分类： 核科学技术 >> 核安全 提交时间： 2025-02-19
摘要： Molten salt reactors (MSRs) are a promising candidatefor Generation IV reactor technologies, and the small modular molten salt reactor (SM-MSR), which utilizes low-enriched uranium and thorium fuels, is regarded as a wise development path to accelerate deployment time. Uncertainty and sensitivity analyses of accidents guide nuclear reactor design and safety analyses. Uncertainty analysis can ascertain the safety margin, and sensitivity analysis can reveal the correlation between accident consequences and input parameters. Loss of forced cooling (LOFC) represents an accident scenario of the SM-MSR, and the study of LOFCcould offer useful information to improve physical thermohydraulicand structural designs. Therefore, this study investigates the uncertainty of LOFCconsequences and the sensitivity of related parameters. The uncertainty of the LOFCconsequences was analyzedusing the Monte Carlo method, and multiple linear regression was employed to analyzethe sensitivity of the input parameters. The uncertainty and sensitivity analyses showed that the maximum reactor outlet fuel salt temperature was 725.5℃, which is lower than the acceptable criterion, and five important parameters influencing LOFCconsequences were identified.
分类： 能源科学 >> 能源（综合） 提交时间： 2024-03-29
Anna Hnydiuk-Stefan
Ke Feng
Patrick Siarry
Grzegorz Królczyk
Z Li
Xinrui Qi
Chunsheng Yang
Mingyang Huang
Zhenjun Ma
摘要： Considering the huge consumption of traditional energy and the rising demand for electricity, the development of renewable energy is very necessary. In this paper, an energy system integrating biomass energy, solar and two-stage organic Rankine cycle (ORC) is proposed, which uses the stable energy output of biomass energy to compensate for the volatility of solar modules. The proposed system comprises a biomass boiler, photovoltaic thermal panels (PV/T), evaporators, condensers, working medium pumps, turbines, a preheater and an air preheater. In addition, conventional and advanced exergy, exergoeconomic and exergoenvironmental (3E) analyses are carried out. Conventional 3E analyses reveal two components that require priority improvement. They are respectively evaporator 1 with the largest exergy destruction (708.2kW) and exergy destruction environmental impact rate (775.3 mPt/h) and evaporator 2 with the largest exergy destruction cost rate (19.15$/h).The results of advanced 3E analyses show that the largest avoidable endogenous exergy destruction is condenser 1 (136.6kW), the largest avoidable endogenous exergy destruction cost rate is condenser 2 (3.377$/h),and the largest avoidable endogenous exergy destruction environmental impact rate is condenser 1 (196.1mPt/h). These mean that these components have great potential for improvement in reducing exergy destruction, saving cost and protecting the environment. In addition, the avoidable endogenous exergy destruction/cost/environmental impact rate of evaporator 2 are negative, so evaporator 2 is not suitable as a priority component for improvement, which is contrary to the conclusions of conventional 3E analyses. It is found that conventional 3E analyses can only point out the biggest exergy destruction point, but cannot indicate whether the components with the greatest exergy destruction have the greatest potential for improvement. However, advanced 3E analyses can show the improvement potential of each component by improving its own performance and the external conditions. Therefore, it is necessary to conduct advanced 3E analyses.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
摘要： We present an amplitude analysis of the decay D0 → K−π+π+π− based on a data sample of 2.93 fb−1 acquired by the BESIII detector at the ψ(3770) resonance. With a nearly background free sample of about 16000 events, we investigate the substructure of the decay and determine the relative fractions and the phases among the different intermediate processes. Our amplitude model includes the two-body decays D0 → K¯ ∗0ρ0, D0 → K−a+(1260) and D0 → K−(1270)π+, the three-body decays D0 → K¯ ∗0π+π− and D0 → K−π+ρ0, as well as the four-body nonresonant decay D0 → K−π+π+π−. The dominant intermediate process is D0 → K−a+(1260), accounting for a fit fraction of 54.6%.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
摘要： Using 448.0 × 106 ψ(3686) events collected with the BESIII detector, an amplitude analysis is performed for ψ(3686) →γχc1, γχc1→ηπ+π− decays. The most dominant two-body structure observed is a0(980)±π∓; a0(980)±→ηπ±. The a0(980) line shape is modeled using a dispersion relation, and a significant nonzero a0(980) coupling to the η′π channel is measured. We observe χc1→a2(1700)π production for the first time, with a significance larger than 17σ. The production of mesons with exotic quantum numbers, JPC = 1−+, is investigated, and upper limits for the branching fractions χc1 →π1(1400)±π∓, χc1→π1(1600)±π∓, and χc1→π1(2015)±π∓, with subsequent π1(X)±→ηπ± decay, are determined.
