Polycomb Requires Chaperonin Containing TCP-1 Subunit 7 for Maintaining Gene Silencing in Drosophila.

In metazoans, heritable states of cell type-specific gene expression patterns linked with specialization of various cell types constitute transcriptional cellular memory. Evolutionarily conserved Polycomb group (PcG) and trithorax group (trxG) proteins contribute to the transcriptional cellular memory by maintaining heritable patterns of repressed and active expression states, respectively. Although chromatin structure and modifications appear to play a fundamental role in maintenance of repression by PcG, the precise targeting mechanism and the specificity factors that bind PcG complexes to defined regions in chromosomes remain elusive. Here, we report a serendipitous discovery that uncovers an interplay between Polycomb (Pc) and chaperonin containing T-complex protein 1 (TCP-1) subunit 7 (CCT7) of TCP-1 ring complex (TRiC) chaperonin in Drosophila. CCT7 interacts with Pc at chromatin to maintain repressed states of homeotic and non-homeotic targets of PcG, which supports a strong genetic interaction observed between Pc and CCT7 mutants. Depletion of CCT7 results in dissociation of Pc from chromatin and redistribution of an abundant amount of Pc in cytoplasm. We propose that CCT7 is an important modulator of Pc, which helps Pc recruitment at chromatin, and compromising CCT7 can directly influence an evolutionary conserved epigenetic network that supervises the appropriate cellular identities during development and homeostasis of an organism.

Optical spin-symmetry breaking for high-efficiency directional helicity-multiplexed metaholograms.

Helicity-multiplexed metasurfaces based on symmetric spin-orbit interactions (SOIs) have practical limits because they cannot provide central-symmetric holographic imaging. Asymmetric SOIs can effectively address such limitations, with several exciting applications in various fields ranging from asymmetric data inscription in communications to dual side displays in smart mobile devices. Low-loss dielectric materials provide an excellent platform for realizing such exotic phenomena efficiently. In this paper, we demonstrate an asymmetric SOI-dependent transmission-type metasurface in the visible domain using hydrogenated amorphous silicon (a-Si:H) nanoresonators. The proposed design approach is equipped with an additional degree of freedom in designing bi-directional helicity-multiplexed metasurfaces by breaking the conventional limit imposed by the symmetric SOI in half employment of metasurfaces for one circular handedness. Two on-axis, distinct wavefronts are produced with high transmission efficiencies, demonstrating the concept of asymmetric wavefront generation in two antiparallel directions. Additionally, the CMOS compatibility of a-Si:H makes it a cost-effective alternative to gallium nitride (GaN) and titanium dioxide (TiO2) for visible light. The cost-effective fabrication and simplicity of the proposed design technique provide an excellent candidate for high-efficiency, multifunctional, and chip-integrated demonstration of various phenomena.

Planar Achiral Metasurfaces-Induced Anomalous Chiroptical Effect of Optical Spin Isolation.

Planar chiral structures respond differently for oppositely handed incident light, and thus can produce extraordinary chiroptical effects such as circular conversion dichroism (CCD) and asymmetric transmission (AT). Such chiroptical effects are powerful tools to realize the fundamental principle of optical spin isolation, which leads to a plethora of applications such as optical conversion diodes, chiral imaging, and sensing. Here, we demonstrate the chiroptical effects of simultaneous CCD and AT through meticulously designed single-layered achiral nanofins. Our metamolecule consists of four achiral hydrogenated amorphous silicon (a-Si:H) nanofins that are carefully oriented and optimized to exhibit considerable CCD and AT. The device demonstrates a circular conversion dichroism of 55% and an asymmetric transmission of 58% at a wavelength of 633 nm. Right-hand circularly polarized light (RHCP) is completely absorbed, while left-hand circularly polarized light (LHCP) is transmitted with a polarization conversion, making it a perfect circular polarization wave isolator with negligible backscattering (due to low reflectance). This unique design and its underlying working mechanism are described comprehensively with three different techniques. These methods validate the proposed design and its methodology. For practical applications such as imaging, the proposed design realizes the Pancharatnam-Berry (PB) phase, achieving a 0-2π phase coverage for transmitted circular polarization. For the proof of concept, a metahologram is designed and demonstrated by employing the achieved full-phase control. The measured response of the fabricated metadevice not only validates the CCD and AT but also exhibits a simulated polarization conversion efficiency of up to 71% and measured efficiency up to 52%, comparable to state-of-the-art metahologram demonstrations.

Ethylene glycol assisted three-dimensional floral evolution of BiFeO3-based nanostructures with effective magneto-electric response.

