45 research outputs found

    High Efficiency Cross-Coupled Charge Pump Circuit with Four-Clock Signals

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    © Allerton Press, Inc. 2018A fully integrated cross-coupled charge pump circuit for boosting dc-to-dc converter applications with four-clock signals has been proposed. With the new clock scheme, this charge pump eliminates all of the reversion power loss and reduces the ripple voltage. In addition, the largest voltage differences between the terminals of all transistors do not exceed the power supply voltage for solving the gate-oxide overstress problem in the conventional charge pump circuits and enhancing the reliability. This proposed charge pump circuit does not require any extra level shifter; therefore, the power efficiency is increased. The proposed charge pump circuit has been simulated using Spectre in the TSMC 0.18 μm CMOS process. The simulation results show that the maximum voltage conversion efficiency of the new 3-stage cross-coupled circuit with an input voltage of 1.5Vis 99.8%. According to the comparison results of the conventional pump and the enhanced charge pump proposed, the output ripple voltage has been significantly reduced.Peer reviewe

    Nanostructured electrospun fibers : from superhydrophobicity to block copolymer self-assembly

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2008.Includes bibliographical references (p. 166-176).Electrospinning has emerged in recent years as a relatively easy, efficient and robust method to make ultrafine continuous fibers with diameter on the order of -100 nm from a variety of materials. As a result, numerous applications for electrospun fibers have already been demonstrated including the commercialized ones in the areas of filtration and tissue engineering. However, in most cases, the nanofibers are homogeneous; the development of external and internal nanostructures could significantly expand the applications of these fibers. The goal of this dissertation is therefore to develop controllable nanostructures for electrospun fibers with an emphasis on the understanding of structure formation and explore their unique applications. Specifically, this dissertation can be divided into two areas. The first part is related to superhydrophobic or "self-cleaning" surfaces. This has been a hot research area due to the wide applications of such materials. Electrospun fibers were first discovered in this dissertation to have sufficient surface roughness for superhydrophobic effect. In contrast to many conventional superhydrophobic surfaces, those composed of electrospun fibers are flexible, breathable and free-standing. It has been demonstrated that superhydrophobic fabrics can be made by either electrospinning a hydrophobic material or applying post-treatment to electrospun mats (e.g. through initiated chemical vapor deposition). Based on an understanding of the role of fibrous structure to create a surface of suitable topology, different strategies have been invented to enhance the superhydrophobic property and its robustness by carefully designing the external nanostructures of individual fibers using various methods such as layer-by-layer assembly. Other functionalities such as transparency and fluorescence were successfully incorporated into superhydrophobic surfaces. In particular, superhydrophobic fibrous membranes with structural colors as those displayed by some beautiful butterfly wings were produced. Besides making superhydrophobic materials from the externally nanostructured fibers, internally nanostructured electrospun fibers were also developed through the microphase separation of cylindrically confined block copolymer systems.(cont.) This is the second part of this dissertation. Continuous nanofibers with long range order internal structure were obtained by two-fluid coaxial electrospinning in which the desired block copolymer is encapsulated as the core component within a polymer shell having a high glass transition temperature (Tg), followed by proper thermal annealing of the fibers. Various interesting, unusual and sometimes unprecedented self-assembly structures of block copolymers under cylindrical confinement have been observed. Based on quantitative analyses, the confinement was found to affect both phase type and fundamental domain sizes of the block copolymer. These internally nanostructured fibers have both practical and fundamental intellectual importance. For example, these nanofibers have unique potential for applications in optics, photonics, drug delivery, and other uses because of their small diameter, unique internal structure, and continuous filamentary nature.by Minglin Ma.Ph.D

    A locally active discrete memristor model and its application in a hyperchaotic map

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    © 2022 Springer Nature Switzerland AG. Part of Springer Nature. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1007/s11071-021-07132-5The continuous memristor is a popular topic of research in recent years, however, there is rare discussion about the discrete memristor model, especially the locally active discrete memristor model. This paper proposes a locally active discrete memristor model for the first time and proves the three fingerprints characteristics of this model according to the definition of generalized memristor. A novel hyperchaotic map is constructed by coupling the discrete memristor with a two-dimensional generalized square map. The dynamical behaviors are analyzed with attractor phase diagram, bifurcation diagram, Lyapunov exponent spectrum, and dynamic behavior distribution diagram. Numerical simulation analysis shows that there is significant improvement in the hyperchaotic area, the quasi-periodic area and the chaotic complexity of the two-dimensional map when applying the locally active discrete memristor. In addition, antimonotonicity and transient chaos behaviors of system are reported. In particular, the coexisting attractors can be observed in this discrete memristive system, resulting from the different initial values of the memristor. Results of theoretical analysis are well verified with hardware experimental measurements. This paper lays a great foundation for future analysis and engineering application of the discrete memristor and relevant the study of other hyperchaotic maps.Peer reviewedFinal Accepted Versio

    Identification of a humanized mouse model for functional testing of immune-mediated biomaterial foreign body response.

