In this article, we review the research state of the bullwhip effect in supply chains with stochastic lead times. We analyze problems arising in a supply chain when lead times are not deterministic. Using real data from a supply chain, we confirm that lead times are stochastic and can be modeled by a sequence of independent identically distributed random variables. This underlines the need to further study supply chains with stochastic lead times and model the behavior of such chains.
This paper presents the results of Pilot Assisting Module research performed on two light aircraft flight simulators developed in parallel at Brno University of Technology, Czech Republic, and Rzeszow University of Technology, Poland. The first simulator was designed as an open platform for the verification and validation of the advanced pilot/aircraft interface systems and inherited its appearance from the cockpit section of the Evektor SportStar. The second flight simulator, the XM-15, has been built around the cockpit of a unique agriculture jet Belfegor. It introduced a system architecture that supports scientific simulations of various aircraft types and configurations, making it suitable for conceptual testing of Pilot Assisting Module. The XM-15 was initially designed to support research on advanced flight control systems, but due to its continuing modernization it evolved into a hardware-in-the-loop test-bed for electromechanical actuators and autopilot CAN based controller blocks. Pilot-in-the-loop experiments of proposed Pilot Assisting Module revealed favorable operational scenarios, under which the proposed system reduces the cockpit workload during single pilot operations.
In high-performance optical systems, small disturbances can be sufficient to put the projected image out of focus. Little stochastic excitations, for example, are a huge problem in those extremely precise opto-mechanical systems. To avoid this problem or at least to reduce it, several possibilities are thinkable. One of these possibilities is the modification of the dynamical behavior. In this method the redistribution of masses and stiffnesses is utilized to decrease the aberrations caused by dynamical excitations. Here, a multidisciplinary optimization process is required for which the basics of coupling dynamical and optical simulation methods will be introduced. The optimization is based on a method for efficiently coupling the two types of simulations. In a concluding example, the rigid body dynamics of a lithography objective is optimized with respect to its dynamical-optical behavior.
The dynamics of the turning process of a thin-walled cylinder in manufacturing is modeled using flexible multibody system theory. The obtained model is time varying due to workpiece rotation and tool feed and retarded, due to repeated cutting of the same surface. Instabilities can occur due to these consecutive cuts that must be avoided in practical application because of the detrimental effects on workpiece, tool and possibly the machine. Neglecting the small feed, the stability of the resulting periodic system with time-delay can be analyzed using the semi-discretization method. The use of an adaptronic tool holder comprising actuators and sensors to improve the dynamic stability is then investigated. Different control concepts, two collocated and two model-based, are implemented in simulation and tuned to increase the domain of stable cutting. Cutting of a moderately thin workpiece exhibits instabilities mainly due to tool vibration. In this case, the stability boundary can be significantly improved. When the instability is due to workpiece vibration, the collocated concepts fail completely. Model based concepts can still obtain some improvements, but are sensitive to modeling errors in the coupling of workpiece and tool.
For the private and public sector in any particular country it is crucial to know, which industries may exhibit comparative advantages, that for some reasons are not realized. This can efficiently help all current and potential actors to improve their economic strategy both at the micro- and macroeconomic level. In this paper we propose an approach of forecasting comparative advantages dynamics in foreign trade. The instrument is based on relative price differences and is efficient for countries in the process of economic liberalization. An empirical analysis based on the example of Central and East European countries confirms a good performance in the sense of predictive power of this instrument. On the example of Russia, experiencing a period of economic liberalization and with the prospect to join the WTO agreements, we demonstrate which sectors are most likely to contain comparative advantages in the near future.
