Dechun Ba

Nanometer-scale recording with transition time at nanosecond

Recording at a nanometer-scale on 3-phenyl-1-ureidonitrile (CPU) thin films is successfully conducted using scanning tunneling microscopy (STM) in ambient conditions. Recorded marks are written when a series of voltage pulses are applied between the STM tip and the freshly cleaned highly ordered pyrolytic graphite (HOPG) substrates. STM current-voltage (I-V) curves of the films show that the electric resistance in the recorded regions is much lower than that in the unrecorded regions. Standard four-point probe measurements indicate that the transition time of the transient conductance is 6 ns. It is suggested ;that CPU organic thin films have potential in the application of future data storage

Pressure analysis in a compressor cylinder based on detached eddy simulation and dynamic mesh

Pressure pulsation has a critical importance in the design of refrigerant compressor since it acts as a noise and vibration source. For capturing the pressure pulsation and the transient flow structure, the numerical simulation based on detached eddy simulation and dynamic mesh approach was performed. Numerical results agree well with experimental data in the frequency band of 1000–2900 Hz. The results show that the vortex flows arise when the pressure disturbances propagate in the refrigerant gases and impact against the wall leading to the dramatic increase of the sound pressure level (the frequency band is about over 1800 Hz) in the cylinder and the noise radiated from compressor shell. Furthermore, we employed the numerical model to analyze the noise reduction mechanism of the muffler hole in the cylinder wall.

A Numerical Research of Herringbone Passive Mixer at Low Reynold Number Regime

Passive mixing based on microfluidics has won its popularity for its unique advantage, including easier operation, more efficient mixing performance and higher access to high integrity. The time-scale and performance of mixing process are usually characterized by mixing quality, which has been remarkably improved due to the introduction of chaos theory into passive micro mixers. In this paper, we focus on the research of mixing phenomenon at extremely low Reynold number (Re) regime in a chaotic herringbone mixer. Three-dimensional (3D) modeling has been carried out using computational fluid dynamics (CFD) method, to simulate the chaos-enhanced advection diffusion process. Static mixing processes using pressure driven and electric field driven modes are investigated. Based on the simulation results, the effects of flow field and herringbone pattern are theoretically studied and compared. Both in pressure driven flow and electro-osmotic flow (EOF), the mixing performance is improved with a lower flow rate. Moreover, it is noted that with a same total flow rate, mixing performance is better in EOF than pressure driven flow, which is mainly due to the difference in flow field distribution of pressure driven flow and EOF.

Pumping performance of a new type of hybrid molecular pump

A new type of hybrid molecular pump of high performance and reliability has been developed. The pump’s rotational speed is 18 000 rpm. The pump is constructed with eleven stages of a turbomolecular pump and a drum multigroove drum molecular pump in which the clearance between rotor and stationary part is 0.35 mm; the rotor’s deformation forms a cuneiform channel of the proper working clearance to ensure the pump’s performance and working reliability. The pump can operate within the pressure range of 5×102–10−6 Pa for a oil‐free vacuum with the maximum speed of 400 l/s. The maximum compression ratio for H2 is over 4000. It can be widely used in vacuum processes, and is suitable for the higher pressures in dry etching, chemical vapor deposition, etc. This article describes the design considerations and structure of the pump and gives the structural parameters of the pump and the curves relating to the performance.

Experimental Study on Noise Reduction of Multistage Dry Roots Vacuum Pump Varying the Amount of Dynamic Unbalance

Multistage dry Roots vacuum pumps (MDRVPs) are vacuum equipments widely used in IC industry. This paper analyzes the influence mechanism of dynamic unbalance to vibration and noise of rotor axis in MDRVPs, and calculates the vibration deformation of the rotor axis caused by dynamic unbalance through the finite element method. Moreover, a series of experiments on noise source identification are carried on a MDRVP sample machine varying the amount of dynamic unbalance. Through the experimental results, conclusions are drawn that the periodic incentives generated by the unbalance of rotor axis are the main attribution of vibration and noise. Therefore the noise reduces when the amount of unbalance of rotor axis deceases. However, when the allowable unbalance of the rotor axis decreases to a certain degree, aerodynamic noise generated at the outlet becomes the main noise with dominant frequency. It is true that noise of MDRVPs should be no more than 72dB, so the allowable amount of dynamic unbalance should be chosen at a moderate lever as 1.0 g•mm/kg. In that way, this conclusion offers a rule for MDRVPs design and dynamic balance operation because this lever would not only meet the demand of noise reduction but also save working hours and cost for dynamic balancing.

