518 research outputs found
Waste processing facility location problem by stochastic programming: Models and solutions
The paper deals with the so-called waste processing facility location problem (FLP), which asks for establishing a set of operational waste processing units, optimal against the total expected cost. We minimize the waste management (WM) expenditure of the waste producers, which is derived from the related waste processing, transportation, and investment costs. We use a stochastic programming approach in recognition of the inherent uncertainties in this area. Two relevant models are presented and discussed in the paper. Initially, we extend the common transportation network flow model with on-and-off waste-processing capacities in selected nodes, representing the facility location. Subsequently, we model the randomly-varying production of waste by a scenario-based two-stage stochastic integer linear program. Finally, we employ selected pricing ideas from revenue management to model the behavior of the waste producers, who we assume to be environmentally friendly. The modeling ideas are illustrated on an example of limited size solved in GAMS. Computations on larger instances were realized with traditional and heuristic algorithms, implemented within MATLAB. © Springer Nature Switzerland AG 2019
A New Monitor and Control Power Supply PCB for Biasing LNAs of Large Radio Telescopes Receivers
The biasing of low noise amplifiers (LNA) is of paramount importance for the receivers of large radio telescopes. High stability, optimal trade-off between gain and noise figure, remote control, and mitigation of the radio frequency interferences (RFIs) are all desirable features in the choice of the electronic board devoted to power supply the LNAs. In this paper, we propose the design and characterization of a multilayer printed circuit board (PCB), named GAIA, able to meet all the aforementioned requirements. The GAIA board is a 3-Unit, four-layer, rack-mountable, programmable PCB for the remote biasing of the LNAs, with monitor and control capabilities, specifically designed to operate in the receivers of the 64-m diameter Sardinia Radio Telescope (SRT). We describe the architecture, layout, and measurements of the GAIA board. Our results show that the GAIA power supply provides high stability of the output bias voltages and, in comparison with the old analogic biasing board used so far in the SRT receivers, it shows comparable or better frequency stability, other than a remarkable mitigation of the RFIs
Muscle Oxygen Delivery in the Forearm and in the Vastus Lateralis Muscles in Response to Resistance Exercise: A Comparison Between Nepalese Porters and Italian Trekkers
Altitude ascending represents an intriguing experimental model reproducing physiological and pathophysiological conditions sharing hypoxemia as the denominator. The aim of the present study was to investigate fractional oxygen extraction and blood dynamics in response to hypobaric hypoxia and to acute resistance exercises, taking into account several factors including different ethnic origin and muscle groups. As part of the âKanchenjunga Exploration & Physiologyâ project, six Italian trekkers and six Nepalese porters took part in a high altitude trek in the Himalayas. The measurements were carried out at low (1,450 m) and high altitude (HA; 4,780 m). Near-infrared spectroscopy (NIRS)-derived parameters, i.e., Tot-Hb and tissue saturation index (TSI), were gathered at rest and after bouts of 3-min resistive exercise, both in the quadriceps and in the forearm muscles. TSI decreased with altitude, particularly in forearm muscles (from 66.9 to 57.3%), whereas the decrement was less in the quadriceps (from 62.5 to 57.2%); Nepalese porters were characterized by greater values in thigh TSI than Italian trekkers. Tot-Hb was increased after exercise. At altitude, such increase appeared to be higher in the quadriceps. This effect might be a consequence of the long-term adaptive memory due to the frequent exposures to altitude. Although speculative, we suggest a long-term adaptation of the Nepalese porters due to improved oxygenation of muscles frequently undergoing hypoxic exercise. Muscle structure, individual factors, and altitude exposure time should be taken into account to move on the knowledge of oxygen delivery and utilization at altitude
A Multistage Stochastic Programming Approach to the Dynamic and Stochastic VRPTW - Extended version
We consider a dynamic vehicle routing problem with time windows and
stochastic customers (DS-VRPTW), such that customers may request for services
as vehicles have already started their tours. To solve this problem, the goal
is to provide a decision rule for choosing, at each time step, the next action
to perform in light of known requests and probabilistic knowledge on requests
likelihood. We introduce a new decision rule, called Global Stochastic
Assessment (GSA) rule for the DS-VRPTW, and we compare it with existing
decision rules, such as MSA. In particular, we show that GSA fully integrates
nonanticipativity constraints so that it leads to better decisions in our
