#mytweet via Instagram: Exploring User Behaviour across Multiple Social Networks

We study how users of multiple online social networks (OSNs) employ and share information by studying a common user pool that use six OSNs - Flickr, Google+, Instagram, Tumblr, Twitter, and YouTube. We analyze the temporal and topical signature of users' sharing behaviour, showing how they exhibit distinct behaviorial patterns on different networks. We also examine cross-sharing (i.e., the act of user broadcasting their activity to multiple OSNs near-simultaneously), a previously-unstudied behaviour and demonstrate how certain OSNs play the roles of originating source and destination sinks.Comment: IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining, 2015. This is the pre-peer reviewed version and the final version is available at http://wing.comp.nus.edu.sg/publications/2015/lim-et-al-15.pd

Gauge invariant hydrogen atom Hamiltonian

For quantum mechanics of a charged particle in a classical external electromagnetic field, there is an apparent puzzle that the matrix element of the canonical momentum and Hamiltonian operators is gauge dependent. A resolution to this puzzle is recently provided by us in [2]. Based on the separation of the electromagnetic potential into pure gauge and gauge invariant parts, we have proposed a new set of momentum and Hamiltonian operators which satisfy both the requirement of gauge invariance and the relevant commutation relations. In this paper we report a check for the case of the hydrogen atom problem: Starting from the Hamiltonian of the coupled electron, proton and electromagnetic field, under the infinite proton mass approximation, we derive the gauge invariant hydrogen atom Hamiltonian and verify explicitly that this Hamiltonian is different from the Dirac Hamiltonian, which is the time translation generator of the system. The gauge invariant Hamiltonian is the energy operator, whose eigenvalue is the energy of the hydrogen atom. It is generally time-dependent. In this case, one can solve the energy eigenvalue equation at any specific instant of time. It is shown that the energy eigenvalues are gauge independent, and by suitably choosing the phase factor of the time-dependent eigenfunction, one can ensure that the time-dependent eigenfunction satisfies the Dirac equation.Comment: 7 pages, revtex4, some further discussion on Dirac Hamiltonian and the gauge invariant Hamiltonian is added, one reference removed; new address of some of the authors added, final version to appear in Phys. Rev.

Efficient Architecture of Variable Size HEVC 2D-DCT for FPGA Platforms

This study presents a design of two-dimensional (2D) discrete cosine transform (DCT) hardware architecture dedicated for High Efficiency Video Coding (HEVC) in field programmable gate array (FPGA) platforms. The proposed methodology efficiently proceeds 2D-DCT computation to fit internal components and characteristics of FPGA resources. A four-stage circuit architecture is developed to implement the proposed methodology. This architecture supports variable size of DCT computation, including 4×4, 8×8, 16×16, and 32×32. The proposed architecture has been implemented in System Verilog and synthesized in various FPGA platforms. Compared with existing related works in literature, this proposed architecture demonstrates significant advantages in hardware cost and performance improvement. The proposed architecture is able to sustain 4K@30fps ultra high definition (UHD) TV real-time encoding applications with a reduction of 31-64% in hardware cost

Impact of Lockdown on Air Pollution: Evidence from the “2+26” Cities in the Beijing-Tianjin-Hebei Region

To prevent the spread of COVID-19 in China, many cities were locked down after January 23, 2020. Based on the panel data of the “2+26” cities from 10 January to 15 March 2020, this paper took the lockdown as a quasi-natural experiment and established a multi-phase DID model to investigate whether the lockdown measures significantly reduced air pollution in locked-down cities in the Beijing-Tianjin-Hebei (BTH) region. The core innovation of this paper is that we considered the urban immigration scale index as a mediating variable , which is rarely adopted in the existing literature, and we identified the relationships between the lockdown, the intracity migration index, the urban immigration scale index and air pollution. The results showed that compared with the non-locked-down cities, the lockdown significantly reduced air pollution. Furthermore, it was found that the lockdown reduced air pollution by reducing intracity migration and the urban scale of immigration. Moreover, compared with the corresponding period in 2019, air pollution was significantly reduced in the locked-down cities of the “2+26” cities. Air pollution is closely related to human activity, and green production and technological innovations are critical for reducing air pollution in the BTH region

Stimulated emission reduced fluorescence microscopy: a concept for extending the fundamental depth limit of two-photon fluorescence imaging

Two-photon fluorescence microscopy has become an indispensable tool for imaging scattering biological samples by detecting scattered fluorescence photons generated from a spatially confined excitation volume. However, this optical sectioning capability breaks down eventually when imaging much deeper, as the out-of-focus fluorescence gradually overwhelms the in-focal signal in the scattering samples. The resulting loss of image contrast defines a fundamental imaging-depth limit, which cannot be overcome by increasing excitation efficiency. Herein we propose to extend this depth limit by performing stimulated emission reduced fluorescence (SERF) microscopy in which the two-photon excited fluorescence at the focus is preferentially switched on and off by a modulated and focused laser beam that is capable of inducing stimulated emission of the fluorophores from the excited states. The resulting image, constructed from the reduced fluorescence signal, is found to exhibit a significantly improved signal-to-background contrast owing to its overall higher-order nonlinear dependence on the incident laser intensity. We demonstrate this new concept by both analytical theory and numerical simulations. For brain tissues, SERF is expected to extend the imaging depth limit of two-photon fluorescence microscopy by a factor of more than 1.8

STOCK PREDICTION VIA SENTIMENT AND ONLINE SOCIAL STATUS

Studies of stock market prediction show that stock movements are related to the sentiment of social media. However, few studies have investigated the role of online social relations in predicting stock movements. This paper aims at constructing features that capture users’ online social status and incorporating these into stock prediction models. Online opinions are often developed through interactions and are weaker in their early stages. We developed a feature-enhancing procedure motivated by statistical surveillance approaches to strengthen the ability to capture emerging trends. We evaluated our feature-enhancing procedure by developing models to predict stock returns in the following 20-minute period. A comparison of experimental results with baseline models shows that our feature-enhancing design helped to predict stock movements. The model (SE_CUSUM) that adopted features enhanced by cumulative sum (CUSUM), a statistical surveillance approach, performed better than baseline models in terms of directional accuracy, balanced error rate, root mean square error, and mean absolute error. Our simulated trading also showed that SE_CUSUM realized a higher profit than the baseline approaches. These results suggest that incorporating online social status and our feature-enhancing procedure improve high frequency stock prediction performance

Novel electromagnetic radiation in a semi-infinite space filled with a double-negative metamaterial

We have theoretically investigated the electromagnetic radiation excited by a charged particle moving along a semi-infinite space filled with a double-negative metamaterial (DNM). Cherenkov radiation in the double-negative region exhibits reversed or backward radiation behavior. The spectral density of reversed Cherenkov radiation has a continuous distribution over the radiation frequency region. The influence of some important parameters on the Cherenkov radiation energy per unit length has been discussed. The surface wave in the vacuum region presented here also is investigated. We conclude that the amplitude of the surface wave is greatly enhanced over some normal dielectric material cases. The enhanced surface wave may be useful for high frequency and high power vacuum electron devices with the DNM.National Natural Science Foundation (China) (Grant 60971031)National Natural Science Foundation (China) (Grant 61125103)Sichuan Youth Foundation (Grant No. 2010JQ0005)Foundation of the National Key Laboratory of Science and Technology on Vacuum Electronics (Grant No. 9140C050102100C05)Fundamental Research Funds for the Central Universities of China (Grant No. ZYGX2010X010