Voltage- and current-activated metal–insulator transition in VO2-based electrical switches: a lifetime operation analysis

Vanadium dioxide is an intensively studied material that undergoes a temperature-induced metal–insulator phase transition accompanied by a large change in electrical resistivity. Electrical switches based on this material show promising properties in terms of speed and broadband operation. The exploration of the failure behavior and reliability of such devices is very important in view of their integration in practical electronic circuits. We performed systematic lifetime investigations of two-terminal switches based on the electrical activation of the metal–insulator transition in VO₂ thin films. The devices were integrated in coplanar microwave waveguides (CPWs) in series configuration. We detected the evolution of a 10 GHz microwave signal transmitted through the CPW, modulated by the activation of the VO₂ switches in both voltage- and current-controlled modes. We demonstrated enhanced lifetime operation of current-controlled VO₂-based switching (more than 260 million cycles without failure) compared with the voltage-activated mode (breakdown at around 16 million activation cycles). The evolution of the electrical self-oscillations of a VO₂-based switch induced in the current-operated mode is a subtle indicator of the material properties modification and can be used to monitor its behavior under various external stresses in sensor applications.     

Properties of large-scale methane/hydrogen jet fires

A future economy based on reduction of carbon-based fuels for power generation and transportation may consider hydrogen as possible energy carrier. Extensive and widespread use of hydrogen might require a pipeline network. The alternatives might be the use of the existing natural gas network or to design a dedicated network. Whatever the solution, mixing hydrogen with natural gas will modify the consequences of accidents, substantially. The French National Research Agency (ANR) funded project called HYDROMEL focuses on these critical questions. Within this project large-scale jet fires have been studied experimentally and numerically. The main characteristics of these flames including visible length, radiation fluxes and blowout have been assessed.     

Improving the reliability of material databases using multiscale approaches

This article addresses the propagation of constitutive uncertainties between scales occurring in the multiscale modelling of fibre-reinforced composites. The amplification of such uncertainties through upward or downward transitions by a homogenisation model is emphasized and exemplified with the Mori–Tanaka model. In particular, the sensitivity to data uncertainty in the inverse determination of constituent parameters based on downward transitions is stressed on an example. Then a database improvement method, which exploits simultaneously the available information on constitutive uncertainties at all scales instead of just propagating those associated with one scale, is presented and shown to yield substantial reductions in uncertainty for both the constitutive parameters and the response of structures. The latter finding is demonstrated on two examples of structures, with significant gains in confidence obtained on both.     

Integration of mud gas isotope logging (MGIL) with field appraisal at Horn Mountain Field, deepwater Gulf of Mexico

Prior applications of gas isotopic data to reservoir studies have often suggested that measured differences of a few per mil in gases sampled between wells indicated hydrocarbon compartmentalization concomitant with poor reservoir communication. These conclusions were generally invoked without adequate consultation and integration of geological and engineering well data, and only revealed to be true in the simplest of circumstances where pressure data clearly suggested the same. Not surprisingly, gas isotope data has yet to find widespread production engineering applications as a convincing tool for reservoir formation evaluation. This situation is unlikely to change due to the prohibitive drilling economics of acquiring adequate quantities of physical gas samples from down-hole tools in every zone of interest across multiple wells in a field. Recent application of a new technique, mud gas isotope logging (MGIL), has shown comparable isotopic data to traditional gas samples collected from down-hole tools while providing the petroleum systems analyst with the necessary large datasets needed to make accurate and confident reservoir evaluations. Many additional benefits of MGIL to formation evaluation have also been recognized, and it is envisaged MGIL possesses the potential to develop as a standard protocol on drilling wells.This paper documents the first published application of MGIL in the context of complete field-scale reservoir integration and production appraisal encompassing 18 well penetrations over a 3-yr drilling program. Case data from the Horn Mountain Field (Gulf of Mexico) are used to demonstrate this technology and its impact to field assessment and appraisal. Initial well data and two 3-D seismic surveys were used to assess reservoir continuity and compartmentalization across the field. Subtle pressure and gas-to-oil ratio (GOR) differences from eight appraisal wells suggested that the main economic M-Sand may be divided into at least two compartments, however the data could not be unambiguously relied upon in itself. MGIL data provided the strongest evidence in confirming the existence of two ‘baffled’ field compartments. Significantly for subsequent development wells, MGIL data were able to accurately discern and allocate compartments in wells without reliable wireline or absent MDT pressure data. MGIL data also recognized the significance of geological features such as a shale-filled channel visible on amplitude maps, and inferred to serve in concert with faults as a baffled flow barrier. Data such as these may have important implications for reservoir energy and pressure support during production. The impact of hydrocarbon stratification attributed to geological reservoir structural features and/or hydrocarbon phase geochemical density characteristics are also examined.Interpretation of the Horn Mountain MGIL data, in addition to characterizing and verifying oil/gas shows, was also successful in providing essential data on highlighting all penetrated pay zones, deconvolving multiple pure biogenic and mixed biogenic/thermogenic zones, identifying stratigraphic trapping seals and providing detailed petroleum system evaluation.     

