arXiv subjects

Jun Ni

Publications and source records attributed to Jun Ni.

24 records · Page 2Linked to original sources

arXiv2018

Invited Article: 4D Printing as a New Paradigm for Manufacturing with Minimum Energy Consumption

4D printing is a new manufacturing paradigm that combines stimuli-responsive materials, mathematics, and multi-material additive manufacturing to yield encoded multi-material structures with intelligent behavior over time. This emerging field has received growing interests from various disciplines such as space exploration, renewable energy, bioengineering, textile industry, infrastructures, soft robotics, and so on. Here, as a first attempt, we consider the energy aspect of 4D printing. By a thermodynamic analysis, we obtain the theoretical limit of energy consumption in 4D printing and prove that 4D printing can be the most energy-efficient manufacturing process. Before that, we clearly underpin 4D printing as a new manufacturing process and identify its unique attributes.

physics.app-ph↗

arXiv2018

Laws of 4D printing

The main difference between 3D and 4D printed structures is one extra dimension that is smart evolution over time. However, currently, there is no general formula to model and predict this extra dimension. Here, by starting from fundamental concepts, we derive and validate a universal bi-exponential formula that is required to model and predict the fourth D of 4D printed multi-material structures. 4D printing is a new manufacturing paradigm to elaborate stimuli-responsive materials in multi-material structures for advanced manufacturing (and construction) of advanced products (and structures). It conserves the general attributes of 3D printing (such as the elimination of molds, dies, and machining) and further enables the fourth dimension of products and structures to provide intelligent behavior over time. This intelligent behavior is encoded (usually by an inverse mathematical problem) into stimuli-responsive multi-materials during printing and is enabled by stimuli after printing. Here, we delve into the fourth dimension and reveal three general laws that govern the time-dependent shape-shifting behaviors of almost all (photochemical-, photothermal-, solvent-, pH-, moisture-, electrochemical-, electrothermal-, ultrasound-, enzyme-, etc.-responsive) multi-material 4D structures. We demonstrate that two different types of time-constants govern the shape-shifting behavior of almost all the multi-material 4D printed structures over time. Our results starting from the most fundamental concepts and ending with governing equations can serve as general design principles for future research in the 4D printing field, where the time-dependent behaviors should be understood, modeled, and predicted, correctly. Future software and hardware developments in 4D printing can also benefit from these results.

physics.app-ph↗

arXiv2018

Autonomous Driving System Design for Formula Student Driverless Racecar

This paper summarizes the work of building the autonomous system including detection system and path tracking controller for a formula student autonomous racecar. A LIDAR-vision cooperating method of detecting traffic cone which is used as track mark is proposed. Detection algorithm of the racecar also implements a precise and high rate localization method which combines the GPS-INS data and LIDAR odometry. Besides, a track map including the location and color information of the cones is built simultaneously. Finally, the system and vehicle performance on a closed loop track is tested. This paper also briefly introduces the Formula Student Autonomous Competition (FSAC) in 2017.

cs.RO↗

arXiv2015

Topological p+ip superconductivity in doped graphene-like single-sheet materials BC$_3$

We theoretically study exotic superconducting phases in graphenelike single-sheet material BC$_3$ doped to its type-II Van Hove singularity whose saddle point momenta are {\it not} time-reversal-invariant. From combined renormalization group analysis and RPA calculations, we show that the dominant superconducting instability induced by weak repulsive interactions is in the time-reversal-invariant $p+ip$ pairing channel because of the interplay among dominant ferromagnetic fluctuations, subleading spin fluctuations at finite momentum, and spin-orbit coupling. Such time-reversal-invariant $p+ip$ superconductivity has nontrivial $\mathbb{Z}_2$ topological invariant. Our results show that doped BC$_3$ provides a promising route to realize a genuine 2D helical $p+ip$ superconductor.

cond-mat.str-el↗

arXiv2015

Double-jump stochastic volatility model for VIX: evidence from VVIX

The paper studies the continuous-time dynamics of VIX with stochastic volatility and jumps in VIX and volatility. Built on the general parametric affine model with stochastic volatility and jump in logarithm of VIX, we derive a linear relation between the stochastic volatility factor and VVIX index. We detect the existence of co-jump of VIX and VVIX and put forward a double-jump stochastic volatility model for VIX through its joint property with VVIX. With VVIX index as a proxy for the stochastic volatility, we use MCMC method to estimate the dynamics of VIX. Comparing nested models on VIX, we show the jump in VIX and the volatility factor is statistically significant. The jump intensity is also statedependent. We analyze the impact of jump factor on the VIX dynamics.

q-fin.CP↗

arXiv2012

Flat Bands near Fermi Level of Topological Line Defects on Graphite

Flat bands play an important role in the study of strongly correlated phenomena, such as ferromagnetism, superconductivity, and fractional quantum Hall effect. Here we report direct experimental evidence for the presence of flat bands, close to the Fermi level, in one-dimensional topological defects on graphite seen as a pronounced peak in the tunnelling density of states. Our ab initio calculations indicate that the flat bands with vanishing Fermi velocity originate from sp2 dangling bonds (with antibonding nature) of undercoordinated carbon atoms at the edges of the defects. We further demonstrate that the presence of flat bands could be a universal behavior of 1D defects of graphene/graphite with undercoordinated carbon atoms at the edges of the defects.

cond-mat.mes-hall↗