bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of heat flow in modified transient plane source (MTPS) measurements of the thermal effusivity and thermal conductivity of materials
Authors: Yeon Sooyeon , Cahill David G.
Published: March 2024

An iterative algorithm for the diffusion of heat in layered structures is solved in cylindrical coordinates for the geometry used in measurements of thermophysical properties of materials by the modified transient plane source (MTPS) method. This solution for the frequency-domain temperature response is then used to model the transient temperature excursion and evaluate the accuracy of the measurements. We evaluate when the MTPS method is capable of separately determining the thermal conductivity and heat capacity per unit volume of a material. For a typical sensor design, data acquisition, and data analysis, the MTPS measurement has a small sensitivity to the thermal diffusivity of the sample when the thermal diffusivity is <5 mm2 s−1. We analyze the propagation of errors from uncertainties in the thermal contact between the sensor and the sample and evaluate the limitations of the MTPS method in accurately measuring samples with extremely low thermal effusivity, e.g., low density foam insulation. We find that uncertainties in the thickness of the contact region limit the accuracy of MTPS measurements when the data are analyzed in a conventional manner based on a single parameter, m−1, the inverse of the slope of the temperature excursion as a function of the square root of time.
Transient response of hybrid and homogeneous pipelines: Laboratory experiments
Authors: Maietta F. , Crispino G. , Capponi C. , Gisonni C. , Brunone B. , Meniconi S.
Published: March 2024

The replacement of deteriorated pipe segments in aging water distribution networks often results in hybrid pipelines, consisting of segments of different materials of comparable length. The fact that short segments of polymeric material have a strong effect on the transient response of metallic pipelines authorizes to consider it important to examine the transient behavior of hybrid pipelines. To this end, transient tests were carried out on a high-density polyethylene (HDPE)+ cast iron (CI) hybrid pipeline at the Water Engineering Laboratory (WEL) of the University of Perugia, Italy. As a reference, tests were also carried out on a homogeneous HDPE pipeline with the same total length. The results of the laboratory tests showed that the value of the pressure local extremes (i.e., pressure peaks) was much higher in the homogeneous pipeline than in the hybrid one. On the contrary, the number of pressure peaks is much smaller in the homogeneous pipeline than in the hybrid one. Such features have been explained by analyzing the mechanisms of interaction of pressure waves at the in-series junction between the two different materials.
Low-frequency whistler waves driven by energetic electrons in plasmas of solely electron cyclotron wave heating
Authors: Wang Mingyuan , Shi Yuejiang , Dong Jiaqi , Gao Xinliang , Lu Quanming , Wang Ziqi , Chen Wei , Liu Adi , Zhuang Ge , Wang Yumin , Cheng Shikui , Tan Mingsheng , Li Songjian , Song Shaodong , Sun Tiantian , Liu Bing , Huang Xianli , Li Yingying , Song Xianming , Yuan Baoshan , Peng Y.-K. Martin
Published: March 2024

Whistler waves are a type of low-frequency electromagnetic wave common in nature, which is usually associated with energetic electron phenomena. This study presents experimental observations of low-frequency whistler wave instabilities driven by energetic electrons through wave–particle interactions on EXL-50. The energetic electrons are generated by electron cyclotron waves (ECWs) through stochastic heating [Wang et al., J. Plasma Phys. 89, 905890603 (2023)] and do not match the characteristics of the runaway electrons [Shi et al., Nucl. Fusion 62, 086047 (2022)]. In the steady-state plasma of the Energy iNNovation XuanLong-50 (EXL-50), whistler waves within the 30–120 MHz frequency range were observed during electron cyclotron resonance heating. These waves displayed multiple frequency bands, and the frequencies of waves were directly proportional to the Alfvén velocity. Furthermore, it was interesting to find that superposition of lower hybrid wave into ECW resulted in the suppression of these whistler waves. The experimental results may indicate that the whistler waves are driven by energetic electrons (excluding runaway electrons). These discoveries carry significant implications for several areas of research, including the investigation of wave–particle interactions, the development of radio frequency wave current drivers, their potential impact on the electron dynamics in future fusion devices, and even the presence of unusually low-frequency whistler waves in Earth's radiation belts.
Sulfolane clustering in aqueous saline solutions
Authors: Pensini Erica , Marangoni Alejandro G. , Bartokova Bibiana , Fameau Anne Laure , Corradini Maria G. , Stobbs Jarvis A. , Arthur Zachary , Prévost Sylvain
Published: March 2024

