科研成果

With MEMS technology developing rapidly, the microfluidic droplet technology has been employed into many biological or chemical experiments. To satisfy the increasingly high demands in various applications of the microfluidic chips, the size of the droplet needs accurate control. We have designed and performed a three-dimensional numerical simulation of a droplet generation in a double T-junction microchannel by a level-set method in COMSOL5.0 for discussing the process of the droplet formation and the influences on the size of the droplet. We have studied out that the flow rate ratio, the continuous phase viscosity, the interfacial tension, and the contact angle influence the size of the droplet. The effective droplet diameter increases when the flow rate ratio and the interfacial tension increase. It decreases when the continuous phase viscosity and the contact angle increase. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

High-order mode employed as the operating mode of a terahertz (THz) gyrotron traveling-wave tube (gyro-TWT) amplifier shows strong dispersion, which deteriorates the device performance in amplifying picosecond THz pulses. Theoretical investigation of a THz gyro-TWT amplifier with a lossy cylindrical circuit is carried out to study the problems, such as lossy structure design, parameters selection, frequency-domain performance, and time-domain dynamics. The robust high growth rate low-kz amplification and the broadband high-kz amplification are two preferred operation conditions. The revealed characteristics are also useful for developing THz gyro-TWTs with other kinds of over-moded circuits.

The near-retirement households among all working-age groups in the United States experienced larger drops in consumption and greater increases in labor force participation during the financial crisis of 2007-2009. Also, the retirement probability for near-retirement homeowners (but not for renters) decreases more in those areas where housing prices also decline more. This paper argues that the wealth effect of housing prices on retirement can account for those issues. It creates an incomplete-market life-cycle partial-equilibrium model with risky housing assets and endogenous retirement and verifies that the joint response of retirement and non-durable consumption implied by the structural model is consistent with the empirical findings using data from the Health and Retirement Study 1992-2012. It then shows that, after an unexpected 28 percent housing price decline, near-retirement homeowners ages 55-64 will reduce their non-durable consumption by 4.6 percent and increase their labor force participation by 1 percentage point immediately and delay their retirement by 2.8 months in the long run. The model also quantifies endogenous retirement as self-insurance for elderly homeowners against housing price risk. (Copyright: Elsevier)

Here we report, for the first time, the growth of single-crystalline mesoporous MOFs with well-controlled orientation on the surface of gold nanorods. Importantly, it showed that trace amounts of water could induce the formation of MOFs of different phases and shapes, which was critical for the synthesis of such mesoporous heterostructures.

Here we report the measurement results of nitrous acid (HONO) and a suite of relevant parameters on the NCAR C-130 research aircraft in the southeastern US during the NOMADSS 2013 summer field study. The daytime HONO concentration ranged from low parts per trillion by volume (pptv) in the free troposphere (FT) to mostly within 5–15pptv in the background planetary boundary layer (PBL). There was no discernible vertical HONO gradient above the lower flight altitude of 300m in the PBL, and the transport of ground surface HONO was not found to be a significant contributor to the tropospheric HONO budget. The total in situ HONO source mean (±1SD) was calculated as 53 (±21)pptvh−1 during the day. The upper-limit contribution from NOx-related reactions was 10 (±5)pptvh−1, and the contribution from photolysis of particulate nitrate (pNO3) was 38 (±23)pptvh−1, based on the measured pNO3 concentrations and the median pNO3 photolysis rate constant of 2.0 × 10−4s−1 determined in the laboratory using ambient aerosol samples. The photolysis of HONO contributed to less than 10% of the primary OH source. However, a recycling NOx source via pNO3 photolysis was equivalent to  ∼ 2.3 × 10−6molm−2h−1 in the air column within the PBL, a considerable supplementary NOx source in the low-NOx background area. Up to several tens of parts per trillion by volume of HONO were observed in power plant and urban plumes during the day, mostly produced in situ from precursors including NOx and pNO3. Finally, there was no observable accumulation of HONO in the nocturnal residual layer and the nocturnal FT in the background southeastern US, with an increase in the HONO∕NOx ratio of  ≤ 3 × 10−4h−1 after sunset.