An energy feedback system for the MIT/Bates linear accelerator

We report the development and implementation of an energy feedback system for the MIT/Bates Linear Accelerator Center. General requirements of the system are described, as are the specific requirements, features, and components of the system unique to its implementation at the Bates laboratory. We demonstrate that with the system in operation, energy fluctuations correlated with the 60 Hz line voltage and with drifts of thermal origin are reduced by an order of magnitude.     

Design, optimization and manufacturing of wood–plastic composite pallet

This paper presents the application of an innovative method of optimization to the design of an I-shape profile used in a wood–plastic composite (WPC) pallet. The pallet was made via assembling three WPC extruded profiles manufactured in the extrusion process. The middle profile was considered to be I-shaped, a design which known to have a high load bearing capability. However, due to the characteristics of WPC products, a delicate design and thus optimization is highly required. A multi-objective-optimization program of micro-genetic algorithm was developed in Visual Basic environment to accomplish the optimization task. By specifying the dimensional variables of the profile section and applying finite elements analysis on the profile and then using the optimization program, an optimal profile section was obtained. The objective was to withstand the maximum load while yielding the minimum deflection and mass. The optimized design was used to manufacture a die and then the product was produced to validate the design. The comparison of simulations and experimental results indicted that the given design method is reasonably reliable. The final mass of the produced pallet was less than 20 kg whereas its strength against bending and distributed smooth restraint loading were greater than 500 kg and 2000 kg, respectively.     

MoOx/Ag/MoOx multilayers as hole transport transparent conductive electrodes for n-type crystalline silicon solar cells

Substitution of highly doped layers with conventional transparent conductive electrodes as carrier collecting and selective contacts in conventional crystalline silicon (c-Si) solar cell configurations is crucial in increasing affordability of solar cells by lowering material costs. In this study, oxide/metal/oxide (OMO) multilayers featuring molybdenum oxide (MoO_x) and silver (Ag) thin films are developed by thermal evaporation technique, as dopant-free hole transport transparent conductive electrodes (HTTCEs) for n-type c-Si solar cells. Semidopant-free asymmetric heterocontact (semi-DASH) solar cells on n-type c-Si utilizing OMO multilayers are fabricated. The effect of outer MoO_x layer thickness and Ag deposition rate on the photovoltaic characteristics of the fabricated semi-DASH solar cells are investigated. A comparison of front side pyramid textured and flat surface solar cells is performed to optimize the optical and electrical properties. Highest efficiency of 9.3% ± 0.2% is achieved in a pyramid textured semi-DASH c-Si solar cell with 15/10/30 nm of HTTCE structure.     

Modification and optimization of benzene alkylation process for production of ethylbenzene

In this paper, an industrial ethylbenzene production unit has been simulated and the results are compared against five-day experimental data. According to prevailing unit condition, i.e. recycled ratio of benzene, benzene selectivity, and energy consumption, the unit is not working under its optimum conditions for minimum cost of ethylbenzene production. In the current design, high amount of benzene recycle (6:1) causes to have an additional cost due to fractionation of ethylbenzene from benzene. A new approach is proposed to modify the benzene alkylation process and reduce the unit's energy consumption. In the newly designed scheme, two double-bed alkylation reactors converted into four single-bed reactors. The amount of injected ethylene, alkylation reactors temperature, and recycled stream are regulated as adjustable parameters for the optimization of the process. In the modified process, the reflux ratio reduced to 1.87 and the benzene selectivity increased. The optimized process shows a considerable decrease in the unit's energy consumption in compare to the current process. Also, the mass fraction of ethylbenzene would reach to 99.12% of purity before entering to the transalkylation reactor for further purification. Therefore, if the presented purity is acceptable for the final application, the transalkylation reactor could be eliminated from the new design.     

A single-chip dual-band direct-conversion IEEE 802.11a/b/g WLAN transceiver in 0.18-/spl mu/m CMOS

This paper presents a single-chip dual-band CMOS direct-conversion transceiver fully compliant with the IEEE 802.11a/b/g standards. Operating in the frequency ranges of 2.412-2.484 GHz and 4.92-5.805 GHz (including the Japanese band), the fractional-N PLL based frequency synthesizer achieves an integrated (10 kHz-10 MHz) phase noise of 0.54/spl deg//1.1/spl deg/ for 2/5-GHz band. The transmitter error vector magnitude (EVM) is -36/-33 dB with an output power level higher than -3/-5dBm and the receiver sensitivity is -75/-74 dBm for 2/5-GHz band for 64QAM at 54 Mb/s.     

A new predictive index for evaluating both thermal sensation and thermal response of the human body

About 20 years ago, Ring and de Dear [Ring JW, de Dear R. Temperature transients: A model for heat diffusion through the skin, thermoreceptor response and thermal sensation. Indoor Air 1991; 1(4):448–56] introduced a thermal response index (R) for evaluating the cutaneous thermoreceptor response and thermal sensation. Although the mentioned index possesses the advantages of simplicity and sensitivity, it has not been commonly used over the years. The main reason for this infrequent using is that the mentioned index is not in conformity with the ASHRAE standard thermal sensation scale. To remedy this deficiency we try to present a new predictive index by finding a relationship between the thermal response index (R) and ASHRAE thermal sensation scale. In the present study, a new thermal response index, TRESP, is introduced on the basis of Ring and de Dear model. The TRESP index has been verified by extensive comparisons with the published analytical and experimental results where a good agreement was found under both steady-state and transient conditions. Results indicate that the new index can accurately predict the thermal sensation with average absolute errors of 0.19 and 0.28 under steady-state and transient conditions, respectively.     

