bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatiotemporal evolution and instability of the mixing layer in supersonic ejector based on large eddy simulation
Authors: Huang Zehua , Wang Lei , Zhang Wei , Wang Zhengdao , Wei Yikun , Yang Hui
Published: October 2024

In this paper, the spatiotemporal evolution and the instability of the turbulence mixing layer in a supersonic ejector are deeply studied based on large eddy simulation. Time-averaged distributions and transient results are discussed based on mixed fluids. In particular, the general flow characteristics are identified through the examination of the spatiotemporal evolution of temperature, entropy, Mach number, and density gradient fields. A thin shear layer is gradually formed, and several ring vortices are effectively captured at the lip of the nozzle. Surprisingly, the annular vortex gradually evolves into a V-shaped vortex with time evolution, which reveals that the transition of turbulence occurs in the first half of the mixing chamber. It is found that the supersonic mixing layer exhibits slow growth initially, and a significant increase in velocity is effectively captured at the throat position based on time averaged velocity profiles. A similar trend is also evident in the transition region of the supersonic ejector throat. The mixing of motive flow and suction flow is effectively enhanced by a shock train generated within the diffusion chamber. A recirculation region is created, which leads to a narrowing of the potential core of the jet, and the symmetry of the flow is broken due to the shock location. It is further found that the instability of the main jet is the dominant factor in the fluid mixing process by studying the power spectrum of the pressure signal and characteristic frequency inside the mixing chamber. It further provides important physical insights into understanding the spatiotemporal evolution of internal turbulence and the mixing mechanism in the supersonic steam ejector.
N-doping strategy for enhancing the adsorption performance of Ti2CT2 MXene for Sr ion
Authors: Li Sifan , Zhang Yujuan , Qiu Kaikai , Zhang Yu , Jin Jingyuan , Shi Weiqun
Published: October 2024

Radionuclides, such as strontium (Sr), are hazardous radioactive isotopes commonly found in nuclear waste, posing serious environmental and health risks due to their long half-lives and ability to bioaccumulate. Inspired by the electronic modification effect, this study theoretically predicts that doping can significantly enhance the adsorptive performance of MXenes for radionuclides. Specifically, we employed comprehensive first-principles simulations to investigate the impact of nitrogen (N) doping on the adsorption behavior of Ti2CT2 (T = O, F, OH) MXenes for Sr ions, focusing on surface N doping and C-site N doping as effective strategies to improve adsorption. The results confirmed that both types of N doping are beneficial for the adsorption performance of Ti2CT2, and the adsorption strengths of Ti2CT2 with surface N doping are significantly enhanced. This was analyzed and attributed to the ability of N doping to enhance the charge transfer between the Ti2CT2 surface and Sr ions, thus enhancing the adsorption properties. By elucidating the N doping mechanisms, this study is expected to provide theoretical guidance for the design of high-performance MXene materials in radionuclides remediation applications.
Investigating the self-assembly of pH-sensitive switchable diamine surfactant using sum frequency generation spectroscopy and molecular dynamics simulations
Authors: Ambagaspitiya Tharushi D. , Garza Danielle John C. , Zuercher Aoife , Asetre Cimatu Katherine Leslee
Published: October 2024

The responses of the N-alkyl diamine groups to variations in pH affect their conformations and surface activities, making them relevant to applications relying on interfacial interactions, such as controlled emulsification and mineral flotation. An in-depth understanding of interfacial self-assembly is crucial. Herein, a molecular-level study was performed to investigate the adsorption and self-assembly of N-dodecylpropane-1,3-diamine (DPDA) at the air–water (A/W) interface using sum frequency generation (SFG) spectroscopy and molecular dynamics (MD) simulations. The SFG spectra of DPDA, acquired under three pH conditions, suggest that the protonation of the DPDA diamine group influences the alkyl chain arrangement at a varying degree at the A/W interface. Analysis of the di-cationic DPDA SFG spectrum at a low pH showed fewer gauche defects at low concentration, as indicated by the relatively higher intensity ratio (ICH3SS/ICH2SS) of 18.1 ± 0.6. The density profiles from MD simulations at different surface areas per molecule and pH conditions, showing varying degrees of packing, support the observation of gauche defects in SFG. With MD simulation, the radial distribution factor for di-cationic species has the highest probability of forming hydrogen bonds compared to mono-cationic and non-ionic species. These g(r) probability results conform with observations obtained from SFG spectroscopy, where we observed a strong hydrogen bond interaction at low pH conditions with di-cationic species, forming tetrahedrally arranged water molecules at the A/W interface. Overall, comprehensive insights will facilitate the visualization of alkyl diamines and their potential derivatives at the A/W interface, enabling a better understanding of their behavior across various applications.
Cavity-modified local and non-local electronic interactions in molecular ensembles under vibrational strong coupling
Authors: Fischer Eric W.
Published: October 2024

