Experimental observation of Weyl points

In 1929, Hermann Weyl derived the massless solutions from the Dirac equation - the relativistic wave equation for electrons. Neutrinos were thought, for decades, to be Weyl fermions until the discovery of the neutrino mass. Moreover, it has been suggested that low energy excitations in condensed matter can be the solutions to the Weyl Hamiltonian. Recently, photons have also been proposed to emerge as Weyl particles inside photonic crystals. In all cases, two linear dispersion bands in the three-dimensional (3D) momentum space intersect at a single degenerate point - the Weyl point. Remarkably, these Weyl points are monopoles of Berry flux with topological charges defined by the Chern numbers. These topological invariants enable materials containing Weyl points to exhibit a wide variety of novel phenomena including surface Fermi arcs, chiral anomaly, negative magnetoresistance, nonlocal transport, quantum anomalous Hall effect, unconventional superconductivity[15] and others [16, 17]. Nevertheless, Weyl points are yet to be experimentally observed in nature. In this work, we report on precisely such an observation in an inversion-breaking 3D double-gyroid photonic crystal without breaking time-reversal symmetry.Comment: 4 pages, 3 figure

Metamaterial Broadband Angular Selectivity

We demonstrate how broadband angular selectivity can be achieved with stacks of one-dimensionally periodic photonic crystals, each consisting of alternating isotropic layers and effective anisotropic layers, where each effective anisotropic layer is constructed from a multilayered metamaterial. We show that by simply changing the structure of the metamaterials, the selective angle can be tuned to a broad range of angles; and, by increasing the number of stacks, the angular transmission window can be made as narrow as desired. As a proof of principle, we realize the idea experimentally in the microwave regime. The angular selectivity and tunability we report here can have various applications such as in directional control of electromagnetic emitters and detectors.Comment: 5 pages, 5 figure

An Invisible Metallic Mesh

We introduce a solid material that is itself invisible, possessing identical electromagnetic properties as air (i.e. not a cloak) at a desired frequency. Such a material could provide improved mechanical stability, electrical conduction and heat dissipation to a system, without disturbing incident electromagnetic radiation. One immediate application would be towards perfect antenna radomes. Unlike cloaks, such a transparent and self-invisible material has yet to be demonstrated. Previous research has shown that a single sphere or cylinder coated with plasmonic or dielectric layers can have a dark-state with considerably suppressed scattering cross-section, due to the destructive interference between two resonances in one of its scattering channels. Nevertheless, a massive collection of these objects will have an accumulated and detectable disturbance to the original field distribution. Here we overcome this bottleneck by lining up the dark-state frequencies in different channels. Specifically, we derive analytically, verify numerically and demonstrate experimentally that deliberately designed corrugated metallic wires can have record-low scattering amplitudes, achieved by aligning the nodal frequencies of the first two scattering channels. This enables an arbitrary assembly of these wires to be omnidirectionally invisible and the effective constitutive parameters nearly identical to air. Measured transmission spectra at microwave frequencies reveal indistinguishable results for all the arrangements of the 3D-printed samples studied.Comment: 11 pages, 3 figure

Negative Group Velocity in the Absence of Absorption Resonance

Scientific community has well recognized that a Lorentzian medium exhibits anomalous dispersion behavior in its resonance absorption region. To satisfy the Krammers-Kronig relation, such an anomalous region has to be accompanied with significant loss, and thus, experimental observations of negative group velocity in this region generally require a gain-assisted approach. In this letter, we demonstrate that the negative group velocity can also be observed in the absence of absorption resonance. We show that the k-surface of a passive uniaxial Lorentzian medium undergoes a distortion near the plasma frequency. This process yields an anomalous dispersion bandwidth that is far away from the absorption resonance region, and enables the observation of negative group velocity at the plasma frequency band. Introducing anomalous dispersion in a well-controlled manner would greatly benefit the research of ultrafast photonics and find potential applications in optical delay lines, optical data storage and devices for quantum information processing

Optical Broadband Angular Selectivity

Light selection based purely on the angle of propagation is a long-standing scientific challenge. In angularly selective systems, however, the transmission of light usually also depends on the light frequency. We tailored the overlap of the band gaps of multiple one-dimensional photonic crystals, each with a different periodicity, in such a way as to preserve the characteristic Brewster modes across a broadband spectrum. We provide theory as well as an experimental realization with an all–visible spectrum, p-polarized angularly selective material system. Our method enables transparency throughout the visible spectrum at one angle—the generalized Brewster angle—and reflection at every other viewing angle.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract W911NF-13-D0001)United States. Dept. of Energy. Solid-State Solar-Thermal Energy Conversion Center (Grant DE-SC0001299

