Evaporative fraction (EF) is the proportion of latent heat flux in surface net energy and reflects the moisture status of an ecosystem. However, the effects of different meteorological factors and ...vegetation changes on EF are not known. In this study, 142 flux tower observations were used to analyze the spatial and temporal variations of EF in different vegetation types and to analyze the response of meteorological factors and vegetation changes to EF. The results showed that evergreen broadleaf forests (EBFs) had the highest multiyear mean EF (0.61), while open shrublands (OSH) had the lowest multiyear mean EF (0.32). Areas with higher EF values were generally found in temperate continental, mediterranean, and oceanic climates. Seasonally, EFs were generally high in the northern and southern hemispheres during the summer and relatively low in the spring and autumn. The correlation analysis showed that EF increased significantly with increasing precipitation and leaf area index (LAI) for all six vegetation types. Deciduous broadleaf forests (<inline-formula> <tex-math notation="LaTeX">R </tex-math></inline-formula> = 0.37, RSS = 6.96, and <inline-formula> <tex-math notation="LaTeX">P < 0.01 </tex-math></inline-formula>) and wetlands (<inline-formula> <tex-math notation="LaTeX">R </tex-math></inline-formula> = 0.26, RSS = 7.03, and <inline-formula> <tex-math notation="LaTeX">P < 0.01 </tex-math></inline-formula>) showed a significant increasing trend with increasing vapor pressure deficit (VPD), and two vegetation types, grasslands (<inline-formula> <tex-math notation="LaTeX">R </tex-math></inline-formula> = −0.35, RSS = 13.44, and <inline-formula> <tex-math notation="LaTeX">P < 0.01 </tex-math></inline-formula>), and EBF (<inline-formula> <tex-math notation="LaTeX">R </tex-math></inline-formula> = −0.19, RSS = 3.77, and <inline-formula> <tex-math notation="LaTeX">P < 0.01 </tex-math></inline-formula>) showed a significant decrease trend with increasing VPD. The monthly mean EF of three vegetation types, grasslands (<inline-formula> <tex-math notation="LaTeX">R </tex-math></inline-formula> = 0.26, RSS = 14.20, and <inline-formula> <tex-math notation="LaTeX">P < 0.01 </tex-math></inline-formula>), deciduous broadleaf forests (<inline-formula> <tex-math notation="LaTeX">R </tex-math></inline-formula> = 0.34, RSS = 7.11, and <inline-formula> <tex-math notation="LaTeX">P < 0.01 </tex-math></inline-formula>), and wetlands (<inline-formula> <tex-math notation="LaTeX">R </tex-math></inline-formula> = −0.40, RSS = 6.37, and <inline-formula> <tex-math notation="LaTeX">P < 0.01 </tex-math></inline-formula>) decreased significantly with increasing wind speed. Our findings provide a scientific basis for assessing surface water conditions and contribute to the understanding of EF interactions with climate and vegetation change.
BPS Kerr-AdS time machines Cvetič, M.; Geng, Wei-Jian; Lü, H. ...
The journal of high energy physics,
07/2018, Letnik:
2018, Številka:
7
Journal Article
Recenzirano
Odprti dostop
A
bstract
It was recently observed that Kerr-AdS metrics with negative mass can describe smooth spacetimes that have a region within which naked closed time-like curves can arise, bounded by a ...velocity of light surface. Such spacetimes are sometimes known as time machines. In this paper we study the BPS limit of these metrics, and find that the mass and angular momenta become discretised. The completeness of the spacetime also requires that the asymptotic time coordinate be periodic, with precisely the same period as that which arises naturally for the global AdS, viewed as a hyperboliod in one extra dimension, in which the time machine spacetime is immersed. For the case of equal angular momenta in odd dimensions, we construct the Killing spinors explicitly, and show they are consistent with the global structure. Thus in examples where the solutions can be embedded in gauged supergravity, they will be supersymmetric. We also compare the global structure of the BPS AdS
3
time machine with the BTZ black hole, and show that the global structure allows two different supersymmetric limits.
