366 research outputs found
Python scripts to test gravity with the dynamics of wide binary stars
No full textA wide binary sample within 200 pc, a virtual Newtonian sample, and several python scripts are provided to supplement Chae, K.-H. 2023, to be published in the Astrophysical Journal (arXiv:2305.04613).
'gaia_dr3_MSMS_d200pc.csv' is the sample of wide binaries extracted from Gaia DR3 (El-Badry, Rix, & Heintz 2021). It includes all information needed for statistical analyses.
A virtual Newtonian sample 'Newton_dr3_MSMS_d200pc_1.csv' was generated with 'make_Newton_sample_gaia.py'. The user can generate his/her own Newtonian sample.
A mass-magnitude (and inverse) relation is needed as an input. Three options are provided.
'accel_plane_ortho_wb.py' can be used to produce figures from one Monte Carlo set. The user is encouraged to start with this code to have a feel for what is going on.
'run_wb.py', based on the python class 'accel_ortho_wb.py', calculates an ensemble of Monte Carlo sets of accelerations. It uses 'multiprocessing' and requires a significant number of cores. The author has been using 128 cores/threads.
The user is strongly encouraged to read carefully Chae, K.-H. 2023, to be published in the Astrophysical Journal (arXiv:2305.04613) before using these codes.
Questions can be directed to [email protected] or [email protected].
Last updated 2023-06-21.Chae, K.-H. 2023, to be published in the Astrophysical Journal (arXiv:2305.04613
Python scripts to test gravity with the dynamics of wide binary stars
No full textA wide binary sample within 200 pc, a virtual Newtonian sample, and several python scripts are provided to supplement Chae, K.-H. 2023, to be published in the Astrophysical Journal (arXiv:2305.04613).
'gaia_dr3_MSMS_d200pc.csv' is the sample of wide binaries extracted from Gaia DR3 (El-Badry, Rix, & Heintz 2021). It includes all information needed for statistical analyses.
A virtual Newtonian sample 'Newton_dr3_MSMS_d200pc_1.csv' was generated with 'make_Newton_sample_gaia.py'. The user can generate his/her own Newtonian sample.
A mass-magnitude (and inverse) relation is needed as an input. Three options are provided.
'accel_plane_ortho_wb.py' can be used to produce figures from one Monte Carlo set. The user is encouraged to start with this code to have a feel for what is going on.
'run_wb.py', based on the python class 'accel_ortho_wb.py', calculates an ensemble of Monte Carlo sets of accelerations. It uses 'multiprocessing' and requires a significant number of cores. The author has been using 128 cores/threads.
The user is strongly encouraged to read carefully Chae, K.-H. 2023, to be published in the Astrophysical Journal (arXiv:2305.04613) before using these codes.
Questions can be directed to [email protected] or [email protected].
Last updated 2023-06-21.Chae, K.-H. 2023, to be published in the Astrophysical Journal (arXiv:2305.04613
Practical Development of Si Anodes for High-Energy Lithium Ion Batteries
No full textDepartment of Energy Engineering (Battery Science and Technology)Since the first commercialization of the lithium ion battery (LIB), LIB has played a significant role as a power source for electric devices. As increasing energy demands with the emergence of the electric vehicle and the energy storage system, improving the energy density of LIB has been recognized as one of the most important issue for battery researchers. Accordingly, the high-capacity materials have been investigated to break the theoretical capacity limit of current LIB chemistry with the carbonaceous anode and the lithium metal oxide cathode. In terms of the anode, silicon (Si) has received great attention because of its low discharge potential and 10 times greater theoretical capacity than the state-of-the-art graphite. However, the intrinsic hurdle of Si anodes, which is the huge volume expansion (300%) during battery operation, retards the application to the practical LIB. Therefore, the concrete strategies for overcoming the challenge are required in order to improve the energy density with utilizing Si anodes. For over twenty years, the nanoengineering has considerably improved the electrochemical performance of the Si anode by alleviating the intensified stress and strain from the volume change. However, there is a significant gap between the nanoengineered Si anode in academic field and the commercial LIB system in terms of the synthesis of Si anode, the battery manufacturing, and the electrochemical cell design. In this regards, to implement the Si anodes in commercial LIBs, several commercial factors such as the scalability, the rational cost, and performance feasibility, should be considered at the beginning of the development. Accordingly, herein, I have covered a comprehensive review about the co-utilization of graphite and Si anodes for commercial LIBs, the development of high-capacity Si anode for commercial high energy LIB, the benchmarking comparison of industrially-developed Si anode, and finally the remaining issues regarding the practical implementation of Si anode.
