Performance Study In Terms Research Articles

Tailored meshing for parallel 3D electromagnetic modeling using high-order edge elements

We present numerical experiments for geophysics electromagnetic (EM) modeling based upon high-order edge elements and supervised h+p refinement approaches on massively parallel computers. Our high-order h+p refinement strategy is based on and extends the PETGEM code. We focus on the performance study in terms of accuracy, convergence rate, and computational effort to solve real-life 3D setups based on synthetic and experimental data for energy reservoir characterization. These test cases show variable resolution discretization needs and realistic physical parameters. In general, our numerical results are consistent theoretically. The use of h-adapted meshes was efficient to achieve a certain accuracy level in the synthetic EM responses. Regarding global p-refinement, p=2 exhibits the best accuracy/performance trade-off. Selective p-refinement might offer a better compromise between accuracy and computational cost. However, for p-refinement at different entities, the best refinement scheme consists of using p=3 at the volume level with p=1 at faces and edges. Thus, p-refinement can be competitive if applied hierarchically. Nevertheless, we acknowledge that the performance of our supervised h+p refinement strategy depends on the input model (e.g., conductivity, frequency, domain decomposition strategy, among others). Whatever the chosen configuration, our numerical results provide an in-depth understanding of EM modeling’s pros and cons when supervised h+p refinement schemes are applied.

Experimental investigation of clay brick with sensible, latent, and hybrid thermal energy storage in buildings

Global warming has caused uneven extremities in the climate such as heat waves, floods, and extreme rise in temperatures. Consequently, there is increase in demand for energy for indoor space cooling in the buildings to create better indoor thermal comfort. Thermal energy storage (TES) using Phase Change Material (PCM) is an effective technology for improving the thermal performance of the building envelope. Energy efficient building envelope can reduce the external heat gain and maintains indoor thermal comfort level easily. In this study, the thermal performance of clay bricks integrated with sensible heat storage material, latent heat storage material, and hybrid (sensible + latent) was investigated. A comparative study of indoor thermal performance in terms of peak temperature, thermal amplitude, time lag, decrement factor of sensible heat storage brick, latent heat storage brick, and hybrid brick in comparison with conventional brick was prepared. Latent heat storage brick has shown the highest percentage average peak temperature reduction of 3.86 % in comparison to conventional brick. Maximum reduction of 13.74 % was shown by latent heat storage brick followed by hybrid heat storage brick and then by sensible heat storage brick. Time lag of 180 min is observed in brick embedded with latent heat storage capacity. Additionally, infrared thermal images suggest that the brick integrated with latent heat storage material shows better indoor thermal performance.

Experimental Analysis of the Application of Serverless Computing to IoT Platforms.

Serverless computing, especially implemented through Function-as-a-Service (FaaS) platforms, has recently been gaining popularity as an application deployment model in which functions are automatically instantiated when called and scaled when needed. When a warm start deployment mode is used, the FaaS platform gives users the perception of constantly available resources. Conversely, when a cold start mode is used, containers running the application’s modules are automatically destroyed when the application has been executed. The latter can lead to considerable resource and cost savings. In this paper, we explore the suitability of both modes for deploying Internet of Things (IoT) applications considering a low resources testbed comparable to an edge node. We discuss the implementation and the experimental analysis of an IoT serverless platform that includes typical IoT service elements. A performance study in terms of resource consumption and latency is presented for the warm and cold start deployment mode, and implemented using OpenFaaS, a well-known open-source FaaS framework which allows to test a cold start deployment with precise inactivity time setup thanks to its flexibility. This experimental analysis allows to evaluate the aptness of the two deployment modes under different operating conditions: Exploiting OpenFaaS minimum inactivity time setup, we find that the cold start mode can be convenient in order to save edge nodes limited resources, but only if the data transmission period is significantly higher than the time needed to trigger containers shutdown.

