Showing papers by "Li Li published in 2019"

Ultrasensitive Tunable Terahertz Sensor With Graphene Plasmonic Grating

Abstract: We propose an ultrasensitive tunable terahertz (THz) sensor which consists of single-layer graphene-based gratings integrated with a Fabry–Perot cavity through numerical simulation. The excitation of standing-wave graphene surface plasmon polaritons can make the probing field strongly confined in a gap cavity. This provides an excellent platform for ultrasensitive and high figure-of-merit (FOM) refractive index sensing at the THz band. Our full-wave electromagnetic simulations show a frequency sensitivity as high as 4.2 THz per refractive index unit and an FOM beyond 12.5 at normal incidence in the THz regime. At oblique incidence, the operation angle for effective THz sensing can be maintained as wide as 75° without inducing degeneration of the sensitivity and FOM. The sensing performance can be readily tuned by electrically controlling the chemical potential of graphene. The proposed graphene plasmonic grating scheme is a promising candidate for the development of on-chip integrated THz biochemical sensors.

Strain-Gradient-Controlled Disorder Dynamics in Chemically Substituted Ferroelectrics

Abstract: A strain gradient $\ensuremath{ abla}S$ deeply influences the properties of a disordered ferroelectric, but the exact mechanism whereby $\ensuremath{ abla}S$ controls the disorder dynamics, especially in bulk material, is still largely unknown. The authors create a macroscopic strain gradient in KTa${}_{1\ensuremath{-}x}$Nb${}_{x}$O${}_{3}$ single crystals by coupling a composition gradient and 180\ifmmode^\circ\else\textdegree\fi{} domains, and field-dependent electro-optic effects reveal the $\ensuremath{ abla}S$-controlled disorder dynamics and local dipole behaviors. This work provides a basis for understanding and harnessing the potential of disordered ferroelectrics, and the $\ensuremath{ abla}S$ design method is valuable for developing functional materials and devices.

Structural variation, functional differentiation and expression characteristics of the AP2/ERF gene family and its response to cold stress and methyl jasmonate in Panax ginseng C.A. Meyer

Abstract: The APETALA2/Ethylene Responsive Factor (AP2/ERF) gene family has been shown to play a crucial role in plant growth and development, stress responses and secondary metabolite biosynthesis. Nevertheless, little is known about the gene family in ginseng ( Panax ginseng ), an important traditional medicinal herb in Asia and North America. Here, we report the systematic analysis of the gene family present in ginseng using several transcriptomic databases. A total of 189 putative AP2/ERF genes, defined as PgERF001 through PgERF189 . The 93 PgERF genes that have the complete AP2 domain in their open reading frames were classified into five subfamilies, DREB, ERF, AP2, RAV and Soloist. The DREB subfamily and ERF subfamily were further clustered four and six groups, respectively, compared to the 12 groups of these subfamilies found in Arabidopsis. Gene ontology categorized these 397 transcripts of the 189 PgERF genes into eight functional subcategories, suggesting their functional differentiation and they have been especially enriched for the nucleic acid binding transcription factor activity subcategory. The expression activity and networks of the 397 PgERF transcripts have substantially diversified across tissues, developmental stages and genotypes. Then, the expression change of six PgERF genes randomly selected from DREB subfamily, i.e., PgERF073 , PgERF079 , PgERF110 , PgERF115 , PgERF120 and PgERF128 responding to cold stress suggesting that DREB subfamily genes played an important role in cold resistance of ginseng. Finally, we studied the responses of the PgERF genes to methyl jasmonate (MeJA). 288 (72.5%) of the 397 PgERF gene transcripts responded to the MeJA treatment, with 136 up-regulated and 152 down-regulated, indicating that most members of the PgERF gene family are responsive to MeJA. These results provide resources and knowledge necessary for family-wide functional analysis of the PgERF genes in ginseng and related species.

Selection and validation of reference genes desirable for gene expression analysis by qRT-PCR in MeJA-treated ginseng hairy roots.

Abstract: Ginseng is a valuable herb of traditional Chinese medicine and ginsenosides, the main bioactive components of ginseng, have been proven to have multiple functions in human therapies and health. Methyl jasmonate (MeJA) is an elicitor that has been demonstrated to have a vital influence on ginsenoside biosynthesis. Quantitative real-time polymerase chain reaction (qRT-PCR) has been widely used in quantification of gene expressions. Here, we report the selection and validation of reference genes desirable for normalization of gene expressions quantified by qRT-PCR in ginseng hairy roots treated with MeJA. Twelve reference genes were selected as candidate genes, and their expressions were quantified by qRT-PCR, and analyzed by geNorm, NormFinder and BestKeeper. CYP and EF-1α were shown to be the most stable reference genes in geNorm, CYP was the most stable reference gene in NormFinder, and 18S was the most stable reference gene in BestKeeper. On this basis, we further quantified the relative expression levels of four genes encoding key enzymes that are involved in ginsenoside biosynthesis using CYP and 18S as the reference genes, respectively. Moreover, correlation analysis was performed between the quantified expressions of four genes and the ginsenoside content in MeJA-treated ginseng hairy roots. The results of relative expressions of the four genes quantified using CYP as the reference gene and their significant correlations with the ginsenoside content were better than those using 18S as the reference gene. The CYP gene, hence, was concluded as the most desirable reference gene for quantification of the expressions of genes in MeJA-treated ginseng hairy roots. This finding, therefore, provides information useful for gene research in ginseng, particularly in MeJA-treated ginseng hairy roots, which includes identification and characterization of genes involved in ginsenoside biosynthesis.

Graphene/liquid crystal hybrid tuning terahertz perfect absorber.

Abstract: We present, by simulations, a metastructured graphene/liquid crystal hybrid tuning terahertz perfect absorber that consists of graphene disk resonator arrays above a metallic layer separated with liquid crystal substrate. The liquid crystal refractive index and the graphene Fermi level are utilized to implement double-tuning operation to push the spectra scanning limit of the terahertz absorber. Our simulations demonstrate high performance of a near-linear broad tuning region and near-unity absorbance with wide incident angle and polarization independence. The range of the resonant frequency scan is notably enlarged at a spectral ratio of as high as Δf/f=50% while ensuring absorbance beyond 90%. Such graphene/liquid crystal hybrid tuning scheme would be preferable to push the working-band limit of terahertz perfect absorbers.

A Positioning Method based on Low-Frequency Artificial Magnetic Signal

Abstract: This work presents a low-frequency artificial magnetic signal positioning method based on aiming at the fact that GNSS signals are susceptible to the influences of weather and location which may even lead to being unable to realize or proceed localization services. The localization method, first proposed by Sheinker. et al. [1], is used for many real-time, low power applications such as indoor robot navigation. On top of that, a low-frequency artificial magnetic signal localization method based on cuckoo search algorithm is proposed. The effectiveness of the localization method is verified by simulation and experiments. Results show that the scheme has the characteristics of strong adaptability and high precision within the range of stable low-frequency magnetic signal.