Reversible Non-Volatile Electronic Switching in a Near Room Temperature van der Waals Ferromagnet

The ability to reversibly toggle between two distinct states in a non-volatile method is important for information storage applications. Such devices have been realized for phase-change materials, which utilizes local heating methods to toggle between a crystalline and an amorphous state with distinct electrical properties. To expand such kind of switching between two topologically distinct phases requires non-volatile switching between two crystalline phases with distinct symmetries. Here we report the observation of reversible and non-volatile switching between two stable and closely-related crystal structures with remarkably distinct electronic structures in the near room temperature van der Waals ferromagnet Fe$_{5-\delta}$GeTe$_2$. From a combination of characterization techniques we show that the switching is enabled by the ordering and disordering of an Fe site vacancy that results in distinct crystalline symmetries of the two phases that can be controlled by a thermal annealing and quenching method. Furthermore, from symmetry analysis as well as first principle calculations, we provide understanding of the key distinction in the observed electronic structures of the two phases: topological nodal lines compatible with the preserved global inversion symmetry in the site-disordered phase, and flat bands resulting from quantum destructive interference on a bipartite crystaline lattice formed by the presence of the site order as well as the lifting of the topological degeneracy due to the broken inversion symmetry in the site-ordered phase. Our work not only reveals a rich variety of quantum phases emergent in the metallic van der Waals ferromagnets due to the presence of site ordering, but also demonstrates the potential of these highly tunable two-dimensional magnets for memory and spintronics applications

Mmwave massive MIMO: one joint beam selection combining cuckoo search and ant colony optimization

Abstract In order to degrade the inter-user interference caused by the same beam selected for different users in mmWave massive MIMO systems, this paper proposes a joint beam selection combining cuckoo search (CS) and ant colony optimization (ACO) (referred to as CSACO). Differently from the existing interference-aware beam selection, a candidate beam set (CBS) for all users is created according to the power distribution of the beamspace channel, thereby all users can be classified into non-interfering users (NIUs) and interfering users (IUs), and NIUs will be assigned the beams with large power directly, while for IUs, the beams are selected by the CSACO; in the proposed CSACO, all beams for IUs are regarded as an optimizable individual, which is continuously evolved towards the direction of sum-rate maximization. Simulation results verify that the proposed beam selection can obtain the higher sum-rate and energy efficiency compared with the existing ones

Rescue the Failed Half-ZFN by a Sensitive Mammalian Cell-Based Luciferase Reporter System

<div><p>ZFN technology is a powerful research tool and has been used for genome editing in cells lines, animals and plants. The generation of functional ZFNs for particular targets in mammalian genome is still challenging for an average research group. The modular-assembly method is relatively fast, easy-to-practice but has a high failure rate. Some recent studies suggested that a ZFP with low binding activity might be able to form a working ZFN pair with another binding active half-ZFP. In order to unveil the potential ZFP candidates among those with low binding activities, this paper established a highly sensitive mammalian cell-based transcriptional reporter system to assess the DNA binding activities of ZFPs by inserting multiple copies of ZFN target sequence fragment (TSF) of an interested gene (e. g., hPGRN or hVEGF). Our results showed that this system increased the screening sensitivity up to 50-fold and markedly amplified the differences in the binding activities between different ZFPs. We also found that the targeted chromosomal gene repair efficiency of each hPGRN or hVEGF ZFN pair was in proportion with the combination of the binding activities of the ZFL (Left zinc finger) and ZFR (Right zinc finger). A hPGRN ZFR with low binding ability was able to form a biological active ZFN if combined with a hPGRN ZFL with relatively high binding ability. Lastly, site-specific genome editing by hPGRN ZFNs generated by this system was confirmed by sequencing, and the PGRN knock-out cell line showed significantly decreased cell growth compared with the control. Our system will provide a valuable tool for further optimizing the nucleases with regard to specificity and cytotoxicity.</p> </div

The target sequences, corresponding key amino acid sequences and binding affinities of hVEGF2 zinc fingers (ZF).