分类： 生物学 >> 生态学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： The Three-River Source Region (TRSR) in China holds a vital position and exhibits an irreplaceable strategic importance in ecological preservation at the national level. On the basis of an in-depth study of the vegetation evolution in the TRSR from 2000 to 2022, we conducted a detailed analysis of the feedback mechanism of vegetation growth to climate change and human activity for different vegetation types. During the growing season, the spatiotemporal variations of normalized difference vegetation index (NDVI) for different vegetation types in the TRSR were analyzed using the Moderate Resolution Imaging Spectroradiometer (MODIS)-NDVI data and meteorological data from 2000 to 2022. In addition, the response characteristics of vegetation to temperature, precipitation, and human activity were assessed using trend analysis, partial correlation analysis, and residual analysis. Results indicated that, after in-depth research, from 2000 to 2022, the TRSR's average NDVI during the growing season was 0.3482. The preliminary ranking of the average NDVI for different vegetation types was as follows: shrubland (0.5762)>forest (0.5443)>meadow (0.4219)>highland vegetation (0.2223)>steppe (0.2159). The NDVI during the growing season exhibited a fluctuating growth trend, with an average growth rate of 0.0018/10a (P<0.01). Notably, forests displayed a significant development trend throughout the growing season, possessing the fastest rate of change in NDVI (0.0028/10a). Moreover, the upward trends in NDVI for forests and steppes exhibited extensive spatial distributions, with significant increases accounting for 95.23% and 93.80%, respectively. The sensitivity to precipitation was significantly enhanced in other vegetation types other than highland vegetation. By contrast, steppes, meadows, and highland vegetation demonstrated relatively high vulnerability to temperature fluctuations. A further detailed analysis revealed that climate change had a significant positive impact on the TRSR from 2000 to 2022, particularly in its northwestern areas, accounting for 85.05% of the total area. Meanwhile, human activity played a notable positive role in the southwestern and southeastern areas of the TRSR, covering 62.65% of the total area. Therefore, climate change had a significantly higher impact on NDVI during the growing season in the TRSR than human activity.
分类： 生物学 >> 生态学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： The Mongolian Plateau in East Asia is one of the largest contingent arid and semi-arid areas of the world. Under the impacts of climate change and human activities, desertification is becoming increasingly severe on the Mongolian Plateau. Understanding the vegetation dynamics in this region can better characterize its ecological changes. In this study, based on Moderate Resolution Imaging Spectroradiometer (MODIS) images, we calculated the kernel normalized difference vegetation index (kNDVI) on the Mongolian Plateau from 2000 to 2023, and analyzed the changes in kNDVI using the Theil-Sen median trend analysis and Mann-Kendall significance test. We further investigated the impact of climate change on kNDVI change using partial correlation analysis and composite correlation analysis, and quantified the effects of climate change and human activities on kNDVI change by residual analysis. The results showed that kNDVI on the Mongolian Plateau was increasing overall, and the vegetation recovery area in the southern region was significantly larger than that in the northern region. About 50.99% of the plateau showed dominant climate-driven effects of temperature, precipitation, and wind speed on kNDVI change. Residual analysis showed that climate change and human activities together contributed to 94.79% of the areas with vegetation improvement. Appropriate human activities promoted the recovery of local vegetation, and climate change inhibited vegetation growth in the northern part of the Mongolian Plateau. This study provides scientific data for understanding the regional ecological environment status and future changes and developing effective ecological protection measures on the Mongolian Plateau.