In the Chapter 1, the graphite Specifically, the development of the Si anodes would be presented with physicochemical analysis, and the practical utilization of Si anodes for high-energy LIB would be discussed. Furthermore, in order to compare the performance of the developed Si anodes, benchmarking with industrial samples would be conducted with the electrochemical characterization and the failure mechanism analysis.
In chapter 2, the high-capacity Si anodes for commercial high energy LIB is proposed with Fe-Cu-Si composite. FeCuSi is built up with Si nanoparticles and numerous nano-sized metal silicides as a form of a secondary particle. In this design, the micron-sized secondary particle exhibits high tap density which is easy to handle in the battery manufacturing process, and the numerous voids between Si nanoparticles effectively accommodated volume expansion of Si. In addition, the metal silicides such as iron silicide and copper silicide reduced interparticle contact resistance between Si nanoparticles. To investigate the commercial feasibility, the graphite-blended electrode with FeCuSi composite was fabricated under the commercial standard. It exhibited the superior electrochemical performances compared to industrially developed SiOx and FeSi anodes.
In chapter 3, the benchmark comparison of industrially developed Si anodes including Si nanolayer-embedded graphite composite, carbon-coated SiOx, Si-containing graphite/carbon composite, has been presented. The benchmarking comparison was performed in graphite-Si blending system (fixed reversible specific capacity of 420 mAh/g) under the industrial electrode density (> 1.6 g/cc), areal capacity (> 3 mAh/cm2), and a small amount of binder (3 wt%). In addition, the one-to-one comparison has included essential items of both material characterization including laser diffraction particle size analysis, BET surface area, tap density, SEM, and HR-TEM, as well as the electrochemical analysis including half-cell and full-cell tests with measuring electrode volume expansion. As a result, the Si nanolayer-embedded graphite composite exhibited a great compatibility with conventional graphite.
In chapter 4, I discuss the critical issues of the practical implementation of Si anode in high-energy LIBs. The electrochemical cell design has been systematically presented with proper examples. I emphasize that the influence of the electrochemical cell design on the battery performances when aimed at high volumetric energy density. In addition, based on the electrochemical design, the limit on the electrode swelling of Si anodes in terms of energy density is suggested. Furthermore, the origin of differences in the capacity fading between in the half-cell and in the full-cell is carefully figured out. Finally, I propose the potential future direction regarding with the electrode swelling, the capacity fading, and the feasibility study.clos
Real-time hybrid simulation for a base-isolated building with the transmissibility-based semi-active controller
No full text© The Author(s) 2022.The transmissibility-based semi-active (TSA) controller was developed in the existing study by the authors, which can effectively enhance the performance of base-isolated buildings under both strong long- and short-period earthquake ground motions. Since the performance of the TSA controller was only evaluated with numerical simulation in the existing study, this paper further validates its performance experimentally by conducting real-time hybrid simulation (RTHS). A three-story base isolated building was designed based on a simplified design procedure, where the base isolation system of the building consisted of three different devices, that is, a magneto-rheological (MR) damper, rubber bearing, and linear bearings. The base isolation system was experimentally tested with the MR damper controlled by the TSA controller, and the building superstructure was analytically modeled. It was shown that the TSA controller makes the system damping high under long-period ground motions and low under short-period ground motions, which performed uniquely as intended. As a result, the isolator displacement was effectively reduced under long-period ground motions, while the story drift and acceleration responses were also reduced under short-period ground motions, all of which are difficult to achieve at the same time using passive damping only.N
Unsymmetrical fluorinated malonatoborate as an amphoteric additive for high-energy-density lithium- ion batteries
No full textHigh-capacity Si-embedded anodes and Li-rich cathodes are considered key compartments for post lithium-ion batteries with high energy densities. However, the significant volume changes of Si and the irreversible phase transformation of Li-rich cathodes prevent their practical application. Here we report lithium fluoromalonato(difluoro)borate (LiFMDFB) as an unusual dual-function additive to resolve these structural instability issues of the electrodes. This molecularly engineered borate additive protects the Li-rich cathode by generating a stable cathode electrolyte interphase (CEI) while simultaneously tuning the fluoroethylene carbonate (FEC)-oriented solid electrolyte interphase (SEI) on the Si-graphite composite (SGC) anode. The complementary electrolyte design utilizing both LiFMDFB and FEC exhibited an improved capacity retention of 85%, a high Coulombic efficiency of ???99.5%, and an excellent energy density of ???400 W h kg−1 in Li-rich/SGC full cells at a practical mass loading after 100 cycles. This dual-function additive approach offers a way to develop electrolyte additives to build a more favorable SEI for high-capacity electrodes
