Wavelet Integrated CNNs for Noise-Robust Image Classification

Convolutional Neural Networks (CNNs) are generally prone to noise interruptions, i.e., small image noise can cause drastic changes in the output. To suppress the noise effect to the final predication, we enhance CNNs by replacing max-pooling, strided-convolution, and average-pooling with Discrete Wavelet Transform (DWT). We present general DWT and Inverse DWT (IDWT) layers applicable to various wavelets like Haar, Daubechies, and Cohen, etc., and design wavelet integrated CNNs (WaveCNets) using these layers for image classification. In WaveCNets, feature maps are decomposed into the low-frequency and high-frequency components during the down-sampling. The low-frequency component stores main information including the basic object structures, which is transmitted into the subsequent layers to extract robust high-level features. The high-frequency components, containing most of the data noise, are dropped during inference to improve the noise-robustness of the WaveCNets. Our experimental results on ImageNet and ImageNet-C (the noisy version of ImageNet) show that WaveCNets, the wavelet integrated versions of VGG, ResNets, and DenseNet, achieve higher accuracy and better noise-robustness than their vanilla versions.Comment: CVPR accepted pape

First principle study of the thermal conductance in graphene nanoribbon with vacancy and substitutional silicon defect

The thermal conductance in graphene nanoribbon with a vacancy or silicon point defect (substitution of C by Si atom) is investigated by non-equilibrium Green's function (NEGF) formalism combined with first-principle calculations density-functional theory with local density approximation. An efficient correction to the force constant matrix is presented to solve the conflict between the long-range character of the {\it ab initio} approach and the first-nearest-neighboring character of the NEGF scheme. In nanoribbon with a vacancy defect, the thermal conductance is very sensitive to the position of the vacancy defect. A vacancy defect situated at the center of the nanoribbon generates a saddle-like surface, which greatly reduces the thermal conductance by strong scattering to all phonon modes; while an edge vacancy defect only results in a further reconstruction of the edge and slightly reduces the thermal conductance. For the Si defect, the position of the defect plays no role for the value of the thermal conductance, since the defective region is limited within a narrow area around the defect center.Comment: accepted by AP

Declining population growth and economic stagnation theory

Thesis (M.A.)--Boston UniversityThe fundamental backgrounds of this thesis are the severe depression and weak recovery of the thirties and the trend of declining population growth since 1925. The stagnation theory relates these economic and demographical phenomenon in the way that the fundamental cause of the trend of the secular under-employment fluctuation is the increasing proportion of total saving and the vanishing of investment opportunities among which declining population growth is almost the most important one. This thesis aims at the investigation of whether and how the decline of population growth affects the business activities and precipitates the under-employment condition as the stagnationists stated. Throughout the study, decline of population growth means the decline of the annual increment of population. This annual increment as well as the total population at any time consists of three different groups of people: the dependant group, young and old, and the working age group. When population growth declines the age composition will be correspondingly shifted. The young people group will be smaller, the working age group will increase slowly and the old aged group will be larger. The continueous decline of population growth is unfavorable to the business' expectation of profit and, therefore, discourages investment. Some businesses like public utilities residential and railroad construction depend primirily upon that increase of population. The shift of age composition will, as a whole, and especially under the condition of rising social income, decrease the demands for necessities like food, clothing and housing which require more capital per worker or per unit of product and increase the demands for luxuries like personal services and fashionable goods which not only require less: capital per worker but also increase the risk and uncertainty of the business. At the same time savings will also be increased which makes the task of maintaining full employment more difficult. All these are long run secular effects. In the short run, these effects are not easy to perceive. However, even if we can not attribute the cause of business cycle to population change, we can see that the decline of population growth tends to shorten the period of prosperity and deepening the period of depression. Chapter on the theoretical controversies throws light on the fact that the predictions of the stagnationists are not well founded although their theoretical analysis seems sound. The anti-stagnationists have good reasons to doubt the predictions but their theoretieal argument are very unsystematical. The last chapter on optimum population was touched by the stagnationists nor by the anti-stagnationists. It was discussed because it was implied in their arguments. As a whole, the stagnationist emphasized the maximization of national product while the anti-stagnationists emphsized the maximization of per capita income. Consequently, in most cases, the optimum population of the stagnationists is larger