分类： 物理学 >> 核物理学 提交时间： 2025-02-24
摘要： Heat pipe reactors use heat pipe for passive cooling and are highly suitable for the energy supply of decentralized markets. Traditional mobile heat pipe reactors have smaller power level and cannot satisfy the higher power requirement of decentralized areas. Mobile heat pipe cooled traveling wave reactor (HPTWR), which uses neutron traveling wave to realize the long-term operation, is an excellent candidate for decentralized markets. In the present work, a radial traveling wave technology and a symmetrical inserted heat pipe technology are applied in the HPTWR core and a mobile symmetrical inserted heat pipe cooled traveling wave reactor (SI-HPTWR) core is developed. The radial traveling wave technology can improve the breeding capability of core and reduce the radial power peaking factor of core. Besides, the symmetrical inserted heat pipe technology can effectively reduce the maximum core temperature. The 60 MWth SI-HPTWR is capable of supporting an around 60-year operation. Compared with other traditional reactors, SI-HPTWR has the higher safety, better mobility and economic benefits in the electricity market and heat utilization of decentralized areas.
分类： 核科学技术 >> 裂变堆工程技术 提交时间： 2024-04-27
摘要： The heavy-water-moderated molten-salt reactor (HWMSR) is a newly proposed reactor concept, in which heavy water is adopted as the moderator and molten salt dissolved with fissile and fertile elements is used as the fuel. Issues arising from graphite in traditional molten-salt reactors, including the positive temperature coefficient and management of highly radioactive spent graphite waste, can be addressed using the HWMSR. Until now, research on the HWMSR has been centered on the core design and nuclear-fuel cycle to explore the viability of the HWMSR and its advantages in fuel utilization. However, the core safety of the HWMSR has not been extensively studied. Therefore, we evaluate typical accidents in a small modular HWMSR, including fuel-salt inlet temperature-overcooling and -overheating accidents, fuel-salt inlet flow-rate decrease, heavy-water inlet temperature-overcooling accidents, and heavy-water inlet mass flow-rate decrease accidents, based on a neutronics and thermal-hydraulics coupled code. The results demonstrated that the core maintained safety during the investigated accidents.
分类： 地球科学 >> 大气科学 提交时间： 2022-12-12 合作期刊: 《干旱区科学》
摘要：Exploring the current runoff characteristics after the large-scale implementation of the Grain for Green (GFG) project and investigating its sensitivities to potential drivers are crucial for water resource prediction and management. Based on the measured runoff data of 62 hydrological stations in the Weihe River Basin (WRB) from 2006 to 2018, we analyzed the temporal and spatial runoff characteristics in this study. Correlation analysis was used to investigate the relationships between different runoff indicators and climate-related factors. Additionally, an improved Budyko framework was applied to assess the sensitivities of annual runoff to precipitation, potential evaporation, and other factors. The results showed that the daily runoff flow duration curves (FDCs) of all selected hydrological stations fall in three narrow ranges, with the corresponding mean annual runoff spanning approximately 1.50 orders of magnitude, indicating that the runoff of different hydrological stations in the WRB varied greatly. The trend analysis of runoff under different exceedance frequencies showed that the runoff from the south bank of the Weihe River was more affluent and stable than that from the north bank. The runoff was unevenly distributed throughout the year, mainly in the flood season, accounting for more than 50.00% of the annual runoff. However, the trend of annual runoff change was not obvious in most areas. Correlation analysis showed that rare-frequency runoff events were more susceptible to climate factors. In this study, daily runoff under 10%–20% exceeding frequencies, consecutive maximum daily runoff, and low-runoff variability rate had strong correlations with precipitation, aridity index, and average runoff depth on rainy days. In comparison, daily runoff under 50%–99% exceeding frequencies, consecutive minimum daily runoff, and high-runoff variability rate had weak correlations with all selected impact factors. The sensitivity analysis results suggested that the sensitivity of annual runoff to precipitation was always higher than that to potential evaporation. The runoff about 87.10% of the selected hydrological stations were most sensitive to precipitation changes, and 12.90% were most sensitive to other factors. The spatial pattern of the sensitivity analysis indicated that in relatively humid southern areas, runoff was more sensitive to potential evaporation and other factors, and less sensitive to precipitation.
