Pseudocapacitive Vanadium-based Materials toward High-Rate Sodium-Ion Storage

Sodium-ion battery materials and devices are promising candidates for largescale applications,owing to the abundance and low cost of sodium sources.Emerging sodium-ion pseudocapacitive materials provide one approach for achieving high capacity at high rates,but are currently not well understood.Herein,a comprehensive overview of the fundamentals and electrochemical behaviors of vanadium-based pseudocapacitive materials for sodium-ion storage is presented.The insight of sodium-ion storage mechanisms for various vanadium-based materials,including vanadium oxides,vanadates,vanadium sulfides,nitrides,and carbides are systematically discussed and summarized.In particular,areas for further development to improve fundamental understanding of electrochemical and structural properties of materials are identified.Finally,we provide a perspective on the application of pseudocapacitive materials in high-power and high-energy sodium-ion storage devices(e.g.,sodium-ion capacitors).

Motion Localization with Optic Flow for Autonomous Robot Teams and Swarms

The ability to localize moving objects within the environment is critical for autonomous robotic systems. This paper describes a moving object detection and localization system using multiple robots equipped with inexpensive optic flow sensors. We demonstrate an architecture capable of detecting motion along a plane by collecting three sets of one-dimensional optic flow data. The detected object is then localized with respect to each of the robots in the system.

Ion acceleration and neutron production in hybrid gas-puff z-pinches on the GIT-12 and HAWK generators

Z-pinch experiments with a hybrid configuration of a deuterium gas puff have been carried out on theHAWK(NRL,Washington,DC)and GIT-12(IHCE,Tomsk)pulsed power generators at 0.7 MA and 3MA currents,respectively.On GIT-12,neutron yields reached an average value of 231012 neutrons,and deuterons were accelerated up to an energy of 30 MeV.This was 50 times the ion energy provided by the generator driving voltage of 0.6 MV and the highest energy observed in z-pinches and dense plasma foci.To confirm these unique results independently on another device,we performed several experimental campaigns on theHAWKgenerator.Comparison of the experiments onGIT-12 andHAWKhelped us to understand which parameters are essential for optimized neutron production.Since theHAWKgenerator is of a similar pulsed power architecture as GIT-12,the experiments on GIT-12 and HAWK are important for the study of how charged-particle acceleration scales with the current.

Lead halide perovskite sensitized WSe_(2) photodiodes with ultrahigh open circuit voltages

Two-dimensional semiconductors(2DSCs)have attracted considerable interests for optoelectronic devices,but are often plagued by the difficulties in tailoring the charge doping type and poor optical absorption due to their atomically thin geometry.Herein,we report a methylammonium lead iodide perovskite(CH_(3)NH_(3)PbI_(3))/2DSC heterojunction device,in which the electric-field controllable ion migration in the perovskite layer is exploited to induce reversible electron-and hole-doping effects in the underlying monolayer tungsten diselenide(WSe_(2))to form a programmable p-n photodiode.At the same time,the CH_(3)NH_(3)PbI_(3) layer functions as a highly efficient sensitization layer to greatly boost the optical absorption and external quantum efficiency(EQE)of the resulting photodiode.By asymmetrically poling the perovskite layer,gold-contacted CH_(3)NH_(3)PbI_(3)/WSe_(2) devices show a switchable open circuit voltage up to 0.78 V,along with a high EQE of 84.3%.The integration of tunable graphene-contacts further improves the photodiode performance to achieve a highest open circuit voltage of 1.08 V and a maximum EQE of 91.3%,greatly exceeding those achieved previously in 2DSC lateral diodes.Our studies establish a non-invasive approach to switch optoelectronic functions and open up a new avenue toward high-performance reconfigurable optoelectronic devices from 2DSCs.

Multimode vibrational strong coupling in direct laser written mid-IR plasmonic MIM nano-patch antennas

Strong coupling of mid-infrared(mid-IR)vibrational transitions to optical cavities provides a means to modify and control a material’s chemical reactivity and offers a foundation for novel chemical detection technology.Currently,the relatively large volumes of the mid-IR photonic cavities and weak oscillator strengths of vibrational transitions restrict vibrational strong coupling(VSC)studies and devices to large ensembles of molecules,thus representing a potential limitation of this nascent field.Here,we experimentally and theoretically investigate the mid-IR optical properties of 3D-printed multimode metal-insulator-metal(MIM)plasmonic nanoscale cavities for enabling strong light-matter interactions at a deep subwavelength regime.We observe strong vibration-plasmon coupling between the two dipolar modes of the L-shaped cavity and the carbonyl stretch vibrational transition of the polymer dielectric.The cavity mode volume is half the size of a typical square-shaped MIM geometry,thus enabling a reduction in the number of vibrational oscillators to achieve strong coupling.The resulting three polariton modes are well described by a fully coupled multimode oscillator model where all coupling potentials are non-zero.The 3D printing technique of the cavities is a highly accessible and versatile means of printing arbitrarily shaped submicron-sized mid-IR plasmonic cavities capable of producing strong light–matter interactions for a variety of photonic or photochemical applications.Specifically,similar MIM structures fabricated with nanoscopic voids within the insulator region could constitute a promising microfluidic plasmonic cavity device platform for applications in chemical sensing or photochemistry.

