Based on the principle of a relativistic electron cyclotron maser, gyrotrons can generate high-power coherent radiation in the millimeter-terahertz (THz) waveband. A pulse magnet can generate an ultra-high field strength, and simultaneously reduces the volume by several times compared with a conventional superconducting magnet, which promotes a THz gyrotron to break the 1 THz barrier. However, only an extremely short duration around the peak field of the pulse magnet can be used for a conventional open-cavity gyrotron fixed-frequency operation. In this letter, a novel gyrotron interaction scheme is proposed to excite the broadband THz radiation by integrating a broadband pre-bunched interaction circuit with a pulse magnet, which is a promising way to expand the frequency tuning bandwidth, enlarge the magnetic field by utilizing the range of the pulse magnet, extend the operating pulse duration of a gyrotron, and realize the quasi-continuous operation of a pulse magnet gyrotron. After an investigation into the frequency and time domains, a broadband pulse gyrotron driven by a 20 kV low-voltage electron beam is predicted to generate radiation with a frequency of between 0.328 and 0.338 THz, with a peak power of 2.1 kW in a 6 ms pulse duration.
A minigyrotron scheme controlled by a compact pulse magnet to excite broadband terahertz (THz) radiation is presented here. In comparison to an open-cavity circuit, the adopted prebunched backward-wave interaction circuit can expand tuning bandwidth tenfold under the control of time-varying magnetic field strength, which also significantly extends the available duration time of the pulse magnet for gyrotron operation. A quasi-optical mode convertor and a Brewster window constitute the output system to transfer the broadband radiation from the circuit into free space. A systematic gyrotron design is also presented. Driven by a low-voltage electron beam, the minigyrotron is predicted to generate radiation with 10-GHz tuning bandwidth around 0.33 THz and a maximum peak power of 2.1 kW with 6-ms pulse duration, using a TE6,2 mode interaction. Such a THz gyrotron with broad tunable bandwidth, kilowatt level power, and with the unique advantage of a compact configuration is the key to high-power THz scientific and industrial applications.
Nanoscale electron sources with high electron-emitting performance are of great interest in vacuum nanoelectronics. Resembling traditional thermionic emission sources based on a hot tungsten filament, a hot carbon nanotube or graphene can function as a nanoscale electron source because of its excellent thermal stability and electrical conductivity. In this article, studies of thermionic emission from single hot carbon nanostructures are overviewed, emphasizing their differences in physics from macroscopic thermionic emission as well as potential applications in vacuum nanoelectronics. Due to their low dimensionality, nanoscale size, and nonequilibrium electron distribution, Richardson’s Law, which governs thermionic emission from macroscopic metals, breaks down in the case of thermionic emission from single carbon nanostructures, and an internal electric field in a carbon nanostructure can contribute directly to its thermionic emission. Graphene-based nanoscale thermionic emission sources, source arrays, and vacuum transistors have been fabricated and demonstrated to exhibit the advantages compared to those based on field emission. The advances imply the promise of realizing high-performance nanoscale electron sources and vacuum electronic devices based on thermionic emission.
To better understand the sources, formation, and the transport of air pollutants over North China Plain (NCP), a four-week intensive campaign during summertime in 2014 was conducted in a central NCP rural site. In this study, particle hygroscopicity and volatility measurements were focused to characterize the thermodynamic properties of nanoparticles and gain insight into chemical composition of nanoparticles during the new particle formation (NPF) events. The water-soluble fractions of 30 and 50 nm newly formed particles were respectively 0.64 +/- 0.06 and 0.61 +/- 0.06, indicating that the water-soluble chemical compounds, most likely ammonium sulfate, dominated the condensational growth of newly formed particles over the NCP. Due to containing higher water-soluble fraction, nanoparticles can be activated as cloud condensation nuclei (CCN) at lower supersaturation in the atmosphere of NCP in contrast to cleaner environments, such as Melpitz (Central European background) and Hyytiala (boreal forest) during the NPF events. Our observations showed that the NPF and subsequent growth significantly resulted in an enhancement in CCN number concentration. The ranges of enhancement factors of CCN number concentration for supersaturation (SS) = 0.2, 0.4, 0.8% were respectively 1.9-7.0, 2.7-8.4, and 3.6-10.1. After being heated to 300 degrees C, the shrink factors for 30 and 50 nm particles were respectively 0.35 and 038. This indicated that non-volatile compounds could be produced during the growth process of newly formed particles. (C) 2017 Elsevier B.V. All rights reserved.
