The effect of array periodicity on the filtering characteristics of metal/dielectric photonic crystals

We present a both theoretical and experimental investigation into the effect of array periodicity on the filtering characteristics of metal/dielectric photonic crystals（MDPhCs） with hexagonal arrays of subwavelength holes in gold/silicon dioxide films,varying the array periodicity from 6 to 8μm every 1μm while the ratio of hole radius to array periodicity is kept constant（1/4）.The results indicate that the reflectance spectrum is highly dependent on the array periodicity.When the array periodicity increases,the reflectance spectrum exhibits a large redshift regularly.The finite difference time domain（FDTD） simulations agree well with the experimental results. By analyzing the relationship between the position of the reflectance minimum and the array periodicity,we find that the filtering characteristics of MDPhCs have an almost linear relationship with the array periodicity under the conditions of keeping the same ratio of hole radius to array periodicity（1/4）.This finding provides an effective way to control the filtering characteristics of MDPhCs,which have potential applications in optical filters,plasmonic thermal emitters and so on.

FLOW CHARACTERISTICS OF WALLFLOW DIESEL PARTICULATE FILTER SYSTEM WITH REVERSE PULSE AIR REGENERATION

To simulate steady airflows inside of wall-flow diesel particulate filters （DPF） with different reverse blowing pipes collocation, a mathematical model of the flow in a DPF is established by an equivalent continuum approach. The experimental results agree well with the theoretical values calculated from the model. Simulation shows that the velocity and the pressure distribution of the filters in the regenerative process are key factors to the filter＇s regeneration. How to decrease the mal-distribution of the flow in the filter and how to achieve the better regenerative performance at the least cost of air consumption in the regenerative process are the ultimate goals of the study. Calculation and experiments show that the goals can be realized through adjusting the angle of two reverse blowing pipes and their relative location suitably.

Improving the Surface Performance of Electrospun Air Filter Paper Using Multi-walled Carbon Nanotubes

In this study,air filter base paper(P)was used as the receiving substrate,polyvinyl alcohol(PVA)and PVA/multi-walled carbon nanotube(MWCNT)spinning solutions were used to prepare electrospun air filter papers(P-PVA and P-PVA/MWCNT,respectively).Then,P-PVA/MWCNT was calendered under different pressures.The effect of MWCNTs on the surface performance of P-PVA/MWCNT was explored and the influence of calendering technology on their structure and filtration characteristics was analyzed.Electron scanning microscope observation showed that the PVA nanofibers on the surface of P-PVA/MWCNT had no beading,and MWCNTs weakened the surface electrostatic phenomenon and had a good micromorphology.During the calendering process,with an increase in pressure,the mean pore size and surface roughness of P-PVA/MWCNT decreased,the initial resistance increased,and the filtration efficiency changed slightly.

Mathematical Description of Acousto-Optic Tunable Filter Orthogonal Polarizing Method

The transfer function of the optical splitting system of the acousto-optic tunable filter （AOTF） is deduced to be a reference to optical design. The characteristic matrix （ transfer function） of AOTF is used to describe quantitatively the characters of polarization elements in the orthogonal polarizing system. According to the characteristic matrix, the included angle of polarizer＇s transmission direction and polarization analyzer＇s transmission direction should be 90°. As a result the signal to noise ratio increased about 20 times though the light intensity was reduced to 54.3%,because both the transmittances of polarizer and polarization analyzer are 0. 74, which is an intrinsic character. The orthogonal polarizing method is an effective method to get rid of the influence of zero order light and improve the spectrum resolution and signal-to-noise ratio.

Influence of coagulation mechanisms and floc formation on filterability

Minimizing particles in water is a key goal for improving drinking water quality and safety.The media filtration process,as the last step of the solid–liquid separation process,is largely influenced by the characteristics of flocs,which are formed and controlled within the coagulation process.In a laboratory-based study,the impacts of the physical characteristics of flocs formed using aluminum sulfate on the filtration treatment of two comparative water samples were investigated using a photometric dispersion analyzer and a filterability apparatus.In general,the optimum dosage for maximizing filterability was higher than that for minimizing turbidity under neutral p H conditions.For a monomeric aluminum-based coagulant,the charge neutralization mechanism produced better floc characteristics,including floc growth speed and size,than the sweep flocculation mechanism.In addition,the charge neutralization mechanism showed better performance compared to sweep flocculation in terms of DOC removal and floc filterability improvement for both waters,and showed superiority in turbidity removal only when the raw water had high turbidity.For the different mechanisms,the ways that floc characteristics impacted on floc filterability also differed.The low variation in floc size distribution obtained under the charge neutralization mechanism resulted in the flocs being amenable to removal by filtration processes.For the sweep flocculation mechanism,increasing the floc size improved the settling ability of flocs,resulting in higher filter efficiency.