SS-IL: Separated Softmax for Incremental Learning

We consider class incremental learning (CIL) problem, in which a learning agent continuously learns new classes from incrementally arriving training data batches and aims to predict well on all the classes learned so far. The main challenge of the problem is the catastrophic forgetting, and for the exemplar-memory based CIL methods, it is generally known that the forgetting is commonly caused by the prediction score bias that is injected due to the data imbalance between the new classes and the old classes (in the exemplar-memory). While several methods have been proposed to correct such score bias by some additional post-processing, e.g., score re-scaling or balanced fine-tuning, no systematic analysis on the root cause of such bias has been done. To that end, we analyze that computing the softmax probabilities by combining the output scores for all old and new classes could be the main source of the bias and propose a new CIL method, Separated Softmax for Incremental Learning (SS-IL). Our SS-IL consists of separated softmax (SS) output layer and ratio-preserving (RP) mini-batches combined with task-wise knowledge distillation (TKD), and through extensive experimental results, we show our SS-IL achieves very strong state-of-the-art accuracy on several large-scale benchmarks. We also show SS-IL makes much more balanced prediction, without any additional post-processing steps as is done in other baselines

Ruthenium nanocrystal decorated vertical graphene nanosheets@Ni foam as highly efficient cathode catalysts for lithium-oxygen batteries

The electrochemical performance of lithium-oxygen (Li-O2) batteries can be markedly improved through designing the architecture of cathode electrodes with sufficient spaces to facilitate the diffusion of oxygen and accommodate the discharge products, and optimizing the cathode catalyst to promote the oxygen reduction reaction and oxygen evolution reaction (OER). Herein, we report the synthesis of ruthenium (Ru) nanocrystal-decorated vertically aligned graphene nanosheets (VGNS) grown on nickel (Ni) foam. As an effective binder-free cathode catalyst for Li-O2 batteries, the Ru-decorated VGNS@Ni foam can significantly reduce the charge overpotential via the effects on the OER and achieve high specific capacity, leading to an enhanced electrochemical performance. The Ru-decorated VGNS@Ni foam electrode has demonstrated low charge overpotential of ~0.45 V and high reversible capacity of 23 864 mAh g−1 at the current density of 200 mA g−1, which can be maintained for 50 cycles under full charge and discharge testing condition in the voltage range of 2.0-4.2 V. Furthermore, Ru nanocrystal decorated VGNS@Ni foam can be cycled for more than 200 cycles with a low overpotential of 0.23 V under the capacity curtained to be 1000 mAh g−1 at a current density of 200 mA g−1. Ru-decorated VGNS@Ni foam electrodes have also achieved excellent high rate and long cyclability performance. This superior electrochemical performance should be ascribed to the unique three-dimensional porous nanoarchitecture of the VGNS@Ni foam electrodes, which provide sufficient pores for the diffusion of oxygen and storage of the discharge product (Li2O2), and the effective catalytic effect of Ru nanocrystals on the OER, respectively. Ex situ field emission scanning electron microscopy, X-ray diffraction, Raman and Fourier transform infrared measurements revealed that Ru-decorated VGNS@Ni foam can effectively decompose the discharge product Li2O2, facilitate the OER and lead to a high round-trip efficiency. Therefore, Ru-decorated VGNS@Ni foam is a promising cathode catalyst for rechargeable Li-O2 batteries with low charge overpotential, long cycle life and high specific capacity

MnO/C core-shell nanorods as high capacity anode materials for lithium-ion batteries

MnO/C core–shell nanorods were synthesized by an in situ reduction method using MnO2 nanowires as precursor and block copolymer F127 as carbon source. Field emission scanning electron microscopy and transmission electron microscopy analysis indicated that a thin carbon layer was coated on the surfaces of the individual MnO nanorods. The electrochemical properties were evaluated by cyclic voltammetry and galvanostatic charge–discharge techniques. The as-prepared MnO/C core–shell nanorods exhibit a higher specific capacity than MnO microparticles as anode material for lithium ion batteries

Investigation of discharge reaction mechanism of lithium/liquid electrolyte/sulfur battery