Resonant vibrational strong coupling (VSC) between molecular vibrations and quantized field modes of low-frequency optical cavities constitutes the conceptual cornerstone of vibro-polaritonic chemistry. In this work, we theoretically investigate the role of complementary nonresonant electron–photon interactions in the cavity Born–Oppenheimer (CBO) approximation. In particular, we study cavity-induced modifications of local and non-local electronic interactions in dipole-coupled molecular ensembles under VSC. Methodologically, we combine CBO perturbation theory (CBO-PT) [E. W. Fischer and P. Saalfrank, J. Chem. Theory Comput. 19, 7215 (2023)] with non-perturbative CBO Hartree–Fock (HF) and coupled cluster (CC) theories. In a first step, we derive up to second-order CBO-PT cavity potential energy surfaces, which reveal non-trivial intra- and inter-molecular corrections induced by the cavity. We then introduce the concept of a cavity reaction potential (CRP), minimizing the electronic energy in the cavity subspace to discuss vibro-polaritonic reaction mechanisms. We present reformulations of CBO-HF and CBO-CC approaches for CRPs and derive second-order approximate CRPs from CBO-PT for unimolecular and bimolecular scenarios. In the unimolecular case, we find small local modifications of molecular potential energy surfaces for selected isomerization reactions dominantly captured by the first-order dipole fluctuation correction. Excellent agreement between CBO-PT and non-perturbative wave function results indicates minor VSC-induced state relaxation effects in the single-molecule limit. In the bimolecular scenario, CBO-PT reveals an explicit coupling of interacting dimers to cavity modes besides cavity-polarization dependent dipole-induced dipole and van der Waals interactions with enhanced long-range character. An illustrative CBO-coupled cluster theory with singles and doubles-based numerical analysis of selected molecular dimer models provides a complementary non-perturbative perspective on cavity-modified intermolecular interactions under VSC.
Toward crack-free AlN growth on silicon (111) by introducing boron incorporated buffer layer via MOCVD
Authors: Nong Mingtao , Tang Xiao , Liao Che-Hao , Cao Haicheng , Liu Tingang , Jiang Zixian , Chettri Dhanu , Ren Kexin , Li Xiaohang
Published: October 2024

High-quality aluminum nitride (AlN) films on silicon substrates are crucial for various applications due to their inherent properties as wide-bandgap semiconductors, cost-effectiveness, and compatibility with silicon-based circuits. Nonetheless, producing high-quality and crack-free AlN on silicon presents significant challenges due to the stress caused by lattice and thermal expansion mismatches. This study introduces a method to mitigate these challenges by incorporating a boron precursor during the metalorganic chemical vapor deposition process to form a BAlN buffer layer. Analytical techniques, such as secondary ion mass spectrometry, atomic force microscopy imaging, XRD rocking curves, reciprocal space map, and Raman spectroscopy, indicate that the BAlN buffer layer promotes the enlargement of seed crystal size, which effectively delays AlN coalescence, mitigates accumulated tensile stress, and enhances the overall crystal quality. Employing this technique has produced a 520 nm thick, crack-free AlN film on silicon (111) with high crystal quality, achieving full width at half maximum values of only 0.2° and 0.3° for XRC (002) and (102), respectively.
Skyrmion motion monitoring based on a ferromagnetic nanodot chain
Authors: Yang Xiaoxue , Ai Xiaolin , Liu Xin , Li Huiting , Ma Xiao-Ping , Shim Je-Ho , Piao Hong-Guang
Published: October 2024

As one of the most promising information carriers, the generation, manipulation, and detection of magnetic skyrmions have emerged as a hot topic in the field of spintronics. However, a major bottleneck to their practical application lies in the existing limitations of detection technology, which fails to accurately locate skyrmions or monitor their real-time motion behavior. In this work, we propose a patterned heterostructure scheme comprising a nanodot chain (NDC) layer and a skyrmion nano-racetrack layer for precise monitoring of skyrmion motion. By exploiting the stray field generated by the moving skyrmion within the racetrack layer, magnetization changes are induced in nanodots within the NDC layer. These changes then translate into high-frequency magnetization oscillation signals that encode valuable information about the dynamic characteristics of driven skyrmions, such as speed and acceleration of the skyrmion, either by spin waves or spin currents. This scheme holds great potential for advancing spintronic devices based on a profound understanding of skyrmion dynamics.
Wetting phenomena of droplets and gas bubbles: Contact angle hysteresis based on varying liquid–solid and solid–gas interfacial tensions
Authors: Aurbach Franziska , Wang Fei , Nestler Britta
Published: October 2024

Wetting phenomena have been widely observed in our daily lives, such as dew on lotus leaf, and applied in technical applications, e.g., ink-jet printing. In contrast to constant liquid–solid and solid–gas interfacial tensions in Young’s law, we here focus on the wetting phenomena by considering varying fluid–solid interfacial tensions. We analyze the energy landscape, the map of Young’s contact angle, the number and corresponding contact angle of local energy minima, and the contact angle hysteresis for a liquid droplet on a solid substrate in a gas phase. In addition, a gas bubble on a solid substrate in a liquid phase has been scrutinized from the aspect of surface energy minimization. The wetting effect has been regarded, where the liquid and gas species penetrate into the solid phase on the microscopic scale [F. Wang and B. Nestler, Phys. Rev. Lett. 132, 126202 (2024)]. We assume the liquid–solid and the solid–gas interfacial tensions to be a function dependent on the volume fraction of the liquid and the gas species and investigate the impact of the size ratio of the droplet to the solid surface that is overlooked in existing theories on the wetting phenomena. Our finding sheds light on the microscopic origin of the contact angle hysteresis and the droplet size effect on the wetting phenomena.
Theoretical insights into the ultrahigh piezoelectric performance of (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices
Authors: Wang Xin , Yang Jucai , Zhao Erjun , Cao Zhenzhu
Published: October 2024

