A polarization-independent ultrawideband metamaterial absorber is proposed for X-band applications. High absorptivity over an ultrawide spectrum is achieved by the combination of an artificial ...impedance surface (AIS) and a resistor-capacitor (RC) layer. In addition, the unique hexagonal shape of an AIS and RC layer enables polarization insensitivity. A circuit analysis is introduced based on a transmission-line model and shows good agreement with the full-wave analysis. Fabrication tolerance issues are considered with parametric studies in the electromagnetic simulation. The proposed absorber is fabricated on low-cost FR4 substrates, and its absorption performance is experimentally demonstrated at different angles and polarizations of incident electric fields.
In this letter, we propose a novel metamaterial absorber with angular and polarization insensitivity using multilayer technology. The miniaturized unit cell of the proposed absorber consists of a ...split-ring-cross resonator (SRCR) on the middle layer with a metallic ring on the top layer and meander line on the bottom layer. Because additional capacitance and inductance are generated by metallic patterns on the top and bottom layers, the resonance frequency is shifted to a lower frequency and the electrical size of the unit cell dramatically decreases. The principle of miniaturizing the unit cell is described in detail by a parametric study, and the performance of the proposed absorber is demonstrated by full-wave simulation and measurement. The proposed absorber can achieve a high absorptivity at 10.28 GHz and maintain it for different polarizations and incidence angles.
In this paper, we present three ultra-thin frequency selective surface (FSS) microwave absorbers on a single layer, that have three remarkable features. First, the various absorbing bandwidths can be ...obtained in our absorber by adjusting the two absorbing peaks, which are produced by two different resonance effects on the FSS. By manipulating the dimension parameters, we design the dual-band, 3-dB and 10-dB band absorbers. We achieved the absorber's thickness of 0.039λ g with the single layer due to high loss of inter-digital capacitor patterns on the FSS. Additionally, the proposed absorbers are insensitive to polarized electromagnetic (EM) waves because of the symmetric structure of the FSS. In this study, the absorber mechanism and transmission line (TL) modeling for the absorber design are studied. Each of the proposed absorbers is analyzed by using the TL equivalent circuit model and full-wave analysis. The loss factor is studied in order to demonstrate the origin of losses, and a parametric study is conducted to explain how to vary the absorbing bandwidths. The performances of each proposed absorber are also experimentally demonstrated.
In this study, we demonstrated a new class of frequency-switchable metamaterial absorber in the X-band. Eutectic gallium-indium (EGaIn), a liquid metal alloy, was injected in a microfluidic channel ...engraved on polymethyl methacrylate (PMMA) to achieve frequency switching. Numerical simulation and experimental results are presented for two cases: when the microfluidic channels are empty, and when they are filled with liquid metal. To evaluate the performance of the fabricated absorber prototype, it is tested with a rectangular waveguide. The resonant frequency was successfully switched from 10.96 GHz to 10.61 GHz after injecting liquid metal while maintaining absorptivity higher than 98%.
Abstract
Clostridium acetobutylicum
is a promising biocatalyst for the renewable production of
n
-butanol. Several metabolic strategies have already been developed to increase butanol yields, most ...often based on carbon pathway redirection. However, it has previously demonstrated that the activities of both ferredoxin-NADP
+
reductase and ferredoxin-NAD
+
reductase, whose encoding genes remain unknown, are necessary to produce the NADPH and the extra NADH needed for butanol synthesis under solventogenic conditions. Here, we purify, identify and partially characterize the proteins responsible for both activities and demonstrate the involvement of the identified enzymes in butanol synthesis through a reverse genetic approach. We further demonstrate the yield of butanol formation is limited by the level of expression of
CA_C0764
, the ferredoxin-NADP
+
reductase encoding gene and the
bcd
operon, encoding a ferredoxin-NAD
+
reductase. The integration of these enzymes into metabolic engineering strategies introduces opportunities for developing a homobutanologenic
C. acetobutylicum
strain.
In this letter, a novel, flexible inkjet-printed metamaterial absorber is proposed. The unit cell consists of a miniaturized Jerusalem-cross resonator and a completely conductive bottom. Because the ...conductive patterns are inkjet-printed using silver nanoparticle inks on paper, the proposed metamaterial absorber is flexible. It is also eco-friendly because it does not produce any chemical waste. In this letter, the working principle of the proposed miniaturized unit cell is explained, and parametric simulations are described. The inkjet-printing process is delineated, and the silver nanoparticle inks and paper used are characterized. The performance of the proposed absorber is demonstrated with a full-wave simulation and measurements at the X-band. The experimental results show that the absorption rate at 9.09 GHz is greater than 99% at the normal incidence. Angular and polarization insensitivity are also experimentally demonstrated.
