Search

A common issue with many system identification problems is that the true input to the system is unknown. This paper extends a previously presented indirect modelling framework that deals with identification of systems where the input is partially or fully unknown. In this framework, unknown inputs are eliminated by using additional measurements that directly or indirectly contain information about the unknown inputs. The resulting indirect predictor model is only dependent on known and measured signals and can be used to estimate the desired dynamics or properties. Since the input of the indirect model contains both known inputs and measurements that could all be correlated with the same disturbances as the output, estimation of the indirect model has similar challenges as a closed-loop estimation problem. In fact, due to the generality of the indirect modelling framework, it unifies a number of already existing system identification problems that are contained as special cases. For completeness, the paper is concluded with one method that can be used to estimate the indirect model as well as an experimental verification to show the applicability of the framework., Funding Agencies|Vinnova Industry Excellence Center LINK-SIC project [2007-02224]

A common issue with many system identification problems is that the true input to the system is unknown. This paper extends a previously presented indirect modelling framework that deals with identification of systems where the input is partially or fully unknown. In this framework, unknown inputs are eliminated by using additional measurements that directly or indirectly contain information about the unknown inputs. The resulting indirect predictor model is only dependent on known and measured signals and can be used to estimate the desired dynamics or properties. Since the input of the indirect model contains both known inputs and measurements that could all be correlated with the same disturbances as the output, estimation of the indirect model has similar challenges as a closed-loop estimation problem. In fact, due to the generality of the indirect modelling framework, it unifies a number of already existing system identification problems that are contained as special cases. For completeness, the paper is concluded with one method that can be used to estimate the indirect model as well as an experimental verification to show the applicability of the framework., Funding Agencies|Vinnova Industry Excellence Center LINK-SIC project [2007-02224]

A common issue with many system identification problems is that the true input to the system is unknown. This paper extends a previously presented indirect modelling framework that deals with identification of systems where the input is partially or fully unknown. In this framework, unknown inputs are eliminated by using additional measurements that directly or indirectly contain information about the unknown inputs. The resulting indirect predictor model is only dependent on known and measured signals and can be used to estimate the desired dynamics or properties. Since the input of the indirect model contains both known inputs and measurements that could all be correlated with the same disturbances as the output, estimation of the indirect model has similar challenges as a closed-loop estimation problem. In fact, due to the generality of the indirect modelling framework, it unifies a number of already existing system identification problems that are contained as special cases. For completeness, the paper is concluded with one method that can be used to estimate the indirect model as well as an experimental verification to show the applicability of the framework., Funding Agencies|Vinnova Industry Excellence Center LINK-SIC project [2007-02224]

In this paper, we discuss the impact of using a frequency-dependent embedding potential in quantum chemical embedding calculations of response properties. We show that the introduction of a frequency-dependent embedding potential leads to further model complications upon solving the central equations defining specific molecular properties. On the other hand, we also show from a numerical point of view that the consequences of using such a frequency-dependent embedding potential is almost negligible. Thus, for the kind of systems and processes studied in this paper the general recommendation is to use frequency-independent embedding potentials since this leads to less complicated model issues. However, larger effects are expected if the absorption bands of the environment are closer to that of the region treated using quantum mechanics. [GRAPHICS], Funding Agencies|Danish Councils for Independent Research (DFF) [FI-0602-02122B]; Villum Foundation; DeIC National HPC Center, SDU; Swedish Research Council [621-2014-4646]

The purpose of this paper is to introduce and explore the use of paradox theory in a logistics and SCM research context. Although logistics and SCM scholars as well as practitioners have been aware about the existence of paradoxes, they have so far lacked a more formal theoretical framework for further identification and classification of these. Framed in the four general paradox classes of learning, belonging, organising and performing, the paper outlines paradoxes inherent in the global sourcing practices of two case companies. The findings demonstrate the paradox theory to be a useful tool for a systematic illumination and classification of paradoxes valuable for practitioners, researchers as well as teachers in the domain of logistics and SCM. The paradox theory may also help to identify and emphasise inconsistencies among different research fields. This is particularly valuable for research areas built upon multiple research disciplines such as global sourcing. In conclusion, the paper suggests that the paradox theory offers a new lens through which an organisation could be better explored, described and understood., Funding Agencies|Jan Wallander and Tom Hedelius Foundation; Swedish Retail and Wholesale Development Council

