Volatile organic compounds (VOCs), which originate from painting, oil refining and vehicle exhaust emissions, are hazardous gases that have significant effects on air quality and human health. The detection of VOCs is of special importance to environmental safety. Among the various detection methods, chemoresistive semiconductor metal oxide gas sensors are considered to be the most promising technique due to their easy production, low cost and good portability. Sensitivity is an important parameter of gas sensors and is greatly affected by the microstructure, defects, catalyst, heterojunction and humidity. By adjusting the aforementioned factors, the sensitivity of gas sensors can be improved further. In this review, attention will be focused on how to improve the sensitivity of chemoresistive gas sensors towards certain common VOCs with respect to the five factors mentioned above.

Breast cancer is a common malignancy threatening women's health around the world. Despite improved treatments for different subtypes of breast tumors that have been put forward, there still exists a poor therapeutic response and prognosis. Magnetic fields, as a non-invasive therapy, have shown anti-tumor effects in vitro and in vivo; however, the detailed mechanisms involved are still not clear. In this study, we found that in exposure to low-frequency magnetic fields (LF-MFs) with an intensity of 1 mT and frequencies of 50, 125, 200, and 275 Hz, separately, the proliferation of breast cancer cells was inhibited and LF-MF with 200 Hz reached the optimum inhibition effect, on exposure time-dependently. Notably, we found that exposure to LF-MF led to MCF-7 and ZR-75-1 cell apoptosis and cell cycle arrest. Moreover, we also discovered that LF-MF effectively increased the level of reactive oxygen species (ROS), suppressed the PI3K/AKT signaling pathway, and activated glycogen synthase kinase-3β (GSK-3β). We demonstrated that the GSK3β activity contributed to LF-MF-induced cell proliferation inhibition and apoptosis, while the underlying mechanism was associated with the inhibition of PI3K/AKT through increasing the intracellular ROS accumulation. These results indicate that LF-MF with a specific frequency may be an attractive therapy to treat breast cancers.Int. J. Mol. Sci. 2020, 21, 2952 2 of 14 processes [9]. Further research has found that low-frequency magnetic fields (LF-MFs), namely, those with a frequency below 300 Hz, possess a variety of effects such as the regulation of immunity [10] and inflammation [11], suppression of angiogenesis [12], contribution to differentiation [13], and induced apoptosis [14]. Although many biological effects of magnetic fields have been reported, the mechanisms involved still remain unclear.Reactive oxygen species (ROS), including superoxide and hydrogen peroxide, are one of the main causes of tumors and play an important role in the process of tumor progression, metastasis and apoptosis [15]. Low-frequency magnetic fields have been demonstrated to significantly increase the intracellular ROS levels in many kinds of cells [16]. The PI3K/AKT pathway is a pivotal signaling pathway, which is closely related to the regulation of cell survival, apoptosis, migration and proliferation [17]. The relationship between ROS and the PI3K/AKT pathway in apoptosis regulation has been confirmed in several studies [18,19]. Glycogen synthase kinase-3β (GSK-3β) is an effector of PI3K/AKT, and is a kind of serine / threonine protein kinase, whose biological function is far beyond the glucose synthesis-regulating enzyme it was initially considered. GSK-3β can phosphorylate many substrates, including metabolism and signal protein, transcription factors of cell structural protein, etc., playing an important role in the process of tumor occurrence and development [20,21]. Baihuan Feng et al. reported that exposure to 50 Hz-0.4 mT MF affected mitochondrial permeability by the ROS-regulating phosphoryla...

Cancer is one of the most common causes of death worldwide. Although the existing therapies have made great progress and significantly improved the prognosis of patients, it is undeniable that these treatment measures still cause some serious side effects. In this context, a new treatment method is needed to address these shortcomings. In recent years, the magnetic fields have been proposed as a novel treatment method with the advantages of less side effects, high efficiency, wide applications, and low costs without forming scars. Previous studies reported that static magnetic fields (SMFs) and low-frequency magnetic fields (LF-MFs, frequency below 300 Hz) exert anti-tumor function, independent of thermal effects. Magnetic fields (MFs) could inhibit cell growth and proliferation; induce cell cycle arrest, apoptosis, autophagy, and differentiation; regulate the immune system; and suppress angiogenesis and metastasis via various signaling pathways. In addition, they are effective in combination therapies: MFs not only promote the absorption of chemotherapy drugs by producing small holes on the surface of cell membrane but also enhance the inhibitory effects by regulating apoptosis and cell cycle related proteins. At present, MFs can be used as drug delivery systems to target magnetic nanoparticles (MNPs) to tumors. This review aims to summarize and analyze the current knowledge of the pre-clinical studies of anti-tumor effects and their underlying mechanisms and discuss the prospects of the application of MF therapy in cancer prevention and treatment.

The development of biofilms and the related changes in porous media in the subsurface cannot be directly observed and evaluated. The primary reason that the mechanism of biofilm clogging in porous media cannot be clearly demonstrated is due to the opacity and structural complexity of three-dimensional pore space. Interest in exploring methods to overcome this limitation has been increasing. In the first part of this review, we introduce the underlying characteristics of biofilm in porous media. Then, we summarize two approaches, non-invasive measurement methods and mathematical simulation strategies, for studying fluid–biofilm–porous medium interaction with spatiotemporal resolution. We also discuss the advantages and limitations of these approaches. Lastly, we provide a perspective on opportunities for in situ monitoring at the field site.

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Magnetic resonance detection of tunnel as a non-invasive, direct and quantitative geophysical method for detecting groundwater has attracted much attention in the research of tunnel water hazard early warning. In view of the complex environment where the magnetic resonance detection signal is only nanovolt and the tunnel space, the peak noise and environmental noise are much greater than those of ground magnetic resonance detection. In this paper, we propose a peak noise suppression method based on collaborative filtering to suppress the peak noise of tunnel magnetic resonance rotation detection. In this method, the co-filtering parameters are calculated by using the data without peak noise, and then the peak noise suppression of rotation detection is realized. Through simulation, this method can effectively suppress the peak noise in the tunnel rotation detection magnetic resonance signal and improve the signal quality without changing the relaxation and attenuation characteristics of the tunnel magnetic resonance detection signal. The noise reduction effect of peak noise suppression method based on collaborative filtering is compared and analyzed when the amplitude and quantity of peak noise are different. The influence of this method on the peak noise suppression effect under different Gaussian noise levels is discussed. It is concluded that collaborative filtering can suppress the peak and part of Gaussian noise well without losing the effective magnetic resonance signal.

To in situ and noninvasively monitor the biofilm development process by low-field nuclear magnetic resonance (NMR), experiments should be made to determine the mechanisms responsible for the T2 signals of biofilm growth. In this paper, biofilms were cultivated in both fluid media and saturated porous media. T2 relaxation for each sample was measured to investigate the contribution of the related processes to T2 relaxation signals. In addition, OD values of bacterial cell suspensions were measured to provide the relative number of bacterial cells. We also obtained SEM photos of the biofilms after vacuum freeze-drying the pure sand and the sand with biofilm formation to confirm the space within the biofilm matrix and identify the existence of biofilm formation. The T2 relaxation distribution is strongly dependent on the density of the bacterial cells suspended in the fluid and the stage of biofilm development. The peak time and the peak percentage can be used as indicators of the biofilm growth states.