分类： 生物学 >> 植物学 >> 植物细胞学与植物遗传学、植物形态学 提交时间： 2016-05-03
摘要： Biological assay has been based on analysis of all individuals collected from sample populations. Bulked sample analysis (BSA), which works with selected and pooled individuals, has been extensively used in gene mapping through bulked segregant analysis with biparental populations, mapping by sequencing with major gene mutants and pooled genomewide association study using extreme variants. Compared to conventional entire population analysis, BSA significantly reduces the scale and cost by simplifying the procedure. The bulks can be built by selection of extremes or representative samples from any populations and all types of segregants and variants that represent wide ranges of phenotypic variation for the target trait. Methods and procedures for sampling, bulking and multiplexing are described. The samples can be analysed using individual markers, microarrays and high-throughput sequencing at all levels of DNA, RNA and protein. The power of BSA is affected by population size, selection of extreme individuals, sequencing strategies, genetic architecture of the trait and marker density. BSA will facilitate plant breeding through development of diagnostic and constitutive markers, agronomic genomics, marker-assisted selection and selective phenotyping. Applications of BSA in genetics, genomics and crop improvement are discussed with their future perspectives.
分类： 统计学 >> 应用统计数学 提交时间： 2023-09-15
摘要： The principal component analysis (PCA) is a frequently used machine learning method. In this paper, the PCA operation is explained by examples with Python program illustration. A proof of the diagonalizability of real symmetric matrix is also included, which may help to understand the mathematics behind PCA.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Particle induced X-ray Emission (PIXE) was used to analyze the proto-porcelain excavated from Tingziqiao kiln site of Warring States (475221 BC) in Deqing County of Zhejiang Province, China. It was found that the porcelain body and glaze differ from each other in recipes. The porcelain clay of high silicon and low aluminum might be used to make the body of proto-porcelain. Lime and plant or wood ashes might be added into the glaze of the proto-porcelain. Cluster analysis was done to reveal the compositional relationship between the proto-porcelain samples.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
D. R. Madison(1
2)
X.-J. Zhu(3
4)
G. Hobbs
W. Coles
R. M. Shannon(4
6)
J. Wang
C. Tiburzi(8
9
10
11)
R. N. Manchester
M. Bailes
N. D. R. Bhat
S. Burke-Spolaor
S.Dai
J. Dempsey
M. Keith
摘要： By regularly monitoring the most stable millisecond pulsars over many years, pulsar timing arrays (PTAs) are positioned to detect and study correlations in the timing behaviour of those pulsars. Gravitational waves (GWs) from supermassive black hole binaries (SMBHBs) are an exciting potentially detectable source of such correlations. We describe a straight-forward technique by which a PTA can be "phased-up" to form time series of the two polarisation modes of GWs coming from a particular direction of the sky. Our technique requires no assumptions regarding the time-domain behaviour of a GW signal. This method has already been used to place stringent bounds on GWs from individual SMBHBs in circular orbits. Here, we describe the methodology and demonstrate the versatility of the technique in searches for a wide variety of GW signals including bursts with unmodeled waveforms. Using the first six years of data from the Parkes Pulsar Timing Array, we conduct an all-sky search for a detectable excess of GW power from any direction. For the lines of sight to several nearby massive galaxy clusters, we carry out a more detailed search for GW bursts with memory, which are distinct signatures of SMBHB mergers. In all cases, we find that the data are consistent with noise.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-02 合作期刊: 《热科学学报》
摘要： Supersonic cavity flows are characterized by compression and expansion waves, shear layer, and oscillations inside the cavity. For decades, investigations into cavity flows have been conducted, mostly with flows at zero pressure gradient entering the cavity in straight walls. Since cavity flows on curved walls exert centrifugal force, the features of these flows are likely to differ from those of straight wall flows. The aim of the present work is to study the flow physics of a cavity that is cut out on a curved wall. Steady and unsteady numerical simulations were carried out for supersonic flow through curved channels over the cavity with L/H = 1. A straight channel flow was also analyzed which serves as the base model. The velocity gradient along the width of the channel was observed to increase with increasing the channel curvature for both concave and convex channels. The pressure on the cavity floor increases with the increase in channel curvature for concave channels and decreases for convex channels. Moreover, unsteady flow characteristics are more dependent on channel curvature under supersonic free stream conditions.
