Noise test and control for household refrigerator compressor
Sound comfort becomes more and more important in residential houses. Home appliance is one of the main sources of indoor noise. Noise emission is a distinctive feature for the selection of the home appliances. Noise levels in household appliances are increasingly attracting attention from manufacturers and customers. Refrigerators as common appliances used by most families run continuously all day. It produces a lot of noises. National standards have published severe rules on the acceptable noise levels, and noise-free operation becomes the preferred choice of customers in the refrigerators choosing. Therefore, it is necessary to reduce the noise level of refrigerator. In this paper, the noise control study has been carried on a type of air-cooled household refrigerator. The noise level of the refrigerator was tested under different operation conditions at first. Then the maximum sound pressure level and noise characters were obtained by analyse the spectra of the noises. Test data shown that the refrigerator noises are mainly composed of compressor and fan noises. According to the characteristics of the compressor and fan noise, a method of using sound insulation board was proposed to reduce the compressor noise. Considering the actual installation restrictions and the compressor cooling demand, a kind of sound insulation board with holes was applied. Experimental studies indicated that the proposed noise control method can suppress the noise of the household refrigerator effectively.
Active control of compressor noise in the machinery room of refrigerators
The low-frequency noise generated by the vibration of the compressor in the machinery room of refrigerators is considered as annoying sound. Active noise control is used to reduce this noise without any change in the design of the compressor in the machinery room. In configuring the
 control system, various signals are measured and analyzed to select the reference signal that best represents the compressor noise. As the space inside the machinery room is small, the size of a speaker is limited, and the magnitude of the controller transfer function is designed to be small
 at low frequencies, the controller uses FIR filter structure converged by the FxLMS algorithm using the pre-measured time signal. To manage the convergence speed for each frequency, the frequency-weighting function is applied to FxLMS algorithm. A series of measurements are performed to design
 the controller and to evaluate the control performance. After the control, the sound power transmitted by the refrigerator is reduced by 9 dB at the first dominant frequency (408 Hz in this case) and 3 dB at the second dominant frequency (459 Hz here), and the overall sound power decreases
 by 2.6 dB. Through this study, an active control system for the noise generated by refrigerator compressors is established.
Mucoadhesive Nanoparticles for Drug Delivery to the Anterior Eye
While the use of topical drops for the delivery of drugs to the anterior of the eye is well accepted, it is far from efficient with as little as 5% of the drug instilled on the eye actually reaching the target tissue. The ability to prolong the residence time on the eye is desirable. Based on the acceptability of 2-hydroxyethyl methacrylate based polymers in contact lens applications, the current work focuses on the development of a poly(2-hydroxyethyl methacrylate (HEMA)) nanoparticle system. The particles were modified to allow for degradation and to permit mucoadhesion. Size and morphological analysis of the final polymer products showed that nano-sized, spherical particles were produced. FTIR spectra demonstrated that the nanoparticles comprised poly(HEMA) and that 3-(acrylamido)phenylboronic acid (3AAPBA), as a mucoadhesive, was successfully incorporated. Degradation of nanoparticles containing N,N′-bis(acryloyl)cystamine (BAC) after incubation with DL-dithiothreitol (DTT) was confirmed by a decrease in turbidity and through transmission electron microscopy (TEM). Nanoparticle mucoadhesion was shown through an in-vitro zeta potential analysis.