Multi-MEMS-microphone schemes in a miniature photoacoustic cell for acetylene trace gas measurement.

Dissolved gas analysis is a strong tool for online health monitoring of electrical power equipment. The industry's large-scale deployment of photoacoustic (PA) sensors is still constrained by cost and sensitivity, despite the great accuracy achieved with a mid-infrared light source or optical sensors. We provide a low-cost PA sensor for ppb-level trace gas sensing based on a near-infrared distributed feedback laser source, miniature gas cell, and multiple microelectromechanical system (MEMS) microphones. Five multi-MEMS-microphones schemes are modeled. The simulation indicates that the sensor, including two MEMS microphones in the center of the resonator, is the most cost-efficient option. The experiments that present this scheme can be realized easily by modifying a traditional single microphone PA cell and with ppb-level sensitivity.

Experimental Investigation of the Dielectric Constants of Thin Noble Metallic Films Using a Surface Plasmon Resonance Sensor.

Gold and silver have an extremely low refractive index value of about 0.04 in the visible to near infrared (NIR) regions, and this induces a relative error of about 50% in refractive index measurements. This can lead to a large uncertainty in the imaginary part of the dielectric constants. A large difference exists between the experimental results and the classic models. The surface plasmon resonance (SPR) sensors, which use tens of nanometer thick noble metal film as the sensing layer, show ultra-high sensitivity (reaching 10-8 RIU) in this spectral range. As the spectral sensitivity and amplitude of SPR curves depend on the thickness and the dielectric constant of the sensing layer, we obtained high precision optical constants of the noble metal film using a multi-wavelength angle-modulated SPR sensing technology. The dielectric constant inferred from the parameters of the SPR curves, rather than from the refractive index and absorption ratio of noble metals, introduced a relative error within 10% of the resonance angle measurement. The measurement results demonstrate that the dielectric constants of gold and silver nano-films are more consistent with the widely used experimental results than with the classical theoretical model and always fall in the upper half of the imaginary part of the uncertainty range in the spectra of 500-900 nm.

Subdivision of Brillouin gain spectrum to improve the spatial resolution of a BOTDA system.

A pulse subdivision analysis method was developed to improve the spatial resolution of a conventional long pump pulse Brillouin optical time domain analysis (BOTDA) system. An exclusive photodetector was used to obtain the accurate energy distribution along the long pulse, based on which the long pulse was subdivided into several sub-pulses with certain energy weights. With these energy weights, the Brillouin spectrum generated by the long pulse was subdivided into equal numbers of sub-spectra. Each sub-spectrum could provide detailed sensing information about a fiber sub-segment related to a sub-pulse. Thus, the actual spatial resolution of the BOTDA system was determined by the sub-pulse instead of the long pulse. As a result, spatial resolution was increased by several times, depending on the subdivision multiples. The method was theoretically simulated and experimentally demonstrated. For experimental demonstration, the recognization capability of the melting point of two different fiber sections and the discrete strain distribution on a sensing fiber were respectively tested. For melting point recognization, thanks to five-multiple subdivision, a 1 m spatial resolution over 31 km sensing fiber was realized using a 50 ns pump pulse. For the strain sensing test, ten-multiple subdivision was performed to distinguish two 0.5 m stretched fiber sections with a 0.2 m interval using a 20 ns pump pulse. The spatial resolution is 0.2 m, which is a ten times' improvement compared with that before subdivision analysis. Due to its simplicity and cost-effectiveness, the method is believed to have extensive application prospects in distributed fiber sensing fields.

Application of lipopolysaccharide in establishing inflammatory models.

Lipopolysaccharide (LPS), a unique component of the outer membrane of Gram-negative bacteria, possesses immune-activating properties. It induces an immune response by stimulating host cells to produce a lot of inflammatory cytokines with a thermogenic effect, which may cause an inflammatory response. In the past few decades, the structure and function of LPS and its mechanism leading to inflammation have been extensively analyzed. Since LPS can cause inflammation, it is often used to establish inflammation models. These models are crucial in the study of inflammatory diseases that pose a serious threat to human health. In addition, the non-pro-inflammatory effects of LPS under certain circumstances are also being studied widely. This review summarizes the methods by which LPS has been used to establish inflammatory models at the cellular and animal levels to study related diseases. It also introduces in detail the evaluation indicators necessary for the successful establishment of these models, providing a reference for future research.

Structure, photoluminescence and wettability properties of well arrayed ZnO nanowires grown by hydrothermal method.

Well aligned ZnO nanowire arrays with high crystal quality were grown on Si substrates at a low temperature (50 degrees C) by hydrothermal method using a pre-formed ZnO seed layer. ZnO seeds were prepared via radio-frequency magnetron sputtering onto Si substrates. The morphologies of the ZnO nanowire arrays were shown by field emission scanning electron microscopy. X-ray diffraction spectra showed that the full width at the half maximum of the (0002) peak of the nanowire arrays without any heat treatment was only 0.07 degrees, indicating very high crystal quality. Furthermore, the room-temperature photoluminescence spectra of the ZnO nanowire arrays exhibited excellent UV emission. The special micro/nano surface structure of the ZnO nanowire arrays can enhance the dewettability for surfaces modified via low surface energy materials such as long chain fluorinated organic compounds. The surface of the ZnO nanowire arrays is also found to be superhydrophobic with a contact angle of 165 degrees +/- 1 degrees, while the sliding angle is 3 degrees.

A reticulate superhydrophobic self-assembly structure prepared by ZnO nanowires.

A simple hydrothermal self-assembly method was adopted to grow a newly reported superhydrophobic reticulate ZnO film with papillary nodes. The formation mechanism has also been explained by the tension junction model. This structure can extremely enhance the dewettability for the surface modification with low-surface-energy materials such as long chain fluorinated organic compounds. The surfaces of the ZnO thin film were superhydrophobic with a contact angle (CA) of 170 degrees +/- 1 degrees, while the sliding angle (SA) is 2 degrees. The samples were characterized by field emission scanning electron microscopy (FESEM).

Flexible and transparent graphene/silver-nanowires composite film for high electromagnetic interference shielding effectiveness.

Herein, an efficient approach to prepare flexible, transparent, and lightweight films based on graphene nanosheets (GNS) and silver nanowires (AgNWs) for high electromagnetic interference (EMI) shielding effectiveness (SE) has been explained. High-conductive GNS were fabricated by liquid phase stripping and composited with AgNWs by a two-step spin-coating method. Owing to the high transparency, good conductivity, and homogeneous distribution of both GNS and AgNWs, the obtained GNS/AgNWs film exhibits superb EMI SE and light transmittance, yielding a significantly high EMI SE up to 26 dB in both Ku-band and K-band and light transmittance higher than 78.4%. Moreover, this GNS/AgNWs film shows good flexibility and excellent structural stability. The obtained flexible, light and transparent film could have a great potential for transparent EMI shielding and smart electronics.