A detailed analysis of self‐consistent potentials, electric fields, electron distributions, and transport properties of dual‐channel (DC) n‐Al0.3Ga0.7N/GaN/i‐AlxGa1−xN/GaN high‐electron‐mobility ...transistors (HEMTs) is performed in this article. The 2D electron gas (2DEG) densities and mobility states limited by different scattering mechanisms in channel 1 and channel 2 are obtained, with varying values of doping concentrations, ambient temperatures, Al components, and thicknesses of the back barrier layer. The reduced and increased 2DEG densities are respectively observed in channel 1 and channel 2 with growing Al fractions and thicknesses of the AlxGa1−xN layer. Alloy disorder scattering exhibits a superior effect on carriers in channel 2 due to the lower barrier height and higher permeable electrons, which together with the interface roughness scattering severely depends on the thicknesses and Al fractions of the back barrier layer. Polar optical phonon scattering becomes important at higher temperatures. The trend of individual mobility in channel 1 is exactly opposite to that in channel 2. The parameter variation of the back barrier layer can effectively change the scattering characteristics of the main channel. Low‐temperature mobilities of n‐Al0.3Ga0.7N/GaN/i‐AlxGa1−xN/GaN HEMTs under varied doping concentrations are also obtained. Finally, the results are verified by comparison with the technology computer‐aided design simulations for DC HEMTs.
With the development of cities, urban area source pollution has become more severe and a significant source of water pollution. To study the relationship between urban area source pollution and water ...environmental quality in a river network, this study uses a city in the Yangtze River Delta, China, as an example. The Storm Water Management Model (SWMM) model and the MIKE11 model were combined into a unified modeling framework and used to simulate dynamic changes in the water quality of a river network under light rain, moderate rain, and heavy rain. In the study period, the annual urban area source input loads of potassium permanganate (COD
), total phosphorus (TP), and ammonia nitrogen were 29.8, 0.9, and 4.8 t, respectively. The influence of light rain on the water quality of the river network was lagging and temporary, and rainfall area pollution was the primary contributor. Under the scenario of moderate rain, overflow from a pipeline network compounded rainfall runoff, resulting in a longer duration of impact on the water quality in the river. Additionally, the water quality in the river course was worse under moderate rain than under light or heavy rain. Under the scenario of heavy rain, rain mainly served a dilutive function. This research can provide support for urban area source pollution control and management.
In this study, Large Eddy Simulation (LES) of supersonic turbulent mixing and combustion adopting a Partially Stirred Reactor (PaSR) sub-grid combustion model is performed for a hydrogen fueled model ...scramjet combustor. The compressible LES solver, which adopts a skeleton of 27 steps and 9 species hydrogen chemical kinetics model, is used to simulate the flowing and combustion processes based on structured hexahedral grids. The code is implemented in an Open Source Field Operation and Manipulation (OpenFOAM) solver, and validated against experimental data in terms of mean axial velocity and static temperature at different cross-sections, all show good predictions. An analysis of the flow field is carried out to investigate the supersonic turbulent flame structure and combustion mode in the combustor. Mixture fraction is extracted to indicate the reaction progress at different sites, which donates the most likely flame locations when at stoichiometric. Comparison of combustion parameters including OH mass fraction, scalar dissipation rate, flame index and heat release rate spatial distribution reveals that the supersonic combustion has the characteristics of a turbulent diffusion flame, where combustion is held at non-premixed mode controlled by turbulent mixing in the shear layers. A time scale analysis, the Damköhler Number is performed to examine these reactive zones in more detail. The role of auto-ignition in flame stabilization and lift-off is revealed.
•A skeleton of 27 steps with 9 species chemical kinetics for hydrogen is applied.•Stoichiometrical flame locations and different combustion modes are recognized.•The Damköhler number is extracted to indicate auto-ignition or flame extinction.•Species concentration and heat release rate is plotted in mixture fraction space.
This paper numerically investigated the dynamic characteristics of combustion in a model scramjet. Three-dimensional compressible large eddy simulation was performed on a hydrogen fueled combustor ...and pressure fluctuations were recorded. The analysis of pressure data showed that the combustion processes are intrinsically unstable under supersonic air inflow conditions. Flame dynamics were convinced by the fluctuations in flame lift-off distance away from the strut base. Combined with the corresponding time interval, instantaneous flame speed was calculated. Results indicated that pressure oscillations at different locations show difference in amplitude, frequency, and the underlying control mechanism. Flame front oscillation analysis showed that the flame–shock interaction in the strut recirculation zone was responsible for the combustion instability. Flame dynamics were compared with low-speed turbulent lifted flames. The transition between flame propagation just after the strut and shock-induced combustion in the subsonic bubble at the intersection of two wall-reflected oblique shocks made for the flame stabilization.