The helical channel pumping mechanism of compound molecular pumps

Abstract It is important to study the pumping mechanism of the helical channel for the purpose of improving pumping performance of molecular pumps. A new model to investigate the moving helical channel is proposed under the condition that the channel depth-to-radial clearance ratio is > 1. The pumping performances of the helical channel are calculated with the new model and the geometric sizes of channels are optimized. In this way, the necessary theoretical basis has been provided to design and improve the pumping performance of compound molecular pump (CMP) or to develop a new type molecular drag pump (MDP).

Damping performance of YSZ coating prepared by different EB-PVD parameters

ABSTRACT A yttrium-stabilised zirconia (YSZ) coating was prepared on Ti–6Al–4 substrates by electron beam physical vapour deposition (EB-PVD). The effect of substrate temperature and beam intensity on the microstructure of the coating was researched. Damping characteristics of the coatings under different processing parameters were compared. The microstructure and crystal structure were determined with scanning electron microscope (SEM) and X-Ray Diffraction (XRD), respectively. The damping properties of the coating were measured by dynamic mechanical analyzer (DMA). The decrease in the substrate temperature leads to diminution of the grain size of coating, which increases the loss factor (Q−1). The crystal defects and micro-cracks of the coating are also the main reasons for the improvement of the damping performance.

A Microfluidic Chip with Double-Slit Arrays for Enhanced Capture of Single Cells

The application of microfluidic technology to manipulate cells or biological particles is becoming one of the rapidly growing areas, and various microarray trapping devices have recently been designed for high throughput single-cell analysis and manipulation. In this paper, we design a double-slit microfluidic chip for hydrodynamic cell trapping at the single-cell level, which maintains a high capture ability. The geometric effects on flow behaviour are investigated in detail for optimizing chip architecture, including the flow velocity, the fluid pressure, and the equivalent stress of cells. Based on the geometrical parameters optimized, the double-slit chip enhances the capture of HeLa cells and the drug experiment verifies the feasibility of the drug delivery.

Study of cell-trap microfluidic chip for platinum drugs treating cancer cell tests

The application of microfluidic technology to manipulate cells or biological particles is becoming one of the rapidly growing areas in recent years. In this paper, we design three categories chip with different microstructure, including seamless, single-slit and double-slit U-type micro-trap, to evaluate the optimal structure and parameter of cell-trap microfluidic chip. Velocity control and optimization during cell transport facilitates high-quality cell capture. Numerical simulation is used to study the capture results of three U-type micro-trap different inlet velocities. By analyzing the velocity distribution of the fluid in the chip and the velocity shift of the micro-ball, the inlet velocity range of the three micro-trap structures can be determined, which are able to capture cells. The results are helpful for optimizing the structural design and get the best category with a high trapping efficiency and a good flow behavior.

Computer modeling of electric potential distribution of ion transport in rectangular Nanofluidic Channel

Based on continuity assumption of fluid, we established a mathematical model of ion transport in the rectangular Nanofluidic Channel with Poisson-Boltzmann equation and modified N-S equations. Through equation derivation, the electric potential distribution function was solved. Next we analyzed how the distribution of the ion electric potential distribution was charged by the solution concentration, the surface charge density and the channel height. Thus we have got the curves between Electric potential distribution and these parameters. Therefore, the main influential factors of the electric potential are the electrolyte concentration, the surface charge density and the channel height. By adjusting the electrolyte concentration, the surface charge density and the nanofluidic channel height, we can control the electric potential.