De novo exploration and self-guided learning of potentialenergy surfaces

Interatomic potential models based on machine learning(ML)are rapidly developing as tools for material simulations.However,because of their flexibility,they require large fitting databases that are normally created with substantial manual selection and tuning of reference configurations.Here,we show that ML potentials can be built in a largely automated fashion,exploring and fitting potential-energy surfaces from the beginning(de novo)within one and the same protocol.The key enabling step is the use of a configuration-averaged kernel metric that allows one to select the few most relevant and diverse structures at each step.The resulting potentials are accurate and robust for the wide range of configurations that occur during structure searching,despite only requiring a relatively small number of single-point DFT calculations on small unit cells.We apply the method to materials with diverse chemical nature and coordination environments,marking an important step toward the more routine application of ML potentials in physics,chemistry,and materials science.

Improved Peptidyl Linkers for Self-Assembly of Semiconductor Quantum Dot Bioconjugates

We demonstrate improved peptide linkers which allow both conjugation to biomolecules such as DNA and self-assembly with luminescent semiconductor quantum dots.A hexahistidine peptidyl sequence was generated by standard solid phase peptide synthesis and modified with the succinimidyl ester of iodoacetamide to yield a thiol-reactive iodoacetyl polyhistidine linker.The reactive peptide was conjugated to dye-labeled thiolated DNA which was utilized as a model target biomolecule.Agarose gel electrophoresis and fluorescence resonance energy transfer analysis confirmed that the linker allowed the DNA to self-assemble with quantum dots via metal-affinity driven coordination.In contrast to previous peptidyl linkers that were based on disulfide exchange and were thus labile to reduction,the reactive haloacetyl chemistry demonstrated here results in a more stable thioether bond linking the DNA to the peptide which can withstand strongly reducing environments such as the intracellular cytoplasm.As thiol groups occur naturally in proteins,can be engineered into cloned proteins,inserted into nascent peptides or added to DNA during synthesis,the chemistry demonstrated here can provide a simple method for self-assembling a variety of stable quantum dot bioconjugates.

ADVANCES IN UNDERSTANDING DIFFICULT CASES OF TROPICAL CYCLONE TRACK FORECASTS

Although tropical cyclone track forecast errors have substantially decreased in recent decades,there are still cases each season with large uncertainties in the forecasts and/or very large track errors.As such cases are challenging for forecasters,it is important to understand the mechanisms behind the low predictability.For this purpose the research community has developed a number of tools.These tools include ensemble and adjoint sensitivity models,ensemble perturbation experiments and nudging experiments.In this report we discuss definitions of difficult cases for tropical cyclone track forecasts,diagnostic techniques to understand sources of errors,lessons learnt in recent years and recommendations for future work.

Spatially and spectrally resolved orbital angular momentum interactions in plasmonic vortex generators

Understanding the near-field electromagnetic interactions that produce optical orbital angular momentum(OAM)is crucial for integrating twisted light into nanotechnology.Here,we examine the cathodoluminescence(CL)of plasmonic vortices carrying OAM generated in spiral nanostructures.The nanospiral geometry defines a photonic local density of states that is sampled by the electron probe in a scanning transmission electron microscope(STEM),thus accessing the optical response of the plasmonic vortex with high spatial and spectral resolution.We map the full spectral dispersion of the plasmonic vortex in spiral structures designed to yield increasing topological charge.Additionally,we fabricate nested nanospirals and demonstrate that OAM from one nanospiral can be coupled to the nested nanospiral,resulting in enhanced luminescence in concentric spirals of like handedness with respect to concentric spirals of opposite handedness.The results illustrate the potential for generating and coupling plasmonic vortices in chiral nanostructures for sensitive detection and manipulation of optical OAM.

FAST discovery of an extremely radio-faint millisecond pulsar from the Fermi-LAT unassociated source 3FGL J0318.1+0252

High sensitivity radio searches of unassociated γ-ray sources have proven to be an effective way of finding new pulsars. Using the Five-hundred-meter Aperture Spherical radio Telescope(FAST) during its commissioning phase, we have carried out a number of targeted deep searches of Fermi Large Area Telescope(LAT) γ-ray sources. On February 27, 2018 we discovered an isolated millisecond pulsar(MSP), PSR J0318+0253, coincident with the unassociated γ-ray source 3 FGL J0318.1+0252. PSR J0318+0253 has a spin period of 5.19 ms, a dispersion measure(DM) of 26 pc cm-3 corresponding to a DM distance of about 1.3 kpc, and a period-averaged flux density of(~11±2) μJy at L-band(1.05-1.45 GHz). Among all high energy MSPs, PSR J0318+0253 is the faintest ever detected in radio bands, by a factor of at least ~4 in terms of L-band fluxes. With the aid of the radio ephemeris, an analysis of 9.6 years of Fermi-LAT data revealed that PSR J0318+0253 also displays strong γ-ray pulsations. Follow-up observations carried out by both Arecibo and FAST suggest a likely spectral turn-over around 350 MHz. This is the first result from the collaboration between FAST and the Fermi-LAT teams as well as the first confirmed new MSP discovery by FAST, raising hopes for the detection of many more MSPs. Such discoveries will make a significant contribution to our understanding of the neutron star zoo while potentially contributing to the future detection of gravitational waves, via pulsar timing array(PTA) experiments.