Controlled growth of nanostructures plays a vital role in tuning the physical and chemical properties of functional materials for advanced energy and memory storage devices. Herein, we synthesized hierarchical micro-sized flowers, built by the self-assembly of highly crystalline, two-dimensional nanoplates of Co- and Ni-doped BiFeO3, using a simple ethylene glycol-mediated solvothermal method. Pure BiFeO3 attained scattered one-dimensional nanorods-type morphology having diameter nearly 60 nm. Co-doping of Co and Ni at Fe-site in BiFeO3 does not destabilize the morphology; rather it generates three-dimensional floral patterns of self-assembled nanoplates. Unsaturated polarization loops obtained for BiFeO3 confirmed the leakage behaviour of these rhombohedrally distorted cubic perovskites. These loops were then used to determine the energy density of the BiFeO3 perovskites. Enhanced ferromagnetic behaviour with high coercivity and remanence was observed for these nanoplates. A detailed discussion about the origin of ferromagnetic behaviour based on Goodenough-Kanamori's rule is also a part of this paper. Impedance spectroscopy revealed a true Warburg capacitive behaviour of the synthesized nanoplates. High magneto-electric (ME) coefficient of 27 mV cm-1 Oe-1 at a bias field of -0.2 Oe was observed which confirmed the existence of ME coupling in these nanoplates.

Dilute magnetic ions mediated magneto-dielectric, optical and ferroelectric response of MgAl2O4 spinels.

Magnesium aluminate (MgAl2O4) commonly termed as spinel has been a subject of intense research due to its excellent thermal, optical and dielectric characteristics. These properties in such compounds can efficiently be tuned by introducing small contents of different transition metals. In this work, dilute contents of transition metals (Mn, Fe, Co, and Ni) are incorporated in MgAl2O4 to produce the dilute magnetic compositions of these aluminates. Crystallographic information reveals the formation of spinel cubic crystal structure with Fd-3m space group. Magnetic measurements demonstrate a clear magnetization response to an external magnetic field establishing dilute magnetic behavior of these spinels. The increase in ferroelectric characteristics with the incorporation of transition elements suggests that these materials are quite suitable for energy storage devices. A sharp variation in dielectric constant and magneto-dielectric coupling with the response to the external magnetic field, further exposes them as an excellent candidate for magneto-dielectric applications.

Twisted non-diffracting beams through all dielectric meta-axicons.

We demonstrate transmission-based all-dielectric, highly efficient (≈73.4%) and polarization-insensitive meta-axicons (for the visible wavelength of 633 nm) to generate zero and higher order Bessel beams without using additional components. The Bessel beams, owing to their diverse applications and non-diffractive properties, attract great interest from the scientific community. It is shown that the propagation length can be increased through a lower numerical aperture (∼2600 λ for NA = 0.1) whereas a higher full width at half maximum (< 0.5 λ) can be obtained for a higher numerical aperture (for NA ≥ 0.7). Our dielectric material, hydrogenated amorphous silicon (a-Si:H), provides a significant efficiency advantage over plasmonic and other high-index all-dielectric (e.g., TiO2 and GaN) metasurfaces in terms of cost, ease of fabrication, and CMOS compatibility. The finite difference time domain (FDTD) technique based numerically simulated and experimental results show excellent agreement. Due to the technological and scientific importance of the Bessel beams, the recommended material and meta-axicons provide an efficient and compact platform for realizing various advanced applications like optical manipulation, optical alignment, laser fabrication, imaging, and laser machining.

One-Pot Synthesis of Heterobimetallic Metal-Organic Frameworks (MOFs) for Multifunctional Catalysis.

A one-pot synthesis of bimetallic metal-organic frameworks (Co/Fe-MOFs) was achieved by treating stoichiometric amounts of Fe and Co salts with 2-aminoterephthalic acid (NH2 -BDC). Monometallic Fe (catalyst A) and Co (catalyst F) were also prepared along with mixed-metal Fe/Co catalysts (B-E) by changing the Fe/Co ratio. For mixed-metal catalysts (B-E) SEM energy-dispersive X-ray (EDX) analysis confirmed the incorporation of both Fe and Co in the catalysts. However, a spindle-shaped morphology, typically known for the Fe-MIL-88B structure and confirmed by PXRD analysis, was only observed for catalysts A-D. To test the catalytic potential of mixed-metal MOFs, reduction of nitroarenes was selected as a benchmark reaction. Incorporation of Co enhanced the activity of the catalysts compared with the parent NH2 -BDC-Fe catalyst. These MOFs were also tested as electrocatalysts for the oxygen evolution reaction (OER) and the best activity was exhibited by mixed-metal Fe/Co-MOF (Fe/Co batch ratio=1). The catalyst provided a current density of 10 mA cm-2 at 410 mV overpotential, which is comparable to the benchmark OER catalyst (i.e., RuO2 ). Moreover, it showed long-term stability in 1 m KOH. In a third catalytic test, dehydrogenation of sodium borohydride showed high activity (turnover frequency=87 min-1 ) and hydrogen generation rate (67 L min-1 g-1 catalyst). This is the first example of the synthesis of bimetallic MOFs as multifunctional catalysts particularly for catalytic reduction of nitroarenes and dehydrogenation reactions.

