Key Physical Parameters Research Articles

Beranek's porous material model: Inspiration for advanced material analysis and design

In 1942, Leo Beranek presented a model for predicting the acoustic properties of porous materials [J. Acoust. Soc. Am. 13, 248 (1942)]. Since then, research into many types of porous materials has grown into a broad field. In addition to Beranek's model, many other models for predicting the acoustic properties of porous materials in terms of key physical material parameters have been developed. Following a brief historical review, this work concentrates on studying porous materials and microperforated panels—pioneered by one of Beranek's early friends and fellow students, Dah-You Maa. Utilizing equivalent fluid models, porous material and microperforated panel theories have recently been unified. In this work, the Bayesian inference framework is applied to single- and multilayered porous and microperforated materials. Bayesian model selection and parameter estimation are used to guide the analysis and design of innovative multilayer acoustic absorbers.

Retention failure analysis of metal-oxide based resistive memory

Resistive switching devices (RRAMs) have been proposed a promising candidate for future memory and neuromorphic applications. Central to the successful application of these emerging devices is the understanding of the resistance switching and failure mechanism, and identification of key physical parameters that will enable continued device optimization. In this study, we report detailed retention analysis of a TaOx based RRAM at high temperatures and the development of a microscopic oxygen diffusion model that fully explains the experimental results and can be used to guide future device developments. The device conductance in low resistance state (LRS) was constantly monitored at several elevated temperatures (above 300 °C), and an initial gradual conductivity drift followed by a sudden conductance drop were observed during retention failure. These observations were explained by a microscopic model based on oxygen vacancy diffusion, which quantitatively explains both the initial gradual conductance drift and the sudden conductance drop. Additionally, a non-monotonic conductance change, with an initial conductance increase followed by the gradual conductance decay over time, was observed experimentally and explained within the same model framework. Specifically, our analysis shows that important microscopic physical parameters such as the activation energy for oxygen vacancy migration can be directly calculated from the failure time versus temperature relationship. Results from the analytical model were further supported by detailed numerical multi-physics simulation, which confirms the filamentary nature of the conduction path in LRS and the importance of oxygen vacancy diffusion in device reliability. Finally, these high-temperature stability measurements also reveal the existence of multiple filaments in the same device.

Importance of Ge surface oxidation with high oxidation rate in obtaining low interface state density at oxide/Ge interfaces

The formation of a gate-insulator/Ge interface with a low interface state density (Dit) starts with oxidation at the Ge surface under appropriate conditions. In this study, a key physical parameter for realizing Dit lower than 1011 eV−1 cm−2 during the oxidation process was clarified by comparison between the experimental results and results calculated based on a proposed model including a time-dependent defect distribution near the Ge-oxide/Ge interface and movement of the interface due to the oxidation at the Ge surface. Dit near the midgap is determined by the competition between the rate of defect creation near the Ge-oxide/Ge interface and the movement rate of the interface, which is the Ge oxidation rate. Oxidation with a Ge oxidation rate of more than 0.1 nm/s can lead to Dit lower than 1011 eV−1 cm−2, taking into account the defect creation rate in a typical Ge device fabrication process, which is 10−2 to 10−4 nm/s.

Electrical characterization of controlled and unintentional modified metal–organic contacts

A method to characterize metal–organic contacts subjected to controlled technological treatments or unintentional degradation processes is proposed. The procedure is useful to characterize different fundamental aspects of a metal–organic structure such as the height of the interface energy barrier, the presence of impurities or trapping effects and the carrier mobility. Current–voltage curves in organic diodes are analyzed and the value of the free carrier density at the metal–organic interface is extracted and discussed. The charge carrier density is chosen for this analysis as this is one of the key physical parameters in the understanding of the physical processes involved in the device operation. The extracted charge, when described as a function of the current density, gives information about the doping and impurity concentration, the effective barrier seen by the carriers at the metal–organic interface or effective barriers seen by the carriers in the hopping processes across the organic material. An important advantage of the proposed procedure is the low computational time. Also, the procedure aims to provide a quick analysis for researchers on how the physical properties of the devices are evolving when they are technologically altered or degraded.