分类： 地球科学 >> 大气科学 提交时间： 2024-08-14 合作期刊: 《干旱区科学》
摘要： The characteristics of drought in Xinjiang Uygur Autonomous Region (Xinjiang), China have changed due to changes in the spatiotemporal patterns of temperature and precipitation, however, the effects of temperature and precipitation—the two most important factors influencing drought—have not yet been thoroughly explored in this region. In this study, we first calculated the standard precipitation evapotranspiration index (SPEI) in Xinjiang from 1980 to 2020 based on the monthly precipitation and monthly average temperature. Then the spatiotemporal characteristics of temperature, precipitation, and drought in Xinjiang from 1980 to 2020 were analyzed using the Theil–Sen median trend analysis method and Mann–Kendall test. A series of SPEI-based scenario-setting experiments by combining the observed and detrended climatic factors were utilized to quantify the effects of individual climatic factor (i.e., temperature and precipitation). The results revealed that both temperature and precipitation had experienced increasing trends at most meteorological stations in Xinjiang from 1980 to 2020, especially the spring temperature and winter precipitation. Due to the influence of temperature, trends of intensifying drought have been observed at spring, summer, autumn, and annual scales. In addition, the drought trends in southern Xinjiang were more notable than those in northern Xinjiang. From 1980 to 2020, temperature trends exacerbated drought trends, but precipitation trends alleviated drought trends in Xinjiang. Most meteorological stations in Xinjiang exhibited temperature-dominated drought trend except in winter; in winter, most stations exhibited precipitation-dominated wetting trend. The findings of this study highlight the importance of the impact of temperature on drought in Xinjiang and deepen the understanding of the factors influencing drought.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2023-09-05
摘要： This study introduces a novel algorithm to detect and identify radioactive materials in urban settings using time-series detector response data. To address the challenges posed by varying backgrounds and to enhance the quality and reliability of the energy spectrum data, we devised a temporal energy window. This partitioned the time-series detector response data, resulting in energy spectra that emphasize the vital information pertaining to radioactive materials. We then extracted characteristic features of these energy spectra, relying on the formation mechanism and measurement principles of the gamma-ray instrument spectrum. These features encompassed aggregated counts, peak-to-flat ratios, and peak-to-peak ratios. This methodology not only simplified the interpretation of the energy spectras physical significance but also eliminated the necessity for peak searching and individual peak analyses. Given the requirements of imbalanced multi-classification, we created a detection and identification model using a weighted k-nearest neighbors (KNN) framework. This model recognized that energy spectra of identical radioactive materials exhibit minimal inter-class similarity. Consequently, it considerably boosted the classification accuracy of minority classes, enhancing the classifiers overall efficacy. We also executed a series of comparative experiments. Established methods for radionuclide identification classification, such as standard k-nearest neighbors (KNN), support vector machine (SVM), Bayesian network, andrandom tree, were used for comparison purposes. Our proposed algorithm realized an F1 measure of 0.9868 on the time-series detector response data, reflecting a minimum enhancement of 0.3% in comparison to other techniques. The results conclusively show that our algorithm outperforms others when applied to time-series detector response data in urban contexts.
