Highly Efficient Broadband Achromatic Microlens Design Based on Low-Dispersion Materials

Metalenses with achromatic performance offer a new opportunity for high-quality imaging with an ultracompact configuration;however,they suffer from complex fabrication processes and low focusing efficiency.In this study,we propose an efficient design method for achromatic microlenses on a wavelength scale using materials with low dispersion,an adequately designed convex surface,and a thickness profile distribution.By taking into account the absolute chromatic aberration,relative focal length shift(FLS),and numerical aperture(NA),microlens with a certain focal length can be realized through our realized map of geometric features.Accordingly,the designed achromatic microlenses with low-dispersion fused silica were fabricated using a focused ion beam,and precise surface profiles were obtained.The fabricated microlenses exhibited a high average focusing efficiency of 65%at visible wavelengths of 410-680 nm and excellent achromatic capability via white light imaging.Moreover,the design exhibited the advantages of being polarization-insensitive and near-diffraction-limited.These results demonstrate the effectiveness of our proposed achromatic microlens design approach,which expands the prospects of miniaturized optics such as virtual and augmented reality,ultracompact microscopes,and biological endoscopy.

Plant Long ncRNAs: A New Frontier for Gene Regulatory Control

Long non-coding RNA (lncRNA) refers to an over 200 nt functional RNA molecule that will not be translated into protein. Previously thought to be dark matters of the genome, lncRNAs have been gradually recognized as crucial gene regulators. Although tremendous progress has been made in animals and human, the study of lncRNAs in plant is still in its infancy. Here, we reviewed the biogenesis and regulation mechanisms of lncRNAs and summarized the achievements that have been made in plant lncRNA identification and functional characterization. Genome-wide identification has uncovered large amount of lncRNAs in Arabidopsis, Rice, Maize and Wheat, and more information from other plant species will be expected with the aid of deep sequencing technologies. Similar to other species, LncRNA-mediated gene regulation also widely exists in plants, even though only a few functionally characterized examples are available. Up to now, at least four divergent lncRNA-mediated regulation mechanisms have been unraveled, including target mimicry, transcription interference, PRC2 associated histone methylation and DNA methylation. lncRNAs may be involved in the regulation of flowering, male sterility, nutrition metabolism, biotic and abiotic stress response in plants.

Facile synthesized Cu-SnO2 anode materials with three-dimensional metal cluster conducting architecture for high performance lithium-ion batteries

Metal oxide anode material is one of promising candidates for the next-generation LIBs, due to its high theoretical capacity and low cost. The poor conductivity and huge volume change during charge/ discharge, however, restrict the commercialization of metal oxide anode material. In this work, we design a novel Cu-SnO2 composite derived from Cu6Sn5 alloy with three dimensional （3D） metal cluster conducting architecture. The novel Cu structure penetrates in the composite particles inducing high conductivity and space-confined SnO2, which restrict the pulverization of SnO2 during lithiation/ delithiation process. The optimized Cu-SnO2 composite anode delivers an initial discharge capacity of 933.7 mA h/g and retains a capacity of 536.1 mA h/g after 200 cycles, at 25℃ and a rate of 100 mA/g. Even at the high rate of 300 mA/g, the anode still exhibits a capacity of more than 29% of that tested at 50 mA/g. Combining with the phase and morphology analysis, the novel Cu-SnO2 composite not only has good electrical conductivity, but also possesses high theoretical capacity （995 mAh/g）, which may pave a new way for the design and construction of next-generation metal oxide anode materials with high power and cycling stability.

Enhanced energy-storage performance in a flexible film capacitor with coexistence of ferroelectric and polymorphic antiferroelectric domains

Advances in flexible electronics are driving dielectric capacitors with high energy storage density toward flexibility and miniaturization.In the present work,an all-inorganic thin film dielectric capacitor with the coexistence of ferroelectric(FE)and antiferroelectric(AFE)phases based on Pb_(0.96)La_(0.04)(Zr_(0.95)Ti_(0.05))O_(3)(PLZT)was prepared on a 2D fluorophlogopite mica substrate via a simple one-step process.The flexible capacitor exhibits a high recoverable energy density(U_(rec))of z 44.2 J/cm^(3),a large electric breakdown strength(E BDS)of 3011 kV/cm,excellent frequency stability(500 Hz-20 kHz)and high thermal stability over 30-190℃.It also demonstrates an outstanding bending endurance,which can maintain a high energy storage performance under various bending radii(R=2-10 mm)or 103 repeated bends at 4 mm.The FE phase is stable near the film surface and the interface with the bottom electrode.The AFE phase with multi-domains has incommensurate modulation structures with super-periodicity of 6.5,6.9 and 5.2.It indicates that the PLZT/LNO/F-Mica capacitor has high potential for energy storage application and may provide great opportunities for exploring new energy storage materials.

Effects of twin orientation and twin boundary spacing on the plastic deformation behaviors in Ni nanowires

Spreading twins throughout nano metals has been proved to effectively mediate the mechanical behaviors in face-centered-cubic(fcc)metals.However,the experimental investigation concerning the roles of twin boundary(TB)during deformation is rarely reported.Here,with the joint efforts of in-situ nanomechani-cal testing and theoretical studies,we provide a systematic investigation regarding the effects of TB orien-tation(θ,the angle between tensile loading direction and the normal of TB)and spacing on deformation mechanisms in Ni nanowires(NWs).As compared with single-crystalline counterparts,it is found that nano-twinned(nt)NWs withθ∼0°exhibit limited ductility,whereas TB can serve as an effective block-age to the dislocation propagation.In contrast,in nt NWs withθ∼20°and 55°,TB migration/detwinning induced by TB-dislocation reaction or partial dislocation movement dominates the plasticity,which con-tributes to enhanced NW ductility.Regarding nt NWs withθ∼90°,dislocations are found to be able to transmit through the TBs,suggesting the limited effect of TB on the NW stretchability.Furthermore,de-creasing TB spacing(λ)can facilitate the detwinning process and thus greatly enhance the ductility of NW withθ∼55°.This study uncovers the distinct roles that TB can play during mechanical deforma-tions in fcc NWs and provides an atomistic view into the direct linkage between macroscopic mechanical properties and microscopic deformation modes.