Fluidized bed CaO hydration-dehydration cycles for application to sorption-enhanced methanation

ABSTRACTA sorption-enhanced methanation concept has been recently presented, which is based on the employment of a sorbent able to capture in situ the H2O produced during the methanation reaction, in order to shift the equilibrium towards the formation of methane. In this work CaO, derived from natural limestone, was tested as a possible sorbent material for H2O capture in a novel configuration based on the concept of chemical looping in dual interconnected fluidized bed systems. The lab-scale experimental campaign was focused on the study of the sorbent performance in terms of hydration and dehydration cycles at different operating conditions relevant for catalytic methanation. The effect of temperature on the sorbent performance, as well the presence of CO2 in the reaction environment, were investigated. The results showed that CaO has good capacity to capture and release steam in the temperature range of interest. Unfortunately, even at the lowest temperatures tested, the sorbent is affected by the presence of CO2 that worsen its performance in terms of H2O capture capacity.

Effect of benzoic acid content on aging of 6FDA copolyimides based thin film composite (TFC) membranes in CO2/CH4 environment

Abstract 6FDA based polyimides possess outstanding properties, with a high free volume fraction entailing in high permselectivity properties for gas separation processes. However, they are very sensitive to aging process. Copolyimdes 6FDA–DAM:DABA were synthesized using different ratios of diamines: (9:1), (3:1) and (2:1) and the homopolyimide 6FDA–DAM. Thin Film Composite membranes were prepared and thermally annealed at 300 °C for 1 h to improve CO2 induced plasticization resistance. For exploring the future applications of these polymers, long–term performance studies of TFC membranes are absolutely needed. For this purpose, TFC membranes were tested for 180 h at 35 °C using a 50/50 vol./vol. CO2/CH4 feed composition at 8 bars of transmembrane pressure and aging was done under similar conditions. As a result, a more accurate behavior of long–term performance under working conditions can be disclosed. Overall, the drop of performance of all TFC membranes was minor, if it is compared with other studies of aging under ambient conditions. It is explained because polymeric materials experience certain swelling under continuous working conditions due to the presence CO2 and they cannot rearrange themselves as fast as under ambient conditions. 6FDA based polyimides are optimal candidates for industrial applications without losing their properties over extended period of time.

Synthesis, characterization of reduced graphene oxide nanosheets and its reinforcement effect on polymer electrolyte for dye sensitized solar cell applications

High performance polymer electrolyte for dye sensitized solar cell application has been prepared using suitable polymer matrix reinforced by reduced graphene oxide (RGO) nanosheets. RGO nanosheet has been synthesized using appropriately modified Hummer’s method. The matrix has been formulized as an optimized blend of polyethylene oxide and polyvinylidene fluoride – hexafluoro propylene (PEO/PVDF-HFP) to get expected high performance characteristics in terms of ionic conductivity, charge carrier concentration and diffusion coefficient. The same has been confirmed using electrochemical impedance spectroscopy and linear steady state voltammetry. Excellent stability of the electrolyte also has been recorded through efficiency retention study. Further, solar cell has been fabricated using the optimized formulation of PEO/PVDF-HFP/RGO nanosheet polymer electrolyte. The optimum performance in comparison with liquid electrolyte based solar cell has been authorized through photo voltaic performance study in terms of open circuit voltage (Voc), short circuit current (Jsc) and solar conversion efficiency.

Adaptive Modulation and Regeneration-Aware Routing and Spectrum Assignment in SBPP-Based Elastic Optical Networks

We focus on the Regenerator sharing, adaptive Modulation, Routing, and Spectrum assignment (RMRS) problem in a shared backup path protection based elastic optical network. Three regenerator placement strategies and the mechanisms of how to efficiently use/share the placed regenerators are proposed. An efficient heuristic algorithm is also developed for the RMRS problem to maximize regenerator and spectrum sharing among protection lightpaths with the joint consideration of modulation format and spectrum conversion capabilities of each traversed regenerator along a lightpath. Based on the performance study in terms of bandwidth blocking probability (BBP), we find that the proposed strategies and heuristic algorithm are efficient in signal regenerator utilization to significantly reduce BBP. It is also found that in addition to signal regeneration, the capabilities of modulation format conversion and spectrum conversion provided by each regenerator are helpful in reducing BBP, and as expected, the capability of spectrum conversion plays a more important role than the modulation format conversion for performance improvement. Finally, it is also interesting to find that there exists a saturation trend between the improvement of BBP performance and the increase in the number of regenerators. A limited number of signal regenerators sparsely placed in a network is sufficient to achieve a good BBP performance.