An advanced method for determination of loss of coolant accident in nuclear power plants

A major objective in reactor design is to provide the capability to withstand a wide range of postulated events without exceeding specified safety limits. Assessment of the consequence of hypothetical loss of coolant accident (LOCA) in primary circuit is an essential element to address fulfilment of acceptance criteria. In addition, finding the position of rupture, one could manage accident in a right direction. In this work, the transient vibration signal from a pipe rupture is used to determine the position of LOCA. A finite element formulation (Galerkin Method) is implemented to include the effect of fluid-structure interaction (FSI). The coupled equations of fluid motion and pipe displacement are solved. The obtained results are in good agreement with published data.Fast Fourier transform (FFT) provides an alternate way of representing data. Instead of representing vibration signal amplitude as a function of time, the signal is represented by the amount of information, which is contained at different frequencies. The most of frequencies of structure and fluid coupled are presented in the FFT of structural response and through it the dominant frequency of excitation is obtained.Furthermore, the power spectral density (PSD), a measurement of energy at various frequencies is worked out. MATLAB software is used to convert signals from the time to frequency domain and to obtain PSD of signals.     

Spirostane,furostane and cholestane saponins from Persian leek with antifungal activity

A phytochemical investigation of the seeds of Persian leek afforded the isolation of two new spirostane glycosides, persicosides A (1) and B (2), four new furostane glycosides, isolated as a couple of inseparable mixture, persicosides C1/C2 (3a/3b) and D1/D2 (4a/4b), one cholestane glycoside, persicoside E (5), together with the furostane glycosides ceposides A1/A2 and C1/C2 (6a/6b and 7a/7b), tropeosides A1/A2 and B1/B2 (8a/8b and 9a/9b), and ascalonicoside A1/A2 (10a/10b), already described in white onion, red Tropea onion, and shallot, respectively. Structure elucidation of the compounds was carried out by comprehensive spectroscopic analyses, including 2D NMR spectroscopy and MS spectrometry, and by chemical evidences. The chemical structure of new compounds were identified as (25S)-spirostan-2α,3β,6β-triol 3-O-[β-d-glucopyranosyl-(1 → 3)] [β-d-xylopyranosyl-(1 → 2)]-β-d-glucopyranosyl-(1 → 4)-β-d-galactopyranoside (1), (25S)-spirostan-2α,3β,6β-triol 3-O-[β-d-xylopyranosyl-(1 → 3)] [α-l-rhamnopyranosyl-(1 → 2)]-β-d-glucopyranosyl-(1 → 4)-O-β-d-galactopyranoside (2), furosta-1β,3β,22ξ,26-tetraol 5-en 1-O-β-d-glucopyranosyl (1 → 3)-β-d-glucopyranosyl (1 → 2)-β-d-galactopyranosyl 26-O-α-l-rhamnopyranosyl (1 → 2)-β-d-galactopyranoside (3a,3b), furosta-2α,3β,22ξ,26-tetraol 3-O-β-d-glucopyranosyl (1 → 3)-β-d-glucopyranosyl (1 → 2)-β-d-galactopyranosyl 26-O-β-d-glucopyranoside (4a,4b), (22S)-cholesta-1β,3β,16β,22β-tetraol 5-en 1-O-α-l-rhamnopyranosyl 16-O-α-l-rhamnopyranosyl (1 → 2)-β-d-galactopyranoside (5).     

Modeling groundwater nitrate concentrations using spatial and non-spatial regression models in a semi-arid environment

Nitrate nitrogen (NO₃^--N) from agricultural activities and in industrial wastewater has become the main source of groundwater pollution, which has raised widespread concerns, particularly in arid and semi-arid river basins with little water that meets relevant standards. This study aimed to investigate the performance of spatial and non-spatial regression models in modeling nitrate pollution in a semi-intensive farming region of Iran. To perform the modeling of the groundwater's NO₃^--N concentration, both natural and anthropogenic factors affecting groundwater NO₃^--N were selected. The results of Moran's I test showed that groundwater nitrate concentration had a significant spatial dependence on the density of wells, distance from streams, total annual precipitation, and distance from roads in the study area. This study provided a way to estimate nitrate pollution using both natural and anthropogenic factors in arid and semi-arid areas where only a few factors are available. Spatial regression methods with spatial correlation structures are effective tools to support spatial decision-making in water pollution control.     

Direct air capture from demonstration to commercialization stage: A bibliometric analysis

Concerns related to increasing CO₂ emission and its effects on global warming and climate change have been increased with increasing the global consumption of fossil fuels. One solution to respond to this challenge is the development and utilization of carbon capturing and storage technologies. Among different carbon capturing technologies, direct air capture (DAC) reduces CO₂ emissions from air. While the technology readiness level (TRL) of DAC is in the demonstration stage, identifying the commercialization research gaps and possible opportunities can help with diffusion and adoption of the technology. This research uses a knowledge discovery in research databases, based on bibliometric analysis and data mining, to understand DAC research and development's current status and future. Then, we identify the critical areas of the research gap for commercialization. The bibliometric analysis results show that DAC has not yet reached its maturity level compared with other carbon capture technologies (CCTs). However, there are different opportunities for the development of this technology. The results indicate that (a) new systematic designs, improvement in nano-catalysts, increase in the capturing capacity, (b) economic and investment improvements in combination with the environmental assessment of the optimized DAC technology, (c) assessment of future prospects, (d) integration with alternative energy supply sources especially renewable energy to respond to the required energy and process integration with current carbon emitted processes, (e) technology demonstration and readiness assessment, and (f) policy and uncertainty analysis of the market are the key areas that should be investigated for the success of this technology in the competitive market.