In this letter, a novel frequency tunable metamaterial absorber is proposed for wireless humidity sensor applications made with natural cork. Natural cork has excellent hygroscopicity and its ...electrical properties can be changed depending on the moisture content. In this work, the absorption ratio of the proposed absorber are simulated and measured in different moisture content ( M = 0%, 1.44%, 5.88%, 13.32%, 18.8%) of the cork substrate. The resonant frequency changed from 4.92 GHz in the dry ( M = 0%) state to 3.49 GHz in the wet ( M = 18.8%) state; the measured absorptivity is higher than 90% in all moisture content values. To the best of our knowledge, it is the first metamaterial absorber using natural cork.
Engineering industrial microorganisms for ambitious applications, for example, the production of second-generation biofuels such as butanol, is impeded by a lack of knowledge of primary metabolism ...and its regulation. A quantitative system-scale analysis was applied to the biofuel-producing bacterium Clostridium acetobutylicum, a microorganism used for the industrial production of solvent. An improved genome-scale model, iCac967, was first developed based on thorough biochemical characterizations of 15 key metabolic enzymes and on extensive literature analysis to acquire accurate fluxomic data. In parallel, quantitative transcriptomic and proteomic analyses were performed to assess the number of mRNA molecules per cell for all genes under acidogenic, solventogenic, and alcohologenic steady-state conditions as well as the number of cytosolic protein molecules per cell for approximately 700 genes under at least one of the three steady-state conditions. A complete fluxomic, transcriptomic, and proteomic analysis applied to different metabolic states allowed us to better understand the regulation of primary metabolism. Moreover, this analysis enabled the functional characterization of numerous enzymes involved in primary metabolism, including (i) the enzymes involved in the two different butanol pathways and their cofactor specificities, (ii) the primary hydrogenase and its redox partner, (iii) the major butyryl coenzyme A (butyryl-CoA) dehydrogenase, and (iv) the major glyceraldehyde-3-phosphate dehydrogenase. This study provides important information for further metabolic engineering of C. acetobutylicum to develop a commercial process for the production of n-butanol.
Currently, there is a resurgence of interest in Clostridium acetobutylicum, the biocatalyst of the historical Weizmann process, to produce n-butanol for use both as a bulk chemical and as a renewable alternative transportation fuel. To develop a commercial process for the production of n-butanol via a metabolic engineering approach, it is necessary to better characterize both the primary metabolism of C. acetobutylicum and its regulation. Here, we apply a quantitative system-scale analysis to acidogenic, solventogenic, and alcohologenic steady-state C. acetobutylicum cells and report for the first time quantitative transcriptomic, proteomic, and fluxomic data. This approach allows for a better understanding of the regulation of primary metabolism and for the functional characterization of numerous enzymes involved in primary metabolism.
The use of environmentally damaging petrochemical feedstocks can be displaced by fermentation processes based on engineered microbial chassis that recycle biomass-derived carbon into chemicals and ...fuels. The stable retention of introduced genes, designed to extend product range and/or increase productivity, is essential. Accordingly, we have created multiply marked auxotrophic strains of
that provide distinct loci (
,
,
,
) at which heterologous genes can be rapidly integrated using allele-coupled exchange (ACE). For each locus, ACE-mediated insertion is conveniently selected on the basis of the restoration of prototrophy on minimal media. The
gene (
) encoding an orthogonal sigma factor (TcdR) was integrated at the
locus under the control of the lactose-inducible,
P
promoter to allow the simultaneous control of genes/operons inserted at other disparate loci (
and
) that had been placed under the control of the P
promoter. In control experiments, dose-dependent expression of a
reporter gene was observed with increasing lactose concentration. At the highest doses tested (10 mM) the level of expression was over 10-fold higher than if
was placed directly under the control of
P
and over 2-fold greater than achieved using the strong P
promoter of the
ferredoxin gene. The utility of the system was demonstrated in the production of isopropanol by the
strain carrying an integrated copy of
following the insertion of a synthetic acetone operon (
) at the
locus and a gene (
) encoding a secondary dehydrogenase at
. Lactose induction (10 mM) resulted in the production of 4.4 g/L isopropanol and 19.8 g/L Isopropanol-Butanol-Ethanol mixture.
•We proposed a novel electromagnetic-based chemical sensor that is realized by using a metamaterial absorber.•The proposed chemical sensor can detect the properties and changes in the concentration ...of liquids by analyzing the shift in absorption resonant frequency.
We proposed a novel electromagnetic-based chemical sensor that is realized by using a metamaterial absorber. The metamaterial absorber comprises a split-ring-cross resonator (SRCR) and a microfluidic channel. The SRCR can generate LC resonance that is very sensitive to changes in the effective dielectric constant around the capacitive gap. In addition, microfluidic channels can change the effective dielectric constant of the dielectric substrate by using an infinitesimal quantity of a liquid on the order of microliters. The proposed chemical sensor can detect the electrical properties of any unidentified liquids injected into the channels, as well as concentration changes in the liquids. The performance of the proposed sensor is demonstrated using the absorption measurements of a fabricated prototype sample with waveguides. In addition, the relationship between the absorption frequency and chemical concentration is demonstrated.
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