Orientation-dependent ductility and deformation mechanisms in body-centered cubic molybdenum nanocrystals

The knowledge regarding anisotropic mechanical behaviors in nanoscale body-centered cubic (bcc) metals remains obscure. Herein, we report the orientation-dependent ductility in bcc Mo nanocrystals (NCs), which exhibit poor ductility along [110] direction but possess relatively better ductility along the [001] and [112] orientations. The origin of different deformability can be traced down to the distinct deformation mechanisms: the unexpected crack nucleation and propagation induce premature fractures in [110]-oriented NCs;in contrast, deformation twinning could contribute to the enhanced ductility in [001]-oriented NCs;interestingly, we find the activation of multiple dislocation slips in [112]-oriented NCs with the highest ductility. Further molecular dynamics simulations provide deeper insights into the defect dynamics that are closely interlinked with experimental observations. Our findings advance the basic understanding of orientation-dependent mechanical properties and help to guide endeavors to architecture the microstructures of bcc metals with enhanced ductility.

Learning-based parameter prediction for quality control in three-dimensional medical image compression

Quality control is of vital importance in compressing three-dimensional(3D)medical imaging data.Optimal com-pression parameters need to be determined based on the specific quality requirement.In high efficiency video coding(HEVC),regarded as the state-of-the-art compression tool,the quantization parameter(QP)plays a dominant role in controlling quality.The direct application of a video-based scheme in predicting the ideal parameters for 3D medical image compression cannot guarantee satisfactory results.In this paper we propose a learning-based parameter prediction scheme to achieve efficient quality control.Its kernel is a support vector regression(SVR)based learning model that is capable of predicting the optimal QP from both vid-eo-based and structural image features extracted directly from raw data,avoiding time-consuming processes such as pre-encoding and iteration,which are often needed in existing techniques.Experimental results on several datasets verify that our approach outperforms current video-based quality control methods.

Large electrocaloric effect over a wide temperature span in lead-free bismuth sodium titanate-based relaxor ferroelectrics

For efficient solid-state refrigeration technologies based on electrocaloric effect(ECE),it is a great challenge of simultaneously obtaining a large adiabatic temperature change(DT)within a wide temperature span(Tspan)in lead-free ferroelectric ceramics.Here,we studied the electrocaloric effect(ECE)in(1-x)(Na_(0.5)Bi_(0.5))TiO_(3)-xCaTiO_(3)((1-x)NBT-xCT)and explored the combining effect of morphotropic phase boundary(MPB)and relaxor feature.The addition of CT not only constructs a MPB region with the coexistence of rhombohedral and orthorhombic phases,but also enhances the relaxor feature.The ECE peak appears around the freezing temperature(Tf),and shifts toward to lower temperature with the increasing CT amount.The directly measured ECE result shows that the ceramic of x=0.10,which is in the MPB region,has an optimal ECE property of DTmax=1.28 K@60℃under 60 kV/cm with a wide Tspan of 65C.The enhanced ECE originates from the electric-field-induced transition between more types of polar nanoregions and long-range ferroelectric macrodomains.For the composition with more relaxor feature in the MPB region,such as x?0.12,the ECE is relatively weak under low electric fields but it exhibits a sharp increment under a sufficiently high electric field.This work provides a guideline to develop the solidestate cooling devices for electronic components.

Catalyzing Singlet Fission by Transition Metals:Second versus Third Row Effects

The synthesis and characterization of platinum(II)and palladium(II)complexes bearing two(dimers Pt(L_(pc))_(2)Cl_(2)and Pd(L_(pc))_(2)Cl_(2)),one(monomers Pt(L_(pc))(L_(ref))Cl_(2)and Pd(L_(pc))(L_(ref))-Cl_(2)),or no(reference compounds Pt(L_(ref))_(2)Cl_(2)and Pd(L_(ref))_(2)Cl_(2))pentacene-based pyridyl ligands are presented.Photophysical properties of the dimers are probed by means of steady-state and time-resolved transient absorption measurements in compar-ison to the monomer and model compounds.Our results document that despite enhanced spin−orbit coupling from the presence of heavy atoms,intramolecular singlet fission(iSF)is not challenged by intersystem crossing.iSF thus yields correlated triplet pairs and even uncorrelated triplet excited states upon decoherence.Importantly,significant separation of the two pentacenyl groups facilitates decoupling of the two chromophores.Furthermore,the mechanism of iSF is altered depending on the respective metal center,that is,Pt(II)versus Pd(II).The dimer based on Pt(II),Pt(L_(pc))2Cl_(2),exhibits a direct pathway for the iSF and forms a correlated triplet pair with singlet−quintet spin-mixing within 10 ns in variable solvents.On the other hand,the dimer based on Pd(II),Pd(L_(pc))_(2)Cl_(2),leads to charge transfer mixing during the population of the correlated triplet pair that is dependent on solvent polarity.Moreover,Pd(L_(pc))_(2)Cl_(2)gives rise to a stable equilibrium between singlet and quintet correlated triplet pairs with lifetimes of up to 170 ns.Inherent differences in the size and polarizability,when contrasting platinum(II)with palladium(II),are the most likely rationale for the underlying trends.