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We report the first systematic study of broadband THz wave generation with ambient air as the nonlinear media. Generation of pulsed THz waves with mixing the fundamental and the second harmonic beams in air has been previously demonstrated by Cook et al. and Hartmut et al. while different groups obtained different results. To verify the proposed mechanism of strong THz wave generation, we measured dependence of generated THz field on the polarization, amplitude and phase of the individually controlled two beams. Our results confirm that four-wave-mixing rectification is the major mechanism this phenomenon, and the amplitude and polarity of generated THz wave can be controlled by the relative phase of the beams. This work is significant by providing the feasibility of THz wave generation and detection with a standoff distance greater than 50 meters.

Different time air plasma treatment was conducted on acrylonitrile–butadiene rubber (NBR) surface, the wettability and friction behavior of the samples surface were measured after two months of storage. The changes in surface composition and microstructure during storage process were observed by X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM), respectively. The results show that the wettability of modified surface has obvious “hydrophobic recovery” phenomenon in the storage process, and the range of contact angle increase is closely related to the plasma treatment time, mainly because the change in surface composition at various time treatment are different during storage; the frictional behavior of plasma-modified NBR surface has not exhibited a “recovery” phenomenon after two months of storage, and the friction coefficient of the surface treated for 4 min and 8 min were even smaller than those before storage, which is due to the smoother and lower roughness of the surface morphology after storage. This study demonstrates that air plasma treatment is a promising technique for improving the wettability and tribological properties of NBR rubber, but the proper treatment time is needed to make the surface have the best wetting and frictional behavior.

We report the first systematic study of broadband THz wave generation with ambient air as the nonlinear media. Generation of pulsed THz waves with mixing the fundamental and the second harmonic beams in air has been previously demonstrated by Cook et al. and Hartmut et al while different groups obtained different results. To verify the proposed mechanism of strong THz wave generation, we measured dependence of generated THz field on the polarization, amplitude and phase of the individually controlled two beams. Our results confirm that four-wave-mixing rectification is the major mechanism this phenomenon, and the amplitude and polarity of generated THz wave can be controlled by the relative phase of the beams. This work is significant by providing the feasibility of THz wave generation and detection with a standoff distance greater than 50 meters.

The need for antimicrobial textiles is increasing nowadays, due to the detrimental effects of micro-organisms on textiles as well as human hygiene. So it is essential to control or inhibit the growth of these organisms on textile fabrics which turns out to be undesirable for the wearer as well as the textile itself. The natural and ecofriendly, antimicrobial agents for textile applications are gaining interest in recent times. Eucalyptus oil, tulsi leaf, Aloe vera, neem leaf extracts, etc., can be used as a bioactive agent for finishing the textile materials. Neem is known for its environmental compatibility and is harmless against non-target materials, besides being skin friendly and non-toxic. This has significantly increased the use of bioactive agents obtained from neem products in the area of antimicrobial textiles. A large amount of biocides has to be applied on to the fabric to control effectively the microbial growth and sustain the durability of the finish. In the present study, hydrophilicity of the cotton fabrics was increased by DC air plasma and cellulase enzyme treatments to improve the uptake of azadirachtin content in the fabrics. The hydrophilicity of the treated fabrics was determined using dynamic wicking test. The physical and chemical modifications on the plasma and enzyme treated fabrics were analyzed using SEM and UATR- FTIR respectively. The fabrics treated with plasma and enzyme is found to exhibit increased hydrophilicity thereby increasing the uptake of neem leaf extract. Methanolic extract of neem leaf was prepared and applied as an antimicrobial finish for the treated cotton fabrics by pad-dry-cure method. The antibacterial and antifungal properties of neem leaf extract finished cotton fabrics were evaluated for its activity against: S.aureus, E.coli, Penicillum, Trichoderma using standard qualitative and quantitative test methods. The synergetic effect of the two treatments on the antimicrobial activity and wash durability of the cotton fabrics were investigated and the results are discussed.