Tri-spin dynamics in alkali metal-noble gas NMR gyroscope

Alkali metal-noble gas NMR gyroscope is widely used for precision rotation measurement in fundamental and applied physics. By numerically simulating the alkali-nuclear-nuclear tri-spin dynamics, we investigate the dependence of gyroscope response on alkali spin relaxation time and nuclear spin magnetization. We found additional resonance peaks appear due to a new source of instability, namely the inherent multistability of tri-spin dynamics. The numerical simulation results agree well with the recent experiment, enabling a better understanding and exploitation of the gyroscope signal.Comment: 12 figure

The Bending Feature of the Fermi Bubbles: A Presumed Horizontal Galactic Wind and Its Implication on the Bubbles' Age

There are two spectacular structures in our Milky Way: the {\it Fermi} bubbles in gamma-ray observations and the North Polar Spur (NPS) structure in X-ray observations. Because of their morphological similarities, they may share the same origin, i.e., related to the past activity of Galactic center (GC). Besides, those structures show significant bending feature toward the west in Galactic coordinates. This inspires us to consider the possibility that the bending may be caused by a presumed global horizontal galactic wind (HGW) blowing from the east to the west. Under this assumption, we adopt a toy shock expansion model to understand two observational features: (1) the relative thickness of the NPS; (2) the bending of the {\it Fermi} bubbles and NPS. In this model, the contact discontinuity (CD) marks the boundary of the {\it Fermi} bubbles, and the shocked interstellar medium (ISM) marks the NPS X-ray structure. We find that the Mach number of the forward shock in the east is $\sim$ 1.9-2.3, and the velocity of the HGW is ~ 0.7-0.9 $c_{s}$. Depending on the temperature of the pre-shock ISM, the velocity of the expanding NPS in Galactic coordinates is around 180-290 km/s, and the HGW is ~ 110-190 km/s. We argue that, the age of the NPS and the {\it Fermi} bubbles is about 18-34 Myr. This is a novel method, independent of injection theories and radiative mechanisms, for the estimation on the age of the {\it Fermi} bubble/NPS.Comment: 6 pages, 4 figure, accepted by ApJ

Estimation of Dynamic Mixed Double Factors Model in High Dimensional Panel Data

The purpose of this article is to develop the dimension reduction techniques in panel data analysis when the number of individuals and indicators is large. We use Principal Component Analysis (PCA) method to represent large number of indicators by minority common factors in the factor models. We propose the Dynamic Mixed Double Factor Model (DMDFM for short) to re ect cross section and time series correlation with interactive factor structure. DMDFM not only reduce the dimension of indicators but also consider the time series and cross section mixed effect. Different from other models, mixed factor model have two styles of common factors. The regressors factors re flect common trend and reduce the dimension, error components factors re ect difference and weak correlation of individuals. The results of Monte Carlo simulation show that Generalized Method of Moments (GMM) estimators have good unbiasedness and consistency. Simulation also shows that the DMDFM can improve prediction power of the models effectively.Comment: 38 pages, 2 figure

The Accretion Wind Model of the Fermi Bubbles (II): Radiation

In a previous work, we have shown that the formation of the Fermi bubbles can be due to the interaction between winds launched from the hot accretion flow in Sgr A* and the interstellar medium (ISM). In that work, we focus only on the morphology. In this paper we continue our study by calculating the gamma-ray radiation. Some cosmic ray protons (CRp) and electrons must be contained in the winds, which are likely formed by physical processes such as magnetic reconnection. We have performed MHD simulations to study the spatial distribution of CRp, considering the advection and diffusion of CRp in the presence of magnetic field. We find that a permeated zone is formed just outside of the contact discontinuity between winds and ISM, where the collisions between CRp and thermal nuclei mainly occur. The decay of neutral pions generated in the collisions, combined with the inverse Compton scattering of background soft photons by the secondary leptons generated in the collisions and primary CR electrons can well explain the observed gamma-ray spectral energy distribution. Other features such as the uniform surface brightness along the latitude and the boundary width of the bubbles are also explained. The advantage of this accretion wind model is that the adopted wind properties come from the detailed small scale MHD numerical simulation of accretion flows and the value of mass accretion rate has independent observational evidences. The success of the model suggests that we may seriously consider the possibility that cavities and bubbles observed in other contexts such as galaxy clusters may be formed by winds rather than jets.Comment: 13 pages,6 figures, accepted for publication in Ap

Internet Activism & the Party-State in China

The history of Internet activism and Internet control in China is one of mutual adaptation between citizen activists and party authorities. The party-state initially reacted to Internet activism with alarm, but has since built a comprehensive approach combining repressive policing with gentler methods of social management. This approach has evolved in response to the diverse forms of and participants in Internet activism. But the adaptability of the Chinese Internet control regime does not mean that it will root out Internet activism. On the contrary, Internet activism will continue to grow and will itself adapt to the changing forms of control. Comparisons with Russia and the United States highlight how political economy, history, and everyday practice shape the forms of Internet activism and control

Environmental NGOs and Institutional Dynamics in China

Environmental non-governmental organizations are becoming increasingly visible players in China’s environmental politics. Adopting a field perspective, this article shows how the rise of environmental NGOs has taken place in interactions with four institutional fields. They not only respond to political conditions, but also to opportunities offered by the media, the internet, and international NGOs. In this process, organizational entrepreneurs play a crucial role in mobilizing resources while other individuals participate in search of self-fulfillment or social experience. These arguments underscore the multi-institutional dynamics of civil society development without underestimating state-centered and market-centered explanations. In conclusion, the article discusses how environmental NGOs can serve as both sites and agents of democratic social change in China

Online Activism

Online activism is a new form of popular contention in China. In some cases, the Internet serves to mobilize street protest. More often, protest takes place online. The most common forms include online petitions, the hosting of campaign websites, and large-scale verbal protests. The most radical is perhaps the hacking of websites. These forms of contention may be found in blogs, Internet bulletin boards, online communities, and podcast and YouTube-type web sites

The Co-Evolution of the Internet and Civil Society in China

Civil society and the Internet energize each other in their co-evolutionary development in China. The Internet facilitates civil society activities by offering new possibilities for citizen participation. Civil society facilitates the development of the Internet by providing the necessary social basis—citizens and citizen groups—for communication and interaction. These arguments are illustrated with an analysis of the discourse in Qiangguo Luntan [Strengthening the Nation Forum] and an ethnographic study of Huaxia Zhiqing [Chinese Educated Youth],