22 research outputs found

    Generation time statistics of Escherichia coli using synchronous culture techniques

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    The distribution of generation times and the correlation coefficient between the generation times of mother and daughter cells are determined for a B strain of Escherichia coli under various conditions of growth. Synchronously dividing cultures of E. coli are produced by the Mitchison-Vincent density gradient centrifugation technique. Very precise data are yielded by cell number counts at frequent intervals with a Coulter electronic particle counter. Culture growth is followed for three and sometimes four generations. Doubling times between 30 and 80 minutes are obtained at 37°C with mineral salts medium supplemented with suitable carbon sources, namely, glucose + methionine + histidine, glucose, sucrose, glycerol, or succinate. On glucose, doubling times between 40 and 90 minutes are obtained by varying the temperature between 37° and 26°C. A mathematical description of synchronous growth is taken from the literature. The rate of increase of cell number concentration is expressed as the sum of a series of functions with properties related to the generation time distribution of the cells and the correlations between the generation times of related cells. Smoothing of the cell number data by digital filtering and subsequent numerical differentiation yields a series of peaks having little apparent skewness for all growth rates. This is confirmed by fitting a sum of Gaussian functions to the peaks by a nonlinear least squares procedure. The parameters of the generation time distribution and the correlation coefficients between the generation times of parent and progeny cells are then extracted directly from the means and variances of the Gaussian functions. The uncertainty associated with each data point is estimated to be within 1½% and the errors in the extracted parameters are determined by repeated simulation of the data analysis procedure using computer generated noisy data. Under all growth conditions the generation time distribution is of Gaussian form with a coefficient of variation of 0.22 ± 0.02. The mother-daughter generation time correlation coefficient was significantly negative at doubling times between 40 and 64 minutes; a constant value of -0.47 ± 0.06 was consistent with the observations. At doubling times of 30 and 80-90 minutes this coefficient tended to be closer to zero but with a higher uncertainty. In succinate medium at 37°C (doubling time 80 minutes) synchrony was noticeably weaker after the first generation compared with the results at higher growth rates. The growth data for this medium indicate a correlation coefficient very close to zero. The implications of the results are discussed in terms of the predictions of a number of models for the control of cell division that have appeared in the literature

    Laser-plasma interactions as tools for studying processes in quantum electrodynamics

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    Conventional particle accelerators and astronomical observations have long been some of the only tools for studying processes in high energy physics. The development of laser-plasma sources and high gradient accelerators will therefore be a key asset to these studies. In particular, laser-plasma accelerators have favourable spatial and temporal properties for studies into intense processes, and can be readily coupled to a wide array of other laser-plasma sources creating unique environments. Here, coupling to an X-ray source and intense laser focus were used to study processes in quantum electrodynamics. To study the linear Breit-Wheeler process, a 40 ps laser was used to drive a volumetric X-ray emitter. Line emission from a thin-foil Ge target, produced a highly efficient (3.4%), dense source of 1.3 − 1.9 keV X-rays, with 3 ± 1 (stat.) ±0.4 (sys.) ×10^{12} photons/eV/sphere. These X-rays were collided with bremsstrahlung gamma rays (with energies up to 800 MeV) to investigate electron-positron pair production. The X-ray source was well-optimised for studying this interaction, and would allow the detection of Breit-Wheeler pairs if used with a moderately improved electron beam for generating bremsstrahlung (3× the highest electron energy and 5× the total charge, as achieved previously). This would constitute the first laser-plasma photon- photon collider with low virtuality (energy off mass-shell ≈ 10^{−20} MeV^2). In order to differentiate between competing models of electron radiation reaction in strong field quantum electrodynamics, a narrow energy-spread electron beam was studied. By utilising shock injection into a laser wakefield accelerator, a high energy (1260±40 MeV), narrow energy- spread (4.1±0.9 %) beam was generated. This is one of only a few studies that have successfully achieved these electron beam properties. While the shot-to-shot reproducibility of the electron beam was limited to 60%, the relative energy-spread was sufficiently small that differentiation of radiation reaction models could be readily achieved in future experiments. With the upcoming commissioning of many multi-PW laser facilities, these studies demonstrate how active research into quantum electrodynamics can be achieved on the smaller, more accessible, laser-laboratory scale.Open Acces

