Control of laser-plasma instabilities by non-collinear polychromatic light

Normal broadband lasers with collinear polychromatic components have immense potential for mitigating laser plasma instabilities (LPIs). However, the projection complexity of collinear polychromatic light (CPL) is a significant challenge owing to the demand for a large bandwidth and beamlet number. Here, we propose a theoretical LPI model and optical design for non-collinear polychromatic light (NCPL), which has a small angle $\sim4^\circ$ and large frequency difference $\sim$1\% between the double-color beamlets. LPI models of the NCPL demonstrate a decoupling threshold for the shared daughter waves under a multibeam configuration. Compared with the CPL, the wavevector couplings are further reduced by the introduced angle. Therefore, both the growth rate and saturation level of LPIs are greatly reduced by using the NCPL. The two- and three-dimensional simulation results indicate that the NCPL reduces the absolute and convective decoupling thresholds of the CPL and is sufficient to effectively mitigate the reflectivity, hot-electron generation, and intensity of cross-beam energy transfer. An optical design for the efficient generation of ultraviolet NCPL has been presented based on the unsaturated optical parametric amplification and non-collinear sum-frequency generation

Hot Compression Test and Microstructure Evolution in LZ50 Axle Steel

True strain-true stress curves of the LZ50 axle steel were obtained after hot compression tests had been performed on a Gleeble-3800 thermal simulator at strain rates of 0.01, 0.1, 1 and 5 s^(-1) and at deformation temperatures from 850 to 1,150 ℃. Following the data processing, the relationship between the flow stress and the deformation temperature of the material under different true strain conditions was analysed. On this basis and according to the influence of deformation factors, the constitutive equation of the Johnson-Cook flow stress model is established, and the model is modified according to the defects of the model, so that the improved model can effectively predict the mechanical behaviour in the range of high strain rates and temperatures. The dynamic material model (DMM) was used to generate the hot working diagram of the material. Through calculation and analysis, the optimum process area in terms of temperature was found to be in the range from 1,050 to 1,150 ℃ and in terms of strain rate in the rage from 1 to 5 s^(-1). Finally, the microstructure evolution of the compressed specimens under different strain rates and temperatures was studied in the metallographic analysis, which provided a theoretical basis and reference value for later damage

Observed Changes of Koppen Climate Zones Based on High-Resolution Data Sets in the Qinghai-Tibet Plateau

Emerging and disappearing climate zones are frequently used to diagnose and project climate change. However, little attempt has been made to quantify shifts of climate zones in Qinghai-Tibet Plateau (QTP) based on the high-resolution data sets. Our results show that highland climate was decreased substantially during 1961–2011 and were mainly replaced by boreal climate. We also found that the mean elevation of boreal and highland climate continues to rise, with obvious longitudinal geographical characteristics over the study period. Furthermore, we found that the climate spaces (a climate space defined as the volume of 10°C × 500 mm here) of both boreal and highland climate types tend to be warm and humid ones, which may provide more suitable climate conditions for species to maintain and promote diversity. Characterization of changes in QTP climate types deepens our understanding of regional climate and its biological impacts.Emerging and disappearing climate zones are frequently used to diagnose and project climate change. However, little attempt has been made to quantify shifts of climate zones in Qinghai-Tibet Plateau (QTP) based on the high-resolution data sets. Our results show that highland climate was decreased substantially during 1961-2011 and were mainly replaced by boreal climate. We also found that the mean elevation of boreal and highland climate continues to rise, with obvious longitudinal geographical characteristics over the study period. Furthermore, we found that the climate spaces (a climate space defined as the volume of 10 degrees C x 500 mm here) of both boreal and highland climate types tend to be warm and humid ones, which may provide more suitable climate conditions for species to maintain and promote diversity. Characterization of changes in QTP climate types deepens our understanding of regional climate and its biological impacts. Plain Language Summary Climate classification is the key to simplifying complex climate and helps to deepen the understanding of regional climate change. Based on the high-resolution data set (LZ0025), the sharp climatic gradient features and their potential biological impact on Qinghai-Tibet Plateau (QTP) was quantified. With the temperature increase, the spatial distribution of highland tundra climate was gradually replaced by boreal climate. More importantly, the contraction of highland climate and the expansion of boreal climate has obvious elevation characteristics. In addition, climate spaces of highland and boreal climate types tend to warm and humid ones, which may provide more climatic niches for different species and contribute to regional biodiversity.Peer reviewe

Research on the Effect of the Friction on an Inchworm- type Piezoelectric-driven Rotary Actuator via Finite Element Method

Abstract: The effect of the friction coefficient at the stator-rotor interface on the working performance of the actuator was investigated by using FEA. In this paper, a piezoelectric-driven stepping rotary actuator based on the inchworm motion is designed. Simulation results showed that the stepping rotary angle decreases from 264 μrad to 64 μrad and output torque of the rotor increases 29.6 N·mm to 315.5 N·mm when the friction coefficient increases from 0.1 to 0.5. Therefore, this factor must be taken into consideration in the design and machining of this kind of actuators