To better understand the sources, formation, and the transport of air pollutants over North China Plain (NCP), a four-week intensive campaign during summertime in 2014 was conducted in a central NCP rural site. In this study, particle hygroscopicity and volatility measurements were focused to characterize the thermodynamic properties of nanoparticles and gain insight into chemical composition of nanoparticles during the new particle formation (NPF) events. The water-soluble fractions of 30 and 50 nm newly formed particles were respectively 0.64 +/- 0.06 and 0.61 +/- 0.06, indicating that the water-soluble chemical compounds, most likely ammonium sulfate, dominated the condensational growth of newly formed particles over the NCP. Due to containing higher water-soluble fraction, nanoparticles can be activated as cloud condensation nuclei (CCN) at lower supersaturation in the atmosphere of NCP in contrast to cleaner environments, such as Melpitz (Central European background) and Hyytiala (boreal forest) during the NPF events. Our observations showed that the NPF and subsequent growth significantly resulted in an enhancement in CCN number concentration. The ranges of enhancement factors of CCN number concentration for supersaturation (SS) = 0.2, 0.4, 0.8% were respectively 1.9-7.0, 2.7-8.4, and 3.6-10.1. After being heated to 300 degrees C, the shrink factors for 30 and 50 nm particles were respectively 0.35 and 038. This indicated that non-volatile compounds could be produced during the growth process of newly formed particles. (C) 2017 Elsevier B.V. All rights reserved.
Recently, perovskite solar cells have attracted tremendous research interest due to their amazing light to electric power conversion efficiency (PCE). However, most high performance devices usually use mesoporous TiO2 as the electron transport layer (ETL), which increases cost for practical application. Here, TiO2/SnOxCly double layer was employed as the ETL for planar perovskite solar cells. Compared with bare TiO2, perovskite solar cell based on TiO2/SnOxCly shows drastically improved power conversion efficiency and reduced hysteresis. These improvements are attributed to TiO2/SnOxCly which could enhance electron extraction and reduce surface trap-state. (C) 2017 Elsevier B.V. All rights reserved.
Tobacco smoking is a preventable environmental factor that contributes to a wide spectrum of age-related health outcomes; however, its association with the development of frailty is not yet well established. We examined the associations of self-reported smoking indicators, serum cotinine levels and smoking-related DNA methylation biomarkers with a quantitative frailty index (FI) in 2 independent subsets of older adults (age 50-75) recruited in Saarland, Germany in 2000 - 2002 (discovery set: n = 978, validation set: n = 531). We obtained DNA methylation profiles in whole blood samples by Illumina HumanMethylation450 BeadChip and calculated the FI according to the method of Mitnitski and Rockwood. Mixed linear regression models were implemented to assess the associations between smoking indicators and the FI. After controlling for potential covariates, current smoking, cumulative smoking exposure (pack-years), and time after smoking cessation (years) were significantly associated with the FI (P-value < 0.05). In the discovery panel, 17 out of 151 previously identified smoking-related CpG sites were associated with the FI after correction for multiple testing (FDR < 0.05). Nine of them survived in the validation phase and were designated as frailty-associated loci. A smoking index (SI) based on the 9 loci manifested a monotonic association with the FI. In conclusion, this study suggested that epigenetic alterations could play a role in smoking-associated development of frailty. The identified CpG sites have the potential to be prognostic biomarkers of frailty and frailty-related health outcomes. Our findings and the underlying mechanisms should be followed up in further, preferably longitudinal studies.