    Affective Computing

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    This book provides an overview of state of the art research in Affective Computing. It presents new ideas, original results and practical experiences in this increasingly important research field. The book consists of 23 chapters categorized into four sections. Since one of the most important means of human communication is facial expression, the first section of this book (Chapters 1 to 7) presents a research on synthesis and recognition of facial expressions. Given that we not only use the face but also body movements to express ourselves, in the second section (Chapters 8 to 11) we present a research on perception and generation of emotional expressions by using full-body motions. The third section of the book (Chapters 12 to 16) presents computational models on emotion, as well as findings from neuroscience research. In the last section of the book (Chapters 17 to 22) we present applications related to affective computing

    Statistical Inference in Auditory Perception

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    The human auditory system effortlessly parses complex sensory inputs despite the ever-present randomness and uncertainty in real-world scenes. To achieve this, the brain tracks sounds as they evolve in time, collecting contextual information to construct an internal model of the external world for predicting future events. Previous work has shown the brain is sensitive to many predictable (and often complex) patterns in sequential sounds. However, real-world environments exhibit a broader spectrum of predictability, and moreover, the level of predictability is constantly in flux. How does the brain build robust internal representations of such stochastic and dynamic acoustic environments? This question is addressed through the lens of a computational model based in statistical inference. Embodying theories from Bayesian perception and predictive coding, the model posits the brain collects statistical estimates from sounds and maintains multiple hypotheses for the degree of context to include in predictive processes. As a potential computational solution for perception of complex and dynamic sounds, this model is used to connect sensory inputs with listeners' responses in a series of human behavioral and electroencephalography (EEG) experiments incorporating uncertainty. Experimental results point toward the underlying sufficient statistics collected by the brain, and the extension of these statistical representations to multiple dimensions is examined along spectral and spatial dimensions. The computational model guides interpretation of behavioral and neural responses, revealing multiplexed responses in the brain corresponding to different levels of predictive processing. In addition, the model is used to explain individual differences across listeners highlighted by uncertainty. The proposed computational model was developed based on first principles, and its usefulness is not limited to the experiments presented here. The model was used to replicate a range of previous findings in the literature, unifying them under a single framework. Moving forward, this general and flexible model can be used as a broad-ranging tool for studying the statistical inference processes behind auditory perception, overcoming the need to minimize uncertainty in perceptual experiments and pushing what was previously considered feasible for study in the laboratory towards what is typically encountered in the "messy" environments of everyday listening

    Cyber–Physical–Social Frameworks for Urban Big Data Systems: A Survey

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    The integration of things’ data on the Web and Web linking for things’ description and discovery is leading the way towards smart Cyber–Physical Systems (CPS). The data generated in CPS represents observations gathered by sensor devices about the ambient environment that can be manipulated by computational processes of the cyber world. Alongside this, the growing use of social networks offers near real-time citizen sensing capabilities as a complementary information source. The resulting Cyber–Physical–Social System (CPSS) can help to understand the real world and provide proactive services to users. The nature of CPSS data brings new requirements and challenges to different stages of data manipulation, including identification of data sources, processing and fusion of different types and scales of data. To gain an understanding of the existing methods and techniques which can be useful for a data-oriented CPSS implementation, this paper presents a survey of the existing research and commercial solutions. We define a conceptual framework for a data-oriented CPSS and detail the various solutions for building human–machine intelligence

    XXI Workshop de Investigadores en Ciencias de la Computación - WICC 2019: libro de actas

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    Trabajos presentados en el XXI Workshop de Investigadores en Ciencias de la Computación (WICC), celebrado en la provincia de San Juan los días 25 y 26 de abril 2019, organizado por la Red de Universidades con Carreras en Informática (RedUNCI) y la Facultad de Ciencias Exactas, Físicas y Naturales de la Universidad Nacional de San Juan.Red de Universidades con Carreras en Informátic

    XXI Workshop de Investigadores en Ciencias de la Computación - WICC 2019: libro de actas

    Get PDF
    Trabajos presentados en el XXI Workshop de Investigadores en Ciencias de la Computación (WICC), celebrado en la provincia de San Juan los días 25 y 26 de abril 2019, organizado por la Red de Universidades con Carreras en Informática (RedUNCI) y la Facultad de Ciencias Exactas, Físicas y Naturales de la Universidad Nacional de San Juan.Red de Universidades con Carreras en Informátic
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