Analysis of a systematic error appearing as a periodic fluctuation in the frequency-domain absorption spectra of metamaterial absorbers.

A metamaterial is a periodic structure which can be considered as an effective medium that exhibits an atypical response for a corresponding range of electromagnetic (EM) waves. For metamaterial absorbers (MMA) working in the GHz regime, the frequency-domain-measurement setup consisting of two horn antennas connected to a network analyzer is widely used. The absorption spectra obtained with this setup usually exhibits some periodic fluctuation (PF) across the entire range of measurement. Typically, this PF in the frequency-domain spectrum is ignored because it is distinct from major features and has a small amplitude. We have examined the PF through a finite-difference time-domain (FDTD) simulation in order to verify the validity of such assumption. We concluded that the PF is caused by a part of EM wave radiated by an antenna (source), and directly propagating to another (detector), resulting in an interference between this leaked EM wave and the one reflected from the sample. We have successfully reproduced the periodic fluctuation of the experimental spectra by FDTD simulation. We examined the angle of incidence dependence. The amplitude increases because the amount of leaked EM waves increases, while the periodicity increases because the distance between the two antennas increases, resulting in a shortened path difference. We conclude that the PF is a systematic error which can be safely ignored.

Experimental Realization of Tunable Metamaterial Hyper-transmitter.

We realized the tunable metamaterial hyper-transmitter in the microwave range utilizing simple planar meta-structure. The single-layer metamaterial hyper-transmitter shows that the transmission peak occurs at 14 GHz. In case of the dual-layer one, it is possible to control the transmission peak from 5 to 10 GHz. Moreover, all the transmission peaks reveal transmission over 100%. We experimentally and theoretically investigated these phenomena through 3-dimensional simulation and measurement. The reason for being over 100% is also elucidated. The suggested hyper-transmitter can be used, for example, in enhancing the operating distance of the electromagnetic wave in Wi-Fi, military radar, wireless power transfer and self-driving car.

Model for regulation of VAMP721/722-mediated secretion: growth vs. stress responses.

The PEN1-SNAP33-VAMP721/722 exocytic pathway is a conserved immunity-associated secretory pathway between monocotyledonous barley and dicotyledonous Arabidopsis plants. In Arabidopsis, this secretory pathway plays an additional role in plant growth and development. However, how this pathway can be manipulated to engage in both growth/development and immunity remains to be answered. To understand its regulation, we recently analyzed the expression of VAMP721/722 genes whose products drive secretory vesicles to the target plasma membrane. By investigating their transcript and protein levels, we found that plants distinctly control the activity of this secretory pathway during biotic or abiotic stress responses. Since stress responses are in general accompanied by growth inhibition in plants and since plants in nature are simultaneously threatened by a number of environmental stresses, understanding of this growth/immunity-related secretory pathway would help to generate more efficiently growth/immunity-balancing plants.

Requirement of vesicle-associated membrane protein 721 and 722 for sustained growth during immune responses in Arabidopsis.

Extracellular immune responses to ascomycete and oomycete pathogens in Arabidopsis are dependent on vesicle-associated secretion mediated by the SNARE proteins PEN1 syntaxin, SNAP33 and endomembrane-resident VAMP721/722. Continuous movement of functional GFP-VAMP722 to and from the plasma membrane in non-stimulated cells reflects the second proposed function of VAMP721/722 in constitutive secretion during plant growth and development. Application of the bacterium-derived elicitor flg22 stabilizes VAMP721/722 that are otherwise constitutively degraded via the 26S proteasome pathway. Depletion of VAMP721/722 levels by reducing VAMP721/722 gene dosage enhances flg22-induced seedling growth inhibition in spite of elevated VAMP721/722 abundance. We therefore propose that plants prioritize the deployment of the corresponding secretory pathway for defense over plant growth. Interstingly, VAMP721/722 specifically interact in vitro and in vivo with the plasma membrane syntaxin SYP132 that is required for plant growth and resistance to bacteria. This suggests that the plant growth/immunity-involved VAMP721/722 form SNARE complexes with multiple plasma membrane syntaxins to discharge cue-dependent cargo molecules.

Vesicle-associated membrane proteins 721 and 722 are required for unimpeded growth of Arabidopsis under ABA application.

Soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) proteins are core factors in driving vesicle fusion with target membranes, which is critical in eukaryotes having distinct subcellular organelles. Amongst them, vesicle-associated membrane proteins (VAMP) 721 and 722 are involved in plant growth/development and immunity. In the course of stress responses, plants often show retarded growth. The precise mechanism of this retardation is not fully understood. The plant stress hormone abscisic acid (ABA), which can cause growth inhibition, down-regulates VAMP721/722 protein levels but not transcript levels. Enhanced growth inhibition and early depletion of the amount of VAMP721/722 caused by ABA in haploinsufficient VAMP721(+/-)VAMP722(-/-) and VAMP721(-/-)VAMP722(+/-) plants suggest that ABA impedes plant growth in part by reducing VAMP721/722 proteins. Since VAMP721/722 are engaged in exocytosis, our data implies that ABA-induced growth retardation may result from diminished secretory activities leading to decreased transport of molecules required for plant growth in the plasma membrane and cell wall.