<p>Binding affinities are expressed as mean fold-activation of transcription in the EZSS system.</p

hPGRN ZFN mediated site-specific genomic integration in mammalian genome.

<p>(A) The PCR analysis of site-specific integration of exogenous expression cassette into the genome of human PGRN in HepG2 cells. Lane1: DNA marker; Lane2: the fragment amplified from the cells treated by hPGRN ZFN plus donor by using two pairs of primers: one located downstream of the down arm in the genome, the other located in exogenous expression cassette; Lane3: the fragment amplified from the cells treated by donor only by using similar primers to Lane2; Lane4: the fragment amplified from the cells treated by hPGRN ZFN plus donor by using two pairs of primers: one located upstream of the up arm in the genome, the other located in exogenous expression cassette; Lane5: the fragment amplified from the cells treated by donor only by using similar primers to Lane 4. (B) eGFP expression by the expression cassette integrated in the genome of HepG2 cell line. HepG2 cells were screened and cloned in the presence of neomycin and GCV post co-transfection of hPGRN ZFN and the donor vector pAd5-E1-hPGRN-CMV-eGFP-T2A-neo-up/down-PGK-TK-T2A-mcherry. (C) The sequence of the region containing down arm of the homologous fragment and 3 terminus of the exogenous expression cassette. (D) The sequence of the region containing up arm of the homologous fragment and 5 terminus of the exogenous expression cassette.</p

Binding capacities of assembled ZFPs assessed by the EZSS system.

<p>(A) A cartoon of the EZSS system, which is composed of a transcription factor (TF)-expressing vector and a reporter vector. The reporter vector is composed of ZFN target sequence fragment (TSF), a mini-CMV promoter and a firefly luciferase reporter gene. The transcription factor (TF)-expressing vector expresses a fusion protein consisting of p65AD and a ZFP. (B) The binding activities of hVEGF1 ZFL and hVEGF1 ZFR. Different copy numbers of TSF for hVEGF1 ZFL or ZFR were inserted upstream of the mini-CMV promoter. The two vectors of the EZSS system were co-transfected into HEK 293 cells. Forty-eight hrs post-transfection, the firefly luciferase and internal control, renilla luciferase activities were quantified. The ratio of firefly luciferase and renilla luciferase activity (FL/RL) was used to reflect the ZFP binding activities.</p

The relative luciferase units revealed by EZSS for hPGRN ZFPs with 1 X TSF, 7 X TSF and the ratios.

<p>The relative luciferase units revealed by EZSS for hPGRN ZFPs with 1 X TSF, 7 X TSF and the ratios.</p

The binding activities of hVEGF2 ZFPs (A, B) and hPGRN ZFPs (C, D) determined by luciferase activities.

<p>Fold activation of transcription in the EZSS system was determined by the ratio of luciferase activity from HEK 293 cells transfected with reporter vector and the plasmid carrying a zinc finger array fused to p65 AD to that from HEK 293 cells transfected with reporter vector only. All determinations were performed in triplicate and the means and standard deviations of these means are shown.</p

Decreased cell growth of PGRN knock-out cell line as determined by the MTT assay.

<p>The control HepG2 or PGRN K.O. HepG2 cells were plated at 5,000 cells/well in 96-well plates with 200 µl DMEM medium and incubated in a humidified atmosphere containing 5% CO2 at 37°C. Then 20 µl 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) stock solution (5 mg/ml) was added to each well at different time points. After 4 h of incubation, the medium was removed carefully and the converted dye was solubilized with 200 µl DMSO. The absorbance of the converted dye was measured at a wavelength of 570 nm. The data are expressed as mean ± SD of three independent experiments. **P<0.001.</p

Tests for population differences of <i>KLOTHO</i> methylation and important parameters.

<p>Tests for population differences of <i>KLOTHO</i> methylation and important parameters.</p