Long term performance studies of large oil-free bakelite resistive plate chamber

Several high energy physics and neutrino physics experiments worldwide require large-size RPCs to cover wide acceptances. The muon tracking systems in the Iron calorimeter (ICAL) experiment in the India based Neutrino Observatory (INO), India and the near detector in Deep Underground Neutrino Experiment (DUNE) at Fermilab are two such examples. A single gap bakelite RPC of dimension 240 cm × 120 cm, with gas gap of 0.2 cm, has been built and tested at Variable Energy Cyclotron Centre, Kolkata, using indigenous materials procured from the local market. No additional lubricant, like oil has been used on the electrode surfaces for smoothening. The chamber is in operation for > 365 days. We have tested the chamber for its long term operation. The leakage current, bulk resistivity, efficiency, noise rate and time resolution of the chamber have been found to be quite stable during the testing peroid. It has shown an efficiency > 95% with an average time resolution of ∼ 0.83 ns at the point of measurement at ∼ 8700 V throughout the testing period. Details of the long term performance of the chamber have been discussed.

Decision to paving solutions in road infrastructures based on life-cycle assessment

The construction and maintenance of a road network involve the expenditure of large budgets. In order to optimize the investments in road infrastructures, designers and decision makers should have the instruments to make the most suitable decision of paving solutions for each particular situation. The life-cycle assessment is an important tool of different road pavement solutions with this purpose. This paper presents a study concerning the life-cycle cost analysis of different flexible and semi-rigid paving alternatives, with the objective to contribute for a better support in the decision process when designing new pavement structures. The analysis was carried out using data on construction costs of certain typical pavement structures and taking into consideration appropriate performance models for each type of structure being selected. The models were calibrated using results from long term performance studies across Europe and the maintenance strategies considered have taken into account the current practice also found in the European context. Besides the life-cycle administration costs, the proposed methodology also deals with user and environmental costs through its inclusion in the decision process using multi-criteria analysis. It was demonstrated that this methodology could be a simple and useful tool in order to achieve the most adequate paving solutions of a road network, in terms of construction and maintenance activities, based simultaneously on technical, economic and environmental criteria.

Modeling and optimization of geometrical characteristics in laser trepan drilling of titanium alloy

Laser drilling has become an alternative to drilling precise holes in advanced difficult-to-cut superalloys. Due to better hole quality and capability to generate macro-size holes, laser trepan drilling is becoming more popular as compared with laser percussion drilling. This paper presents a study of laser trepan drilling process performance in terms of geometrical quality characteristics, such as hole taper and circularity for drilling small diameter hole in difficult-to-cut Titanium alloy sheet. Due to involvement of different process parameters such as laser power, pulse width, pulse frequency, workpiece thickness, material composition, cutting speed, stand of distance and assist gas pressure, the laser cutting is a highly nonlinear and complex process. To handle this nonlinearity and complexity, genetic algorithm has been applied for the optimization. We used assist gas pressure, pulse width, pulse frequency and trepanning speed as input process parameters. The effect of significant process parameters on hole characteristics are discussed on the basis of data obtained through a well designed orthogonal array experimental matrix. Reliable empirical models have been developed for different quality characteristics. Improvements of 49% and 8% have been registered in hole taper and circularity, respectively, at optimum level of process parameters.

