Proactive inventory policy intervention to mitigate risk within cooperative supply chains

This exploratory paper will investigate the concept of supply chain risk management involving supplier monitoring within a cooperative supply chain. Inventory levels and stockouts are the key metrics. Key to this concept is the assumptions that (1) out-of-control supplier situations are causal triggers for downstream supply chain disruptions, (2) these triggers can potentially be predicted using statistical process monitoring tools, and (3) carrying excess inventory only when needed is preferable as opposed to carrying excess inventory on a continual basis. Simulation experimentation will be used to explore several supplier monitoring strategies based on statistical runs tests, specifically "runs up and down" and/or "runs above and below" tests. The sensitivity of these tests in detecting non-random supplier behavior will be explored and their performance will be investigated relative to stock-outs and inventory levels. Finally, the effects of production capacity and yield rate will be examined. Results indicate out-of-control supplier signals can be detected beforehand and stock-outs can be significantly reduced by dynamically adjusting inventory levels. The largest benefit occurs when both runs tests are used together and when the supplier has sufficient production capacity to respond to downstream demand (i.e., safety stock) increases. When supplier capacity is limited, the highest benefit is achieved when yield rates are high and, thus, yield loss does not increase supplier production requirements beyond its available capacity

Topographical Impact on Space Charge Injection, Accumulation and Breakdown in Polymeric HVDC Cable Interfaces

Extruded HVDC cable systems feature a variety of interface types, for which physio-chemical properties will depend on the type of application. Such applications can be joints, terminations or the cable itself, all introducing different material combinations and manufacturing methods. To ensure beyond 40 years of faultless cable system operation, the interface’s design and quality control procedures are essential. Interfacial control requires detailed knowledge on how measurable physio-chemical properties of polymer surfaces relate to their electrical performance, through features such as localized electric field strength, space charge injection and breakdown strength. This work aims to expand such understanding by assessing polymer surfaces created with different, industrialized preparation methods, featuring different degrees of surface roughness. Surface preparation was carried out on real HVDC cable prototypes, from which cable peelings were extracted, ensuring replication of the material’s bulk and interfacial natures into the small-scale tests. Also, DC breakdown tests on medium voltage cables revealed strong impact of surface roughness, pinpointing the need for an accurate roughness evaluation.\ua0While chemical characterization assessed certain features brought about in the preparation, physical assessments such as optical profilometry quantified the surfaces’ topographies. It was found that, the topography, featuring micro and sub micrometer geometrical variation, could be readily adopted in a mesoscopic modelling approach. Thereby, the geometric impact on local quantities of field strength, charge density and injection current density was estimated. Also, a set of roughness enhanced charge injection equations were derived for charge injection types such as Schottky, Fowler-Nordheim and hopping injection mechanisms. Such equations, featuring surface specific field (β) parameters, were employed in a one-dimensional bipolar charge transport model. Through careful model calibration against the results of space charge measurements, the parameters for roughness enhanced charge injection, together with parameters for charge transport, trapping, detrapping and recombination, were estimated. This calibration verified roughness enhanced injection and generated a description of the density of states in the material’s bulk. Furthermore, DC breakdown tests performed on the cable peelings for establishing the relationship between surface roughness and breakdown strength. An adopted multi-scale simulation approach, based on the calibrated parameter set, estimated local field strength, charge density and other quantities in the surface domain.\ua0Conclusively, surface topography causes a local redistribution of the electric field, in turn locally increasing charge injection due to its strong field dependency at the rough asperities. Ultimately, coinciding high field strength and high charge density, at repeated positions along the surface, yields a lower breakdown strength. Such knowledge allows for tailoring the methodologies of surface preparation and quality control in HVDC cable systems, and other HV apparatuses. Control over mesoscopic surface effects will allow engineers to design ever more advanced and long-lasting HV components, meeting humanity’s renewable energy transmission needs for decades to come

Modeling Supply Networks and Business Cycles as Unstable Transport Phenomena

Physical concepts developed to describe instabilities in traffic flows can be generalized in a way that allows one to understand the well-known instability of supply chains (the so-called ``bullwhip effect''). That is, small variations in the consumption rate can cause large variations in the production rate of companies generating the requested product. Interestingly, the resulting oscillations have characteristic frequencies which are considerably lower than the variations in the consumption rate. This suggests that instabilities of supply chains may be the reason for the existence of business cycles. At the same time, we establish some link to queuing theory and between micro- and macroeconomics.Comment: For related work see http://www.helbing.or

Energy Dissipation and Transport in Nanoscale Devices

Understanding energy dissipation and transport in nanoscale structures is of great importance for the design of energy-efficient circuits and energy-conversion systems. This is also a rich domain for fundamental discoveries at the intersection of electron, lattice (phonon), and optical (photon) interactions. This review presents recent progress in understanding and manipulation of energy dissipation and transport in nanoscale solid-state structures. First, the landscape of power usage from nanoscale transistors (~10^-8 W) to massive data centers (~10^9 W) is surveyed. Then, focus is given to energy dissipation in nanoscale circuits, silicon transistors, carbon nanostructures, and semiconductor nanowires. Concepts of steady-state and transient thermal transport are also reviewed in the context of nanoscale devices with sub-nanosecond switching times. Finally, recent directions regarding energy transport are reviewed, including electrical and thermal conductivity of nanostructures, thermal rectification, and the role of ubiquitous material interfaces