A review of the International Handbook of Computer-Supported Collaborative Learning 2021

International Journal of Computer-Supported Collaborative Learning -     

DTN performance analysis of multi-asset Mars-Earth communications

The delay-/disruption-tolerant networking (DTN) architecture is considered the key enabling technology for future space communications, as confirmed by the current standardization within CCSDS and the experiments carried out onboard the International Space Station. Despite the scientific community efforts to analyze DTN architecture performance, most of the studies have focused on individual protocols, or have considered simple test cases, thus missing a whole system view. To bridge these research gaps, this paper presents a comprehensive analysis of DTN performance in Mars-Earth communications, considering a realistic and complex end-to-end scenario, where multiple assets and multiple data flows are involved, as envisioned for future space missions. To this end, a virtualized testbed based on ION software was used for an extensive emulation campaign, focusing particularly on Bundle and Licklider Protocol interaction with the CGR routing algorithm.     

Modeling of an aluminum melting process using constructive polynomial functions

Constantly increasing quality requirements and ever-stricter conditions pose difficult challenges for the foundry industry. They must produce the high-quality components demanded by the market at a reasonable cost. Modern technologies and innovative methods help to master this challenge. Until recently, production, from the design of the aluminum melting furnace to daily process, relied largely on traditional methods and experience. However, important data and information about the melting process—for example, the temperatures and the shape of the aluminum block in the furnace—can hardly be obtained with conventional experimental methods, as the temperatures exceed 700 °C. Therefore, this research project investigates the method of monitoring a melting process by means of optical sensors for the first time. The purpose of this paper is to predict the surface shape of the block during the melting process, as it is not possible to maintain a constant monitoring due to the heat and energy loss during measurement Behrens (Einsatz einer Lichtfeldkamera im Hochtemperaturbereich beim Schmelzvorgang von Aluminium, wt Werkstattstechnik online, 2016). To generate the necessary data, a 3D light-field camera is installed on top of an aluminum melting furnace in order to monitor the process. The basic idea is to find a general method for curve modeling from scattered range data on the aluminum surface in 3D space. By means of the (x, y, z) data from the 3D camera, the aluminum surface is modeled as a polynomial function with coefficient derived using various interpolation and approximation methods. This study presents an attempt to find the optimal polynomial function model that describes the aluminum surface during the melting process by interpolation or approximation methods. The best method for curve fitting will be extended and implemented for surface modeling. Based on this method, the melting process can be better controlled while the furnace operates continuously under stable conditions and the efficiency can therefore be increased. The proposed model can be modified for a wide variety of melting furnaces.     

Enabling and Localizing Omnidirectional Nonlinear Deformation in Liquid Crystalline Elastomers

Liquid crystalline elastomers (LCEs) are widely recognized for their exceptional promise as actuating materials. Here, the comparatively less celebrated but also compelling nonlinear response of these materials to mechanical load is examined. Prior examinations of planarly aligned LCEs exhibit unidirectional nonlinear deformation to mechanical loads. A methodology is presented to realize surface‐templated homeotropic orientation in LCEs and omnidirectional nonlinearity in mechanical deformation. Inkjet printing of the homeotropic alignment surface localizes regions of homeotropic and planar orientation within a monolithic LCE element. The local control of the self‐assembly and orientation of the LCE, when subject to rational design, yield functional materials continuous in composition with discontinuous mechanical deformation. The variation in mechanical deformation in the film can enable the realization of nontrivial performance. For example, a patterned LCE is prepared and shown to exhibit a near‐zero Poisson's ratio. Further, it is demonstrated that the local control of deformation can enable the fabrication of rugged, flexible electronic devices. An additively manufactured device withstands complex mechanical deformations that would normally cause catastrophic failure.     

Nanoparticle dispersion in porous media: Effects of hydrodynamic interactions and dimensionality

We investigate the effect of steric and hydrodynamic interactions (HI) on quiescent diffusion and flow-driven transport of finite-sized nanoparticles through periodic 2D (two-dimensional) and 3D (three-dimensional) nanopost arrays using Stokesian dynamics simulations. We find that steric and HI hinder particle diffusivity under quiescent conditions and enhance longitudinal dispersion under flow. Moreover, the presence of HI leads to a power-law increase in the longitudinal dispersion coefficient with Pe due to spatial variations in the fluid velocity. Lastly, our simulations reveal that longitudinal particle dispersion coefficients behave similarly in 2D and 3D when HI are included.     