Sensitivity analysis on resin transfer molding processes with edge effect and curing reaction characteristics

The mold filling time and resin flow front shape are of fundamental importance during resin transfer molding (RTM) processes, because the former influences productivity and the latter affects composites quality. In this article, considering both edge effect and curing reaction characteristics of the resin flow process, the sensitivity analysis method is introduced to investigate the sensitive degree of mold filling time and resin flow front shape to the key material and processing parameters. The function employed to describe the resin flow front shape is defined, and the mathematical relationships of the key physical parameters, such as fluid pressure sensitivity, flow velocity sensitivity, mold filling time sensitivity, and resin flow front shape sensitivity, are established simultaneously. In addition, then the resin infiltration process is simulated by means of a semi-implicit iterative calculation method and the finite volume method. The simulated results are in agreement with the analytical ones. The results show that under constant injection velocity conditions, both the change in the resin temperature and the alteration of the inlet velocity hardly affect the resin flow front shape, whereas the influence of edge permeability on the resin flow front shape is the greatest. This study is helpful for designing and optimizing RTM processes. POLYM. COMPOS., 36:2008–2016, 2015. © 2014 Society of Plastics Engineer

A model for precipitation strengthening in multi-particle systems

In this work, we present a consistent model describing the increase of yield strength caused by precipitation of second phase particles. Shearing and non-shearing mechanisms are accounted for, depending on the coherency between precipitates and matrix.The physical key parameters entering the model are critically evaluated on basis of the dislocation line tension, free distance between two particles and precipitate radius. A set of equations is derived, which describes the yield strength increase due to the interaction between dislocations and precipitates. Based on coupling equations for the individual strengthening mechanisms, the model allows for a predictive simulation of the final yield strength caused by precipitation in multi-particle, multi-phase systems. With the aid of contemporary computational power, the enhanced strengthening equations deliver more accurate results compared to the conventional equations.

Nanotube based hybrid plasmon polariton waveguide for propagation loss reduction and enhanced field confinement inside the gap region at the subwavelength scale

We present a comprehensive numerical investigation on the guiding properties of a nanotube based hybrid plasmonic waveguide, which comprises a high-index dielectric nanotube placed above a metallic substrate. It is shown that the incorporation of the nanotube offers additional freedom for tuning the optical performance of the hybrid plasmonic structure when compared to the traditional nanowire based hybrid counterparts, which enables further reduction of the propagation loss and enhanced field confinement inside the gap region, while simultaneously maintaining a subwavelength mode size at appropriate geometries. Systematic geometric parameters mapping considering the size of the nanotube and the dimension of the gap reveals that the tradeoff between the confinement and loss could be further balanced through optimizing key physical parameters. These investigations potentially lay the groundwork for the further applications of nanotube based hybrid structures.

Physical investigation of square cylinder array dynamical response under single-phase cross-flow

Fluid structure interaction and flow-induced vibration in square cylinder arrangement under single-phase incompressible laminar cross flow are investigated in the present paper. Dynamic instability governed by damping generation is studied without any consideration about mixing with turbulence effects. Conservative and non-conservative effects are pointed out and dynamical stability limit sensitivity to physical parameters is analyzed. Finally the influence of key physical parameters on fluid solid dynamics interaction is quantified.

Extended Electrochemical Reliability Study of All-Solid-State Thin Film Microbatteries

The all-solid-state thin-film lithium microbatteries fulfill the requirements of a wide range of new markets and applications. Innovative due to the absence of liquid electrolyte, these systems are meant to replace conventional energy storage systems that cannot meet the size requirements of present and future microelectronic devices, such as smart cards, battery-assisted RFID tags, wireless sensor networks, Real-Time Clock back-up batteries, and multiple healthcare applications. Long-time leader in power technologies, STMicroelectronics has realized significant investments in the development of new miniaturized solutions for energy storage. This study focuses on the reliability performances of EnFilm™ HiCap batteries, characterized by 1x1 inch footprint and a nominal capacity of 700µA.h between 4.2V and 3.6V. The positive electrode material is made of lithium cobalt oxide (LiCoO2) and the solid electrolyte is a lithium phosphorus oxynitride (LiPON), a material originally developed and patented by Oak Ridge National Laboratories [1]. Both thin films are deposited by sputtering techniques. Despite many recent studies, the all-solid-state systems remain minority regarding liquid electrolyte Li-ion technologies. Today widely developed, the Li-ion batteries are extensively used in portable instruments especially due to their large capacities. However, the Li-ion systems present a few vulnerabilities. As highlighted by several studies, the graphite/electrolyte interface is considered by many researchers to be the major source of reliability issue, due to reactions between the anode and the electrolyte [2]. Indeed, many works reveal that a large irreversible capacity loss is initiated by the formation of an interfacial SEI film, resulting from the irreversible consumption of Li+. Hence, thin film batteries should present a great interest regarding reliability behavior, since no formation of SEI layer is expected. In this paper we propose to investigate further the ageing characteristics of all-solid-state Li/LiPON interface during an extended electrochemical cycling study.Experimentally, batteries were submitted to series of potentiodynamic charges and galvanostatic discharges (1.4C current rate) at a temperature of 60°C, in order to accelerate the ageing mechanisms. Electrochemical impedance spectroscopy (EIS) measurements were regularly performed at 30°C, in order to detect any evolution of each contributor of internal resistance [3]. The equivalent circuit shown in figure 1 was used to model the impedance data, so that some key physical parameters might be extracted, such as the exchange current density at Li/LiPON interface. As shown in figure 2, the impedance data analysis reveals the relatively great stability of interfacial contributions, even after 3000 cycles. These results prove that the solid character of the electrolyte confers to the system an electrochemical integrity for very long periods of use. Furthermore, the stability of the exchange current extracted for Li/electrolyte interface (table 1) reveals the absence of any chemical or morphological modifications, which are at the origin of most failures reported for liquid electrolyte Li-ion systems.To conclude, this paper highlights the reliability performances of all-solid-state thin film batteries technology, through the electrochemical characterization of the Li/LiPON interface at different steps of the cycle life. Besides, this study demonstrates that EIS measurement turns out to be a successful tool of failure mechanisms investigation and understanding. [1] X. Yu et al., J. Electrochem. Soc., 1997, 144, 524-532 [2]J. Vetter et al., A. J. Power Sources, 2005, 147, 269-281 [3] S. D.Fabre et al., J. Electrochem. Soc., 2011, 159, A104-A115

