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The viscosity of carboxymethylchitosan solutions was measured via an Ubbelohde viscometer. The effect of carboxymethylchitosan concentration, pH of the carboxymethylchitosan solution, and concentration of added NaCl and CaCl 2 on the reduced viscosity of the carboxymethylchitosan solutions were comparatively investigated. The results showed that the reduced viscosity of the carboxymethylchitosan solution decreased with the increase of carboxymethylchitosan concentration. The reduced viscosity of carboxymethylchitosan decreased with the addition of NaCl and CaCl 2 , and CaCl 2 affected the viscosity more significantly than NaCl. With the increase of pH, the reduced viscosity first decreased and then increased. The interaction between Ca 2+ ions and carboxymethylchitosan was studied by means of dynamic light scattering and scanning electron microscopy.

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We present MaskReminder, an automatic maskwearing status estimation system based on smartwatches, to remind users who may be exposed to the COVID-19 virus transmission scenarios, to wear a mask. MaskReminder with the powerful MLP-Mixer deep learning model can effectively learn long-short range information from the inertial measurement unit readings, and can recognize the mask-related hand movements such as wearing a mask, lowering the metal strap of the mask, removing the strap from behind one side of the ears, etc. Extensive experiments on 20 volunteers and 8000+ data samples show that the average recognition accuracy is 89%. Moreover, MaskReminder is capable to remind a user to wear with a success rate of 90% even in the user-independent setting. Code is publicly available at https://github.com/aiotgroup/MaskReminder