Pro-Angiogenic Role of LncRNA HULC in Microvascular Endothelial Cells via Sequestrating miR-124

Background/Aims: HULC is a multifunctional lncRNA that has pro-angiogenic function in various cancers. The present study was designed to see the role of lncRNA HULC in normal endothelial cells angiogenesis. Methods: Cell viability, apoptosis, migration, tube formation and expression levels of angiogenesis-related proteins were respectively assessed in human microvascular endothelial HMEC-1 cells after lncRNA HULC was silenced by shRNA transfection. Cross-regulation between lncRNA HULC and miR-124, and between miR-124 and MCL-1 were detected by qRT-PCR, sequence analysis, and luciferase reporter assay. Results: Silence of lncRNA HULC significantly reduced viability, migration, tube formation and protein levels of VEGF, VEGFR2, CD144 and eNOS in HMEC-1 cells. Meanwhile, silence of lncRNA HULC induced apoptosis in HMEC-1 cells, as Bcl-2 was down-regulated, Bax was up-regulated, and caspase-3 and -9 were cleaved. miR-124 expression was negatively regulated by lncRNA HULC, and HULC worked as a molecular sponge for miR-124, in having miR-124 exhausted. Besides, MCL-1 was a target gene of miR-124. Rescue assay results showed that the effects of lncRNA HULC silence on HMEC-1 cells growth, migration and angiogenesis were abolished by miR-124 suppression. Similarly, the effects of miR-124 on HMEC-1 cells were abolished by MCL-1 overexpression. Furthermore, MCL-1 activated PI3K/AKT and JAK/STAT signaling pathways. Conclusion: These findings suggest a pro-angiogenic role of lncRNA HULC in endothelial cells. The pro-angiogenic actions of lncRNA HULC may be through sponging miR-124, preventing MCL-1 from degradation by miR-124

Random Mutagenesis Applied to Reveal Factors Involved in Oxidative Tolerance and Biofilm Formation in Foodborne Cronobacter malonaticus

Cronobacter species are linked with life-treating diseases in neonates and show strong tolerances to environmental stress. However, the information about factors involved in oxidative tolerance in Cronobacter remains elusive. Here, factors involved in oxidative tolerance in C. malonaticus were identified using a transposon mutagenesis. Eight mutants were successfully screened based on a comparison of the growth of strains from mutant library (n = 215) and wild type (WT) strain under 1.0 mM H2O2. Mutating sites including thioredoxin 2, glutaredoxin 3, pantothenate kinase, serine/threonine protein kinase, pyruvate kinase, phospholipase A, ferrous iron transport protein A, and alanine racemase 2 were successfully identified by arbitrary PCR and sequencing alignment. Furthermore, the comparison about quantity and structure of biofilms formation among eight mutants and WT was determined using crystal violet staining (CVS), scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). Results showed that the biofilms of eight mutants significantly decreased within 48 h compared to that of WT, suggesting that mutating genes play important roles in biofilm formation under oxidative stress. The findings provide valuable information for deeply understanding molecular mechanism about oxidative tolerance of C. malonaticus

Genetic analysis of chikungunya viruses imported to mainland China in 2008

<p>Abstract</p> <p>Background</p> <p>Chikungunya virus (CHIKV) has caused large outbreaks worldwide in recent years, especially on the islands of the Indian Ocean and India. The virus is transmitted by mosquitoes (<it>Aedes aegypti</it>), which are widespread in China, with an especially high population density in southern China. Analyses of full-length viral sequences revealed the acquisition of a single adaptive mutation providing a selective advantage for the transmission of CHIKV by this species. No outbreaks due to the local transmission of CHIKV have been reported in China, and no cases of importation were detected on mainland China before 2008. We followed the spread of imported CHIKV in southern China and analyzed the genetic character of the detected viruses to evaluate their potential for evolution.</p> <p>Results</p> <p>The importation of CHIKV to mainland China was first detected in 2008. The genomic sequences of four of the imported viruses were identified, and phylogenetic analysis demonstrated that the sequences were clustered in the Indian Ocean group; however, seven amino acid changes were detected in the nonstructural protein-coding region, and five amino acid changes were noted in the structural protein-coding regions. In particular, a novel substitution in E2 was detected (K252Q), which may impact the neurovirulence of CHIKV. The adaptive mutation A226V in E1 was observed in two imported cases of chikungunya disease.</p> <p>Conclusions</p> <p>Laboratory-confirmed CHIKV infections among travelers visiting China in 2008 were presented, new mutations in the viral nucleic acids and proteins may represent adaptive mutations for human or mosquito hosts.</p