The use of elastic bodies within a multibody simulation became more and more important within the last years. To include the elastic bodies, described as a finite element model in multibody simulations, the dimension of the system of ordinary differential equations must be reduced by projection. For this purpose, in this work, the modal reduction method, a component mode synthesis based method and a moment-matching method are used. Due to the always increasing size of the non-reduced systems, the calculation of the projection matrix leads to a large demand of computational resources and cannot be done on usual serial computers with available memory. In this paper, the model reduction software Morembs++ is presented using a parallelization concept based on the message passing interface to satisfy the need of memory and reduce the runtime of the model reduction process. Additionally, the behaviour of the Block-Krylov-Schur eigensolver, implemented in the Anasazi package of the Trilinos project, is analysed with regard to the choice of the size of the Krylov base, the blocksize and the number of blocks. Besides, an iterative solver is considered within the CMS-based method.
The nonlinear mathematical model of behavior of controllable viscosity fluid (CVF) under applied external field is presented. A large family of these fluids is commonly used to control responding forces of dampers in vibration control applications. The responding force of a damper with CVF has two components. The first one - uncontrollable - is proportional to the viscosity of a base fluid and velocity of its motion, the second one, which is controllable, depends on the strength of the applied external field. Both are involved in the process of dissipation of unwanted energy from the vibrating systems. An equivalent damping factor based on the principle of energy dissipated during one cycle of damper work under a constant strength external field was calculated. When mass or stiffness is variable the equivalent damping factor can be set accordingly by adjusting the strength of external field to have vibrating damped system purposely/continuously working in the critical or other chosen state. This paper also presents cases of applying periodically changing strengths of an external field synchronized with cycles of periodical motion of the vibrating system to continuously control the damping force within each cycle.
The recent financial crisis has seen huge swings in corporate bond spreads. It is analyzed what quality VAR-based forecasts would have had prior and during the crisis period. Given that forecasts of the mean of interest rates or financial market prices are subject to large uncertainty independent of the class of models used, major emphasis is put on the quality of measures of forecast uncertainty. The VAR considered is based on a model first suggested in the literature in 2005. In a rolling window analysis, both the model’s forecasts and joint prediction bands are calculated making use of recently proposed methods. Besides a traditional analysis of the forecast quality, the performance of the proposed prediction bands is assessed. It is shown that the actual coverage of joint prediction bands is superior to the coverage of naïve prediction bands constructed pointwise.
Technological development offers a wide range of new possibilities for implementation of production processes. Continual production development is the main key to success and competitiveness improvement, labour productivity and image-building for all manufacturing companies. The article deals with designing of new workplace with implementation and utilization of automated robot for faster and safer handling of cast stock. The new layout of workplace is created in software Process Simulate.
Due to globalized business operations, companies in different economic sectors are part of complex supply chain networks. Their value-added processes comprise product and information flows, e.g. with a focus on manufacturing, service or trade. Until the final product is delivered to the end customer, it needs to pass many different processes in cooperating organizations. As a result, there a lot of business-to-business (B2B) interactions with crossenterprise transactions, often including cross-border communications and sometimes even cross-industry trades with technological and often cultural implications. Especially the interfaces of supply chain networks are prone to inefficiencies, misunderstandings and delays due to a lack of standardized B2B transactions, which leads to waste in form of rework, errors and mistakes. In addition, new customers are hard to find for the manufacturing or trading company, since potential customers are so far limited to a regional network. The advantages of extending the customer base still need to be explored by many organizations. This paper discusses the opportunities by streamlining the communication along supply chain networks in a general fashion and then describes the application in a B2B automotive retail business. A concept of a web-based trading platform, which provides a seamless service for all steps of a convenient and efficient used vehicle remarketing business, is developed. It includes all phases, like offering and price finding in a comprehensive online platform, which also covers further activities, such as logistic services, financial transactions, and a mandatory feedback loop. The suggested B2B vehicle-trading platform enables a quick turnover of each transaction, which is analyzed and optimized based on the application of cross-enterprise Value Stream Management.
