Temporal-spatial distributions of road silt loadings and fugitive road dust emissions in Beijing from 2019 to 2020.

Road silt loading (sL) is an important parameter in the fugitive road dust (FRD) emissions. In this study, the improved Testing Re-entrained Aerosol Kinetic Emissions from Roads (TRAKER) combined with the AP-42 method was firstly developed to quickly measure and estimate the sLs of paved roads in Beijing, China. The annual average sLs in Beijing was 0.59±0.31 g/m2 in 2020, and decreased by 22.4% compared with that in 2019. The seasonal variations of sLs followed the order of spring > winter > summer > autumn in the two years. The seasonal mean road sLs on the same type road in the four seasons presented a decline trend from 2019 to 2020, especially on the Express way, decreasing 47.4%-72.7%. The road sLs on the different type roads in the same season followed the order of Major arterial ∼ Minor arterial ∼ Branch road > Express road, and Township road ∼ Country highway > Provincial highway ∼ National highway. The emission intensities of PM10 and PM2.5 from FRD in Beijing in 2020 were lower than those in 2019. The PM10 and PM2.5 emission intensities at the four planning areas in the two years all presented the order of the capital functional core area > the urban functional expansion area > the urban development new area > the ecological conservation and development area. The annual emissions of PM10 and PM2.5 from FRD in Beijing in 2020 were 74,886 ton and 18,118 ton, respectively, decreasing by ∼33.3% compared with those in 2019.

Simultaneous AC and DC measurement based on an FBG-magnetostrictive fiber sensor.

Simultaneous alternating current (AC) and direct current (DC) measurement is demonstrated with a new fiber sensor that combines fiber Bragg gratings (FBGs) with giant magnetostrictive materials (GMMs). Deformation of GMMs, proportional to the central wavelength shift of FBGs, is different when applying DC and AC to a solenoid where the whole sensing structure is located. DC introduces a constant deformation while AC causes a periodic variation. Therefore, the central wavelength of FBG has a periodic harmonic variation, which makes it possible to demodulate the values of DC and AC at the same time. In addition, the proposed method has potential significance for reducing temperature cross talk caused by the thermal sensitivity of FBGs. The experimental results show that the sensitivity of the AC current can reach up to 0.090576 nm/A in the range of 0 to 1 A, and in different AC environments, the sensitivity of the DC current can reach up to 0.2378 nm/A.

Air pollutant emissions from the asphalt industry in Beijing, China.

Improving our understanding of air pollutant emissions from the asphalt industry is critical for the development and implementation of pollution control policies. In this study, the spatial distribution of potential maximum emissions of volatile organic compounds (VOCs) in the complete life cycle of asphalt mixtures, as well as the particulate matter (PM), asphalt fume, nonmethane hydrocarbons (NMHCs), VOCs, and benzoapyrene (BaP) emissions from typical processes (e.g., asphalt and concrete mixing stations, asphalt heating boilers, and asphalt storage tanks) in asphalt mixing plants, were determined in Beijing in 2017. The results indicated that the potential maximum emissions of VOCs in the complete life cycle of asphalt mixtures were 18,001 ton, with a large contribution from the districts of Daxing, Changping, and Tongzhou. The total emissions of PM, asphalt fume, NMHC, VOCs, and BaP from asphalt mixing plants were 3.1, 12.6, 3.1, 23.5, and 1.9 × 10-3 ton, respectively. The emissions of PM from asphalt and concrete mixing stations contributed the most to the total emissions. The asphalt storage tank was the dominant emission source of VOCs, accounting for 96.1% of the total VOCs emissions in asphalt mixing plants, followed by asphalt heating boilers. The districts of Daxing, Changping, and Shunyi were the dominant regions for the emissions of PM, asphalt fume, NMHC, and BaP, while the districts of Shunyi, Tongzhou, and Changping contributed the most emissions of VOCs.

Photo-induced enhanced negative absorption in the graphene-dielectric hybrid meta-structure.

Recently, the negative absorption in graphene-based metamaterials became a very attractive direction of THz electronic devices. Here we propose a graphene-dielectric hybrid meta-structure to realize photo-induced enhanced negative absorption in the THz regime, which results from strong graphene-light interaction. The negative absorption is derived from the degradation of the conductivity of graphene under optical pump. Meanwhile, the graphene-dielectric hybrid meta-structure introduces dispersion relation and resonance mode, which can couple with the incident wave to construct a strong resonance. In this case, both the dispersion of the propagating waves and resonance are contributed to the graphene-light interaction and enhance the negative absorption, in which the resonance coupling determines the distribution of negative absorption, and the maximum is dominated by dispersion. More importantly, compared with the previous work, the negative absorption is increased by nearly 100 times by adopting this meta-structure.

High-Speed Efficient Terahertz Modulation Based on Tunable Collective-Individual State Conversion within an Active 3 nm Two-Dimensional Electron Gas Metasurface.

