80,688 research outputs found

    Flexible protein folding by ant colony optimization

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    Protein structure prediction is one of the most challenging topics in bioinformatics. As the protein structure is found to be closely related to its functions, predicting the folding structure of a protein to judge its functions is meaningful to the humanity. This chapter proposes a flexible ant colony (FAC) algorithm for solving protein folding problems (PFPs) based on the hydrophobic-polar (HP) square lattice model. Different from the previous ant algorithms for PFPs, the pheromones in the proposed algorithm are placed on the arcs connecting adjacent squares in the lattice. Such pheromone placement model is similar to the one used in the traveling salesmen problems (TSPs), where pheromones are released on the arcs connecting the cities. Moreover, the collaboration of effective heuristic and pheromone strategies greatly enhances the performance of the algorithm so that the algorithm can achieve good results without local search methods. By testing some benchmark two-dimensional hydrophobic-polar (2D-HP) protein sequences, the performance shows that the proposed algorithm is quite competitive compared with some other well-known methods for solving the same protein folding problems

    Design, implementation, and testing of advanced virtual coordinate-measuring machines

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    Copyright @ 2011 IEEE. This article has been made available through the Brunel Open Access Publishing Fund.Advanced virtual coordinate-measuring machines (CMMs) (AVCMMs) have recently been developed at Brunel University, which provide vivid graphical representation and powerful simulation of CMM operations, together with Monte-Carlo-based uncertainty evaluation. In an integrated virtual environment, the user can plan an inspection strategy for a given task, carry out virtual measurements, and evaluate the uncertainty associated with the measurement results, all without the need of using a physical machine. The obtained estimate of uncertainty can serve as a rapid feedback for the user to optimize the inspection plan in the AVCMM before actual measurements or as an evaluation of the measurement results performed. This paper details the methodology, design, and implementation of the AVCMM system, including CMM modeling, probe contact and collision detection, error modeling and simulation, and uncertainty evaluation. This paper further reports experimental results for the testing of the AVCMM

    Extended internal orientation and its effect on employees behaviour: migrant workers in Chinese manufacturing industry

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    Manufacturers in China face a severe labour shortage as well as labour qualification, which have affected their product quality and productivity severely. One of the causing reasons for that is the new generation of migrant workers who are different from their parent's generation. The new generation of migrant workers seeks not only the right working environment, flexible working time, good salary but also the balance between work and life. The new phenomenon has challenged the way to manage workers in manufacturers in China. This PhD project aims to explore how the application of the internal market orientation, a tool for satisfying the employees' needs while achieving the organisational objectives, can tackle these issues in China. The original internal market orientation construct only covers the needs and wants from the work aspect, this research extends the internal market orientation to include employees' needs and wants in life to achieve a better work-life balance among migrant workers. Following the social exchange theory, work-family border theory, and the theory of planned behaviour, the extended internal market orientation construct is proposed to affect the employees' attitude (employee morale and happiness), and the employees' behaviour (intention to stay and employee productivity). To achieve the proposed research objectives, this study first carried out in-depth interviews with migrant worker and their supervisors to develop new internal market orientation scales that are fit for the Chinese context. Interviews with migrant works are undertaken to identify their needs and wants, while interviews with supervisors are conducted to collect their opinions on the adoption of internal market orientation in the Chinese manufacturing industry. Followed this stage, the qualitative data is embedded in the design of the quantitative survey. The subsequent quantitative study is completed via online questionnaires to examine how the extended internal market orientation affects employees' attitude and behaviour. These results of this study confirm that the extended internal market orientation is a second-order construct constituting internal information collection, internal information dissemination, and internal information responsiveness in work and life, respectively. The extended internal market orientation contributes to improving employee behaviour, in particular, employee productivity when there is a higher level of employee morale and happiness. The supervisor support has a moderating influence on the relationship between the extended internal market orientation and employee happiness rather than employee morale. This study suggests that the organisation should care for employee's psychological wellbeing, which conduces to improving the employees' behaviour and the management should provide and satisfy their needs not only in work but also in life

    Dynamics of multiply charged ions in intense laser fields

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    We numerically investigate the dynamics of multiply charged hydrogenic ions in near-optical linearly polarized laser fields with intensities of order 10^16 to 10^17 W/cm^2. Depending on the charge state Z of the ion the relation of strength between laser field and ionic core changes. We find around Z=12 typical multiphoton dynamics and for Z=3 tunneling behaviour, however with clear relativistic signatures. In first order in v/c the magnetic field component of the laser field induces a Z-dependent drift in the laser propagation direction and a substantial Z-dependent angular momentum with repect to the ionic core. While spin oscillations occur already in first order in v/c as described by the Pauli equation, spin induced forces via spin orbit coupling only appear in the parameter regime where (v/c)^2 corrections are significant. In this regime for Z=12 ions we show strong splittings of resonant spectral lines due to spin-orbit coupling and substantial corrections to the conventional Stark shift due to the relativistic mass shift while those to the Darwin term are shown to be small. For smaller charges or higher laser intensities, parts of the electronic wavepacket may tunnel through the potential barrier of the ionic core, and when recombining are shown to give rise to keV harmonics in the radiation spectrum. Some parts of the wavepacket do not recombine after ionisation and we find very energetic electrons in the weakly relativistic regime of above threshold ionization.Comment: submitte

    Coherent population trapping in a dressed two-level atom via a bichromatic field

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    We show theoretically that by applying a bichromatic electromagnetic field, the dressed states of a monochromatically driven two-level atom can be pumped into a coherent superposition termed as dressed-state coherent population trapping. Such effect can be viewed as a new doorknob to manipulate a two-level system via its control over dressed-state populations. Application of this effect in the precision measurement of Rabi frequency, the unexpected population inversion and lasing without inversion are discussed to demonstrate such controllability.Comment: 14 pages, 6 figure

    Nonequilibrium Phase Transitions of Vortex Matter in Three-Dimensional Layered Superconductors

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    Large-scale simulations on three-dimensional (3D) frustrated anisotropic XY model have been performed to study the nonequilibrium phase transitions of vortex matter in weak random pinning potential in layered superconductors. The first-order phase transition from the moving Bragg glass to the moving smectic is clarified, based on thermodynamic quantities. A washboard noise is observed in the moving Bragg glass in 3D simulations for the first time. It is found that the activation of the vortex loops play the dominant role in the dynamical melting at high drive.Comment: 3 pages,5 figure

    Spin relaxation and decoherence of two-level systems

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    We revisit the concepts of spin relaxation and spin decoherence of two level (spin-1/2) systems. From two toy-models, we clarify two issues related to the spin relaxation and decoherence: 1) For an ensemble of two-level particles each subjected to a different environmental field, there exists an ensemble relaxation time T1T_1^* which is fundamentally different from T1T_1. When the off-diagonal coupling of each particle is in a single mode with the same frequency but a random coupling strength, we show that T1T_1^* is finite while the spin relaxation time of a single spin T1T_1 and the usual ensemble decoherence time T2T_2^* are infinite. 2) For a two-level particle under only a random diagonal coupling, its relaxation time T1T_1 shall be infinite but its decoherence time T2T_2 is finite.Comment: 5 pages, 2 figure
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