Perovskite structures have attracted extensive attention in microelectromechanical systems and nanoelectromechanical systems devices due to the high piezoelectric response and the low dielectric constant. The piezoelectric and dielectric properties of the tetragonal BiFeO3/BaTiO3 superlattices grown along the c-axis direction are investigated using density functional theory (DFT) and density functional perturbation theory. The calculated results demonstrate that the (BiFeO3)n/(BaTiO3)n (n = 1–5) superlattices exhibit a profoundly increased piezoelectric response compared to their bulk structures. The (BiFeO3)2/(BaTiO3)2 possesses the highest piezoelectric d33 of 697 pC/N among known lead-free perovskite systems. Furthermore, the (BiFeO3)2/(BaTiO3)2 superlattice possesses a low dielectric ɛ33, and its d33 at 2% tensile strain is 16 times larger than that of an unstrained equilibrium structure. This demonstrates that biaxial tensile strain significantly enhances the piezoelectric response. Combining the special quasirandom structure method with DFT, the structures of a 0.5BiFeO3–0.5BaTiO3 solid solution are predicted, and its calculated d33 is 58 pC/N, which is much smaller than that of a (BiFeO3)2/(BaTiO3)2 superlattice. The results suggest that the (BiFeO3)2/(BaTiO3)2 superlattice might be a potential candidate for nonvolatile random access memory, transducers and actuators, and nanoscale electronic devices.
The mechanism of proppant transport dynamic propagation in rough fracture for supercritical CO2 fracturing
Authors: Sun Yuanxiu , He Liwei , Dong Bo , Tuerhongbaiyi Nuerlanjiang , Li Xiuxia , Zhang Qiushi
Published: October 2024

Supercritical CO2 fracturing technology has shown great potential for enhancing production in unconventional reservoirs. It is essential to clarify the transport mechanism of proppant under the dynamic propagation conditions within rough fractures. A realistic rough fracture model is reconstructed, and Computational Fluid Dynamics simulations are conducted to track proppant movement during fracture propagation. The typical transport characteristics of proppant within rough fractures are revealed, and the effects of fracture propagation rate, proppant density, mass flow rate, particle size, sand ratio, and temperature on the support effect are discussed. The results show that the flow channels formed by sand carrying fluid in rough fractures are complex, with fracture propagation changing some flow channels. The proppant forms an irregular sand bed interspersed with unfilled areas, and complex flow characteristics are generated. The increase in fractal dimension increases the resistance in the fluid flow process and affects the movement of the proppant, which tends to create unfilled areas. Low density and size of proppant can improve the proppant placement length. In a certain temperature range, high temperature injection of sand carrying fluid can improve the proppant placement effect. In addition, the low sand ratio and high mass flow rate pumping can be used to form the dominant channel, followed by pumping with a high sand ratio and low mass flow rate for effective support.
Experimental study on critical heat flux and thermal instability under hypergravity
Authors: Li Chong , Fang Xiande , Yang Quanquan , Chen Zhong , Du Siliang
Published: October 2024

The critical heat fluxes (CHF) for R245fa flowing inside a horizontal microchannel with diameter of 0.94 mm and heated length of 170 mm under different gravity levels were experimentally studied. Taking the thermal oscillation parameters occurring in the post-dryout region as the research object, which differed from the parameter oscillations during the occurrence of CHF in past literature, and revealing the formation mechanism of thermal oscillations when dryout type CHF occurred, as well as the impact of gravity level on thermal oscillations. The experimental parameters are: mass fluxes of G = 200 and 300 kg/m2 s, inlet pressure of Pin = 211.72 kPa, inlet subcooling of ΔTsub = 5–10 K, and nominal hypergravity of an = 1–1.53 g. The results show that CHF increases with the increase in mass flux, inlet subcooling, and gravity level, which is mainly related to the rates of liquid film evaporation, mainstream droplet entrainment, and droplet deposition onto the wall. The process of post-dryout occurs simultaneously with thermal instability. In addition, the increase in gravity level helps to alleviate the heat transfer deterioration at the test section outlet and suppresses the oscillations in wall temperature and inlet pressure.
Q&A: Engineer Stewart Isaacs seeks equitable climate change solutions
Authors: Feder Toni
Published: October 2024

Hard work, creativity, and problem-solving are key to Isaacs’s success in both science and another passion: jump rope.
Avoid getting burned: lessons from the McKinley wildfire in rural Alaska, USA
Authors: Schmidt Jennifer I. , Berman Matthew , Waigl Christine F.
Published: October 2024

