The recently observed excess in gamma-ray signal near the Galactic center suggests that dark matter particles may annihilate into charged fermions that produce gamma-ray to be observed. In this ...paper, we consider a leptonic dark matter, which annihilates into the standard model leptons, μ+μ− and τ+τ−, by the interaction of the gauged lepton number U(1)Lμ−Lτ and fits the observed excess. Interestingly, the necessary annihilation cross section for the observed gamma-ray flux provides a good fit to the value for the relic abundance of dark matter. We identify the preferred parameter space of the model after taking the existing experimental constraints from the precision measurements including the muon (g−2), tau decay, neutrino trident production, dark matter direct detection, LHC, and LEP experiments.
Non-thermal WIMP baryogenesis Choi, Ki-Young; Kang, Sin Kyu; Kim, Jongkuk
Physics letters. B,
07/2018, Letnik:
782
Journal Article
Recenzirano
Odprti dostop
We propose a model of baryogenesis achieved by the annihilation of non-thermally produced WIMPs from decay of heavy particles, which can result in low reheating temperature. Dark matter (DM) can be ...produced non-thermally during a reheating period created by the decay of long-lived heavy particle, and subsequently re-annihilate to lighter particles even after the thermal freeze-out. The re-annihilation of DM provides the observed baryon asymmetry as well as the correct relic density of DM. We investigate how washout effects can affect the generation of the baryon asymmetry and study a model suppressing them. In this scenario, we find that DM can be heavy enough and its annihilation cross section can also be larger than that adopted in the usual thermal WIMP baryogenesis.
Tetrahedral amorphous carbon (ta-C) has emerged as an excellent coating material for improving the reliability of application components under high normal loads. Herein, we present the results of our ...investigations regarding the mechanical and tribological properties of a 2-µm-thick multilayer ta-C coating on high-speed steel substrates. Multilayers composed of alternating soft and hard layers are fabricated using filtered a cathodic vacuum arc with alternating substrate bias voltages (0 and 100 V or 0 and 150 V). The thickness ratio is discovered to be 1:3 for the sp
2
-rich and sp
3
-rich layers. The results show that the hardness and elastic modulus of the multilayer ta-C coatings increase with the sp
3
content of the hard layer. The hardness reached approximately 37 GPa, whereas an improved toughness and a higher adhesion strength (> 29 N) are obtained. The friction performance (
µ
= 0.07) of the multilayer coating is similar to that of the single layer ta-C thick coating, but the wear rate (0.13 × 10
−6
mm
3
/(N·m)) improved under a high load of 30 N. We further demonstrate the importance of the multilayer structure in suppressing crack propagation and increasing the resistance to plastic deformation (
H
3
/
E
2
) ratio.
The effect of nitrogen doping on the mechanical and electrical performance of single-layer tetrahedral amorphous carbon (ta-C:N) coatings of up to 1μm in thickness was investigated using a ...custom-made filtered cathode vacuum arc (FCVA). The results obtained revealed that the hardness and electrical resistance of the coatings decreased from 65±4.8GPa (3kΩ/square) to 25±2.4GPa (10Ω/square) with increasing nitrogen gas ratio, which indicates that nitrogen doping occurs through substitution in the sp2 phase. Subsequent AES analysis showed that the N/C ratio in the ta-C:N thick-film coatings ranged from 0.03 to 0.29 and increased with the nitrogen flow rate. Variation in the G-peak positions and I(D)/I(G) ratio exhibit a similar trend. It is concluded from these results that micron-thick ta-C:N films have the potential to be used in a wide range of functional coating applications in electronics.
Improved electrical resistance and high hardness of thick ta-C:N coating with nitrogen gas doping (20sccm) using filtered cathode vacuum arc technique. Display omitted
•One micron thick ta-C:N coatings were successfully deposited by FCVA.•The hardness of these coatings was controllable from 65 to 25GPa.•Their electrical resistance after nitrogen gas doping was 10Ω/square.•Nitrogen doping creates CC bonds with CNC groups.•Higher nitrogen concentrations reduce hardness but improve electrical resistance.
Diamond-Like Carbon (DLC) coating is an effective surface treatment method for improving the tribological properties of machine elements and tool materials. Among them, the tetrahedral amorphous ...carbon (ta-C) coating has recently received much attention due to its high hardness and good heat resistance. When characterizing friction and wear patterns related to the lifetime and cost, the thickness of the ta-C coating and the type of substrates play an important role. In this paper, ta-C coatings of two thicknesses are deposited on 304 stainless steel (SS) and cemented carbide (WC–Co), which have significant differences in mechanical properties, through filtered cathodic vacuum arc (FCVA) equipment. After ta-C coating on substrates, the tribological properties of each sample are investigated. As a result, compared to bare materials, ta-C-coated materials have a reduced coefficient of friction and improved wear resistance. However, as the base material is softer, tearing occurs in a thin coating so that a thicker ta-C coating might improves the tribological properties. Since thicker ta-C coatings do not always improve tribological properties, the efficiency can be increased by customizing the ta-C coating thickness according to the substrate layer material.
•A tribological investigation of DLC coating effects on base materials was conducted.•304 SS and WC-Co were coated with tetrahedral amorphous carbon (ta-C) nanofilms.•We investigated each sample’s tribological properties after ta-C coating.•ta-C-coated materials have an improved coefficient of friction and wear resistance.•The Hertzian contact stress generated on ta-C was studied with finite element method.