The influence of current density on the discharge reaction of Li–S batteries is investigated by discharge tests (first discharge curve), differential scanning calorimetry (DSC), X-ray diffraction (XRD) (discharge products), and scanning electron microscopy (the surface morphology of sulfur electrodes). The first discharge capacity and the plateau potential both decrease with increasing current density. When the current density is increased from 100 to 1600 mA g−1 S, the discharge capacity decreases from 1178 to 217 mAh g−1 S. When the Li–S battery is discharged at low current density, i.e., below 400 mA g−1 S, elemental sulfur is fully converted to Li2S, which is observable from XRD and DSC data. Only one plateau is observed in the discharge curve for current densities above 400 mA g−1 S. Part of the elemental sulfur still remains after discharging at high current densities (over 800 mA g−1 S). Thus the discharge capacity at high current density is smaller than that at low current density due to un-reacted elemental sulfur after discharge

Polyhedral magnetite nanocrystals with multiple facets: Facile synthesis, structural modelling, magnetic properties and application for high capacity lithium storage

Polyhedral magnetite nanocrystals with multiple facets were synthesised by a low temperature hydrothermal method. Atomistic simulation and calculations on surface attachment energy successfully predicted the polyhedral structure of magnetite nanocrystals with multiple facets. X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission microscopy confirmed the crystal structure of magnetite, which is consistent with the theoretical modelling. The magnetic property measurements show the superspin glass state of the polyhedral nanocrystals, which could originate from the nanometer size of individual single crystals. When applied as an anode material in lithium ion cells, magnetite nanocrystals demonstrated an outstanding electrochemical performance with a high lithium storage capacity, a satisfactory cyclability, and an excellent high rate capacity

Electrochemical properties of Fe2O3 thin film fabricated by electrostatic spray deposition for lithium-ion batteries

Fe2O3 thin films are important for the fabrication of rechargeable lithium microbatteries. Thin films of Fe2O3 were prepared by the electrostatic spray deposition (ESD) technique by using iron chloride as the precursor. The thin film electrodes, without inert additives such as polymer binder and conducting material, can deliver a first discharge capacity of 912 mA h g−1 and retain a discharge capacity of 537 mA h g−1 at a current density of 200 mA g−1 to the 100th cycle. The coulombic efficiency of the Fe2O3 thin-film electrode was over 96% after several cycles

The Origin of an Unexpected Increase in NH3-SCR Activity of Aged Cu-LTA Catalysts

We have recently reported an increase in low-temperature NH3-SCR activity of the copper-exchanged (Cu/Al = 0.50), high-silica (Si/Al = 23) LTA catalyst when it is hydrothermally aged at 1023-1173 K. Here we demonstrate that this unexpected phenomenon originates from the migration of Cu+ ions present inside the sod cages of Cu-LTA to the vacant single 6-rings which accompanies their oxidation to Cu2+ ions during (hydro)thermal aging. Hence, the sod cages, which are inaccessible to almost all reactant species so as to be regarded as useless for zeolite catalysis, were found to serve as a "catalyst reservoir" during the course of nitrogen oxides (NOx) reduction with NH3.118Nsciescopu

Self-Assembly of Pulverized Nanoparticles: An Approach to Realize Large-Capacity, Long-Lasting, and Ultra-Fast-Chargeable Na-Ion Batteries

The fabrication of battery anodes simultaneously exhibiting large capacity, fast charging capability, and high cyclic stability is challenging because these properties are mutually contrasting in nature. Here, we report a rational strategy to design anodes outperforming the current anodes by simultaneous provision of the above characteristics without utilizing nanomaterials and surface modifications. This is achieved by promoting spontaneous structural evolution of coarse Sn particles to 3D-networked nanostructures during battery cycling in an appropriate electrolyte. The anode steadily exhibits large capacity (similar to 480 mAhg(-1)) and energy retention capability (99.9%) during >1500 cycles even at an ultrafast charging rate of 12 690 mAg(-1) (15C). The structural and chemical origins of the measured properties are explained using multiscale simulations combining molecular dynamics and density functional theory calculations. The developed method is simple, scalable, and expandable to other systems and provides an alternative robust route to obtain nanostructured anode materials in large quantities.11Nsciescopu