Optimized Hierarchical Power Oscillations Control for Distributed Generation Under Unbalanced Conditions

Control structures have critical influences on converter-interfaced distributed generations (DG) under unbalanced conditions. Most of previous works focus on suppressing active power oscillations and ripples of DC bus voltage. In this paper, the relationship between amplitudes of the active power oscillations and the reactive power oscillations are firstly deduced and the hierarchical control of DG is proposed to reduce power oscillations. The hierarchical control consists of primary and secondary levels. Current references are generated in primary control level and the active power oscillations can be suppressed by a dual current controller. Secondary control reduces the active power and reactive power oscillations simultaneously by optimal model aiming for minimum amplitudes of oscillations. Simulation results show that the proposed secondary control with less injecting negative-sequence current than traditional control methods can effectively limit both active power and reactive power oscillations.Comment: Accepted by Applied Energ

Modulation and Long-term Release of Cardiac Fibroblast Secretome to Enhance Cardiac Cell Survival under Hypoxia

The irreversible damage to the heart caused by myocardial infarction (MI) leads to over one million deaths in the United States every year. There are several approaches to treat MI, such as angioplasty, redirected blood flow, and electrical medical devices, but they cannot promote new cardiac tissue generation, thus leading to potential high risk of re-surgeries. To overcome this limitation, stem cell therapy is regarded as a promising method. However, the implantation of stem cells has ethical and safe concern and the efficiency is limited due to low cell engraftment. Moreover, the effect of stem cell is predominantly attributed to paracrine effect. Therefore, the delivery of stem cell secretome is expected to be a prominent approach, since it has potential to achieve similar effect without causing safety and ethical problems with cell implantation. Among different cells, cardiac fibroblast (CF) is the largest cell population in the heart, and its secretome has been shown to protect cardiomyocytes under hypoxia. Thus, the objective of this work is to deliver CF secretome to the heart after MI. In the first part of this thesis, CF secretome was optimized in vitro by adjusting environmental oxygen condition and substrate stiffness. We found that the secretome collected under hypoxic condition (1% O2) and soft substrate (6 kPa) can most effectively boost the survival of endothelial cells and cardiomyocytes under hypoxia. In the second part, we developed platelet-membrane coated nanoparticles as a delivery vehicle for CF secretome. The nanoparticles had the capability of sustainedly releasing various growth factors such as PDGF, VEGF and bFGF. This secretome delivery system has potential to promote cardiac repair after MI

The endocytosis and intracellular fate of nanomedicines: Implication for rational design

AbstractNanomedicines employ multiple endocytic pathways to enter cells. Their following fate is interesting, but it is not sufficient understood currently. This review introduces the endocytic pathways, presents new technologies to confirm the specific endocytic pathways and discusses factors for pathway selection. In addition, some intriguing implication about nanomedicine design based on endocytosis will also be discussed at the end. This review may provide new thoughts for the design of novel multifunctional nanomedicines

Enhanced GPS Measurements Simulation for Space-oriented Navigation System Design

AbstractAt the stage of preliminary scheme and algorithm design for spaceborne navigation systems, a precise and high-fidelity software global positioning system (GPS) simulator is a necessary and feasible testing facility in laboratory environments, with consideration of the tradeoffs where possible. This article presents a software GPS measurements simulator on the L1 C/A code and carrier signal for space-oriented navigation system design. The simulator, coded in MATLAB language, generates both C/A code pseudorange and carrier phase measurements. Mathematical models in the Earth centered inertial (ECI) frame are formulated to simulate the GPS constellation and to generate GPS measurements. A series of efficient measures are investigated and utilized to rationalize the enhanced simulator, in terms of ephemeris data selection, space ionospheric model and range rate calculation, etc. Such an enhanced simulator has been facilitating our current work for designing a space integrated GPS/inertial navigation system (INS) navigation system. Consequently, it will promote our future research on space-oriented navigation system

Design of a Carburizing Treatment of Steel Base Gear in the Materials Science Course

Diffusion PDE Application to Carburizing Treatment of Steel Base Gear An introductory materials-science course is required in the mechanical engineering curriculum of many universities. This article describes an example effort to incorporate programming, diffusion transfer, heat treatment process and mechanical-property determination as an integral part of the materials-science course instruction. This effort was undertaken in order to give students additional experience in Fick’s 1st and 2nd laws and in-depth understanding of physics and mathematics involved in diffusion analysis. We chose to focus on Fick’s second law because its applications are not restricted to the materials-science field [1]. As a matter of fact, the same form of parabolic partial differential equation also finds applications in financial derivatives pressure, heat transfer, and soil mechanics consolidation [2,3]. For instance, the diffusion coefficients all share the units of m2/s [2]. From the perspective of materials science, diffusion refers to an observable net flux of atoms or other species [1,4,5]. It depends upon the concentration gradient and temperature. It is vital for the carburization process (Carbon diffusion into steel), determining the proper hardness values not only for surface hardness of gear teeth but also for carbon penetration into specified depths. Students will be required to write a MATLAB program with input parameters of diffusion couple to calculate the atomic flux on the basis of diffusivity and concentration gradient. They are able to predict heat furnace design temperature and time required to heat the metal using error function values and one-dimensional diffusion equation with the specified boundary conditions. This paper focuses on the application of diffusion to material science engineering and provides an example of how diffusion may be adopted in an integrated instruction of materials science instructions. Keywords: Materials Science, Diffusion, Carburizing, PDE Solutions, MATLAB Programmin

Application of Computational Tools to Spaghetti-Based Truss Bridge Design

Application of Computational Tools to Spaghetti-Based Truss Design Statics and Strength of Materials are two foundational courses for Mechanical/Civil Engineering. In order to assist students in better understanding and applying concepts to a meaningful design task, SolidWorks and theoretical calculation were used for a spaghetti-bridge design contest with the constraints of given maximum weight and allowable support-material weight. As the first step of this iterative designing process, both extrude feature and structural member were introduced to model planar bridge trusses. Then SolidWorks’ Statics module was used to run FEA analysis of the structural performance in efforts to optimize the load-carrying capacity of the structure. To make simulation possible, a universal material-response testing apparatus was used to measure the key mechanical properties of the bridge material, namely spaghetti bundles, and add it to SolidWorks’ material database. The building stage started upon completion of design refinement, and the project culminated with performance prediction (as to the weakest spots of the structure) and testing. The theoretical calculation went down two paths—A full truss analysis was performed based on the method of joints, along with more thorough FEA analysis through coding, before comparing the internal forces, displacements, etc., with the simulation results. Through the holistic design process, the course turned out more engaging and students gained experience of solving a typical real-life engineering problem involving trade-off between economy and quality