Evaluation of Vaporized Hydrogen Peroxide Fumigation as a Method for the Bio-decontamination of the High Efficiency Particulate Air Filter Unit

Objective To evaluate the performance of vaporized hydrogen peroxide （VHP） for the bio-decontamination of the high efficiency particulate air （HEPA） filter unit. Methods Self-made or commercially available bioindicators were placed at designated locations in the HEPA filter unit under VHP fumigation. The spores on coupons were then extracted by 0.5 h submergence in eluent followed by 200- time violent knocks. Results Due to the presence of HEPA filter in the box, spore recovery from coupons placed at the bottom of the filter downstream was significantly higher than that from coupons placed at the other locations. The gap of decontamination efficiency between the top and the bottom of the filter downstream became narrower with the exposure time extended. The decontamination efficiency of the bottom of the filter downstream only improved gently with the injection rate of H202 increased and the decontamination efficiency decreased instead when the injection rate exceeded 2.5 g/min. The commercially available bioindicators were competent to indicate the disinfection efficiency of VHP for the HEPA filter unit. Conclusion The HEPA filter unit is more difficult than common enclosure to decontaminate using VHP fumigation. Complete decontamination can be achieved by extending fumigation time. VHP fumigation can be applied for in-situ biodecontamination of the HEPA filter unit as an alternative method to formaldehyde fumigation.

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures （CCSs） in two-dimensional （2D） photonic crystals （PCs） are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain （FDTD） method, and the results show that within a very short coupling distance of about 3λ, where ）, is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.

Ion beam figuring of continuous phase plates based on the frequency filtering process

Ion beam figuring （IBF） technology is an effective technique for fabricating continuous phase plates （CPPs） with small feature structures. This study proposes a multi-pass IBF approach with different beam diameters based on the frequency filtering method to improve the machining accuracy and efficiency of CPPs during IBF. We present the selection principle of the frequency filtering method, which incorporates different removal functions that maximize material removal over the topographical frequencies being imprinted. Large removal functions are used early in the fabrication to figure the surface profile with low frequency. Small removal functions are used to perform final topographical correction with higher fre- quency and larger surface gradient. A high-precision surface can be obtained as long as the filtering frequency is suitably selected. This method maximizes the high removal efficiency of the large removal function and the high corrective capability of the small removal function. Consequently, the fast convergence of the machining accuracy and efficiency can be achieved.

An efficient method for designing variable digital filters

The digital filters with adjustable frequency-domain characteristics are called variable filters. Variable filters are useful in the applications where their characteristics are required to be changeable during the course of signal processing. Generally speaking, the variable frequency responses of a variable filters are the functions of a set of spectral parameters defining the desired frequencyUomain characteristics. In this paper, we first sample the given variable maghtode specifications and use them to construct a multi-dimensional (M - D) specification array, then propose an outer product expansion method for expanding it as the sum of the outer products of vectors. Using the outer product expansion, we can simplify the difficult problem of desighng a variable filter as the easy one that only needs constant 1 - D filter designs and 1 - D polynoIhal approximations. The method can obtain variable filters having arbitrary desired variable magnitude characteristics with a high design acctiracy.

Coordinated adaptive beamformer over distributed antenna network

The spatial diversity of distributed network demands the individual filter to accommodate the topology of interference environment. In this paper, a type of distributed adaptive beamformer is proposed to mitigate interference over coordinated antenna arrays network. The proposed approach is formulated as generalized sidelobe canceller （GSC） structure to facilitate the convex combination of neighboring nodes＇ weights, and then it is solved by unconstrained least mean square （LMS） algorithm due to simplicity. Numerical results show that the robustness and convergence rate of antenna arrays network can be significantly improved in strong interference scenario. And they also clearly illustrate that mixing vector is optimized adaptively and adjusted according to the spatial diversity of the distributed nodes which are placed in different power of received signals to interference ratio （SIR） environments.

Estimation and feedback control of air-fuel ratio for gasoline engines

In 4-stroke internal combustion engines, air-fuel ratio control is a challenging task due to the rapid changes of engine throttle,especially during transient operation. To improve the transient performance, managing the cycle-to-cycle transient behavior of the mass of the air, the fuel and the burnt gas is a key issue due to the imbalance of cyclic combustion process. This paper address the model-based estimation and control problem for cyclic air-fuel ratio of spark-ignition engines. A discrete-time model of air-fuel ratio is proposed, which represents the cycle-to-cycle transient behavior of in-cylinder state variables under the assumptions of cyclic measurability of the total in-cylinder charge mass, combustion efficiency and the residual gas fraction. With the model,a Kalman filter-based air-fuel ratio estimation algorithm is proposed that enable us to perform a feedback control of air-fuel ratio without using lambda sensor. Finally, experimental validation result is demonstrated to show the effectiveness of proposed estimation and control scheme that is conducted on a full-scaled gasoline engine test bench.