1. Global environmental change can dramatically alter the composition of floral and faunal communities, and elucidating the mechanisms underlying this process is important for predicting its ...outcomes. Studies on global climate change have mostly focused on statistical summaries within wide spatial and temporal scales; less attention has been paid to variability in microclimates at narrower spatial and temporal scales. 2. The microclimate is the suite of climatic conditions measured in a local area. Environmental variables at the microclimatic scale can be critical for the ecology of organisms inhabiting each area. The effect of spatial and temporal changes in the microclimate on the ecology of carabid beetle communities in three sites on Mount Odaesan, Korea was examined. 3. Carabid beetle communities and quantified site-specific environmental factors from measurements of air temperature, air humidity, light intensity and soil temperature over 5 years (2010-2015) were surveyed. 4. It was found that microclimatic variables and the patterns of temporal changes in carabid beetle communities differed between the three sites within the single mountain system. Microclimatic variables influencing temporal changes in beetle communities also differed between the sites. Therefore, it is suggested that variation in local microclimates affects spatial and temporal variation in carabid beetle communities at a local scale. 5. The present results demonstrate the importance of regular surveys of communities at local scales. Such surveys are expected to reveal an additional fraction of variation in communities and underlying processes that have been overlooked in studies of global community patterns and change.
A tetrahedral amorphous carbon (ta-C) is widely used in industrial environments. However, application in extreme environments requires improved interfacial adhesion strength. This study proposes a ...new method to determine the adhesion strength of ta-C coating using the microtensile test, which is applied to improve the adhesion strength of ta-C coating by varying the Ti buffer layer microstructure. The tensile properties recorded in the stress-strain curve can be used to determine the difference between the absorbed energy and resistance to plastic deformation, which is then used to calculate fracture toughness. Moreover, to determine the adhesion strength, the crack density and spallation size were evaluated by measuring the cracks on the slip surface. The results show that compared to the columnar Ti buffer layer microstructure, the ta-C coating with a dense and flat Ti buffer layer microstructure more effectively improved the composite mechanical properties (columnar Ti layer H = ∼39 GPa, E = ∼430 GPa; dense Ti layer H = ∼48 GPa, E = ∼468 GPa), crack resistance (crack density = 6.4 % on columnar Ti layer; 1.5 % on dense Ti layer) and increased the dissipation energy during plastic deformation. Additionally, the dense Ti buffer layer microstructure reduced the wear rate (3.1 × 10−7 mm3/N∙m) and inhibited crack generation under long-term continuous frictional contact due to stress release in the ta-C coating. This finding clarifies the importance of the buffer layer with the suggested microstructural modifications for the wear resistance of ta-C coating.
•Ti buffer layer microstructure affected substrate adhesion of tetrahedral amorphous coating•Flat microstructure of Ti buffer layer reduced the wear rate and inhibited crack generationdue to stress release in the ta-C coating•The micro-tensile method can quantitatively determine the interface failure and adhesion properties•The continuous sliding contact confirmed that the microstructure of the Ti buffer layer is an important factor increasing adhesion, wear resistance as well as crack resistance
(ta-C) films coated through the filtered cathodic vacuum arc (FCVA) process as a hole transport layer (HTL) for perovskite solar cells (PSCs) and quantum dot light-emitting diodes (QDLEDs). The ...p-type ta-C film has several remarkable features, including ease of fabrication without the need for thermal annealing, reasonable electrical conductivity, optical transmittance, and a high work function. X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy examinations show that the electrical properties (sp
3
/sp
2
hybridized bond) and work function of the ta-C HTL are appropriate for PSCs and QDLEDs. In addition, in order to correlate the performance of the devices, the optical, surface morphological, and structural properties of the FCVA-grown ta-C films with different thicknesses (5 ~ 20 nm) deposited on the ITO anode are investigated in detail. The optimized ta-C film with a thickness of 5 nm deposited on the ITO anode had a sheet resistance of 10.33 Ω
−2
, a resistivity of 1.34 × 10
−4
Ω cm, and an optical transmittance of 88.97%. Compared to the reference PSC with p-NiO HTL, the PSC with 5 nm thick ta-C HTL yielded a higher power conversion efficiency (PCE, 10.53%) due to its improved fill factor. Further, the performance of QDLEDs with 5 nm thick ta-C hole injection layers (HIL) showed better than the performance of QDLEDs with different ta-C thicknesses. It is concluded that ta-C films have the potential to serve as HTL and HIL in next-generation PSCs and QDLEDs.
Spatial and temporal variation in ecological environments may result in spatial and temporal variation in communities. Temporal studies of biodiversity are essential for forecasting future changes in ...community structure and ecosystem function. Therefore, determining the mechanisms that drive temporal change in communities remains an important and interesting challenge in ecology. We quantified spatial and temporal variations in carabid beetle communities and site-specific environmental factors for 5 years at nine study sites on three mountains in the Baekdudaegan Mountain Range, Korea. Carabid beetle communities exhibited significant temporal variation, which was larger than spatial variations between and within mountains. Environmental factors mostly varied between sites within mountains. Community variation was only weakly associated with environmental factors at wide scales, i.e., between sites on three mountains, but was strongly associated at narrow spatial scales, i.e., between sites within one mountain. Our results indicate that temporal variation in communities occurs in response to variations in the local climate, and that the patterns of temporal variation differ between mountains. Thus, temporal surveys of insect communities and climates at local scales are important for predicting temporal changes in the communities.
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