Background Climate change and continued development in the wildland–urban interface (WUI) have increased risks to property and infrastructure from destructive wildfires. Aims A better understanding of the factors associated with building survival will promote resilience of WUI communities. Methods We studied factors associated with the likelihood that a building burned during the 2019 McKinley fire in the Alaska boreal forest, USA. We examined the potential influence of both ecological or socio-economic factors on building loss. Key results The probability of a building burning was significantly associated (P < 0.001) with a building burning nearby (within 30 m). Having less flammable deciduous cover nearby (within 100 m) improved survival. Buildings with lower value on larger parcels were more likely to burn, as were buildings with larger perimeters. Other important factors associated with burning included the number of buildings both nearby (within 30 m) and within the property parcel boundary. Conclusions Our results suggest that social and ecological factors contribute to building survival, indicating that a comprehensive social-ecological approach would provide the most effective support to WUI communities with wildfire risks. Implications A comprehensive approach that integrates social, economic, and ecological factors is important in understanding building loss in WUI wildfires.
Suggestions for a new model of functional phraseme categorization for applied purposes
Authors: Fankhauser Anna
Published: October 2024

Although the significance of phraseology in various fields of applied linguistics such as
translation, language teaching, and (bilingual) learner lexicography is generally agreed upon, existing models of
phraseme categorization largely fail to account for the needs of language practitioners and learners. Yet, a
classification model for applied purposes is required, for example, to provide language practitioners and learners
with a systematic list of useful phraseological items that can be applied to individual situations of language
production and reception. The model suggested in the present paper consistently applies functional classification
criteria and is derived from an extensive corpus study of spoken British and American English. It is hoped that the
empirical approach and the focus on functional properties of phrasemes will ensure that the model is of maximum
relevance for applied purposes.
A comprehensive Japanese MWE lexicon
Authors: Takahashi Masahito , Tanabe Toshifumi , Halpern Jack , Shudo Kosho
Published: October 2024

JMWEL (Japanese MWE Lexicon) is a comprehensive lexicon of Japanese Multiword Expressions (MWEs)
with a rich set of grammatical attributes fine-tuned for phrase-based processing of a wide range of Japanese
documents. It has about 160,000 MWE lemmas covering almost every kind of linguistically idiosyncratic but commonly
used Japanese phrases, e.g., idioms, quasi-idioms, collocations, quasi-collocations, clichés, quasi-clichés,
institutionalized phrases, proverbs, and old sayings, excepting technical terms in specialized fields or named
entities. JMWEL consists of sixteen sub-lexicons reflecting their distinctive features. The comprehensiveness of the
collected MWEs and the detailed morpho-syntactic information given to each MWE, which may include internal modifiers,
are notable features of JMWEL. In this paper, we introduce the newest version of JMWEL.
Ontology-based formalisation of Italian clitic verbal MWEs
Authors: di Buono Maria Pia , Monti Johanna , Caruso Valeria
Published: October 2024

In this paper we present the development of an ontology-based bilingual (IT-EN) lexicographic
resource of Italian clitic Verbal MultiWord Expressions (VMWEs) to support machine translation. Starting from an
analysis of these units and their linguistic features, we examine how Neural Machine Translation (NMT) handles complex
VMWEs and the related translations issues. Finally, we propose a bilingual resource, formalised by means of the
OntoLex-Lemon model, which accounts for morphological, syntactic, and semantic features of Italian clitic verbs, in
order to enhance automatic translation of VMWEs.
Chapter 8. Disagreements and conflicts in Wikipedia talk pages
Authors: Poudat Céline , Chandelier Marie
Published: October 2024

Collaborative situations inevitably generate disagreements and even conflicts. Over the last decade, Wikipedia has been extensively studied, but mostly from the perspective of social sciences. Conflicts have been described in great detail, along with phenomena such as quality, coordination, or in relation to maintenance work. However, most of the studies available did not define, nor measure conflicts from a linguistic perspective. The following chapter concentrates on two types of speech acts, which we consider to be of particular significance, namely speech acts expressing disagreement on the one hand, and a set of clearly offensive speech acts, such as insults or derogatory language, on the other hand. Our approach is corpus-based: the two typologies which are presented in our chapter were developed based on an annotation of speech acts in a corpus of Wikipedia discussions in French, partly extracted from the WikiDemoCorpus. The chapter then expands on the annotation which was carried out, and on the specific features of conflicts and disagreements in Wikipedia.
Separate magnetic and structural phase transitions in Mn50−xFexRh50 films grown on MgO
Authors: Li Qifeng , Yuan Xiaojuan , Liu Yong , Zhang Zhenhua , Lu Zhihong , Xiong Rui
Published: October 2024

