigorous research methodology to treat the survey data. We identified four success factors of quality management, which are top management commitment and participation, quality information and performance measurement, employee training and empowerment, and customer focus, and developed a functional instrument to measure quality management in the shipping industry. This paper contributes to research by identifying the success factors of quality management, and provides managerial insights on the successful management of quality, in the shipping industry. Maritime Economics & Logistics (2007) 9, 234–253. doi:10.1057/palgrave.mel.9100179