Chiral Flat Bands: Existence, Engineering and Stability

We study flat bands in bipartite tight-binding networks with discrete translational invariance. Chiral flat bands with chiral symmetry eigenenergy E = 0 and host compact localized eigenstates for finite range hopping. For a bipartite network with a majority sublattice chiral flat bands emerge. We present a simple generating principle of chiral flat band networks and as a showcase add to the previously observed cases a number of new potentially realizable chiral flat bands in various lattice dimensions. Chiral symmetry respecting network perturbations - including disorder and synthetic magnetic fields - preserve both the flatband and the modified compact localized states. Chiral flatbands are spectrally protected by gaps, and pseudogaps in the presence of disorder due to Griffiths effects

Flat-band localization and self-collimation of light in photonic crystals

We investigate the optical properties of a photonic crystal composed of a quasi-one-dimensional flat-band lattice array through finite-difference time-domain simulations. The photonic bands contain flat bands (FBs) at specific frequencies, which correspond to compact localized states as a consequence of destructive interference. The FBs are shown to be nondispersive along the $\Gamma\rightarrow X$ line, but dispersive along the $\Gamma\rightarrow Y$ line. The FB localization of light in a single direction only results in a self-collimation of light propagation throughout the photonic crystal at the FB frequency.Comment: 18 single-column pages, 7 figures including graphical to

Topological flat Wannier-Stark bands

We analyze the spectrum and eigenstates of a quantum particle in a bipartite two-dimensional tight-binding dice network. In the absence of a dc bias, it hosts a chiral flatband with compact localized eigenstates. In the presence of a dc bias, the energy spectrum consists of a periodic repetition of one-dimensional energy band multiplets, with one member in the multiplet being strictly flat. The corresponding flatband eigenstates cease to be compact, and are localized exponentially perpendicular to the dc field direction, and superexponentially along the dc field direction. The band multiplets are characterized by a topological quantized winding number (Zak phase), which changes at specific values of the varied dc field strength. These changes are induced by gap closings between the flat and dispersive bands, and reflect the number of these closings. © 2018 American Physical Society

Unconventional Flatband Line States in Photonic Lieb Lattices

Flatband systems typically host "compact localized states"(CLS) due to destructive interference and macroscopic degeneracy of Bloch wave functions associated with a dispersionless energy band. Using a photonic Lieb lattice(LL), we show that conventional localized flatband states are inherently incomplete, with the missing modes manifested as extended line states which form non-contractible loops winding around the entire lattice. Experimentally, we develop a continuous-wave laser writing technique to establish a finite-sized photonic LL with specially-tailored boundaries, thereby directly observe the unusually extended flatband line states.Such unconventional line states cannot be expressed as a linear combination of the previously observed CLS but rather arise from the nontrivial real-space topology.The robustness of the line states to imperfect excitation conditions is discussed, and their potential applications are illustrated

Nutrigenomics: future for sustenance

Nutrigenomics deals with the effect of foods and food constituents on gene expression. It is a new concept in disease prevention and cure. Nutrigenomics conveys how nutrients influence our body to express genes, whereas nutrigenetics refers to how our body responds to nutrients. The various bioactive food components can alter the gene expression mechanisms. But our actual knowledge is so insufficient that the only use of such information may help to satisfy our imagination. If science could arrive at some more precise facts, that would have vast applications in medicine

New record of blunthead pufferfish, Sphoeroides pachygaster (Muller & Troschel, 1848 (Tetraodontiformes: Tetraodontidae) from Indian water along with DNA barcode and some biological aspects

Blunthead pufferfish, Sphoeroides pachygaster (Muller and Troschel 1848) was recorded for the first time in Indian seas. A single female specimen of S. pachygaster was caught in bottom trawl operation at 263 – 310 m depth of the Eastern Arabian Sea. Morphometric and meristic description are presented in detail and compared with the pertinent records available elsewhere. The specimen collected was fully matured with Gonado Somatic Index (GSI) of 17.9 %. Gonad occupied two-third of the abdominal cavity, ova diameters ranged between 0.45 and 0.6 mm and the absolute fecundity estimated was 0.238 million eggs. Histological studies revealed that, this species performs single spawning strategy and it is the first information on the reproduction of S. pachygaster in India. Available reports on the occurrence of this species indicated distribution in the Mediterranean Sea, Atlantic, Indian and Pacific Oceans; however, the present record confirms its distribution in the Arabian Sea. Wide variations in the meristic counts among the specimens of this species collected from various locations are also discussed. Molecular analysis of the present specimen using Mitochondrial 16S rRNA gene sequences, confirmed the identity as S. pachygaster with intra specific divergence of 00.0 – 0.04 %. This report is the first well documented, confirmed record and re-description of S. pachygaster from the Indian Ocean, which documents a new addition to the family, Tetraodontidae of the Indian ichthyofauna

Contribution of infection and vaccination to population-level seroprevalence through two COVID waves in Tamil Nadu, India.

This study employs repeated, large panels of serological surveys to document rapid and substantial waning of SARS-CoV-2 antibodies at the population level and to calculate the extent to which infection and vaccination separately contribute to seroprevalence estimates. Four rounds of serological surveys were conducted, spanning two COVID waves (October 2020 and April-May 2021), in Tamil Nadu (population 72 million) state in India. Each round included representative populations in each district of the state, totaling ≥ 20,000 persons per round. State-level seroprevalence was 31.5% in round 1 (October-November 2020), after India's first COVID wave. Seroprevalence fell to 22.9% in round 2 (April 2021), a roughly one-third decline in 6 months, consistent with dramatic waning of SARS-Cov-2 antibodies from natural infection. Seroprevalence rose to 67.1% by round 3 (June-July 2021), with infections from the Delta-variant induced second COVID wave accounting for 74% of the increase. Seroprevalence rose to 93.1% by round 4 (December 2021-January 2022), with vaccinations accounting for 63% of the increase. Antibodies also appear to wane after vaccination. Seroprevalence in urban areas was higher than in rural areas, but the gap shrunk over time (35.7 v. 25.7% in round 1, 89.8% v. 91.4% in round 4) as the epidemic spread even in low-density rural areas

Flat-band localization and self-collimation of light in photonic crystals

We investigate the optical properties of a photonic crystal (PC) composed of a quasi-one-dimensional flat-band lattice array through finite-difference time-domain simulations. The photonic bands contain flat bands (FBs) at specific frequencies, which correspond to compact localized states as a consequence of destructive interference. The FBs are shown to be nondispersive along the Г → X line, prohibiting optical transmission with incident light in x direction. On the other hand, the photonic band for the FB frequency is found to be dispersive along the Г → Y line, resulting in nonzero optical transmission. Such anisotropic optical response of the PC due to the FB localization of light in a single direction only results in a self-collimation of light propagation throughout the PC at the FB frequency. © 2019, The Author(s