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  • 1
    Electronic Resource
    Electronic Resource
    Piecewise deterministic Markov process model for flexible manufacturing systems with preventive maintenance (1994)
    Springer
    Journal of optimization theory and applications 81 (1994), S. 259-275 
    Details
    ISSN: 1573-2878
    Keywords: Flexible manufacturing systems ; controlled piecewise deterministic Markov process ; maintenance and production planning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we consider a maintenance and production model of a flexible manufacturing system. The maintenance activity involves lubrication, routine adjustments, etc., which reduce the machine failure rates and therefore reduce the aging of the machines. The objective of the problem is to choose the rate of maintenance and the rate of production that minimize the overall costs of inventory/shortage, production, and maintenance. It is shown that the value function is locally Lipschitz. Then, the existence of the optimal control policy is shown, and necessary and sufficient conditions for optimality are obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02191664
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Periodic maintenance and repair rate control in stochastic manufacturing systems (1996)
    Springer
    Journal of optimization theory and applications 91 (1996), S. 347-361 
    Details
    ISSN: 1573-2878
    Keywords: Flexible manufacturing systems ; controlled Markov processes ; production planning ; repair rate control ; maintenance scheduling ; Hamilton-Jacobi-Bellman equation ; viscosity solution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we consider a periodic preventive maintenance, repair, and production model of a flexible manufacturing system with failure-prone machines, where the control variables are the repair rate and production rate. We use periodic preventive maintenance to reduce the machine failure rates and improve the productivity of the system. One of the distinct features of the model is that the repair rate is adjustable. Our objective is to choose a control process that minimizes the total cost of inventory/shortage, production, repair, and maintenance. Under suitable conditions, we show that the value function is locally Lipschitz and satisfies an Hamilton-Jacobi-Bellman equation. A sufficient condition for optimal control is obtained. Since analytic solutions are rarely available, we design an algorithm to approximate the optimal control problem. To demonstrate the performance of the numerical method, an example is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02190100
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Minimax production planning in failure-prone manufacturing systems (1995)
    Springer
    Journal of optimization theory and applications 87 (1995), S. 269-286 
    Details
    ISSN: 1573-2878
    Keywords: Flexible manufacturing systems ; minimax production planning ; Hamilton-Jacobi-Isaacs equation ; viscosity solutions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we consider a minimax production planning model of a flexible manufacturing system with machines that are subject to random breakdown and repair. The objective is to choose the rate of production that minimizes the related minimax cost of production and inventory/shortage. The value function is shown to be the unique viscosity solution to the associated Hamilton-Jacobi-Isaacs equation. Under certain conditions, it is shown that the value function is continuously differentiable. A verification theorem is given to provide a sufficient condition for optimal control. Finally, two examples are solved explicitly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02192564
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    Paper (German National Licenses)
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  • 4
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    Equivalence principle of GPS algorithms and an independent parametrization method (2007)
    In:  20th International Technical Meeting of the Satellite Division of The Institute of Navigation - ION GNSS (Fort Worth, Texas, USA 2007)
    Details
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/conferenceObject
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  • 5
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    Real-time clock offset prediction with an improved model (2014)
    In:  GPS Solutions
    Details
    Publication Date: 2020-02-12
    Description: The GPS orbit precision of the IGS ultra-rapid predicted (IGU-P) products has been remarkably improved since 2007. However, the satellite clock offsets of the IGU-P products have not shown sufficient high-quality prediction to achieve sub-decimeter precision in real-time precise point positioning (RTPPP), being at the level of 1–3 ns (30–90 cm) RMS in recent years. An improved prediction model for satellite clocks is proposed in order to enhance the precision of predicted clock offsets. First, the proposed prediction model adds a few cyclic terms to absorb the periodic effects, and a time adaptive function is used to adjust the weight of the observation in the prediction model. Second, initial deviations of the predictions are reduced by using a recomputed constant term. The simulation results have shown that the proposed prediction model can give a better performance than the IGU-P clock products and can achieve precision better than 0.55 ns (16.5 cm) in real-time predictions. In addition, the RTPPP method was chosen to test the efficiency of the new model for real-time static and kinematic positioning. The numerical examples using the data set of 140 IGS stations show that the static RTPPP precision based on the proposed clock model has been improved about 22.8 and 41.5 % in the east and height components compared to the IGU-P clock products, while the precisions in the north components are the equal. The kinematic example using three IGS stations shows that the kinematic RTPPP precision based on the proposed clock model has improved about 30, 72 and 44 % in the east, north and height components.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 6