Investigations of the magnetic and structural characteristics of Mn50−x
Fe
x
Rh50 alloys are important due to their notable phase transition behavior. In this study, a series of highly ordered epitaxial films with varying Fe concentrations are grown on MgO (001) substrate. At low Fe concentrations (x = 0, 2, 6), a separation between the structural phase transition and the magnetic phase transition is observed. Unlike structural phase transitions, temperature-dependent magnetization exhibits fairly large temperature hysteresis. In addition, the structural transition induces further tetragonal distortion, resulting in an intermediate phase between the B2 and L10 structures. This separated magnetic and structural phase transitions have been further validated through x-ray diffraction, anisotropic magnetoresistance and spin-pumping measurements. Moreover, as the Fe concentration is increased, the Mn50−x
Fe
x
Rh50 films exhibit ferromagnetic behavior due to competitive magnetic exchange interactions, while the structural phase transition is suppressed.
Role of mechanical stress localizations on the radiation hardness of AlGaN/GaN high electron mobility transistors
Authors: Al-Mamun Nahid Sultan , Rasel Abu Jafar , Islam Zahabul , Tzolov Marian B , Smyth Christopher M , Haque Aman , Wolfe Douglas E , Ren Fan , Pearton Stephen
Published: October 2024

Multi-material, multi-layered systems such as AlGaN/GaN high electron mobility transistors (HEMTs) contain residual mechanical stresses that arise from sharp contrasts in device geometry and materials parameters. These stresses, which can be either tensile or compressive, are difficult to detect and eliminate because of their highly localized nature. We propose that their high-stored internal energy makes potential sites for defect nucleation sites under radiation, particularly if their locations coincide with the electrically sensitive regions of a transistor. In this study, we validate this hypothesis with molecular dynamic simulation and experiments exposing both pristine and annealed HEMTS to 2.8 MeV Au+3 irradiation. Our unique annealing process uses mechanical momentum of electrons, also known as the electron wind force (EWF) to mitigate the residual stress at room temperature. High-resolution transmission electron microscopy and cathodoluminescence spectra reveal the reduction of point defects and dislocations near the two-dimensional electron gas region of EWF-treated devices compared to pristine devices. The EWF-treated HEMTs showed relatively higher resilience with approximately 10% less degradation of drain saturation current and ON-resistance and 5% less degradation of peak transconductance. Both mobility and carrier concentration of the EWF-treated devices were less impacted compared to the pristine devices. Our results suggest that the lower density of nanoscale stress localization contributed to the improved radiation tolerance of the EWF-treated devices. Intriguingly, the EWF is found to modulate the defect distribution by moving the defects to electrically less sensitive regions in the form of dislocation networks, which act as sinks for the radiation induced defects and this assisted faster dynamic annealing.
Cantilever configurations in vibration-based piezoelectric energy harvesting: a comprehensive review on beam shapes and multi-beam formations
Authors: Sadaf Asef Ishraq , Ahmed Riaz , Ahmed Hossain
Published: October 2024

Vibration-based energy harvesting technology is a well-established research area that has attracted tremendous interest over the last decade. This interest is primarily owing to its extension into a wide range of engineering domains, particularly in microelectromechanical systems. The cantilever beam is the most common and widely used model for vibration-based energy harvester, driven by two key factors: (a) simplicity in design, and (b) high output power density. Numerous studies over the years have focused on optimizing the cantilever beam design to increase output power capacity and/or widen the frequency bandwidth of the harvester. While researchers have proposed a plethora of cantilever beam configurations for specific purposes (e.g. low-frequency harvesting, multi-directional frequency harvesting, etc), there is a notable lack of detailed literature on the types and configurations of cantilever beams. This gap hinders researchers from gaining a comprehensive understanding of the cantilever beams already introduced. Following the need, in this article a comprehensive review is made to list the types of cantilever beams proposed by the researchers over the years. This review covers the working principles of piezoelectric energy harvesting, analyses existing solutions geared towards increasing power output and widening working frequency, and discusses diverse configurations including single and multiple beam setups. The listed beams are categorized based on their structural shape and organization such that it can be helpful for a reader to anticipate which cantilever beam design can be suitable for a specific need. Power output capacity and operating frequency for every beam design are also presented in a tabular form, under each beam category. This would enable the researchers to tailor their designs for specific applications, enhance material efficiency, drive innovation, and open new application possibilities.
Enhancement of transverse magneto-optical Kerr effect using transition metals in a grating-based gyro-electric structure
Authors: Amanollahi Mansoureh , Zamani Mehdi
Published: October 2024

This study proposes a new magneto-plasmonic structure based on a grating which is made of Co6Ag94 (a gyro-electric medium) and a layer of transition metals (platinum, silver, copper, gold, and palladium) is placed on it. First, the impact of surface plasmon polaritons on enhancing the transverse magneto-optical Kerr effect when exposed to TM- and TE-polarized waves has been investigated. The results indicate that the gyro-electric magneto-optics material effectively responds to TM-polarized waves, and the transverse Kerr effect is significantly amplified. Such reinforcement has made this structure suitable for use in the sensing field, which has shown a sensitivity of 100 deg RIU−1 and a figure of merit of about 1000 RIU−1. These results clearly show the effect of using different metals in magneto-plasmonic structures for sensing applications. Also, by comparing the metals used and examining the characteristics and weaknesses of each, it is concluded that gold and silver are the best choices for this structure. Compared to other works that have been done, this work has shown that by using available and affordable materials, it is possible to design grating-based magneto-plasmonic structures that enhance magneto-optical effects and use them in various applications.
Gravitational wave luminosity distance-weighted anisotropies
Authors: Begnoni Andrea , Dall'Armi Lorenzo Valbusa , Bertacca Daniele , Raccanelli Alvise
Published: October 2024