SCIENCE WITH A WIDE-FIELD UV TRANSIENT EXPLORER

The time-variable electromagnetic sky has been well-explored at a wide range of wavelengths. Numerous high-energy space missions take advantage of the dark Gamma-ray and X-ray sky and utilize very wide field detectors to provide almost continuous monitoring of the entire celestial sphere. In visible light, new wide-field ground-based surveys cover wide patches of sky with ever decreasing cadence, progressing from monthly-weekly time scale surveys to sub-night sampling. In the radio, new powerful instrumentation offers unprecedented sensitivity over wide fields of view, with pathfinder experiments for even more ambitious programs underway. In contrast, the ultra-violet (UV) variable sky is relatively poorly explored, even though it offers exciting scientific prospects. Here, we review the potential scientific impact of a wide-field UV survey on the study of explosive and other transient events, as well as known classes of variable objects, such as active galactic nuclei and variable stars. We quantify our predictions using a fiducial set of observational parameters which are similar to those envisaged for the proposed ULTRASAT mission. We show that such a mission would be able to revolutionize our knowledge about massive star explosions by measuring the early UV emission from hundreds of events, revealing key physical parameters of the exploding progenitor stars. Such a mission would also detect the UV emission from many tens of tidal-disruption events of stars by super massive black holes at galactic nuclei and enable a measurement of the rate of such events. The overlap of such a wide-field UV mission with existing and planned gravitational-wave and high-energy neutrino telescopes makes it especially timely.

Numerical simulation of pulsation processes in hydraulic turbine based on 3D model of cavitating flow

A new approach was proposed for simulation of unsteady cavitating flow in the flow passage of a hydraulic power plant. 1D hydro-acoustics equations are solved in the penstock domain. 3D equations of turbulent flow of isothermal compressible liquid-vapor mixture are solved in the turbine domain. Cavitation is described by a transfer equation for liquid phase with a source term which is responsible for evaporation and condensation. The developed method was applied for simulation of pulsations in pressure, discharge, and total energy propagating along the flow conduit of the hydraulic power plant. Simulation results are in qualitative and quantitative agreement with experiment. The influence of key physical and numerical parameters like discharge, cavitation number, penstock length, time step, and vapor density on simulation results was studied.

Investigation on inter-modulation products (IMPs) for IM-DD SCM optical links

The implementation of the subcarrier multiplexing (SCM) as the signaling format has been extensively researched in various analog and digital lightwave based broadband applications because of its promising versatility, cost effectiveness, convenient and simple offerings. However performance degradation is a matter of serious concern in such multi-channel intensity modulation-direct detection (IM-DD) systems caused by inter-modulation distortion (IMD) mechanism. In this paper the impact of key operational and physical parameters of a laser source on an IMD dominated two-tone IM-DD SCM system has been investigated which can thereby be exploited favorably to develop a reasonably IMD immune optical link.