分类： 地球科学 >> 地理学 提交时间： 2023-08-15 合作期刊: 《干旱区科学》
摘要： Otindag Sandy Land in China is an important ecological barrier to Beijing; the changes in its ecological quality are major concerns for sustainable development and planning of this area. Based on principal component analysis and path analysis, we first generated a modified remote sensing ecological index (MRSEI) coupled with satellite and ground observational data during 20012020 that integrated four local indicators (greenness, wetness, and heatness that reflect vegetation status, water, and heat conditions, respectively, as well as soil erosion). Then, we assessed the ecological quality in Otindag Sandy Land during 20012020 based on the MRSEI at different time scales (i.e., the whole year, growing season, and non-growing season). MRSEI generally increased with an upward rate of 0.006/a during 20012020, with clear seasonal and spatial variations. Ecological quality was significantly improved in most regions of Otindag Sandy Land but degraded in the southern part. Regions with ecological degradation expanded to 18.64% of the total area in the non-growing season. The area with the worst grade of MRSEI shrunk by 15.83% of the total area from 2001 to 2020, while the area with the best grade of MRSEI increased by 9.77% of the total area. The temporal heterogeneity of ecological conditions indicated that the improvement process of ecological quality in the growing season may be interrupted or deteriorated in the following non-growing season. The implementation of ecological restoration measures in Otindag Sandy Land should not ignore the seasonal characteristics and spatial heterogeneity of local ecological quality. The results can explore the effectiveness of ecological restoration and provide scientific guides on sustainable development measures for drylands.
分类： 数字出版 >> 数字技术 提交时间： 2023-07-23
摘要： Under the backdrop of the COVID-19 pandemic, social issues are emerging more frequently, and the guidance of experts on public social life is becoming increasingly important. However, on the Internet, media outlets tend to quote experts out of context, stigmatizing the experts and causing their credibility to decline constantly. This study selected media reports about experts that appeared in the Weibo Hot Search Topics from mid-2022 to early 2023, using frame theory as theoretical support and combining Fairclough's discourse analysis theory with other text research methods to compare and analyze the reported texts and the original experts' statements from multiple dimensions. The study finds that the media constructed an aggressive persuasive framework, shaped a dualistic oppositional conflict perspective by adapting texts and contexts, and stript experts of their professionalism and academic nature, which created a parental, provocative, and unprofessional media image of experts as a result. This is closely related to the pursuit of interests and social ecology of online media under the "Eyeball Economy," posing challenges and obstacles to building trust between experts and the public.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Identification and characterization of L-, D- and DL- penicillamine were demonstrated by Terahertz time-domain spectroscopy (THz-TDS). To understand the physical origins of the low frequency resonant modes, the density functional theory (DFT) was adopted for theoretical calculation. It was found that the collective THz frequency motions were decided by the intramolecular and intermolecular hydrogen bond interactions. Moreover, the quantification of penicillamine enantiomers mixture was demonstrated by a THz spectra fitting method with a relative error of less than 3.5%. This technique can be a valuable tool for the discrimination and quantification of chiral drugs in pharmaceutical industry.
分类： 心理学 >> 认知心理学 提交时间： 2020-02-05
摘要： BACKGROUND: Saccade-induced retrieval enhancement (SIRE) refers to the phenomenon that active engaging of horizontal eye movements before recall would enhance subsequent memory performance. This effect is generally thought to be the result of interhemispheric interaction stimulated by saccades. Nonetheless, recent findings do not fully support this hypothesis. An alternative explanation is that saccades promote memory retrieval by improving top-down attention control. Thus, the mechanisms of SIRE are unclear, the present meta-analysis quantitatively analyzed the effect of saccades on memory performance and examined the mechanisms of SIRE through moderator analysis. METHODS: We searched "Web of Science", "PubMed", and "Springer" for peer reviewed papers using the keywords "eye movements + memory" and "saccades + memory". Twenty-two papers were included in the final analysis. RESULTS: There was a significant facilitation of horizontal saccades on overall memory performance, with a pooled effect size (Cohen’s d) of 0.45 (p < 0.001). However, the overall effect of vertical saccades was not significant (d = 0.1, p = 0.14). Moderation analysis showed that the handedness of participants was a significant moderator of the SIRE, with strongly right-handed individuals benefited more from horizontal saccades than non-strongly right-handed individuals (p < 0.01). CONCLUSION: Horizontal saccades improved memory performances, particularly for the strongly right-handed individuals, these results support the interhemispheric interaction hypothesis.
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