Correction: Polarisation insensitive multifunctional metasurfaces based on all-dielectric nanowaveguides.

Correction for 'Polarisation insensitive multifunctional metasurfaces based on all-dielectric nanowaveguides' by Nasir Mahmood et al., Nanoscale, 2018, 10, 18323-18330.

Improvement of salivary flow and oral wetness by a lip trainer device and sonic toothbrush in older Japanese men and women with dry mouth.

Dry mouth, caused by decreased salivary gland function and/or weak salivary stimulation, can severely affect oral health in older individuals. Therefore, the aim of this study is to evaluate whether a lip trainer device and sonic toothbrush can improve salivary flow and oral wetness in older patients complaining of dry mouth. Overall, 39 subjects aged ≥60 years who had at least 20 natural teeth were randomly assigned to use a lip trainer device (group P, n = 13) or a sonic toothbrush (group S, n = 13). The subjects who did not experience oral dryness were included as controls (group C; n = 13). The unstimulated and stimulated salivary flow rates and oral wetness were measured at baseline, 1 and 6 months. The unstimulated salivary flow significantly increased in both groups at 1 and 6 months (P < 0.05). The stimulated salivary flow was also significantly increased in group P (P < 0.01) compared with the level at baseline. However, no significant difference was observed over time in group S. Oral wetness of the tongue and buccal mucosa in group P had significantly improved at 1 and 6 months (P < 0.05). Dry mouth in older individuals may be improved by using a lip trainer device or a sonic toothbrush.

Fluoride ion assisted growth of hierarchical flowerlike nanostructures of Co/Ni ferrites and their magnetoresistive response.

One-dimensional nanorod arrays exhibiting hierarchical flowerlike morphologies, of Co and Ni based ferrites were synthesized by hydrothermal treatment and using ammonium fluoride (NH4F) as a mineralizing agent. The effects of NH4F concentration and synthesis temperature were probed to control the morphology of these nanorods that were formed as a result of crystal nucleation. It was observed that a higher concentration of NH4F leads to several other nucleation sites above these nanorods while controlled concentration of precursors and NH4F results in the synthesis of floral patterns. The specific geometries of these nanorods leads to a shape anisotropy effect resulting in increased magnetic coercive fields. To study the effect of magnetic field on the resistance and current density, impedance spectroscopy and I-V-R characteristics, respectively, were performed. Nanorods show enhanced values for resistance with the increase in magnetic field confirming the effect of magnetoresistive coupling while a decrease in current densities with increasing magnetic field highlights the potential of these structures for magnetoresistive applications.

Polarisation insensitive multifunctional metasurfaces based on all-dielectric nanowaveguides.

Metasurfaces, two dimensional (2D) metamaterials comprised of subwavelength features, can be used to tailor the amplitude, phase and polarisation of an incident electromagnetic wave propagating at an interface. Though many novel metasurfaces have been explored, the hunt for cost-effective, highly efficient, low-loss and polarisation insensitive applications is ongoing. In this work, we utilise an efficient and cost-effective dielectric material, hydrogenated amorphous silicon (a-Si:H), to create a ultra-thin transmissive surface that simultaneously controls phase. This material exhibits significantly lower absorption in the visible regime compared to standard amorphous silicon, making it an ideal candidate for various on-chip applications. Our proposed design, which works on the principle of index waveguiding, integrates two distinct phase profiles, that of a lens and of a helical beam, and is versatile due to its polarisation-insensitivity. We show how this metasurface can lead to highly concentrated optical vortices in the visible domain, whose focused ring-shaped profiles carry orbital angular momentum at the miniaturised scale.

Dielectric Meta-Holograms Enabled with Dual Magnetic Resonances in Visible Light.

Efficient transmission-type meta-holograms have been demonstrated using high-index dielectric nanostructures based on Huygens' principle. It is crucial that the geometry size of building blocks be judiciously optimized individually for spectral overlap of electric and magnetic dipoles. In contrast, reflection-type meta-holograms using the metal/insulator/metal scheme and geometric phase can be readily achieved with high efficiency and small thickness. Here, we demonstrate a general platform for design of dual magnetic resonance based meta-holograms based on the geometric phase using silicon nanostructures that are quarter wavelength thick for visible light. Significantly, the projected holographic image can be unambiguously observed without a receiving screen even under the illumination of natural light. Within the well-developed semiconductor industry, our ultrathin magnetic resonance-based meta-holograms may have promising applications in anticounterfeiting and information security.