More Like this

1. A Circuit for Simultaneous Reception of Data and Power using a Solar Cell

   https://doi.org/10.1109/TGCN.2021.3087008  

   Kadirvelu, Sindhubala; Leon-Salas, Walter D.; Fan, Xiaozhe; Kim, Jongseok; Peleato, Borja; Mohammadi, Saeed; Vijayalakshmi, B. (June 2021, IEEE Transactions on Green Communications and Networking)

   null (Ed.)

   This paper presents a circuit for simultaneous reception of optical power and data using a solar cell. The circuit employs a switched-inductor boost DC-DC converter for energy harvesting and a low-power thresholding receiver for data reception. The thresholding data receiver comprises a current-sense resistor that monitors the current output of the solar cell, an instrumentation amplifier, a band-pass filter and a comparator. A system-level analysis of an optical communication system employing the proposed circuit is presented along with a circuit-level analysis and implementation. As a proof-of-concept, the proposed circuit for simultaneous power and data reception is implemented using off-the-shelf components and tested using a custom-built test setup. Measurement results, including harvested power, electronic noise and bit error rate (BER), are reported for a GaAs solar cell and a red LED light source. Results show that 223 μW of power are harvested by the DC-DC converter at a distance of 32.5 cm and a radiated power of 9.3 mW. At a modulation depth of 50% and a transmission speed of 2.5 kbps, a BER of 1.008×10^-3 is achieved. Measurement results reveal that the proposed solution exhibits a trade-off between harvested power, transmission speed and BER. 

   more » « less
2. Challenging the limits of nitrogen and oxygen content of fused rings

   https://doi.org/10.1039/d0ta05933a  

   Hu, Lu; Gao, Haixiang; Shreeve, Jean'ne M. (September 2020, Journal of Materials Chemistry A)

   null (Ed.)

   Heat of formation and density have a significant influence on the detonation performance of a compound and are greatly influenced by the nitrogen and oxygen content of a material. Here a family of new materials with high oxygen and nitrogen content was synthesized and characterized. Compound 1 has a nitrogen and oxygen content of 85.3%, with a high density (1.93 g cm −3 ) and high detonation properties (detonation velocity v D = 9503 m s −1 ; detonation pressure P = 41 GPa). The ammonium salt 3 has a nitrogen and oxygen content of 84.9%, a density of 1.86 g cm −3 , a detonation velocity of 9317 m s −1 , and acceptable sensitivities (8 J, 120 N) which are similar to those of HMX . The potassium salt ( 5 ) was characterized by single-crystal X-ray diffraction. 

   more » « less
3. Optimal Estimation of Sparse Topic Models

   Bing, X; Bunea, F; Wegkamp, M (July 2020, Journal of machine learning research)

   Dalalyan, Aynak (Ed.)

   Topic models have become popular tools for dimension reduction and exploratory analysis of text data which consists in observed frequencies of a vocabulary of p words in n documents, stored in a p×n matrix. The main premise is that the mean of this data matrix can be factorized into a product of two non-negative matrices: a p×K word-topic matrix A and a K×n topic-document matrix W. This paper studies the estimation of A that is possibly element-wise sparse, and the number of topics K is unknown. In this under-explored context, we derive a new minimax lower bound for the estimation of such A and propose a new computationally efficient algorithm for its recovery. We derive a finite sample upper bound for our estimator, and show that it matches the minimax lower bound in many scenarios. Our estimate adapts to the unknown sparsity of A and our analysis is valid for any finite n, p, K and document lengths. Empirical results on both synthetic data and semi-synthetic data show that our proposed estimator is a strong competitor of the existing state-of-the-art algorithms for both non-sparse A and sparse A, and has superior performance is many scenarios of interest. 

   more » « less
4. Recent progress in the science of complex coacervation

   https://doi.org/10.1039/D0SM00001A  

   Sing, Charles E.; Perry, Sarah L. (March 2020, Soft Matter)

   Complex coacervation is an associative, liquid–liquid phase separation that can occur in solutions of oppositely-charged macromolecular species, such as proteins, polymers, and colloids. This process results in a coacervate phase, which is a dense mix of the oppositely-charged components, and a supernatant phase, which is primarily devoid of these same species. First observed almost a century ago, coacervates have since found relevance in a wide range of applications; they are used in personal care and food products, cutting edge biotechnology, and as a motif for materials design and self-assembly. There has recently been a renaissance in our understanding of this important class of material phenomena, bringing the science of coacervation to the forefront of polymer and colloid science, biophysics, and industrial materials design. In this review, we describe the emergence of a number of these new research directions, specifically in the context of polymer–polymer complex coacervates, which are inspired by a number of key physical and chemical insights and driven by a diverse range of experimental, theoretical, and computational approaches. 

   more » « less
5. Polymer blend-filled nanoparticle films via monomer-driven infiltration of polymer and photopolymerization

   https://doi.org/10.1039/C7ME00099E  

   Qiang, Yiwei; Manohar, Neha; Stebe, Kathleen J.; Lee, Daeyeon (January 2018, Molecular Systems Design & Engineering)

   Incorporation of nanoparticles into polymer blend films can lead to a synergistic combination of properties and functionalities. Adding a large concentration of nanoparticles into a polymer blend matrix via conventional melting or solution blending techniques, however, is challenging due to the tendency of particles to aggregate. Herein, we report a straightforward approach to generate polymer blend/nanoparticle ternary composite films with extremely high loadings of nanoparticles based on monomer-driven infiltration of polymer and photopolymerization. The fabrication process consists of three steps: (1) preparing a bilayer with a nanoparticle (NP) layer atop a polymer layer, (2) annealing of the bilayer with a vapour mixture of a monomer and a photoinitiator, which undergoes capillary condensation and imparts mobility to the polymer layer and (3) exposing this film to UV light to induce photopolymerization of the monomer. The monomer used in this process is chemically different from the repeat unit of the polymer in the bilayer and is a good solvent for the polymer. The second step leads to the infiltration of the plasticized polymer, and the third step results in a blend of two polymers in the interstices of the nanoparticle layer. By varying the thickness ratio of the polymer and nanoparticle layers in the initial bilayers and changing the UV exposure duration, the volume fraction of the two polymers in the composite films can be adjusted. This versatile approach enables the design and engineering of a new class of nanocomposite films that contain a nanoscale-blend of two polymers in the interstices of a nanoparticle film, which could have combinations of unique mechanical and transport properties desirable for advanced applications such as membrane separations, conductive composite films and solar cells. Moreover, these polymer blend-filled nanoparticle films could serve as model systems to study the effect of confinement on the miscibility and morphology of polymer blends. 

   more » « less