Invariance of fluid limits for the Shortest Remaining Processing Time and Shortest Job First policies

We consider a single-server queue with renewal arrivals and i.i.d. service times, in which the server employs either the preemptive Shortest Remaining Processing Time (SRPT) policy, or its non-preemptive variant, Shortest Job First (SJF). We show that for given stochastic primitives (initial condition, arrival and service processes), the model has the same fluid limit under either policy. In particular, we conclude that the well-known queue length optimality of preemptive SRPT is also achieved, asymptotically on fluid scale, by the simpler-to-implement SJF policy. We also conclude that on fluid scale, SJF and SRPT achieve the same performance with respect to response times of the longest-waiting jobs in the system.Comment: 24 page

Coherence and transparency: some advice for qualitative researchers

This is an Open Access Article. It is published by Brazilian Association of Production Engineering (ABEPRO) under the Creative Commons Attribution 4.0 International Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/There is relatively little advice in the Engineering domain for undertaking qualitative studies. Researchers have to rely on generic guidance that may result in imprecise application of qualitative methods. A related discipline to Engineering is Information Systems (IS) and the experiences of the IS domain may provide some useful insights for undertaking qualitative studies. This paper synthesizes the guidance from the IS community for crafting high quality qualitative studies and manuscripts. It reports on five themes: i) Establishing philosophical underpinnings; ii) Clarifying theoretical aims; iii) Selecting qualitative methods; iv) Demonstrating rigour in qualitative data analysis; and v) Grappling with generalisation. The review stresses the importance of coherence and transparency for crafting qualitative research manuscripts and provides a list of reflective questions for qualitative research design

Environmental performance assessment of hardboard manufacture

11 páginas, 5 figuras, 4 tablas -- PAGS nros. 456-466Background, aim and scope The forest-based and related industries comprise one of the most important industry sectors in the European Union, representing some 10% of the EU's manufacturing industries. Their activities are based on renewable raw material resources and efficient recycling. The forest-based industries can be broken down into the following sectors: forestry, woodworking, pulp and paper manufacturing, paper and board converting and printing and furniture. The woodworking sector includes many sub-sectors; one of the most important is that of wood panels accounting for 9% of total industry production. Wood panels are used as intermediate products in a wide variety of applications in the furniture and building industries. There are different kinds of panels: particleboard, fibreboard, veneer, plywood and blockboard. The main goal of this study was to assess the environmental impacts during the life cycle of wet-process fibreboard (hardboard) manufacturing to identify the processes with the largest environmental impacts. Methods The study covers the life cycle of hardboard production from a cradle-to-gate perspective. A hardboard plant was analysed in detail, dividing the process chain into three subsystems: wood preparation, board forming and board finishing. Ancillary activities such as chemicals, wood chips, thermal energy and electricity production and transport were included within the system boundaries. Inventory data came from interviews and surveys (on-site measurements). When ecessary, the data were complemented with bibliographic resources. The life cycle assessment procedure followed the ISO14040 series. The life cycle inventory (LCI) and impact assessment database for this study were constructed using SimaPro Version 7.0 software. Results Abiotic depletion (AD), global arming (GW), ozone layer depletion (OLD), human toxicity (HT), ecotoxicity, photochemical oxidant formation (PO), cidification (AC) and eutrophication (EP) were the impact categories analysed in this study. The wood preparation subsystem contributed more than 50% to all impact categories, followed by board forming and board finishing, which is mainly due to chemicals consumption in the wood preparation subsystem. In addition, thermal energy requirements (for all subsystems) were fulfilled by on-site wood waste burning and, accordingly, biomass energy converters were considered. Several processes were identified as hot spots in this study: phenol-formaldehyde resin production (with large contribution to HT, fresh water aquatic ecotoxicity and PO), electricity production (main contributor to marine aquatic cotoxicity), wood chips production (AD and OLD) and finally, biomass burning for heat production (identified as the largest contributor to AC and EP due to NOX emissions). In addition, uncontrolled formaldehyde emissions from manufacturing processes at the plant such as fibre drying should be controlled due to relevant contributions to terrestrial ecotoxicity and PO. A sensitivity analysis of electricity profile generation (strong geographic dependence) was carried out and several European profiles were analysed.Peer reviewe

The Raman non-coincidence effect of the 12C=O stretching mode of liquid acetone in chemical and in isotopic mixtures

Abstract The concentration dependences of the first moments of both the isotropic and anisotropic Raman bands of the C=O stretching mode (12C=O) of acetone in chemical mixtures of type [(CH3)2CO]x \u2013 [CCl4]1-x are compared with their dependences in isotopic mixtures of type [(CH3)212CO]x - [(CH3)213CO]1-x . The role of the intermolecular resonant vibrational coupling is discussed via the experimentally observable Raman non-coincidence effect, i.e. the difference in the frequency position between the anisotropic and isotropic first moments. The experimental results are in good agreement with (1) molecular dynamics simulations and Monte Carlo simulations and (2) analytical predictions within the framework of the mean-spherical approximation of the dipole-dipole interaction. With the help of [(CH3)213CO] occurring at natural abundance in the chemical mixture, and of [(CH3)213CO] at close to infinite dilution in the isotopic mixture, we are able to separate the environmentally induced frequency shifts from the measured anisotropic and isotropic first moments, thereby isolating the frequency shifts induced just by the intermolecular resonant vibrational coupling