The purpose of this paper is to introduce and explore the use of paradox theory in a logistics and SCM research context. Although logistics and SCM scholars as well as practitioners have been aware about the existence of paradoxes, they have so far lacked a more formal theoretical framework for further identification and classification of these. Framed in the four general paradox classes of learning, belonging, organising and performing, the paper outlines paradoxes inherent in the global sourcing practices of two case companies. The findings demonstrate the paradox theory to be a useful tool for a systematic illumination and classification of paradoxes valuable for practitioners, researchers as well as teachers in the domain of logistics and SCM. The paradox theory may also help to identify and emphasise inconsistencies among different research fields. This is particularly valuable for research areas built upon multiple research disciplines such as global sourcing. In conclusion, the paper suggests that the paradox theory offers a new lens through which an organisation could be better explored, described and understood., Funding Agencies|Jan Wallander and Tom Hedelius Foundation; Swedish Retail and Wholesale Development Council

The paper discusses new cubature formulas for the Riesz potential and the fractional Laplacian (-Delta)(alpha/2), 0 < alpha < 2, in the framework of the method approximate approximations. This approach, combined with separated representations, makes the method successful also in high dimensions. We prove error estimates and report on numerical results illustrating that our formulas are accurate and provide the predicted convergence rate 2, 4, 6, 8 up to dimension 10(4)., Funding Agencies|RUDN University Strategic Academic Leadership Program

MRP theory is a theoretical body treating production-inventory systems, in which produced items are made up of sets of produced or purchased sub-items, required to be available a lead-time before each product is completed. The hierarchical dependence between items is captured using input matrices from input-output-analysis, the necessary advanced timing by employing Laplace transform methodology, and the economic consequences by applying the net present value. Little attention has hitherto been given to aspects of a non-empty initial state, e.g. an initial inventory position. Since such states are common in industry, there is a strong need for this theory to include such aspects, in order to gain further practical acceptance. In this paper, theoretical consequences from having a non-empty initial state are investigated. A method for finding the Lot-for-Lot solution is developed using the concept of a truncated monotonically non-decreasing time function, generalising the approach of the generalised Leontief inverse and instrumental for designing plans meeting the necessary inner-corner requirement for optimality. Also the definition of inventory-related costs needs a modification for this concept to be consistent with NPV. These findings are applied in an extensive numerical example. Immediate future research concerns investigating principles for the optimal removal of initial backlogs.

In this paper, we consider the estimated weights of the tangency portfolio. We derive analytical expressions for the higher order non-central and central moments of these weights when the returns are assumed to be independently and multivariate normally distributed. Moreover, the expressions for mean, variance, skewness and kurtosis of the estimated weights are obtained in closed forms. Later, we complement our results with a simulation study where data from the multivariate normal and t-distributions are simulated, and the first four moments of estimated weights are computed by using the Monte Carlo experiment. It is noteworthy to mention that the distributional assumption of returns is found to be important, especially for the first two moments. Finally, through an empirical illustration utilizing returns of four financial indices listed in NASDAQ stock exchange, we observe the presence of time dynamics in higher moments., Funding Agencies|Orebro University; Jan Wallander and Tom Hedelius Foundation [P18-0201]

In this paper, we consider the estimated weights of the tangency portfolio. We derive analytical expressions for the higher order non-central and central moments of these weights when the returns are assumed to be independently and multivariate normally distributed. Moreover, the expressions for mean, variance, skewness and kurtosis of the estimated weights are obtained in closed forms. Later, we complement our results with a simulation study where data from the multivariate normal and t-distributions are simulated, and the first four moments of estimated weights are computed by using the Monte Carlo experiment. It is noteworthy to mention that the distributional assumption of returns is found to be important, especially for the first two moments. Finally, through an empirical illustration utilizing returns of four financial indices listed in NASDAQ stock exchange, we observe the presence of time dynamics in higher moments., Funding Agencies|Orebro University; Jan Wallander and Tom Hedelius Foundation [P18-0201]