This review is focused on molecular momentum transport at fluid-solid interfaces mainly related to microfluidics and nanofluidics in micro-/nano-electro-mechanical systems (MEMS/NEMS). This broad subject covers molecular dynamics behaviors, boundary conditions, molecular momentum accommodations, theoretical and phenomenological models in terms of gas-solid and liquid-solid interfaces affected by various physical factors, such as fluid and solid species, surface roughness, surface patterns, wettability, temperature, pressure, fluid viscosity and polarity. This review offers an overview of the major achievements, including experiments, theories and molecular dynamics simulations, in the field with particular emphasis on the effects on microfluidics and nanofluidics in nanoscience and nanotechnology. In Section 1 we present a brief introduction on the backgrounds, history and concepts. Sections 2 and 3 are focused on molecular momentum transport at gas-solid and liquid-solid interfaces, respectively. Summary and conclusions are finally presented in Section 4.

No abstract

No abstract

A high power microwave generator based on a relativistic backward wave oscillator with a resonant reflector (BWO-RR) has been proposed in order to improve microwave conversion efficiency. In this device, the slow wave structure is separated by a modulation cavity, which significantly decreases the energy spread of the modulated beam electrons. At the end of the slow wave structure, an extraction cavity is employed to increase the beam-wave interaction and optimize the extraction of the output power. Particle-in-cell simulations show that a microwave efficiency of 46% has been obtained compared with that of 34% obtained with the BWO-RR.

Plant bacterial pathogens usually cause diseases by secreting and translocating numerous virulence effectors into host cells and suppressing various host immunity pathways. It has been demonstrated that the extensive ubiquitin systems of host cells are frequently interfered with or hijacked by numerous pathogenic bacteria, through various strategies. Some type-III secretion system (T3SS) effectors of plant pathogens have been demonstrated to impersonate the F-box protein (FBP) component of the SKP1/CUL1/F-box (SCF) E3 ubiquitin system for their own benefit. Although numerous putative eukaryotic-like F-box effectors have been screened for different bacterial pathogens by bioinformatics analyses, the targets of most F-box effectors in host immune systems remain unknown. Here, we show that XopI, a putative F-box effector of African Xoo (Xanthomonas oryzae pv. oryzae) strain BAI3, strongly inhibits the host's OsNPR1-dependent resistance to Xoo. The xopI knockout mutant displays lower virulence in Oryza sativa (rice) than BAI3. Mechanistically, we identify a thioredoxin protein, OsTrxh2, as an XopI-interacting protein in rice. Although OsTrxh2 positively regulates rice immunity by catalyzing the dissociation of OsNPR1 into monomers in rice, the XopI effector serves as an F-box adapter to form an OSK1-XopI-OsTrxh2 interaction complex, and further disrupts OsNPR1-mediated resistance through proteasomal degradation of OsTrxh2. Our results indicate that XopI targets OsTrxh2 and further represses OsNPR1-dependent signaling, thereby subverting systemic acquired resistance (SAR) immunity in rice.

The tangential momentum accommodation coefficient (TMAC), usually used in slip boundary conditions in micro-gas flows, is reported to be always less than unity and greatly influenced by temperature and the strength of gas-wall interactions. According to the definitions of accommodation coefficients, a proper statistical algorithm in non-equilibrium molecular dynamics method was described and verified. In planar Poiseuille gas flow in a smooth microchannel, the TMAC were calculated considering both the effects of temperature and gas-wall interaction. In the simulation processes, more gas molecules began to be adsorbed near walls under the condition of stronger gas-wall interaction and lower temperature. The gas adsorption resulted in a longer gas-wall interaction time so that the TMAC increased. While the gas-wall interaction became much stronger, more and more gas molecules were adsorbed to form an explicit layer above the wall. The full coverage of gas molecules on the wall prevented further adsorption; therefore the TMAC did not keep on increasing as the interaction strength continued to increase. Meanwhile, the normal momentum accommodation coefficient (NMAC) was also calculated according to the definition. In the isothermal flow, the average gas momentum normal to the wall was in complete accommodation with the wall, and the NMAC was almost unity in smooth micro channels.

No abstract

An overmoded rectangularly corrugated relativistic surface wave oscillator is designed and theoretically analyzed to produce the high power terahertz radiation with a TM01 mode. The design is fully verified and optimized by 2.5D particle-in-cell simulations. A high power terahertz wave is obtained with the output power of 285 MW at the frequency of 0.148 THz with conversion efficiency 20% when beam voltage is about 400 kV, current 3.8  kA, and the magnetic field 6 T.