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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. [ABSTRACT FROM PUBLISHER]

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 FROM AUTHOR]

Background: Clostridium acetobutylicum possesses two homologous adhE genes, adhE1 and adhE2, which have been proposed to be responsible for butanol production in solventogenic and alcohologenic cultures, respectively. To investigate their contributions in detail, in-frame deletion mutants of each gene were constructed and subjected to quantitative transcriptomic (mRNA molecules/cell) and fluxomic analyses in acidogenic, solventogenic, and alcohologenic chemostat cultures. Results: Under solventogenesis, compared to the control strain, only ΔadhE1 mutant exhibited significant changes showing decreased butanol production and transcriptional expression changes in numerous genes. In particular, adhE2 was over expressed (126-fold); thus, AdhE2 can partially replace AdhE1 for butanol production (more than 30 % of the in vivo butanol flux) under solventogenesis. Under alcohologenesis, only ΔadhE2 mutant exhibited striking changes in gene expression and metabolic fluxes, and butanol production was completely lost. Therefore, it was demonstrated that AdhE2 is essential for butanol production and thus metabolic fluxes were redirected toward butyrate formation. Under acidogenesis, metabolic fluxes were not significantly changed in both mutants except the complete loss of butanol formation in ΔadhE2, but numerous changes in gene expression were observed. Furthermore, most of the significantly up- or down-regulated genes under this condition showed the same pattern of change in both mutants. Conclusions: This quantitative system-scale analysis confirms the proposed roles of AdhE1 and AdhE2 in butanol formation that AdhE1 is the key enzyme under solventogenesis, whereas AdhE2 is the key enzyme for butanol formation under acidogenesis and alcohologenesis. Our study also highlights the metabolic flexibility of C. acetobutylicum to genetic alterations of its primary metabolism. [ABSTRACT FROM AUTHOR]

A novel active metasurface is proposed in this paper. The proposed metasurface can be electronically switched between the reflection and the absorption modes by a tunable component, such as a PIN diode. When the PIN diode is in the on-state, the proposed metasurface exhibits near-perfect absorptivity at 10 GHz. On the other hand, when the PIN diode is in the off-state, the proposed metasurface exhibits near-perfect reflectivity over a wide bandwidth at 10 GHz. A unit cell is designed to include a DC bias network, which yields reliable performance. [ABSTRACT FROM AUTHOR]

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. Ferredoxin-NAD(P) + oxidoreductases are important enzymes for redox balancing in n-butanol production by Clostridium acetobutylicum, but the encoding genes remain unknown. Here, the authors identify the long sought-after genes and increase n-butanol production by optimizing the levels of the two enzymes. [ABSTRACT FROM AUTHOR]

In this paper, we proposed a novel ethanol concentration sensor using microfluidic 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 absorber can detect the electrical properties of different concentration of ethanol. The performance of the proposed absorber is demonstrated using the absorption measurements of a fabricated prototype sample with waveguides. In addition, the simulated results and measurement results show good agreement. [ABSTRACT FROM AUTHOR]

The article lists the reviewers who have contributed to the journal in Volume 7 of 2014 including Gabriel Acien, Ana Arabolaza and Robert Bakker.

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 0.039\lambdag 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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM PUBLISHER]

In this study, a novel ultra-wideband antenna with a tri-band notch capability is proposed. The proposed antenna can reject worldwide interoperability for microwave access (WiMAX, 3.3–3.7 GHz), wireless local area network (WLAN) IEEE802.11a/n (5.15–5.825 GHz), and international telecommunication union (ITU, 8.025–8.4 GHz) bands. The band notch capability is achieved by merely a split ring resonator (SRR) and complementary-SRR (CSRR) patterns. The SRR under the radiating patch, the CSRR loaded on the radiating patch, and the CSRRs on the ground of the CPW feeding reject the WiMAX, WLAN, and ITU bands, respectively. The simulation and measurement results demonstrate the performance of the proposed antenna. [ABSTRACT FROM AUTHOR]

Background: Clostridium acetobutylicum and Clostridium saccharobutylicum are Gram-positive, spore-forming, anaerobic bacterium capable of converting various sugars and polysaccharides into solvents (acetone, butanol, and ethanol). The sequencing of their genomes has prompted new approaches to genetic analysis, functional genomics, and metabolic engineering to develop industrial strains for the production of biofuels and bulk chemicals. Results: The method used in this paper to knock-out, knock-in, or edit genes in C. acetobutylicum and C. saccharobutylicum combines an improved electroporation method with the use of (i) restrictionless Δupp (which encodes uracil phosphoribosyl-transferase) strains and (ii) very small suicide vectors containing a markerless deletion/insertion cassette, an antibiotic resistance gene (for the selection of the first crossing-over) and upp (from C. acetobutylicum) for subsequent use as a counterselectable marker with the aid of 5-fluorouracil (5-FU) to promote the second crossing-over. This method was successfully used to both delete genes and edit genes in both C. acetobutylicum and C. saccharobutylicum. Among the edited genes, a mutation in the spo0A gene that abolished solvent formation in C. acetobutylicum was introduced in C. saccharobutylicum and shown to produce the same effect. Conclusions: The method described in this study will be useful for functional genomic studies and for the development of industrial strains for the production of biofuels and bulk chemicals. [ABSTRACT FROM AUTHOR]