Measurements of the luminosity distance of propagating gravitational waves can provide invaluable information on the geometry and content of our Universe. Due to the clustering of cosmic structures, in realistic situations we need to average the luminosity distance of events coming from patches inside a volume. In this work we evaluate, in a gauge-invariant and fully-relativistic treatment, the impact of cosmological perturbations on such averaging process. We find that clustering, lensing and peculiar velocity effects impact estimates for future detectors such as Einstein Telescope, Cosmic Explorer, the Big Bang Observer and DECIGO. The signal-to-noise ratio of the angular power spectrum of the average luminosity distance over all the redshift bins is 17 in the case of binary black holes detected by Einstein Telescope and Cosmic Explorer. We also provide fitting formulas for the corrections to the average luminosity distance due to general relativistic effects.
Effective quantum gravitational collapse in a polymer framework
Authors: Boldorini Lorenzo , Montani Giovanni
Published: October 2024

We study how the presence of an area gap, different than zero, affects the gravitational collapse of a dust ball. The implementation of such discreteness is achieved through the framework of polymer quantization, a scheme inspired by loop quantum gravity (LQG). We study the collapse using variables which represent the area, in order to impose the non-zero area gap condition. The collapse is analyzed for both the flat and spherical Oppenheimer-Snyder models. In both scenarios the formation of the singularity is avoided, due to the inversion of the velocity at finite values of the sphere surface. This happens due to the presence of a negative pressure, with origins at a quantum level. When the inversion happens inside the black hole event horizon, we achieve a geometry transition to a white hole. When the inversion happens outside the event horizon, we find a new possible astrophysical object. A characterization of such hypothetical object is done. Some constraints on the value for the area gap are also imposed in order to maintain the link with our already established physical theories.
Influence of guide groove structure on in-flow drag reduction in spiral axial gas-liquid mixing pumps
Authors: Han Wei , Yang Yubin , Xiao Mingzhen , Hou Yuyan , Zhao Longlong , Dong Yifan , Bai Lu , Xue Tonqing , Xing Yifan
Published: October 2024

With the onset of the fossil energy crisis, demand for oil has skyrocketed, and the spiral axial flow gas-liquid mixing pump has emerged as the primary piece of equipment for deep-sea oil extraction. However, at high gas content, the problems of separation of mixed media from hydraulic components, gas-liquid separation and gas phase aggregation are faced. The difficulties of gas-phase aggregation and bubble trajectory in the impeller channel have received much attention, while the problem of increased medium flow resistance induced by flow separation has received less attention. The spiral axial gas-liquid mixing pump is numerically calculated using the Eulerian multiphase flow model and the SST k- turbulence model in this work. The pump is designed with the design flow rate Q = 100 m3/h, rotational speed n = 4500 rmin, and head H = 30m by arranging guide slots with different relative depths and different number of slots to reduce the dissipative vortices, thus reducing the flow resistance in the 1/5 region behind the suction surface. The findings reveal that when the relative depth of the slots is 1/7 and the number of guide slots arranged is 5, the highest drag reduction rate in this location is 69.6% under the design flow condition. When the relative depth of the guide channel is1/7 and the number of guide channels is 3, the performance of the mixing pump is improved most, with an efficiency increment of 1.9% and a head increment of 4.2%, which can provide technical support for the flow resistance reduction of gas-liquid mixing pumps.
Model test and analyses for a mixed-flow pumping system in the S-to-N Water Diversion Project of China
Authors: Liu Xueqin , Zhang Juan , Zhu Honggeng , Zhu Feng , Zhou Wei , Zhang Rentian
Published: October 2024

Baoying Pumping Station as the first station built in the East Route of the S-to-N Water Diversion Project in China, due to the importance of water source project and its 5000 hours yearly operating time, a serial of model tests and other measures were taken to secure its safety and high efficiency operation. Through the comparative model tests in the preliminary design stage, it was made clear that mixed-flow pump was the right direction of pump selection. The acceptance model test indicated that all performance requirements were satisfied and the head-weighted efficiency of the pumping system reached 80.5%, which was about 7 percentages higher than that obtained in the preliminary research and a good foundation for its efficient and economical operation was laid. The optimization design of inlet and outlet flow passages was not significant for improve the efficiency of pumping system. The verification test results were very close to the acceptance test results, and have been confirmed each other. The international bidding and mechanism of joint venture in purchasing main equipment for Baoying pumping station proved to be a success in introducing advanced foreign technology, and its construction experience can provide a useful reference for similar pumping stations.
Study on the influence of sediment erosion of Francis turbine runner under different water heads
Authors: Wang Jinliang , Wang Jiabing , Wang Zhengwei
Published: October 2024

