The Human Centrifuge

Life on Earth has developed at unit gravity, 9.81 m/s², which was a major factor especially when vertebrates emerged from water onto land in the late Devonian, some 375 million years ago. But how would nature have evolved on a larger planet? We are able to address this question simply in experiments using centrifuges. Based on these studies we have gained valuable insights in the physiological process in plants and animals. They adapt to a new steady state suitable for the high-g environments applied. Information on mammalian adaptations to hyper-g is interesting or may be even vital for human space exploration programs. It has been shown in long duration animal hypergravity studies, ranging from snails, rats to primates, that various structures like muscles, bones, neuro-vestibular, or the cardio-vascular system are affected. However, humans have never been exposed to a hyper-g environment for long durations. Centrifuge studies involving humans are mostly in the order of hours. The current work on human centrifuges are all focused on short arm systems to apply short periods of artificial gravity in support of long duration space missions in ISS or to Mars. In this paper we will address the possible usefulness of a large human centrifuge on Earth. In such a centrifuge a group of humans can be exposed to hypergravity for, in principle, an unlimited period of time like living on a larger planet. The input from a survey under scientists working in the field of gravitational physiology, but also other disciplines, will be discussed.     

Comparing drop impact test method using strain gauge measurements

In this paper, strain gauges are used to measure the dynamic response during drop impact. A set of high-speed data acquisition system is used to capture the real-time strain response of critical locations. Finite Element Modelling is used to determine where to place the strain gauges. Two board level drop impact test methods, A and B, are compared by the strain gauge measurements. Results show significant differences in strain amplitude, strain rate, frequency, rebound, and damping. Method B produces higher strain amplitude, stronger rebound, and less damping, while method A produces higher frequency and strain rate. Damping and rebound are important factors for both test methods. The differences of two test methods are due to the contributions from test condition and test board. Combination test were conducted to investigate the contribution of test condition and test board. Results show that test board dominates strain amplitude, frequency, mode and damping, while test condition shows influence on strain amplitude and rebound. Test condition A produces higher strain amplitude, while test condition B produces stronger rebound. Test board A produces higher frequency, while test board B produces higher strain amplitude and less damping. Test board contributes more to the strain amplitude than test condition. Strain rate is dependent on both the test condition and test board.     

Modelling the effectiveness and risks of vaccination strategies to control classical swine fever epidemics

In a recent update of the Dutch contingency plan for controlling outbreaks of classical swine fever (CSF), emergency vaccination is preferred to large-scale pre-emptive culling. This policy change raised two questions: can emergency vaccination be as effective as pre-emptive culling, and what are the implications for showing freedom of infection? Here, we integrate quantitative information available on CSF virus transmission and vaccination effects into a stochastic mathematical model that describes the transmission dynamics at the level of animals, farms and livestock areas. This multilevel approach connects individual-level interventions to large-scale effects. Using this model, we compare the performance of five different control strategies applied to hypothetical CSF epidemics in The Netherlands and, for each of these strategies, we study the properties of three different screening scenarios to show freedom of infection. We find that vaccination in a ring of 2 km radius around a detected infection source is as effective as ring culling in a 1 km radius. Feasible screening scenarios, adapted to the use of emergency vaccination, can reduce the enhanced risks of (initially) undetected farm outbreaks by targeting vaccinated farms. Altogether, our results suggest that emergency vaccination against CSF can be equally effective and safe as pre-emptive culling.     

Relating microbiological criteria to food safety objectives and performance objectives

Microbiological criteria, food safety objectives and performance objectives, and the relationship between them are discussed and described in the context of risk-based food safety management. A modified method to quantify the sensitivity of attributes sampling plans is presented to show how sampling plans can be designed to assess a microbiological criterion. Examples presented show that testing of processed foods for confirmation of safety is often not a practical option, because too many samples would need to be analysed. Nonetheless, in such cases the classical “ICMSF cases” and sampling schemes still offer a risk-based approach for examining food lots for regulatory or trade purposes.     

A heuristic to manage perishable inventory with batch ordering,positive lead-times,and time-varying demand

So far the literature on inventory control for perishable products has mainly focused on (near-) optimal replenishment policies for a stylized environment, assuming no lead-time, no lot-sizing, stationary demand, a first in first out withdrawal policy and/or product life time equal to two periods. This literature has given fundamental insight in the behavior and the complexity of inventory systems for perishable products. In practice, many grocery retailers have recently automated the inventory replenishment for non-perishable products. They recognize they may need a different replenishment logic for perishable products, which takes into account e.g. the age of the inventory in the system. Due to new information technologies like RFID, it now also becomes more economically feasible to register this type of information. This paper suggests a replenishment policy for perishable products which takes into account the age of inventories and which requires only very simple calculations. It will be shown that in an environment, which contains important features of the real-life retail environment, this new policy leads to substantial cost reductions compared with a base policy that does not take into account the age of inventories.     

Experimental evaluation of losses in magnetic components for powerconverters

A very versatile experimental method for measuring losses in magnetic components is presented. This is not subject to the bandwidth constraints associated with the direct wattmeter method. The proposed method features accurate measurement of conduction losses, separation of core and conduction losses, measurement at high frequencies, and scale modeling of magnetic components. The experimental measurements are compared with theoretical predictions of components as applicable to certain power electronic converters     

Optimum nonlinear turn-off snubbers: design and application

The optimization of the general turn-off snubber, consisting of a nonlinear saturable snubber capacitor with an energy recovery circuit, is done in terms of minimum total energy loss in the power electronic turn-off circuit. To analyze this nonlinear circuit without a computer simulation, a two-step piecewise-linear approximation of the capacitor's capacitance-voltage curve is presented. Results regarding the total energy loss in the circuit during the switch turn-off indicate that the nonlinear capacitor as a snubber element is superior to the normal linear capacitor even if the ceramic capacitor is used only up to its specified voltage value