•The reasons for pressure oscillation at different locations are distinguished.•Flame lift-off distance and the instantaneous flame speed are quantified.•Intermittent formation of subsonic bubble controls the combustion oscillation.•Flame propagation and shock-induced combustion jointly stabilize the flame.
We construct a class of Einstein-vector theories where the vector field couples bilinearly to the curvature polynomials of arbitrary order in such a way that only the Riemann tensor rather than its ...derivative enters the equations of motion. The theories can thus be ghost free. The U(1) gauge symmetry may emerge in the vacuum and also in some weak-field limit. We focus on the two-derivative theory and study a variety of applications. We find that in this theory, the energy-momentum tensor of dark matter provides a position-dependent gauge-violating term to the Maxwell field. We also use the vector as an inflaton and construct cosmological solutions. We find that the expansion can accelerate without a bare cosmological constant, indicating a new candidate for dark energy. Furthermore, we obtain exact solutions of de Sitter bounce, generated by the vector which behaves like a Maxwell field at later times. We also obtain a few new exact black holes that are asymptotic to flat and Lifshitz spacetimes. In addition, we construct exact wormholes and Randall-Sundrum II domain walls.
This paper focuses on the nonlinear free and forced vibrations of porous sigmoid functionally graded material plates resting on nonlinear elastic foundations. Two types of porosity distributions, ...even and uneven, were considered. A nonlinear three-parameter foundation model was employed to estimate the plate-foundation interactions. The material properties of the plates, described by the sigmoid distribution law, were assumed to be graded in the thickness direction. All four edges of the plates were simply supported and had no in-plane displacements. Based on a higher-order shear deformation plate theory and general von Kármán-type equation, the equations of motion with the effects of nonlinear elastic foundations were developed. The equations of motion were solved by an improved perturbation technique to determine the nonlinear frequencies and dynamic responses of the plates. The numerical illustrations are presented in both tabular and graphical forms to show the effects of the nonlinear foundation parameters, pore volume fraction, and material volume fraction on the nonlinear vibration and dynamic responses of the plates.
Gastrointestinal cancer, the most common solid tumor, has a poor prognosis. With the development of high-throughput sequencing and detection technology, recent studies have suggested that many ...chemical modifications of human RNA are involved in the development of human diseases, including cancer. m
A, the most abundant modification, was revealed to participate in a series of aspects of cancer progression. Recent evidence has shown that methyltransferase-like 3 (METTL3), the first identified and a critical methyltransferase, catalyzes m
A methylation on mRNA or non-coding RNA in mammals, affecting RNA metabolism. Abnormal m
A levels caused by METTL3 have been reported to be involved in different aspects of cancer development, including proliferation, apoptosis, and metastasis. In this review, we will shed light on recent findings regarding the biological function of METTL3 in gastrointestinal cancer and discuss future research directions and potential clinical applications of METTL3 for gastrointestinal cancer.
High-efficiency video coding (HEVC/H.265) is one of the most widely used video coding standards. HEVC introduces a quad-tree coding unit (CU) partition structure to improve video compression ...efficiency. The determination of the optimal CU partition is achieved through the brute-force search rate-distortion optimization method, which may result in high encoding complexity and hardware implementation challenges. To address this problem, this paper proposes a method that combines convolutional neural networks (CNN) with joint texture recognition to reduce encoding complexity. First, a classification decision method based on the global and local texture features of the CU is proposed, efficiently dividing the CU into smooth and complex texture regions. Second, for the CUs in smooth texture regions, the partition is determined by terminating early. For the CUs in complex texture regions, a proposed CNN is used for predictive partitioning, thus avoiding the traditional recursive approach. Finally, combined with texture classification, the proposed CNN achieves a good balance between the coding complexity and the coding performance. The experimental results demonstrate that the proposed algorithm reduces computational complexity by 61.23%, while only increasing BD-BR by 1.86% and decreasing BD-PSNR by just 0.09 dB.
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