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    Real-time estimation of satellite clock offset using adaptively robust Kalman filter with classified adaptive factors (2012)
    In:  GPS Solutions
    Details
    Publication Date: 2020-02-12
    Description: In order to estimate the satellite clock offset in a real-time mode, a new algorithm of adaptively robust Kalman filter with classified adaptive factors for clock offset estimation is proposed. Compared with standard Kalman filter clock offset model, the new method can detect and control outliers and clock jumps automatically in real-time. Moreover, the clock model parameters, which contain the clock offset, clock speed and clock shift, are classified to decide the adaptive factors in the new model. Thus, clock jumps with different characteristics can be distinguished more effectively. Meanwhile, the dynamic noise characteristics of clock offset series are used for stochastic modeling. An actual numerical example is presented, which shows that the proposed filter can give a better performance than other commonly used filters.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 7
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    Solar oblateness and Mercury's perihelion precession (2011)
    In:  Monthly Notices of the Royal Astronomical Society
    Details
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 8
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    GNSS Precise Point Prositioning Algorithm Based von Parameter Equivalent Reduction Principle [C] (2013)
    In:  China Satellite Navigation Conference - CSNC (Wuhan, China 2013)
    Details
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/conferenceObject
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  • 9
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    Quality Variation of GPS Satellite Clocks On-orbit Using IGS Clock Products (2012)
    In:  Advances in Space Research
    Details
    Publication Date: 2020-02-12
    Description: Over 60% clocks on board of the GPS satellites are working longer than their designed life. Therefore realizing their stabilities in a long time scales is essential to GPS navigation and positioning plus IGS time scale maintaining. IGS clock products from 2001 to 2010 are used to analyze the GPS satellite clock qualities such as frequency stabilities and clock noise level. We find out that for the clocks of Block IIA satellites the frequency stabilities and clock noise are 10 times worse than that of the Block IIR and IIR-M satellites. Moreover, the linear relationships between frequency stabilities and clock residuals have been deduced with an accuracy of better than 0.02 ns. Specially, it is noticed that the clock of the PRN27 is instable and the relationship between the frequency stability and residuals is at least a quadratic curve. Therefore, we suggested that GPS satellite clocks should be weighted by their quality levels in application, and the observations of the Block IIA should not be used for real-time positioning which required precision better than one meter.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 10
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    Fragmented Indian plate and vertically coherent deformation beneath eastern Tibet (2012)
    In:  Journal of Geophysical Research
    Details
    Publication Date: 2020-02-12
    Description: Using fundamental mode Rayleigh waves from the INDEPTH-IV and Namche-Barwa seismic experiments for periods between 20 and 143 s, we have investigated the lithospheric structure beneath eastern Tibet. We have found a ∼200-km-wide high velocity body, starting at ∼60 km depth and roughly centered beneath the Bangong-Nijuang Suture, which is most likely a piece of the underthrusting Indian continental lithosphere. The sub-horizontal underthrusting of the Indian lithosphere beneath eastern Tibet appears to be accompanied by its lateral tearing into at least two fragments, and subsequent break-off of the westernmost portion at ∼91°E-33°N. The uppermost mantle low velocity zone we observe beneath the N. Qiangtang and Songpan-Ganzi terranes is most probably due to warmer and thinner lithosphere relative to southern Tibet. We attribute the low velocity zones concentrated along the northern and southern branches of the eastern Kunlun fault at lithospheric depths to strain heating caused by shearing. The azimuthal fast directions at all periods up to 143 s (∼200 km peak sensitivity depth) beneath the N. Qiangtang and Songpan-Ganzi terranes are consistent, suggesting vertically coherent deformation between crust and uppermost mantle. Furthermore, the low velocity zone below the Kunlun Shan reaching down to 〉200 km argues against a present southward continental subduction along the southern margin of Qaidam Basin.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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