A Closer Look at the Personality-Turnover Relationship: Criterion Expansion, Dark Traits, and Time
No full textRecent advances in the personality and turnover literatures suggest the importance of expanding current turnover criteria, incorporating dark personality traits, and examining the role of time in these relationships. The present study investigates these issues by considering both the speed and the reasons for leaving, examining a wider range of personality variables as predictors by including both “bright” and “dark” traits, and exploring the potential moderating effect of time in such predictions. Data were collected from a sample of 617 employees working in an electronics manufacturing firm in the United States. Using a Bayesian survival analysis framework, we found that dark traits were just as useful in predicting turnover outcomes as traditional personality traits and best predicted the specific turnover reasons, “deviant behavior” and “no call no show.” Investigating the role of time showed that job satisfaction and intellectual curiosity (i.e., Openness) grew in predictive strength over the course of organizational tenure but that the time-dependent effects of other predictors were negligible. © 2016, The Author(s) 2016.11Nssciscopu
Stationary Navier-Stokes equations in an exterior domain, and some integral identities for Euler and Navier-Stokes equations
No full textWe study: 1) the stationary Navier-Stokes equations in a two-dimensional exterior domain, 2) some integral identities for the Euler and the Navier-Stokes equations. For the first topic, we consider the non-homogenous boundary value problem in a two-dimensional exterior domain together with a prescribed condition at infinity and establish existence of a solution to the problem provided that the boundary value on the boundary of the domain is close to a potential flow; this assumption allows some large boundary value. Indeed, we utilize results of Galdi in 2004 on the Oseen equations, a linearization around a constant nonzero vector. Then we apply ideas used in Russo and Starita's work (in 2008) in three dimension, which is to perturb around a potential flow; in conjunction with the compactness of some linear operator related to the Oseen equations, which is a result again of Galdi in 2004.
For the second topic, Dobrokhotov and Shafarevich in 1994 proved some integral identities for the Euler and Navier-Stokes equations. Chae in 2012 proved these integral identities on a hyperplane for a weak solution with some integrability assumptions on the solution. In this thesis, we prove the integral identities on a hyperplane with some different integrability assumptions. It also furnishes a Liouville type theorem as an immediate application, providing a different approach to some of the results of Hamel and Nadirashvili in 2017, 2019, Chae and Constantin in 2015.Ph.D.Includes bibliographical reference
An Antiaging Electrolyte Additive for High???Energy???Density Lithium???Ion Batteries
No full textHigh???capacity Li???rich layered oxide cathodes along with Si???incorporated graphite anodes have high reversible capacity, outperforming the electrode materials used in existing commercial products. Hence, they are potential candidates for the development of high???energy???density lithium???ion batteries (LIBs). However, structural degradation induced by loss of interfacial stability is a roadblock to their practical use. Here, the use of malonic acid???decorated fullerene (MA???C60) with superoxide dismutase activity and water scavenging capability as an electrolyte additive to overcome the structural instability of high???capacity electrodes that hampers the battery quality is reported. Deactivation of PF5 by water scavenging leads to the long???term stability of the interfacial structures of electrodes. Moreover, an MA???C60???added electrolyte deactivates the reactive oxygen species and constructs an electrochemically robust cathode???electrolyte interface for Li???rich cathodes. This work paves the way for new possibilities in the design of electrolyte additives by eliminating undesirable reactive substances and tuning the interfacial structures of high???capacity electrodes in LIBs
Challenges in Accommodating Volume Change of Si Anodes for Li-Ion Batteries
No full textSi has been considered as a promising alternative anode for next-generation Li-ion batteries (LIBs) because of its high theoretical energy density, relatively low working potential, and abundance in nature. However, Si anodes exhibit rapid capacity decay and an increase in the internal resistance, which are caused by the large volume changes upon Li insertion and extraction. This unfortunately limits their practical applications. Therefore, managing the total volume change remains a critical challenge for effectively alleviating the mechanical fractures and instability of solid-electrolyte-interphase products. In this regard, we review the recent progress in volume-change-accommodating Si electrodes and investigate their ingenious structures with significant improvements in the battery performance, including size-controlled materials, patterned thin films, porous structures, shape-preserving shell designs, and graphene composites. These representative approaches potentially overcome the large morphologic changes in the volume of Si anodes by securing the strain relaxation and structural integrity in the entire electrode. Finally, we propose perspectives and future challenges to realize the practical application of Si anodes in LIB systems.close0
Inside Cover: Challenges in Accommodating Volume Change of Si Anodes for Li‐Ion Batteries (ChemElectroChem 11/2015)
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