| 1. |
- Miehe, Georg, et al.
(author)
-
The Kobresia pygmaea ecosystem of the Tibetan highlands – Origin, functioning and degradation of the world's largest pastoral alpine ecosystem: Kobresia pastures of Tibet
- 2019
-
In: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 648, s. 754-771
-
Journal article (peer-reviewed)abstract
- With 450,000 km2 Kobresia (syn. Carex) pygmaea dominated pastures in the eastern Tibetan highlands are the world's largest pastoral alpine ecosystem forming a durable turf cover at 3000–6000 m a.s.l. Kobresia's resilience and competitiveness is based on dwarf habit, predominantly below-ground allocation of photo assimilates, mixture of seed production and clonal growth, and high genetic diversity. Kobresia growth is co-limited by livestock-mediated nutrient withdrawal and, in the drier parts of the plateau, low rainfall during the short and cold growing season. Overstocking has caused pasture degradation and soil deterioration over most parts of the Tibetan highlands and is the basis for this man-made ecosystem. Natural autocyclic processes of turf destruction and soil erosion are initiated through polygonal turf cover cracking, and accelerated by soil-dwelling endemic small mammals in the absence of predators. The major consequences of vegetation cover deterioration include the release of large amounts of C, earlier diurnal formation of clouds, and decreased surface temperatures. These effects decrease the recovery potential of Kobresia pastures and make them more vulnerable to anthropogenic pressure and climate change. Traditional migratory rangeland management was sustainable over millennia, and possibly still offers the best strategy to conserve and possibly increase C stocks in the Kobresia turf.
|
|
| 2. |
- Liu, Jian, et al.
(author)
-
Numerical investigations of endwall film cooling design of a turbine vane using four-holes pattern
- 2022
-
In: International Journal of Numerical Methods for Heat and Fluid Flow. - 0961-5539. ; 32:6, s. 2177-2197
-
Journal article (peer-reviewed)abstract
- Purpose: Endwall film cooling protects vane endwall by coolant coverage, especially at the leading edge (LE) region and vane-pressure side (PS) junction region. Strong flow impingement and complex vortexaa structures on the vane endwall cause difficulties for coolant flows to cover properly. This work aims at a full-scale arrangement of film cooling holes on the endwall which improves coolant efficiency in the LE region and vane-PS junction region. Design/methodology/approach: The endwall film holes are grouped in four-holes constructal patterns. Three ways of arranging the groups are studied: based on the pressure field, the streamlines or the heat transfer field. The computational analysis is done with the k-ω SST model after validating the turbulence model properly. Findings: By clustering the film cooling holes in four-holes patterns, the ejection of the coolant flow is stronger. The four-holes constructal patterns also improve the local coolant coverage in the “tough” regions, such as the junction region of the PS and the endwall. The arrangement based on streamlines distribution can effectively improve the coolant coverage and the arrangement based on the heat transfer distribution (HTD) has benefits by reducing high-temperature regions on the endwall. Originality/value: A full-scale endwall film cooling design is presented considering interactions of different film cooling holes. A comprehensive model validation and mesh independence study are provided. The cooling holes pattern on the endwall is designed as four-holes constructal patterns combined with several arrangement choices, i.e. by pressure, by heat transfer and by streamline distributions.
|
|
| 3. |
- Liu, Siyu, et al.
(author)
-
Probing the Multiexcitonic Dynamics in CsPbI3 Nanocrystals across the Temperature-Induced Reversible Phase Transitions
- 2023
-
In: Advanced Energy Materials. - 1614-6832. ; 13:30
-
Journal article (peer-reviewed)abstract
- CsPbI3 nanocrystals (CPI NCs) have become a trending research topic due to their impressive potential in functional optoelectronic devices and optical gain applications. Their optical responses are governed by carrier dynamics, which is greatly influenced by temperature and corresponding phase structure due to the effects of inherently electron-phonon coupling. Notably, CPI NCs have been identified to adopt an unexpectedly stable cubic phase from room temperature to liquid helium temperature. Here, using in situ cryogenic electron diffraction measurements, it is unambiguously demonstrated that CPI NCs undergo consecutive cubic-tetragonal-orthorhombic phase transitions from 298 to 100 K. The corresponding temperature-dependent multiexcitonic dynamics are investigated in each phase by combining time-resolved photoluminescence and transient absorption spectroscopy. In addition to the temperature dependency, the lifetime of both excitons and biexcitons evidently depends on the phase structures of the CPI NCs, highlighting the crucial effect of crystal structure on the carrier dynamics. Moreover, the biexciton binding energy increases with higher crystal symmetry due to the decrease of the dielectric constant. The findings shed light on the structural phase transition and its relationship to the carrier dynamics in all-inorganic perovskite NCs, which provides critical insight into the structure-performance relationship in CPI NCs for promising applications in optoelectronic devices.
|
|
| 4. |
- Song, Jiawen, et al.
(author)
-
Heat Transfer Enhancement of Regenerative Cooling Channel with Pyramid Lattice Sandwich Structures
- 2023
-
In: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 44:14, s. 1271-1285
-
Journal article (peer-reviewed)abstract
- To meet the requirements of high heat transfer efficiency and light weight, the pyramid lattice structures are applied to the regenerative cooling design of scramjets. This study numerically investigates heat transfer and fluid flow characteristics of kerosene in a regenerative channel with pyramid lattice sandwich structures. At the same porosity, the maximum wall temperature of the pyramid lattice sandwich regenerative cooling channel decreases by 30%. With increased porosity, the cooling capacity of the pyramid regenerative cooling channel decreases gradually. The numerical results show that a complex secondary flow appears in the flow field in the pyramid lattice structures. In the downstream region of each strut, a spiral vortex is formed which accelerates the flow velocity approaching the wall with heat transfer enhancement. Because of the disturbing effect of the strut, a high turbulent kinetic energy region is formed in the upstream region of each strut and the heat transfer is enhanced. In general, the local heat transfer in the upstream region of the pyramid strut is better than that in the downstream region. For pyramid lattice structures, the cooling structures with high convective heat transfer and relatively low pressure drop can be obtained by optimization of the design parameters.
|
|
