arXiv subjects

Jun Huang

Publications and source records attributed to Jun Huang.

184 records · Page 11Linked to original sources

arXiv2016

Discovery of homogeneously dispersed pentacoordinated Al(V) species on the surface of amorphous silica-alumina

The dispersion and coordination of aluminium species on the surface of silica-alumina based materials are essential for controlling their catalytic activity and selectivity. Al(IV) and Al(VI) are two common coordinations of Al species in the silica network and alumina phase, respectively. Al(V) is rare in nature and was found hitherto only in the alumina phase or interfaces containing alumina, a behavior which negatively affects the dispersion, population, and accessibility of Al(V) species on the silica-alumina surface. This constraint has limited the development of silica-alumina based catalysts, particularly because Al(V) had been confirmed to act as a highly active center for acid reactions and single-atom catalysts. Here, we report the direct observation of high population of homogenously dispersed Al(V) species in amorphous silica-alumina in the absence of any bulk alumina phase, by high resolution TEM/EDX and high magnetic-field MAS NMR. Solid-state 27Al multi-quantum MAS NMR experiments prove unambiguously that most of the Al(V) species formed independently from the alumina phase and are accessible on the surface for guest molecules. These species are mainly transferred to Al(VI) species with partial formation of Al(IV) species after adsorption of water. The NMR chemical shifts and their coordination transformation with and without water adsorption are matching that obtained in DFT calculations of the predicted clusters. The discovery presented in this study not only provides fundamental knowledge of the nature of aluminum coordination, but also paves the way for developing highly efficient catalysts.

physics.chem-ph↗

arXiv2014

A Novel Admission Control Model in Cloud Computing

With the rapid development of Cloud computing technologies and wide adopt of Cloud services and applications, QoS provisioning in Clouds becomes an important research topic. In this paper, we propose an admission control mechanism for Cloud computing. In particular we consider the high volume of simultaneous requests for Cloud services and develop admission control for aggregated traffic flows to address this challenge. By employ network calculus, we determine effective bandwidth for aggregate flow, which is used for making admission control decision. In order to improve network resource allocation while achieving Cloud service QoS, we investigate the relationship between effective bandwidth and equivalent capacity. We have also conducted extensive experiments to evaluate performance of the proposed admission control mechanism.

cs.NI↗

arXiv2012

Global existence and large time behavior for the system of compressible adiabatic flow through porous media in $\mathbb{R}^{3}$

The system of compressible adiabatic flow through porous media is considered in $\mathbb{R}^{3}$ in the present paper. The global existence and uniqueness of classical solutions are obtained when the initial data is near its equilibrium. We also show that the pressure of the system converges to its equilibrium state at the same $L^2$-rate $(1+t)^{-3/4}$ as the Navier-Stokes equations without heat conductivity, but the velocity of the system decays at the $L^2$-rate $(1+t)^{-5/4}$, which is faster than the $L^2$-rate $(1+t)^{-3/4}$ for the Navier-Stokes equations without heat conductivity [3].

math.AP↗

arXiv2012

Time-dependent barrier passage in External Noise Modulated System-reservoir Environment

The time-dependent barrier passage of an anomalous system-reservoir coupling non-equilibrium open environment is studied where the heat bath is modulated by an external noise. The time-dependent barrier passing probability is obtained analytically by solving the generalized Langevin equation. The escaping rate and effective transmission coefficient are calculated by using of the reactive flux method in the particular case of external $δ$-correlated noise modulated internal Ornstein-Uhlenbeck process. It is found that not all the cases of external noise modulating is harmful to the rate process. Sometimes it is even beneficial to the diffusion of the particle. There exists an optimal strength of external noise modulation for the particle to obtain a biggest probability to escape from the potential well to form a notable rate of effective net flux.

physics.chem-ph↗