stochastic context. We describe a new heuristic approach for efficiently
approximating our GSA rule. We introduce a new waiting strategy. Experiments on
dynamic and stochastic benchmarks, which include instances of different degrees
of dynamism, show that not only our approach is competitive with
state-of-the-art methods, but also enables to compute meaningful offline
solutions to fully dynamic problems where absolutely no a priori customer
request is provided.Comment: Extended version of the same-name study submitted for publication in
conference CPAIOR201
A brief bout of exercise in hypoxia reduces ventricular filling rate and stroke volume response during muscle metaboreflex activation
Purpose: The hemodynamic consequences of exercise in hypoxia have not been completely investigated. The present investigation aimed at studying the hemodynamic effects of contemporary normobaric hypoxia and metaboreflex activation. Methods: Eleven physically active, healthy males (age 32.7 ± 7.2 years) completed a cardiopulmonary test on an electromagnetically braked cycle-ergometer to determine their maximum workload (Wmax). On separate days, participants performed two randomly assigned exercise sessions (3 minutes pedalling at 30% of Wmax): (1) one in normoxia (NORMO), and (2) one in normobaric hypoxia with FiO2 set to 13.5% (HYPO). After each session, the following protocol was randomly assigned: either (1) post-exercise muscle ischemia (PEMI) to study the metaboreflex, or (2) a control exercise recovery session, i.e., without metaboreflex activation. Hemodynamics were assessed with impedance cardiography. Results: The main result was that the HYPO session impaired the ventricular filling rate (measured as stroke volume/diastolic time) response during PEMI versus control condition in comparison to the NORMO test (31.33 ± 68.03 vs. 81.52 ± 49.23 ml·sâ1,respectively, p = 0.003). This caused a reduction in the stroke volume response (1.45 ± 9.49 vs. 10.68 ± 8.21 ml, p = 0.020). As a consequence, cardiac output response was impaired during the HYPO test. Conclusions: The present investigation suggests that a brief exercise bout in hypoxia is capable of impairing cardiac filling rate as well as stroke volume during the metaboreflex. These results are in good accordance with recent findings showing that among hemodynamic modulators, ventricular filling is the most sensible variable to hypoxic stimuli
Service Level Constrained Inventory Systems
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151878/1/poms13060_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151878/2/poms13060.pd
Early effects of lipopolysaccharide-induced inflammation on foetal brain development in rat
Studies in humans and animal models link maternal infection and imbalanced levels of inflammatory mediators in the foetal brain to the aetiology of neuropsychiatric disorders. In a number of animal models, it was shown that exposure to viral or bacterial agents during a period that corresponds to the second trimester in human gestation triggers brain and behavioural abnormalities in the offspring. However, little is known about the early cellular and molecular events elicited by inflammation in the foetal brain shortly after maternal infection has occurred. In this study, maternal infection was mimicked by two consecutive intraperitoneal injections of 200 ÎŒg of LPS (lipopolysaccharide)/kg to timed-pregnant rats at GD15 (gestational day 15) and GD16. Increased thickness of the CP (cortical plate) and hippocampus together with abnormal distribution of immature neuronal markers and decreased expression of markers for neural progenitors were observed in the LPS-exposed foetal forebrains at GD18. Such effects were accompanied by decreased levels of reelin and the radial glial marker GLAST (glial glutamate transporter), and elevated levels of pro-inflammatory cytokines in maternal serum and foetal forebrains. Foetal inflammation elicited by maternal injections of LPS has discrete detrimental effects on brain development. The early biochemical and morphological changes described in this work begin to explain the sequelae of early events that underlie the neurobehavioural deficits reported in humans and animals exposed to prenatal insults
A L\'evy input fluid queue with input and workload regulation
We consider a queuing model with the workload evolving between consecutive
i.i.d.\ exponential timers according to a
spectrally positive L\'evy process that is reflected at zero, and
where the environment equals 0 or 1. When the exponential clock
ends, the workload, as well as the L\'evy input process, are modified; this
modification may depend on the current value of the workload, the maximum and
the minimum workload observed during the previous cycle, and the environment
of the L\'evy input process itself during the previous cycle. We analyse
the steady-state workload distribution for this model. The main theme of the
analysis is the systematic application of non-trivial functionals, derived
within the framework of fluctuation theory of L\'evy processes, to workload and
queuing models
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