In situ estimates of submesoscale horizontal eddy diffusivity across an ocean front

In the last decade, the rapid advancements in computational power have favored the development of high‐resolution numerical models capable of directly resolving small‐scale structures such as fronts and filaments. Such models have greatly improved our understanding of submesoscale dynamics. At the same time, the small dimensions and short duration of these structures still pose major challenges for small‐scale dedicated field experiments. For this reason, submesoscale studies from in situ observations are still relatively scarce and quantitative estimates of key physical parameters for high‐resolution numerical models, such as horizontal eddy diffusivity, are still lacking. This study presents a novel approach for computing in situ horizontal eddy diffusivity associated with frontal structures by combining cross‐front widths derived from surface thermosalinograph sections with stirring rates estimated from Lagrangian drifter trajectories. The method is applied to the measurements collected across a frontal structure observed in the western part of the Gulf of Lion during the Latex10 campaign (LAgrangian Transport EXperiment, 1–24 September 2010). A total of 76 estimates of eddy diffusivity were obtained for strain rates of 0.70 and 1.21 day−1 and front widths (horizontal scales) ranging between 1 and 4 km. The estimates are log‐normally distributed, with 70% of the values ranging between 0.4 and 5 m2 s−1. Further analysis based on high‐resolution simulations and remote sensed observations, as well as dedicated field experiments will help to assess the robustness of some of the assumptions at the base of the proposed approach, and to extend the results to different ocean regions.

Fluid-solid coupling model based on endochronic damage for roller compacted concrete dam

According to the characteristics of thin-layer rolling and pouring construction technology and the complicated mechanical behavior of the roller compacted concrete dam (RCCD) construction interface, a constitutive model of endochronic damage was established based on the endochronic theory and damage mechanics. The proposed model abandons the traditional concept of elastic-plastic yield surface and can better reflect the real behavior of rolled control concrete. Basic equations were proposed for the fluid-solid coupling analysis, and the relationships among the corresponding key physical parameters were also put forward. One three-dimensional finite element method (FEM) program was obtained by studying the FEM type of the seepage-stress coupling intersection of the RCCD. The method was applied to an actual project, and the results show that the fluid-solid interaction influences dam deformation and dam abutment stability, which is in accordance with practice. Therefore, this model provides a new method for revealing the mechanical behavior of RCCD under the coupling field.

Mattress recycling

Mattresses, which are classed as bulky items, can enter the waste stream either by kerbside collection or by way of household waste recycling centres. They are of a composite construction, with a material panel over a steel spring assembly. The design is heavily influenced by type and manufacturer. An analysis of a range of mattresses entering a recycling facility was undertaken and key physical parameters were determined to assess type, size, mass and methods of construction. Of the mattresses entering the facility, 58% were classed as double size and the remaining 42% were single. It was found that the panels were attached to the spring assembly by staples and they were either unstitched, stitched together using a range of designs or joined using tufted buttons. Furthermore, 98% of the mattresses examined were of a simple open spring design. The average mass varied from 15 kg for single mattresses to 25 kg for doubles. The steel spring assembly accounted for about 45% of the total mass. Currently, recycling takes place in dedicated centres using manual or automated processes. The type of construction heavily influences the recycling route: stitched panels are sent to energy from waste plants, whereas unstitched material is sent for further processing due to its ease of separation. The calorific value of the panel material ranged from 18·55 to 23·78 MJ/kg, making them ideally suited to energy applications.

Dark energy in systems of galaxies

The precise observational data of the Hubble Space Telescope have been used to study nearby galaxy systems. The main result is the detection of dark energy in groups, clusters, and flows of galaxies on a spatial scale of about 1–10 Mpc. The local density of dark energy in these systems, which is determined by various methods, is close to the global value or even coincides with it. A theoretical model of the nearby Universe has been constructed, which describes the Local Group of galaxies with the flow of dwarf galaxies receding from this system. The key physical parameter of the group-flow system is zero gravity radius, which is the distance at which the gravity of dark matter is compensated by dark-energy antigravity. The model predicts the existence of local regions of space where Einstein antigravity is stronger than Newton gravity. Six such regions have been revealed in the data of the Hubble space telescope. The nearest of these regions is at a distance of 1–3 Mpc from the center of the Milky Way. Antigravity in this region is several times stronger than gravity. Quasiregular flows of receding galaxies, which are accelerated by the dark-energy antigravity, exist in these regions. The model of the nearby Universe at the scale of groups of galaxies (∼1 Mpc) can be extended to the scale of clusters (∼10 Mpc). The systems of galaxies with accelerated receding flows constitute a new and probably widespread class of metagalactic populations. Strong dynamic effects of local dark energy constitute the main characteristic feature of these systems.