A fast digital chip implementing a real-time noise-resistant algorithm for estimating blood pressure using a non-invasive,cuffless PPG sensor

Microsystem Technologies - A fast digital chip is designed and fabricated successfully to implement the algorithm for estimating blood pressure (BP) in real time by a non-invasive cuffless...     

Continuous emission monitoring systems at power plants in China: Improving SO2 emission measurement

The Chinese Government recently mandated the installation of continuous emission monitoring systems (CEMS) at state-controlled key polluting facilities in order to provide direct, real-time, continuous measurements of sulfur dioxide (SO₂) emissions. By 2010, most coal-fired power plants in China have installed and are operating SO₂ CEMS. As China's Central Government strengthens the SO₂ control program and implements new nitrogen oxides (NO_X) and carbon dioxide (CO₂) control programs, the quality of and confidence in CEMS data will become more important. This study utilizes field surveys and existing literature on Chinese CEMS to analyze their operation and management. Our study found that the Chinese government has issued a set of regulations and technical guidance documents to standardize CEMS operation, management, and supervision, and to improve the quality of CEMS data. Many power plants have followed key parts of the national CEMS rules and guidance and are periodically inspected by local environmental authorities. This study suggests several options for addressing some of the gaps and problems with the CEMS operation and supervision and thus enhancing China's CEMS program.     

Factors influencing relationships between personal and ambient concentrations of gaseous and particulate pollutants

Previous exposure studies have shown considerable inter-subject variability in personal-ambient associations. This paper investigates exposure factors that may be responsible for inter-subject variability in these personal-ambient associations. The personal and ambient data used in this paper were collected as part of a personal exposure study conducted in Boston, MA, during 1999-2000. This study was one of a group of personal exposure panel studies funded by the U.S. Environmental Protection Agency's National Exposure Research Laboratory to address areas of exposure assessment warranting further study, particularly associations between personal exposures and ambient concentrations of particulate matter and gaseous co-pollutants. Twenty-four-hour integrated personal, home indoor, home outdoor and ambient sulfate, elemental carbon (EC), PM_2.5, ozone (O₃), nitrogen dioxide (NO₂) and sulfur dioxide were measured simultaneously each day. Fifteen homes in the Boston area were measured for 7 days during winter and summer. A previous paper explored the associations between personal-indoor, personal-outdoor, personal-ambient, indoor-outdoor, indoor-ambient and outdoor-ambient PM_2.5, sulfate and EC concentrations. For the current paper, factors that may affect personal exposures were investigated, while controlling for ambient concentrations. The data were analyzed using mixed effects regression models. Overall personal-ambient associations were strong for sulfate during winter (p < 0.0001) and summer (p < 0.0001) and PM_2.5 during summer (p < 0.0001). The personal-ambient mixed model slope for PM_2.5 during winter but was not significant at p = 0.10. Personal exposures to most pollutants, with the exception of NO₂, increased with ventilation and time spent outdoors. An opposite pattern was found for NO₂ likely due to gas stoves. Personal exposures to PM_2.5 and to traffic-related pollutants, EC and NO₂, were higher for those individuals living close to a major road. Both personal and indoor sulfate and PM_2.5 concentrations were higher for homes using humidifiers. The impact of outdoor sources on personal and indoor concentrations increased with ventilation, whereas an opposite effect was observed for the impact of indoor sources.     

Aging of the LiFePO4 positive electrode interface in electrolyte

The evolution of lithium-containing species on the surface of grains of 500 nm LiFePO₄ and 100 nm carbon-coated LiFePO₄ materials during the aging process in LiPF₆ electrolyte has been followed using coupled ⁷Li MAS NMR, EIS (Electrochemical Impedance Spectroscopy) and XPS for materials synthesized with and without carbon coating.LiFePO₄ undergoes surface reactivity upon immersion in classical LiPF₆ electrolyte, although its open circuit voltage (∼3.2 V) lies in the thermodynamical stability voltage range. The evolution of the NMR signal shows that the reaction of formation of the interphase is very slow as no evidence of passivation could be found even after 1 month of contact with the electrolyte. ⁷Li MAS NMR combined with XPS indicates that carbon coating has a strong protective role towards formation of surface species on the material and hinders iron dissolution at elevated temperature. Coupled NMR, EIS and XPS experiments showed that the surface of the material grains is not covered by an homogenous layer. Increasing the storage temperature from 25 °C to 55 °C promotes the formation of organic species on the surface, most probably covering inorganic species such as LiF, Li_xPF_y and LiPO_yF_z. No evidence of the formation of a resistive film is deduced from the evolution of EIS measurements. The interphase growth can accelerate the degradation of the electrochemical performance, leading to a loss of electrical contact within the electrode.