Humidity monitoring of exhaled breath has emerged as a vital approach for noninvasive respiratory health assessment, underscoring the need for sensitive and reliable humidity sensors. Despite its high conductivity and hydrophilic functional groups, reduced graphene oxide (rGO) often undergoes irreversible moisture adsorption and gradual oxidation by residual water, resulting in sensitivity degradation and long-term instability during cycling. In this study, a montmorillonite/reduced graphene oxide (MMT/rGO) composite is developed as a room-temperature humidity-sensing material, exhibiting an optimized response of 115%, more than 14 times higher than that of pristine rGO. This superior performance originates from the synergistic interaction between the reversible MMT swelling and the conductive rGO network near the electrical percolation transition, which ensures excellent stability and repeatability under repeated humidity cycles. These findings suggest that the MMT/rGO composite provides a cost-effective and biocompatible platform for next-generation wearable humidity sensors capable of continuous respiratory monitoring.

Magnetoelectric(ME) bulk composites with PZT- PYN- PZN/FeO1 were prepared by using a conventional ceramic methods and investigated on the ME voltage vs frequency of ac magnetic fields. We made the electric equivalent circuits by using the Maxwell-Wagner model and simulated the frequency dependence of ME voltage in low frequency region. IVIE devices were described by a series of two equivalent circuits of piezoelectric and magnetic, which have the relaxation time T due to the interaction between ME device and load resistor. Equivalent circuit of piezoelectric material is independent of frequency. However ferrite magnetic materials have Debye absorption and dipolar dispersion, whose equivalent circuit is a function of frequency. Therefore we suggest the resistance in the equivalent circuit is proportion to (1 + w2t2) and the capacitance is in inverse proportion to (1 + w w2t2) in the magnetic materials.

The Hall factor in a quantum well structure with X or L-type indirect conduction valleys is calculated for various strain conditions. The two-dimentsional constant energy of occupied valleys are proven to be identical. As a result the Hall factor depends on the direction of occupied valleys to the growth direction, regardless of the number of occupied valleys. This work is widely applicable to the two-dimensional structure with indirect conduction minima for any growth direction and under different strain conditions.

Optical gain characteristics of 1.3 ㎛ type-II GaAsSb/InGaNAs/GaAs trilayer quantum well structures were studied using multi-band effective mass theory. The results were compared with those of 1.3 ㎛ GaAsSb/InGaNAs/GaAs trilayer quantum well structures. In the case of 1.3 ㎛ GaAsSb/InGaNAs/GaAs trilayer quantum well structure, the energy difference between the first two subbands in the valence band is smaller than that of 1.3 ㎛ GaAsSb/InGaNAs/GaAs trilayer quantum well structure. Also, 1.3 ㎛ GaAsSb/InGaNAs/GaAs trilayer quantum well structure shows larger optical gain than 1.3 ㎛ GaAsSb/InGaNAs/GaAs trilayer quantum well structure. This means that GaAsSb/InGaNAs/GaAs system is promising as long-wavelength optoelectronic devices for optical communication.