An optimally tuned ensemble of the "eb_go_gs" configuration of GENIE: parameter sensitivity and bifurcations in the Atlantic overturning circulation

Abstract. The key physical parameters for the "eb_go_gs" configuration of version 2.7.4 of GENIE, an Earth system model of intermediate complexity (EMIC), are tuned using a multi-objective genetic algorithm. An ensemble of 90 parameter sets is tuned using two ocean and two atmospheric state variables as targets. These are "Pareto-optimal", representing a range of trade-offs between the four tuning targets. For the leading five parameter sets, simulations are evaluated alongside a simulation with untuned "default" parameters, comparing selected variables and diagnostics that describe the state of the atmosphere, ocean and sea ice. Further experiments are undertaken with these selected parameter sets to compare equilibrium climate sensitivities and transient climate responses. The pattern of warming under doubled CO2 is strongly shaped by changes in the Atlantic meridional overturning circulation (AMOC), while the pattern and rate of warming under rising CO2 is closely linked to changing sea ice extent. One of the five tuned parameter sets is identified as marginally optimal, and the objective function (error) landscape is further analysed in the vicinity of the tuned values of this parameter set. "Cliffs" along some dimensions motivate closer inspection of corresponding variations in the AMOC. This reveals that bifurcations in the AMOC are highly sensitive to parameters that are not typically associated with MOC stability. Specifically, the state of the AMOC is sensitive to parameters governing the wind-driven circulation and atmospheric heat transport. For the GENIE configuration presented here, the marginally optimal parameter set is recommended for single simulations, although the leading five parameter sets may be used in ensemble mode to admit a constrained degree of parametric uncertainty in climate prediction.

Spreading and solidification of metal-melt droplets under conditions of substrate submelting. Theory and model experiment

Spreading and solidification of metal-melt droplets upon their collision with a surface are of particular interest for thermal spraying, molding, melt spinning for obtaining amorphous and microcrystal powders, etc. The scenarios of the formation of splats (spread and solidified particles on the substrate) can be significantly different and are determined by thermophysical properties of materials of the particle and substrate, as well as by key physical parameters (KPPs): velocity up0, size Dp, and temperature Tp0 of the droplet and substrate Tb0 and the state of its surface. An attempt was made to theoretically and experimentally study the formation of splats for the case in which the substrate is submelted in the spot of the contact with the particle in the process of spreading and solidification of metal-melt droplets.

Nuclear data sensitivity and uncertainty for the Canadian supercritical water-cooled reactor

Accurate and complete nuclear data are a fundamental requirement for any nuclear reactor model. Present nuclear data evaluations have been tested and validated against experiments that cover operating conditions and materials that are typical of conventional reactors (e.g. thermal light and heavy water moderated reactors, and some fast reactors). The Canadian supercritical water-cooled reactor (SCWR) is an advanced reactor concept for which, like all advanced GEN-IV reactor concepts, operating conditions and materials differ significantly from conventional reactors. Consequently, current nuclear data evaluations may not be suitable for modeling the Canadian SCWR, either due to assumptions or gaps in the evaluations or gaps in the experimental data on which the evaluations are based. In this paper, a simplified model of an SCWR fuel channel with fresh fuel is analyzed in order to determine the sensitivities and uncertainties of the model to nuclear data. The results are used to determine which isotopes and which reactions make the largest contributions to the sensitivity and uncertainties in key reactor physics parameters such as the neutron multiplication factor, k, and various lattice reactivity coefficients.

Theoretical tools for studies of low‐frequency thermospheric variability

This paper supports studies of low‐frequency variability (LFV) within the thermosphere by deriving approximate integral and closed‐form solutions of a nontrivial model of thermospheric temperature, density, and composition depending on altitude and time. We also provide a paradigm for applying dimensional analysis in such studies. The domain is the region between the mesopause and the exobase. The solutions emphasize the connectedness of the thermosphere, i.e., nonlocal influences of LFV in key physical parameters and phenomena. The present focus is seasonal variability, within which the origin of a sizable semiannual variation in the thermosphere remains under active investigation. Following from the thermodynamic differential equation for temperature is a filtered, integral solution consistent with the Π theorem of dimensional analysis. A key result is the explicit demonstration that lower thermospheric boundary conditions affect low‐frequency variability throughout the thermosphere, making accurate boundary conditions essential to modeling LFV. In addition, LFV of the temperature varies inversely with variability of the net heating profile and has directly and inversely proportional contributions from variations in the thermal conductivity profile, which can include an “eddy diffusivity” component. Given a temperature profile, diffusive equilibrium defines model composition. For rapid calculations and transparency, we develop an approximate, closed‐form solution for temperature, density, and composition depending only on a minimal set of observable parameters, and from that, we demonstrate the essential role of the phase and amplitude profile of the temperature LFV in determining the corresponding profile of variability in composition and density.