Ion acceleration in "dragging field" of a light-pressure-driven piston

We propose a new acceleration scheme that combines shock wave acceleration (SWA) and light pressure acceleration (LPA). When a thin foil driven by light pressure of an ultra-intense laser pulse propagates in underdense background plasma, it serves as a shock-like piston, trapping and reflecting background protons to ultra-high energies. Unlike in SWA, the piston velocity is not limited by the Mach number and can be highly relativistic. Background protons can be trapped and reflected forward by the enormous "dragging field" potential behind the piston which is not employed in LPA. Our one- and two-dimensional particle-in-cell simulations and analytical model both show that proton energies of several tens to hundreds of GeV can be obtained, while the achievable energy in simple LPA is below 10 GeV.Comment: submitte

Development of novel inks and approaches for printing tissues and organs

Tissue engineering is a multidisciplinary field that investigates and develops new methods to repair, regenerate and replace damaged tissues and organs, or to develop biomaterial platforms as in vitro models. Tissue engineering approaches require the fabrication of scaffolds using biomaterials or fabrication of living tissues using cells. As the demands of customized, implantable tissue/organs are increasing and becoming more urgent, conventional scaffold fabrication approaches are difficult to meet the requirements, especially for complex large-scale tissue fabrication. In this regard, three-dimensional (3D) printing attracted more interest over the past decades due to its unrivaled ability to fabricate highly customized tissues or scaffolds from patients’ medical images using computer aided design (CAD), as well as its flexibility, cost-effectiveness, and high efficiency. And more recently, 3D bioprinting can fabricate cellular constructs using a “bioink”, an aqueous composite formulation that contained live cells as a mandatory component, which is a big step towards functional organ fabrications. However, to fully realize the potential of 3D (bio)printing in tissue engineering, there are still a lot of barriers before implantable artificial organs, including but not limited to vascularization of fabricated tissue/organs, multicellular biofabrication, limited functional biomaterial, and dynamic maintenance/remodeling. To address some of these problems, this dissertation aims to develop novel inks and approaches for printing tissue and organs. Firstly, a novel bioprinting approach is developed to create user-defined complex perfusable channels within cell-laden hydrogels, which uses commercially available bioprinters, hydrogels, and open-source software. The printing process is cell-friendly, and the channels could be further endothelialized to make the cell-laden hydrogel a vascularized tissue. Secondly, novel bioinks from UV-responsive norbornene-functionalized carboxymethyl cellulose macromers are developed. The cost-effectiveness, tunability, degradability, and cytocompatibility make this bioink platform a good addition to the current available bioink library. Thirdly, considering the demands of fabricating hard degradable scaffolds for bone tissue engineering, a polyester-based ink platform with tunable bioactivity is developed. Functionalized 3D printed scaffolds show a significant impact that enhanced the osteogenesis of human stem cells. Finally, the impact of the architectures of the 3D printed scaffolds on stem cell differentiation is investigated, which demonstrated enhanced osteogenesis of human stem cells on scaffolds with wavy architectures, compared with on scaffolds with orthogonal architectures

Dissolution kinetics of model api in molten polymer excipients during batch processing

In the pharmaceutical industrial application field, hot-melt extrusion (HME) has been recently introduced to develop new solid dosage forms and products. By dissolving the poorly–soluble active pharmaceutical ingredients (API) into water-soluble polymers, the bioavailability of the Class II (with low solubility and high permeability in water) API in Biopharmaceutical Classification System (BCS) could be significantly improved in the body. For readily water-soluble API, HME provides a new approach to produce a controlled release drug system. Hence, pharmaceutical HME is a promising processing method in the pharmaceutical industry. However, HME has not been widely applied into the pharmaceutical industry. The thermal degradation of the polymer (and/or other excipients) and API are major concerns in the pharmaceutical HME process: researchers aim to dissolve the total loading of the API into the excipient within the short residence time with minimal API degradation. Therefore, the kinetics of the dissolving process should be known. In this work, the expression of dissolution process and the impact of shear rate, API concentration and API species in dissolution kinetics are determined. The viscosities of the mixture at different shear rates are also measured. A model API shall be dissolved into a polymeric excipient by conducting melt-mixing experiments using the Brabender Batch Mixer

Hashing for Similarity Search: A Survey

Similarity search (nearest neighbor search) is a problem of pursuing the data items whose distances to a query item are the smallest from a large database. Various methods have been developed to address this problem, and recently a lot of efforts have been devoted to approximate search. In this paper, we present a survey on one of the main solutions, hashing, which has been widely studied since the pioneering work locality sensitive hashing. We divide the hashing algorithms two main categories: locality sensitive hashing, which designs hash functions without exploring the data distribution and learning to hash, which learns hash functions according the data distribution, and review them from various aspects, including hash function design and distance measure and search scheme in the hash coding space

Coherence retrieval using trace regularization

The mutual intensity and its equivalent phase-space representations quantify an optical field's state of coherence and are important tools in the study of light propagation and dynamics, but they can only be estimated indirectly from measurements through a process called coherence retrieval, otherwise known as phase-space tomography. As practical considerations often rule out the availability of a complete set of measurements, coherence retrieval is usually a challenging high-dimensional ill-posed inverse problem. In this paper, we propose a trace-regularized optimization model for coherence retrieval and a provably-convergent adaptive accelerated proximal gradient algorithm for solving the resulting problem. Applying our model and algorithm to both simulated and experimental data, we demonstrate an improvement in reconstruction quality over previous models as well as an increase in convergence speed compared to existing first-order methods.Comment: 28 pages, 10 figures, accepted for publication in SIAM Journal on Imaging Science

Structures research

The main objective of the structures group is to provide quality aerospace research with the Center for Aerospace Research - A NASA Center for Excellence at North Carolina Agricultural and Technical State University. The group includes dedicated faculty and students who have a proven record in the area of structures, in particular space structures. The participating faculty developed accurate mathematical models and effective computational algorithms to characterize the flexibility parameters of joint dominated beam-truss structures. Both experimental and theoretical modelling has been applied to the dynamic mode shapes and mode frequencies for a large truss system. During the past few months, the above procedures has been applied to the hypersonic transport plane model. The plane structure has been modeled as a lumped mass system by Doctor Abu-Saba while Doctor Shen applied the transfer matrix method with a piecewise continuous Timoshenko tapered beam model. Results from both procedures compare favorably with those obtained using the finite element method. These two methods are more compact and require less computer time than the finite element method. The group intends to perform experiments on structural systems including the hypersonic plane model to verify the results from the theoretical models