Diurnal measurements of photosynthetic pr ocesses, effective quantum yield of photosystem II ( F PSII ), photosynthetic electron transport rate (ETR) were done in three domi− nant species of Arctic tundra ( Silene acaulis , Dryas octopetala , Salix polaris ) in Petunia− bukta, Spitsbergen. Daily courses of net photosynthesis (P N ) were calculated from chloro− phyll fluorescence data and daily photosynthesi s evaluated. The short−term field measure− ments were carried out in summer 2009, and 2010. Fluorometric parameters ( F PSII and ETR) were measured each 5 minutes as well as microc limate characteristics of the site for 10 (2009) and 8 days (2010), respectively. In all species photosynthetic ETR was well related to incident photosynthetically active radiation a nd leaf temperature. In general, D. octopetala exhibited slightly lower ETR than the other two speci es. Estimated maximu m photosynthetic rate (P Nmax ) reached 17.6, 21.4, and 22.9 μmol CO 2 m −2 s −1 for S. polaris , S. acaulis ,and D. octopetala , respectively. Daily photosynthesis reach ed comparable values in all species, D. otopetala , however, exhibited slightly lower values than the other two species both for overcast and fully sunny days (3.9 and 13.4 mmol CO 2 m −2 d −1 , respectively). The range of daily photosynthesis for S. polaris and S. acaulis studied, reached the ranges of 4.6–6.9 and 14.6–15.2 mmol CO 2 m −2 d −1 for overcast and fully sunny day, respectively.
Rescheduling is a frequently used reactive strategy in order to limit the effects of disruptions on throughput times in multi-stage production processes. However, organizational deficits often cause delays in the information on disruptions, so rescheduling cannot limit disruption effects on throughput times optimally. Our approach strives for an investigation of possible performance improvements in multi-stage production processes enabled by realtime rescheduling in the event of disruptions. We developed a methodology whereby we could measure these possible performance improvements. For this purpose, we created and implemented a simulation model of a multi-stage production process. We defined system parameters and varied factors according to our experiment design, such as information delay, lot sizes and disruption durations. The simulation results were plotted and evaluated using DoE methodology. Dependent on the factor settings, we were able to prove large improvements by real-time rescheduling regarding the absorption of disruption effects in our experiments.
This article provides an overview of the approach taken by the International Court of Justice and its predecessor, the Permanent Court of International Justice, to questions of municipal law. Beginning with an outline of the theoretical framework, it discusses the conventional position that domestic law is a factual issue for the Court, before considering the ways in which the two Courts have utilised municipal law. It also considers to what extent the Court employs domestic law in ascertaining international legal rules.
Abstract In the last decade contradictory results have been published as to whether exogenous salicylic acid (SA) can increase salt stress tolerance in cultivated plants by inducing an antioxidant response. Salt stress injury in tomato was mitigated only in cases when the plant was hardened with a high concentration of SA (~10−4 M), low concentrations were ineffective. An efficient accumulation of Na+ in older leaves is a well-known response to salt stress in tomato plants (Solanum lycopersicum cv. Rio fuego) but it remains largely unexplored whether young and old leaves or root tissues have a distinct antioxidant status during salt stress after hardening with 10−7 M or 10−4 M SA. The determination of superoxide dismutase (SOD) and catalase (CAT) activity revealed that the SA-induced transient increases in these enzyme activities in young leaf and/or root tissues did not correlate with the salt tolerance of plants. Salt stress resulted in a tenfold increase in ascorbate peroxidase (APX) activities of young leaves and significant increases in APX and glutathione reductase (GR) activities of the roots hardened with 10−4 M SA. Both total ascorbate (AsA) and glutathione pools reached their highest levels in leaves after 10−7 M SA pre-treatment. However, in contrast to the leaves, the total pool of AsA decreased in the roots under salt stress and thus, due to low APX activity, active oxygen species were scavenged by ascorbate non-enzymatically in these tissues. The increased GR activities in the roots after treatment with 10−4 M SA enabled plants to enhance the reduced glutathione (GSH) pool and maintain the redox status of AsA under high salinity, which led to increased salt tolerance.