The average measured sediment concentration of the river section where Wanjiazhai Hydropower Station is located over the years is 5.7kg/m 3, The maximum measured sediment concentration reaches 37.6kg/m 3, The erosion of the flow components of hydraulic turbines caused by sand containing water flow is becoming increasingly severe, coupled with the frequent impact of load changes during peak shaving operation, the problems exposed during the operation of hydraulic turbines are becoming more prominent, which affects the stable operation of the units. This article uses numerical simulation and experimental testing to study the sediment wear characteristics and hydraulic performance of the water turbine at Wanjiazhai Hydropower Station. Research has revealed the effects of working head on impeller wear. The increase in working head will exacerbate the impact wear on the main channel wall of the unit. The surface of water turbine blades is the main wear area, and the high-speed impact of particles causes an increase in the wall wear rate. The probability of particles coming into contact with the wall at the outlet increases, resulting in rapid wear at this point. The increase in head will intensify the wear intensity of the unit surface, and the flow velocity in the gap indicates that the local high-speed jet in the gap is the main cause of gap wear. Therefore, in order to ensure the efficient anti-wear performance of the water turbine, multiple factors need to be comprehensively considered to cope with sediment wear of the water turbine, including regular cleaning, optimized structural design, use of wear-resistant materials, replacement of worn parts, and optimization of operating parameters. These measures help to reduce the damage of sediment wear to water turbines and extend their service life.
Optimization and Regulation Method for Large Blade-regulating Pump Stations Considering Safety Constraints
Authors: Tan Yuxiang , Liang Yunhui , Qian Lihua , Yuan Zhibo
Published: October 2024

In plain areas, making flood control and drought resistance a heavy task. Large water pumping stations undertake the important task of water lifting and scheduling. Due to the physical characteristics of large pumping stations, they are often affected by the upstream and downstream water levels during water lifting scheduling, resulting in low head operating conditions. Low head operating conditions can easily cause pumping stations to operate at excessive power, thereby affecting the health of pumping station equipment. Based on the head efficiency curve of a large blade regulating pump station in this article, by optimizing the regulating mathematical model and considering constraints such as water level, flow rate, power, efficiency, and blade angle adjustment time interval under low head conditions, a dynamic programming calculation method is adopted to construct an optimized regulating method for the pump station. Based on real-time water level, various operating data of the unit are optimized to ensure the blade angle, power, and the flow rate and other parameters are all within the safety constraint range. And various operating data could be used to guiding the real-time optimization and adjustment of the pumping station, and additionally providing the operating foundation for the intelligent pumping station.
Numerical study on unsteady characteristics of backflow vortex cavitation in an axial flow pump
Authors: Cai Shuting , Huang Renfang , An Yi , Wang Yiwei , Li Ning
Published: October 2024

Axial pumps play a crucial role in various industries such as agriculture, construction, and chemical engineering, exhibiting optimal efficiency under design conditions. However, in practical applications, these pumps often operate under off-design conditions due to environmental constraints, which would lead to a series of problems such as increased vibration, elevated noise levels, and a shortened pump lifespan, thereby endangering its safe and stable operation. This study addresses the issue by using a modified RNG k-ε turbulence model combined with the Zwart cavitation model to simulate the cavitation characteristics of an axial-flow pump. The calculated cavitation characteristics are consistent with the experimental results, proving the exactitude of the numerical approach. A noteworthy observation is the severe cavitation occurrences at the backflow vortex, termed backflow vortex cavitation. This phenomenon undergoes inception, development, and eventual collapse constantly. According to the severity of the backflow vortex cavitation, different periods are divided into the bimodal stage and small-peak stage. Significantly, it is identified that the backflow vortex cavitation interacts with the impeller blades, as the impeller moves, thereby inducing blade vibration, and noise, and exacerbating cavitation erosion. The research results offer a theoretical foundation that is beneficial to enhancing the safe and stable operation of axial flow pumps.
Study on the Performance of Pressure Balance Pipe of Pump-turbine
Authors: Liu Jiayi , Zhang Fei , Zhu Baoshan , Chen Zhenmu
Published: October 2024

For pump-turbine, axial water thrust can cause damage to the unit. It is important to realise automatic levelling by using pressure balance pipe. To study the influence of the pressure balance pipe on the performance of the reversible pump-turbine, axial water thrust and pressure fluctuation have been carried out for reversible pump-turbine with different guide vane opening and different operating heads by numerical and experimental analysis. The unsteady simulation results for the full flow channel of the pump-turbine show that the 298 mm guide blade opening meets the test standards of flow and power. Furthermore, CFD tests were carried out for different water heads at 298mm guide vane opening. At last, under the typical working conditions of 298mm guide vane opening and 400 m water head, pressure fluctuation, the axial water thrust in the vaneless zone are analyzed.
Wear Measurement of a Francis Runner damaged by sediment erosion: A case study
Authors: Poudyal Atmesh , Neopane Hari Prasad , Chitrakar Sailesh
Published: October 2024