Study on characteristics of particulate emission of diesel aftertreatment with reciprocating flow

© 2021 The Authors. Energy Science & Engineering published by the Society of Chemical Industry and John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. https://creativecommons.org/licenses/by/4.0/In this article, in order to optimize diesel aftertreatment system with periodically reciprocating flow (PRF), an experimental study is conducted to investigate its characteristics such as pollution emissions, regeneration of diesel particulate filter (DPF), concentration and size distribution of particulate matter (PM) escaped as well as temperature distribution under unidirectional flow and PRF operating conditions. The effects of reciprocating flow cycle and exhaust gas flow on the performance of aftertreatment system are investigated in detail. The energy efficiency analysis of the aftertreatment system is also carried out. Experimental results show that (i) as the temperature is lower than the light-off threshold of combustible gas, the aftertreatment system cannot restrain the formation of second particles under the present experiment condition of unidirectional flow; (ii) the aftertreatment system demonstrates excellent performance of trapping particles and filter regeneration as the symmetrical temperature distribution is formed. The PM filter efficiency α_PM is 92% and the specific energy consumption β is 124% for symmetrical temperature distribution; (iii) the increase of reciprocating flow cycle could lead to the shifting of the temperature profiles, this would affect the particle size distribution; (iv) a certain increase of exhaust gas flow from engine would have insignificant change for the temperature distribution; (v) The critical energy efficiency η_c of the system could reach 96.61%.Peer reviewedFinal Published versio

A complete mitochondrial genome sequence of the wild two-humped camel (Camelus bactrianus ferus): an evolutionary history of camelidae

<p>Abstract</p> <p>Background</p> <p>The family Camelidae that evolved in North America during the Eocene survived with two distinct tribes, Camelini and Lamini. To investigate the evolutionary relationship between them and to further understand the evolutionary history of this family, we determined the complete mitochondrial genome sequence of the wild two-humped camel (<it>Camelus bactrianus ferus</it>), the only wild survivor of the Old World camel.</p> <p>Results</p> <p>The mitochondrial genome sequence (16,680 bp) from <it>C. bactrianus ferus </it>contains 13 protein-coding, two rRNA, and 22 tRNA genes as well as a typical control region; this basic structure is shared by all metazoan mitochondrial genomes. Its protein-coding region exhibits codon usage common to all mammals and possesses the three cryptic stop codons shared by all vertebrates. <it>C. bactrianus ferus </it>together with the rest of mammalian species do not share a triplet nucleotide insertion (GCC) that encodes a proline residue found only in the <it>nd1 </it>gene of the New World camelid <it>Lama pacos</it>. This lineage-specific insertion in the <it>L. pacos </it>mtDNA occurred after the split between the Old and New World camelids suggests that it may have functional implication since a proline insertion in a protein backbone usually alters protein conformation significantly, and <it>nd1 </it>gene has not been seen as polymorphic as the rest of ND family genes among camelids. Our phylogenetic study based on complete mitochondrial genomes excluding the control region suggested that the divergence of the two tribes may occur in the early Miocene; it is much earlier than what was deduced from the fossil record (11 million years). An evolutionary history reconstructed for the family Camelidae based on <it>cytb </it>sequences suggested that the split of bactrian camel and dromedary may have occurred in North America before the tribe Camelini migrated from North America to Asia.</p> <p>Conclusion</p> <p>Molecular clock analysis of complete mitochondrial genomes from <it>C. bactrianus ferus </it>and <it>L. pacos </it>suggested that the two tribes diverged from their common ancestor about 25 million years ago, much earlier than what was predicted based on fossil records.</p

Spatial Aggregation of Global Dry and Wet Patterns Based on the Standard Precipitation Index

Quantifying the spatial integrity and patterns of dry/wet events over land is essential to understand how the local hydrological regime responds to environmental changes. Spatial aggregation changes in dry and wet areas over land have not been studied extensively. Based on a patch-mosaic landscape model, we analyzed spatial aggregation changes at two levels corresponding to landscape design during 1949 and 2018. At the landscape level, the global aggregation degree increased initially and then weakened around 2006. However, the spatial aggregation process between dry and wet patterns was inconsistent. For the dry pattern, spatial aggregation was mainly caused by area decline induced decreases in the patch number. For the wet pattern, spatial aggregation was caused by area enlargement induced decreases in the patch number. At the class level, with increases in the dry/wet magnitude, the correlation between the affected area and aggregation strengthened. Our results provide new insights to understand the spatial processes and future trends of dry/wet patterns over land. We argue that future vulnerability of agriculture and ecosystems to drought is likely to be further mediated by the changes in drought patterns' spatial structure.Peer reviewe