Electroacoustic Process Study of Plasma Sparker Under Different Water Depth

The plasma sparker has been applied in oceanic high-resolution seismic exploration for decades. Normally it is towed on the water surface. This is suitable for shallow water, but if the water depth is great, the resolution will decrease dramatically, especially in the horizontal direction. This paper proposes the concept of a deep-towed plasma sparker and presents an experimental study of plasma sparker performance in terms of electric parameters, bubble behavior, and acoustic characteristics. The results show that hydrostatic pressure at a source depth ranging from 1 to 2000 m has a negligible influence on the electric parameters but a strong influence on bubble behavior, wherein both the maximum bubble radius and oscillation period are decreased. The collapse pulse vanishes when the source depth reaches 1000 m or deeper, and no bubble oscillation can be distinguished. The source level (evaluated by the expansion pulse) is also decreased as the source depth increases; moreover, the greater the discharge energy, the smaller the source level loss. The discharge energy per electrode should be greater than 20 J for the deep-towed plasma sparker, which can make the source level loss induced by hydrostatic pressure smaller than the transmission loss. The fast Fourier transform (FFT) results show that the dominant energy is around 20 kHz, which is mainly induced by the expansion pulse and its oscillation. According to the simulation results, the fundamental frequency of the acoustic waveform increases with source depth in accord with a log linear trend, and also reaches tens of kilohertz in deep water. So, before the development of deep-towed plasma sparker, a new technical solution will need to be developed to solve this problem.

Investigation of Empty Space in Nanoscale Double Gate (ESDG) MOSFET for High Speed Digital Circuit Applications

The impact of Empty Space layer in the channel region of a Double Gate (i.e. ESDG) MOSFET has been studied, by monitoring the DC, RF as well as the digital performance of the device using ATLAS 3D device simulator. The influence of temperature variation on different devices, i.e. Double Gate incorporating Empty Space (ESDG), Empty Space in Silicon (ESS), Double Gate (DG) and Bulk MOSFET has also been studied. The electrical performance of scaled ESDG MOSFET shows high immunity against Short Channel Effects (SCEs) and temperature variations. The present work also includes the linearity performance study in terms of VIP2 and VIP3. The proper bias point to get the higher linearity along with the higher transconductance and device gain has also been discussed.

Experimental and simulation of both Pd and Pd/Ag for a water gas shift membrane reactor

The study of the water gas shift reaction performance in terms of complete conversions is presented. The behaviour of a membrane reactor (MR) consisting of a tubular microporous ceramic within a thin palladium membrane was compared with a membrane reactor using a palladium/silver membrane. Membranes were developed in order to obtain a metallic layer thick enough to avoid any defects of the metallic layer and ensure infinite hydrogen selectivity with respect to other gases. The lumen of both membrane reactors was filled with the catalyst. The experiments were carried out by using nitrogen as inert gas in the streep having a flow rate ranging between 1×10−4 and 4×10−4 mol s−1 in co-current and counter-current mode in the temperature range 331–350°C and in the feed molar flow range 3.05×10−5–7.1×10−5 mol s−1. Hydrogen was the only one gas passing through both membranes. A complete separation of hydrogen from the other gases of the reaction system was obtained. The water gas shift reaction conversion was close to 100% by using the Pd/Ag membrane. A mathematical model was developed to interpret the experimental data. It described the system under isothermal conditions and considered an axial differential mass balance in terms of partial pressure for each chemical species. The simulation study and the experimental results show a satisfactory agreement and both highlight the possibility to shift towards 100% the conversion of the considered reaction.

A firm order vendor evaluation using a stratified sample

This paper examines a firm order vendor evaluation done at the Eisenhower Library, Johns Hopkins University. The entire population of firm orders for domestic publications was used as the sample for a controlled study of vendor performance in terms of order fill rate, vendor efficiency, and cost effectiveness. We attempted to ensure the accuracy of our study by stratifying the sample population, and by performing tests for statistical significance on our results. The final results of the survey helped determine the domestic vendor policy at the Eisenhower Library.

Intelligence measurements.

RECENT work by Furneaux1–3 represents certainly the most original contribution to the exact measurement of attributes of mental functioning for many decades. There is growing interest in the study of mental test performance in terms of individual items in precisely denned dimensions. It is unfortunate, however, but unavoidable, that the argument and symbolic expression used in the basic work have a forbidding complexity4. Not a little of the difficulty in following the development of Furneaux's argument is contributed by the first published paper1. In this paper a set of three fundamental equations was stated. These govern the probabilities of item solution, completion and error. All three equations appear to contain errors.