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    Biomedical devices comprise a major component of modern medicine, however immune-mediated fibrosis and rejection can limit their function over time. Here, we describe a humanized mouse model that recapitulates fibrosis following biomaterial implantation. Cellular and cytokine responses to multiple biomaterials were evaluated across different implant sites. Human innate immune macrophages were verified as essential to biomaterial rejection in this model and were capable of cross-talk with mouse fibroblasts for collagen matrix deposition. Cytokine and cytokine receptor array analysis confirmed core signaling in the fibrotic cascade. Foreign body giant cell formation, often unobserved in mice, was also prominent. Last, high-resolution microscopy coupled with multiplexed antibody capture digital profiling analysis supplied spatial resolution of rejection responses. This model enables the study of human immune cell-mediated fibrosis and interactions with implanted biomaterials and devices

    Zwitterionically modified alginates mitigate cellular overgrowth for cell encapsulation

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    Foreign body reaction (FBR) to implanted biomaterials and medical devices is common and can compromise the function of implants or cause complications. For example, in cell encapsulation, cellular overgrowth (CO) and fibrosis around the cellular constructs can reduce the mass transfer of oxygen, nutrients and metabolic wastes, undermining cell function and leading to transplant failure. Therefore, materials that mitigate FBR or CO will have broad applications in biomedicine. Here we report a group of zwitterionic, sulfobetaine (SB) and carboxybetaine (CB) modifications of alginates that reproducibly mitigate the CO of implanted alginate microcapsules in mice, dogs and pigs. Using the modified alginates (SB-alginates), we also demonstrate improved outcome of islet encapsulation in a chemically-induced diabetic mouse model. These zwitterion-modified alginates may contribute to the development of cell encapsulation therapies for type 1 diabetes and other hormone-deficient diseases

    Combinatorial hydrogel library enables identification of materials that mitigate the foreign body response in primates

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    The foreign body response is an immune-mediated reaction that can lead to the failure of implanted medical devices and discomfort for the recipient. There is a critical need for biomaterials that overcome this key challenge in the development of medical devices. Here we use a combinatorial approach for covalent chemical modification to generate a large library of variants of one of the most widely used hydrogel biomaterials, alginate. We evaluated the materials in vivo and identified three triazole-containing analogs that substantially reduce foreign body reactions in both rodents and, for at least 6 months, in non-human primates. The distribution of the triazole modification creates a unique hydrogel surface that inhibits recognition by macrophages and fibrous deposition. In addition to the utility of the compounds reported here, our approach may enable the discovery of other materials that mitigate the foreign body response.Leona M. and Harry B. Helmsley Charitable Trust (3-SRA-2014-285-M-R)United States. National Institutes of Health (EB000244)United States. National Institutes of Health (EB000351)United States. National Institutes of Health (DE013023)United States. National Institutes of Health (CA151884)United States. National Institutes of Health (P41EB015871-27)National Cancer Institute (U.S.) (P30-CA14051

    All Current Mode RF Receiver Front End

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    Core-shell Hydrogel Microcapsules for Improved Islets Encapsulation

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    Islets microencapsulation holds great promise to treat type 1 diabetes. Currently used alginate microcapsules often have islets protruding outside capsules, leading to inadequate immuno-protection. A novel design of microcapsules with core–shell structures using a two-fluid co-axial electro-jetting is reported. Improved encapsulation and diabetes correction is achieved in a single step by simply confining the islets in the core region of the capsules.This is the peer reviewed version of the following article: Ma, M., Chiu, A., Sahay, G., Doloff, J. C., Dholakia, N., Thakrar, R., Cohen, J., Vegas, A., Chen, D., Bratlie, K. M., Dang, T., York, R. L., Hollister-Lock, J., Weir, G. C. and Anderson, D. G. (2013), Core–Shell Hydrogel Microcapsules for Improved Islets Encapsulation. Advanced Healthcare Materials, 2: 667–672, which has been published in final form at doi:10.1002/adhm.201200341. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. Posted with permission.</p
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