The time and frequency standard system for FAST receivers

This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing observations.The stability and drift rate of the frequency standard are calculated using 1-year monitoring data.The UTC-NIM Disciplined Oscillator(NIMDO)system improves the system time accuracy and stability to the level of 5 ns.Pulsar timing observations were carried out for several months.The weighted RMS of timing residuals reaches the level of less than 3.0μs.

Progress of Research on Aṣtāṅgahṛdaya Saṃhitā

Aṣtāṅgahṛdaya Saṃhitā(Compendium of the Essence of the Eight Branches)is one of the most important works on Ayurvedic medicine from ancient India.It provides a comprehensive overview and synthesis of Ayurvedic theories from different schools of thought.With concise and clear contents,it was an essential textbook for Ayurvedic medicine in India and many other regions at the time it was written.This article summarizes the main contents of the book,reviews the current status of research,and finds that the modern research on Aṣtāṅgahṛdaya Saṃhitāfocuses on religious philosophy,the theory of bodily humors,discussion of drug use,and its relationship with Chinese medicine.The book was widely disseminated in the areas surrounding India and influenced Tibetan and Arabic medicine,as well as multiethnic medicine along the Silk Road.

Soluble Polyimide-reinforced TGDDM and DGEBA Epoxy Composites

Polyimide(PI)synthesized from aromatic diamine and dianhydrides via two-step poly-condensation method was highly soluble in TGDDM(MY-720)and DGEBA(E-51)at desirable temperature.TGDDM-PI(M-PI)and DGEBA-PI(E-PI)composites within 0.5%-3%PI loading could be prepared without organic solvent.On the cryogenically fractured surfaces of M-PI and E-PI composites,no obvious heterogeneous phase was observed by SEM.The mechanical properties were promoted significantly by PI,especially for impact strength.Adding 2%PI-2W into MY-720 and E-51 composites,the impact strength increased to 21 and 51 kJ/m2,the tensile strength increased by 62%and 19%,and the flexural strength by 18%and 13%,respectively,with slight increases in tensile modulus.These results were related to the promotion in plasticity of composites and changes in fragile→ductile fracture mode.Moreover,Tg and thermal stability of M-PI and E-PI were increased effectively.

Catalytic oxidation of ethyl acetate on Ce-Mn-O catalysts modified by La

La/Ce_(0.5)Mn_(0.5) catalysts prepared by wetness impregnation of Ce_(_(0.5))Mn_(_(0.5)) with La(NO_(3))_(3)(aq) were used in catalytic oxidation of ethyl acetate.Characterization by X-ray diffractometer(XRD),H2 temperature programmed reduction(H2-TPR),X-ray photoelectron spectroscopy(XPS) and Raman shows that La/Ce_(0.5)Mn_(0.5) catalysts have fluorite-like structure.LalCe_(0.5)Mn_(0.5) catalyst presents high activity with T90(the temperature needed for 90% conversion) of 200℃,where ethyl acetate is almost completely converted into CO_(2).The conversion at 195℃ maintains at 80% for at least 100 h.The intermediates were mainly ethanol and acetaldehyde whose amounts are below250 × 10^(-6) and 16 × 10^(-6),respectively.In situ FTIR indicates that the modes of dissociative adsorption of ethyl acetate are related to surface oxygen species,which affect the stability of catalysts and the selectivity for ethanol and acetaldehyde intermediates.

Numerical investigations of the effects of blade shape on the flow characteristics in a stirred dead-end membrane bioreactor

Numerical simulations of turbulent flows in a stirred dead-end membrane bioreactor are performed by using the RNG k-? model based on the finite volume method with the software Fluent. Comparisons of numerical and experimental results confirm the reliability and the feasibility of the constructed model. The flow structures such as the wake flows and the circulation loops in the stirred flows are well simulated. An increase of stirring speed is proposed to minimize the low velocity region. The single vane stirrer is found to be beneficial for biological separations. Results suggest that the increase of the vane number can enhance the mixing effect in the flow domains. However, a circular disk stirrer goes against the formation of vertical circulations. The six-vane stirrer is found to be able to provide a uniform distribution of the high shear stress.

Three-dimensional numerical study of flow characteristics and membrane fouling evolution in an enzymatic membrane reactor

In order to enhance the understanding of the membrane fouling mechanism, the hydrodynamics of the granular flow in a stirred enzymatic membrane reactor is numerically investigated in the present paper. A three-dimensional Euler-Euler model, coupled with the k-ε mixture turbulence model and the drag function proposed by Syamlal and O＇Brien（1989） for the interphase momentum exchange, is built to simulate the two-phase（fluid-solid） turbulent flow. Numerical simulations of single-or two-phase turbulent flows at various stirring speeds are carried out. The numerical results agree very well with the published experimental data. Results include the distributions of the velocity, the shear stress and the turbulent kinetic energy. It is shown that the increase of the stirring speed not only enlarges the circulation loops in the reactor, but also increases the shear stress on the membrane surface and accelerates the mixing process for the granular materials. The time evolution of the volumetric function of the granular materials on the membrane surface can qualitatively explain the evolution of the membrane fouling.