Terahertz (THz) modulators are always realized by dynamically manipulating the conversion between different resonant modes within a single unit cell of an active metasurface. In this Letter, to achieve real high-speed THz modulation, we present a staggered netlike two-dimensional electron gas (2DEG) nanostructure composite metasurface that has two states: a collective state with massive surface resonant characteristics and an individual state with meta-atom resonant characteristics. By controlling the electron transport of the nanoscale 2DEG with an electrical grid, collective-individual state conversion can be realized in this composite metasurface. Unlike traditional resonant mode conversion confined in meta-units, this state conversion enables the resonant modes to be flexibly distributed throughout the metasurface, leading to a frequency shift of nearly 99% in both the simulated and experimental transmission spectra. Moreover, such a mechanism can effectively suppress parasitic modes and significantly reduce the capacitance of the metasurface. Thereby, this composite metasurface can efficiently control the transmission characteristics of THz waves with high-speed modulations. As a result, 93% modulation depth is observed in the static experiment and modulated sinusoidal signals up to 3 GHz are achieved in the dynamic experiment, while the -3 dB bandwidth can reach up to 1 GHz. This tunable collective-individual state conversion may have great application potential in wireless communication and coded imaging.

Gbps terahertz external modulator based on a composite metamaterial with a double-channel heterostructure.

The past few decades have witnessed a substantial increase in terahertz (THz) research. Utilizing THz waves to transmit communication and imaging data has created a high demand for phase and amplitude modulation. However, current active THz devices, including modulators and switches, still cannot meet THz system demands. Double-channel heterostructures, an alternative semiconductor system, can support nanoscale two-dimensional electron gases (2DEGs) with high carrier concentration and mobility and provide a new way to develop active THz devices. In this Letter, we present a composite metamaterial structure that combines an equivalent collective dipolar array with a double-channel heterostructure to obtain an effective, ultrafast, and all-electronic grid-controlled THz modulator. Electrical control allows for resonant mode conversion between two different dipolar resonances in the active device, which significantly improves the modulation speed and depth. This THz modulator is the first to achieve a 1 GHz modulation speed and 85% modulation depth during real-time dynamic tests. Moreover, a 1.19 rad phase shift was realized. A wireless free-space-modulation THz communication system based on this external THz modulator was tested using 0.2 Gbps eye patterns. Therefore, this active composite metamaterial modulator provides a basis for the development of effective and ultrafast dynamic devices for THz wireless communication and imaging systems.

Assessing vestibular function using electroencephalogram rhythms evoked during the caloric test.

Introduction: The vestibular system is responsible for motion perception and balance preservation in the body. The vestibular function examination is useful for determining the cause of associated symptoms, diagnosis, and therapy of the patients. The associated cerebral cortex processes and integrates information and is the ultimate perceptual site for vestibular-related symptoms. In recent clinical examinations, less consideration has been given to the cortex associated with the vestibular system. As a result, it is crucial to increase focus on the expression of the cortical level while evaluating vestibular function. From the viewpoint of neuroelectrophysiology, electroencephalograms (EEG) can enhance the assessments of vestibular function at the cortex level. Methods: This study recorded nystagmus and EEG data throughout the caloric test. Four phases were considered according to the vestibular activation status: before activation, activation, fixation suppression, and recovery. In different phases, the distribution and changes of the relative power of the EEG rhythms (delta, theta, alpha, and beta) were analyzed, and the correlation between EEG characteristics and nystagmus was also investigated. Results: The results showed that, when the vestibule was activated, the alpha power of the occipital region increased, and the beta power of the central and top regions and the occipital region on the left decreased. The changes in the alpha and beta rhythms significantly correlate with nystagmus values in left warm stimulation. Discussion: Our findings offer a fresh perspective on cortical electrophysiology for the assessment of vestibular function by demonstrating that the relative power change in EEG rhythms can be used to assess vestibular function.

Selection of ovine oocytes by brilliant cresyl blue staining.

Sheep oocytes derived from the ovaries collected from the slaughterhouse are often used for research on in vitro embryo production, animal cloning, transgenesis, embryonic stem cells, and other embryo biotechnology aspects. Improving the in vitro culture efficiency of oocytes can provide more materials for similar studies. Generally, determination of oocyte quality is mostly based on the layers of cumulus cells and cytoplasm or cytoplasm uniformity and colors. This requires considerable experience to better identify oocyte quality because of the intense subjectivity involved (Gordon (2003), Madison et al. (1992) and De Loos et al. (1992)). BCB staining is a function of glucose-6-phosphate dehydrogenase (G6PD) activity, an enzyme synthesized in developing oocytes, which decreases in activity with maturation. Therefore, unstained oocytes (BCB-) are high in G6PD activity, while the less mature oocytes stains are deep blue (BCB+) due to insuffcient G6PD activity to decolorize the BCB dye.

Caffeine and dithiothreitol delay ovine oocyte ageing.