Hydropower is one the biggest sources of electricity all over the world and the largest by far in Nepal. Francis Turbines are extensively used in hydropower plants due to flexible ranges of head and discharge. Sediment erosion has been a major cause of damage and efficiency reduction in Francis Turbine components. As a stepping stone towards making erosion resilient turbine components, the measurement of wear due to erosion is essential. This study was conducted on the 35 MW Francis Runner installed at the Middle Marsyangdi Hydro Power Station of Nepal. The Runner was found to be heavily damaged after three years of continuous operation. The approach of measuring wear at various sections of the Runner using basic hand tools was adopted. The outer wearing rings on both the hub and shroud sections were found to be substantially reduced in diameter due to erosion, correlating to typical side wall erosion occurring in Francis Turbines. Substantial erosion was found on the blade inlets at both the hub and shroud sections, correlating to typical leakage gap erosion from the guide vanes. Substantial cavitation wear was found at the suction side of the blades at both the inlet and outlet of blades as well as at the wearing rings on both the hub and shroud sections. The wear on blades was found to be substantially higher at the outlet of the Runner with all 13 blades cracked at the outlet. The eroded mass of the Runner calculated through volumetric analysis was found to be 294 kg. The result was compared to the mass obtained by using a weight scale before and after the restoration of the Runner at a commercial workshop and a 5.16 % error was obtained which seems acceptable considering the simplicity of the process. The cost estimation for repairing the damaged Runner was also done based on the obtained result of eroded mass.
Three-dimensional modelling and numerical analysis of Pelton turbine runner buckets
Authors: Wang H B , Li D Y , Fu X L , Gong R Z , Wang H J
Published: October 2024

The Pelton turbine, a hydraulic prime mover, harnesses high-pressure water jets’ kinetic energy to drive the rotation of its runner buckets, converting water energy into mechanical energy. Due to its straightforward design and applicability in high to super high head scenarios, it has been a mainstay in power stations for many years. The bucket, a critical component of the Pelton turbine’s runner, plays a pivotal role in the unit’s performance. Using Non-Uniform Rational B-Splines (NURBS) to develop a parametric water bucket model enhances adaptability. Also, performing unsteady numerical simulations on the model analyses its hydraulic characteristics and flow state distribution. The numerical calculations fundamentally capture the unsteady flow conditions within the rotating buckets, with the results of the flow pattern distribution largely aligning with those documented in existing research. This provides a reference for enhancing the hydraulic performance of Pelton turbine runners.
Study on Internal Flow Characteristics and Pressure Pulsation Features of Pump-Turbine under the no-load Startup Condition with Different Heads
Authors: Dong Haiyang , Lu Yonggang , Wang Long , Liu Zhiwang , Mei Xiang , Zhang Shuaishuai , Wang Zhengwei
Published: October 2024

Unstable operation during the no-load startup of pumped storage hydroelectric power plants is a significant factor affecting the successful grid connection of units. To investigate the internal flow and pressure pulsation characteristics during the no-load startup of pump-turbine under varying heads, the vertical single-stage mixed-flow reversible pump-turbine is studied. Numerical simulations are performed using the SST k-ω turbulence model, and the Fast Fourier Transform (FFT) method is employed to analyze the pressure pulsation signals. A comparative study is conducted on the pressure pulsation characteristics and internal flow features at different positions under various heads. The results indicate that the pressure pulsation in the draft tube cone region is the most severe, with the dominant blade passing frequency (fBPF
) and its harmonics caused by rotor-stator interaction (RSI) in the spectra of pressure pulsations at various heads in the draft tube cone region. Additionally, the pressure pulsation amplitude increases as the head decreases, while low-frequency pulsation signals are prevalent throughout the entire flow passage. Compared to the flow condition, the influence of rotor-stator interaction on pressure pulsation is more significant. During the no-load startup at the highest head, the pump-turbine exhibits the most vortex structures and the poorest flow condition, while the intensity of pressure pulsation in the draft tube cone region is the lowest. These research findings provide a basis for the stable no-load startup of pump-turbine.
Analysis of Aerostatic Performance of a Flexure Pivot Tilting Pad Air Journal Bearing
Authors: Zhong Yi , Böhle Martin
Published: October 2024

Aerostatic performance of a flexure pivot tilting pad air journal bearing is examined with several numerical simulation under various working conditions. The air pressure distribution in the bearing clearance is obtained by solving the Reynolds equation with the finite difference method (FDM). The code consists of 3 main parts: mass flow rate equilibrium, moment equilibrium, and shaft equilibrium. They are used to study the gas pressure at the downstream of the nozzles, the motion of pads, and the position of the shaft in the bearing, respectively. Code accuracy is verified by comparing the results with those in other articles. This work lays the foundation for future research.
Numerical study of the influence of structural parameters on the performance of annular ejector
Authors: Liu Kang , Cao Zhengqing , Fang Kaiyue , Zhang Xinchen , Yang Xuelong
Published: October 2024

Compared with the central ejector, the annular ejector is widely used in refrigeration, coal mining and chemical industry because the working fluid enters the suction chamber through the annular nozzle, the contact area with the ejection fluid increases, and the ejection fluid does not need to change the flow direction. In order to solve the problem of low performance of annular gas ejector, this paper designs an annular gas ejector with reference to the relevant model, and the axial length and suction angle of the mixing tube of the annular gas ejector are mainly studied. The results show that there is an optimal value for the length of the ring gas ejector mixing tube, and the length of the mixing tube is too long or too short is not conducive to the gas extraction of the ring gas ejector. Under the same annular gap, with the increase of the jet angle, the amount of gas consumed in the primary stream does not change much, and the gas to be pumped decreases, resulting in the performance of the annular gas ejector being reduced, which is not conducive to the suction of the ejector.