Fire behaviour of concrete filled elliptical steel columns

In this work, a non-linear three-dimensional finite element model is presented in order to study the behaviour of axially loaded concrete filled elliptical hollow section (CFEHS) columns exposed to fire. This study builds on previous work carried out by the authors on concrete filled circular hollow section (CFCHS) columns both at room temperature and in fire. The numerical model is first validated at room temperature against a series of experiments on CFEHS stub columns available in the literature and subsequently extended to study the performance of slender columns at elevated temperatures. The aim of this work is to understand and represent the behaviour of axially loaded CFEHS columns in fire situations and to compare their effectiveness with that of the circular concrete filled tubular (CFT) columns. Parametric studies to explore the influence of variation in global member slenderness, load level, cross-section slenderness and section size are presented. Finally, guidance on the fire design of CFEHS columns is proposed: it is recommended to follow the guidelines of Clause 4.3.5.1 in EN 1994-1-2, but employing the flexural stiffness reduction coefficients established in the French National Annex with an equivalent EHS diameter equal to P/π, where P is the perimeter of the ellipse.     

Activity-Based Costing as a Tool for Process Improvement Evaluations

Many corporate processes common to the design and construction of major engineered projects are composed of individual activities that are variable by nature. Additionally, the process itself may have a high degree of variability, meaning that certain activities may or may not actually be performed in a given pass through the process. We may ascribe to such activities a “probability of occurrence.” True modeling of real world processes will often require that we describe the process as having activities with stochastic durations, each linked together in a precedence logic that itself is variable and subject to uncertainty or chance. If corporate resources, such as labor, material, and equipment, are required to perform the individual activities, then an activity-based costing technique must be developed that can accommodate the inherent variability in a process if actual costs are to be accurately predicted. If process cycle time and process cost per cycle can be accurately predicted for complex, highly variable processes, companies are in a much better position to determine how proposed corporate initiatives for process improvement might actually impact overall process performance. This technique has application across a wide number of disciplines including design, construction, and administrative processes.     

An accuracy assessment experiment of the BRDF measured at coarse spatial resolution from space

The accuracy assessment of the Bidirectional Reflectance Distribution Function (BRDF) acquired from satellite sensors at coarse spatial resolution (1 or more km) is not straightforward. One possible strategy is to compare BRDF measurements from spaceborne and airborne sensors on a test area with appropriate characteristics of spatial homogeneity. This Letter describes an experiment based on this principle, aiming at the control of the BRDF measured by POLDER/ADEOS. The BRDF derived from the satellite data is compared with that derived from spatially averaged airborne POLDER data over a forested area of the Landes region. The magnitude and shape of the BRDF measured by both sensors are found to be consistent within an accuracy of 0.01 in reflectance units, except for the principal plane in the blue band where some inconsistency is found. Similar experiments could be used for the verification of other sensors data, such as those of MISR and MODIS onboard Terra, and POLDER 2 onboard ADEOS 2 in the near future.     

Estimating the Fraction of Acceptable Product

Minimum variance unbiased estimates are given of the cumulative distribution function for the normal, binomial, Poisson, and negative exponential distributions. Although diverse areas of application might lead to interest in estimating the cumulative distribution function, most of the examples in this paper suppose that one is interested in the fraction of product meeting fixed specification limits.     

Simulation of special bubble detectors for PICASSO

The PICASSO project is a cold dark matter (CDM) search experiment relying on the superheated droplet technique. The detectors use superheated freon liquid droplets (active material) dispersed and trapped in a polymerised gel. This detection technique is based on the phase transition of superheated droplets at about room temperature and ambient pressure. The phase transition is induced by nuclear recoils when an atomic nucleus in the droplets interacts with incoming subatomic particles. This includes CDM particles candidate as the neutralino (a yet-to-discover particle predicted in extensions of the standard model of particle physics). Simulations performed to understand the detector response to neutrons and alpha particles are presented along with corresponding data obtained at the Montreal Laboratory.