The intracellular glutathione levels and developmental competence of aged oocytes after parthenogenetic activation, somatic cell nuclear transfer and intracytoplasmic sperm injection in the presence or absence of caffeine or dithiothreitol (DTT) were examined. The following results were found: (1) ovine oocytes were fully aged 30 h post-onset of maturation culture; (2) the appropriate concentrations of caffeine and DTT for oocyte culture were 5 mM and 1 mM, respectively; (3) when nuclear transfer-reconstructed embryos were treated with caffeine or DTT following fusion, no increase in the frequency of development to blastocyst was observed (P > 0.05), but the cell numbers of blastocysts increased (P < 0.05); (4) both caffeine and DTT increased the blastocyst formation rates of intracytoplasmic sperm-injected embryos (P < 0.05); (5) caffeine increased the glutathione content of aged oocytes (P < 0.05). The glutathione content of DTT-treated aged oocytes was higher than that of oocytes matured for 36 h (P < 0.05). In conclusion, caffeine and dithiothreitol delay oocyte ageing but only to a limited extent.

A Review of THz Modulators with Dynamic Tunable Metasurfaces.

Terahertz (THz) radiation has received much attention during the past few decades for its potential applications in various fields, such as spectroscopy, imaging, and wireless communications. To use terahertz waves for data transmission in different application systems, the efficient and rapid modulation of terahertz waves is required and has become an in-depth research topic. Since the turn of the century, research on metasurfaces has rapidly developed, and the scope of novel functions and operating frequency ranges has been substantially expanded, especially in the terahertz range. The combination of metasurfaces and semiconductors has facilitated both new opportunities for the development of dynamic THz functional devices and significant achievements in THz modulators. This paper provides an overview of THz modulators based on different kinds of dynamic tunable metasurfaces combined with semiconductors, two-dimensional electron gas heterostructures, superconductors, phase-transition materials, graphene, and other 2D material. Based on the overview, a brief discussion with perspectives will be presented. We hope that this review will help more researchers learn about the recent developments and challenges of THz modulators and contribute to this field.

In Vitro Modeling of Human Germ Cell Development Using Pluripotent Stem Cells.

Due to differences across species, the mechanisms of cell fate decisions determined in mice cannot be readily extrapolated to humans. In this study, we developed a feeder- and xeno-free culture protocol that efficiently induced human pluripotent stem cells (iPSCs) into PLZF+/GPR125+/CD90+ spermatogonium-like cells (SLCs). These SLCs were enriched with key genes in germ cell development such as MVH, DAZL, GFRα1, NANOS3, and DMRT1. In addition, a small fraction of SLCs went through meiosis in vitro to develop into haploid cells. We further demonstrated that this chemically defined induction protocol faithfully recapitulated the features of compromised germ cell development of PSCs with NANOS3 deficiency or iPSC lines established from patients with non-obstructive azoospermia. Taken together, we established a powerful experimental platform to investigate human germ cell development and pathology related to male infertility.

Derivation and characterization of ovine embryonic stem-like cell lines in semi-defined medium without feeder cells.

Domestic animal embryonic stem (ES) cells would provide an invaluable research tool for genetic breeding and the production of transgenic animals. Unfortunately, authentic domestic animals ES cells have not been established despite progress made over more than two decades. Here, we show that ovine ES-like cells can be efficiently derived and propagated in a semi-defined medium that contains N2, B27, GSK3 inhibitor (CHIR99021), and basic fibroblast growth factor (bFGF). These ovine ES-like cells had a characteristic three-dimensional appearance, showed a bFGF dose-dependence, expressed specific markers such as alkaline phosphatase (AP), Oct-4, Sox2, Nanog and can be maintained for 30 passages. Moreover, these cells differentiated in vitro into neuronal cells, and formed teratomas containing a variety of different tissues including cartilage and neural tissue when injected into kidney capsules of severe combined immunodeficiency (SCID) mice. But the cell lines fail to contribute to embryonic development upon blastocyst transplantation. To our knowledge, this is the first experiment to use semi-defined medium without feeder-cells to derive ES-like cells from ovine blastocysts, and opens the door to deriving authentic ES cells from domesticated ungulates.

[Pluripotency candidate signaling network and transcription factors in domesticated ungulates: a review].

Domesticated ungulates embryonic stem (ES) cells have great significances in biology and wide application prospects. This review compared the key signaling pathways related with pluripotency between mouse and human ES cells, and the difference of transcription factors in mouse, human and domesticated ungulates ES cells were elaborated. Finally the pluripotency candidate signaling network and transcription factors related in the derivation of domesticated ungulates ES cell were discussed combined with practical experience of ovine embryonic stem cell derivation in our laboratory.

[Differentiation of bovine male germ-line stem cells in vitro].

Male germ-line stem cells (mGSCs) have the capability of self-renewal and latent capability of differentiation. mGSCs is the unique diploid immortal cell which can transfer genetic information to filial generation. The combination of transgenic technology and mGSCs heterotransplanting will supply new opportunities and paths to cloning animal, transgenic animal and gene therapy of some human hereditary disease. We studied the isolation and cultivation of mGSCs that were isolated and purified from 5-6 month old bovine fetal testis, new born bovine testis by adopting mixed enzymes digestion and different attaching velocities methods. The results showed that Sertoli cells were indispensable to mGSC's proliferation and differentiation in vitro. The Sertoli cells in logarithmic phase have a significant effect on mGSC's attaching, proliferation and differentiation. Co-culture with Sertoli cells, mGSCs differentiated to long sperm after 16 days. A preliminary system for mGSC's inducing differentiation was established.