Sulfolane is a groundwater pollutant. While sulfolane is miscible in pure water, its miscibility in the presence of ions has not been widely investigated. This aspect is relevant to predict sulfolane migration in groundwater. Na2SO4 separates sulfolane from water, yielding bulk separation, emulsions seen by optical microscopy or molecular sulfolane clusters. We study these clusters with fluorescence spectroscopy, small-angle x ray (SAXS) and neutron (SANS) scattering, and x-ray absorption fine structure (XAFS). Fluorescence spectroscopy reveals non-monotonic changes in the local viscosity of the water phase with 10% sulfolane and 0.25-1M Na2SO4, likely resulting from the interplay between sulfolane clustering and enhanced interactions between water molecules. NaCl affects the micro-viscosity of water similarly to Na2SO4, but at higher concentrations. At low sulfolane percentages, Cl− decreases the activity coefficients of water and sulfolane, suggesting stronger sulfolane–sulfolane and water–water interactions. SAXS confirms that Na2SO4 induces sulfolane clustering. SAXS data modeled with a power law and a Gaussian reveal a correlation length ξ = 16.3 Å, which we view as the radius of a sulfolane cluster surrounded by water and Na+ ions. SANS also shows that 2 mol. % of sulfate and chloride salts induce sulfolane clustering, with sulfates having a more marked effect. Furthermore, XAFS reveals that sulfates affect sulfolane sorption onto Si3N4 surfaces. Without Na2SO4, sulfolane directly sorbs onto Si3N4 surfaces. Conversely, with Na2SO4, water is directly sorbed onto Si3N4, likely because it surrounds sulfolane clusters. Also, hydrated Na+ ions are in Si3N4 surface proximity.
Quantum Drude oscillators coupled with Coulomb potential as an efficient model for bonded and non-covalent interactions in atomic dimers
Authors: Ditte Matej , Barborini Matteo , Tkatchenko Alexandre
Published: March 2024

The quantum Drude oscillator (QDO) model has been widely used as an efficient surrogate to describe the electric response properties of matter as well as long-range interactions in molecules and materials. Most commonly, QDOs are coupled within the dipole approximation so that the Hamiltonian can be exactly diagonalized, which forms the basis for the many-body dispersion method [Phys. Rev. Lett. 108, 236402 (2012)]. The dipole coupling is efficient and allows us to study non-covalent many-body effects in systems with thousands of atoms. However, there are two limitations: (i) the need to regularize the interaction at short distances with empirical damping functions and (ii) the lack of multipolar effects in the coupling potential. In this work, we convincingly address both limitations of the dipole-coupled QDO model by presenting a numerically exact solution of the Coulomb-coupled QDO model by means of quantum Monte Carlo methods. We calculate the potential-energy surfaces of homogeneous QDO dimers, analyzing their properties as a function of the three tunable parameters: frequency, reduced mass, and charge. We study the coupled-QDO model behavior at short distances and show how to parameterize this model to enable an effective description of chemical bonds, such as the covalent bond in the H2 molecule.
First detection and absolute transition frequencies in the (3–0) band of D2
Authors: Kassi S. , Fleurbaey H. , Campargue A.
Published: March 2024

Three electric quadrupole transitions in the second overtone band of D2 are newly measured by comb-referenced cavity ring down spectroscopy around 1.18 µm. These extremely weak transitions (line intensities smaller than 10−29 cm/molecule) are the first to be detected in the (3–0) band of D2. The spectra of the O(3), O(2), and Q(2) lines near 8321, 8446, and 8607 cm−1, respectively, are recorded at room temperature for pressure values ranging between 100 and 600 Torr. Accurate transition frequencies and line intensities of the three D2 transitions are determined from a line fitting procedure using beyond-Voigt profiles, including strong Dicke narrowing. Considering statistical fit errors and possible biases due to the interference with water lines (which are six orders of magnitude stronger than the studied D2 lines), total uncertainties on the frequencies extrapolated at zero pressure are estimated below 14 MHz (∼4.7 × 10−4 cm−1). The derived experimental frequencies and intensities are compared to ab initio values. An overall agreement is achieved, confirming the positional accuracy of the most advanced theoretical calculations.
Recent advance and design strategies of chalcogenides for high-performance aqueous zinc-ion batteries
Authors: Wang Lujing , Li Shuyue , Wang Chunzhong , Yao Shiyu , Chen Gang , Du Fei
Published: March 2024

Aqueous zinc-ion batteries (AZIBs) have emerged as competitive alternatives for energy storage systems. By comparison with traditional cathode materials, the unique combination advantages of improved specific capacity, high electrical conductivity and tunable structures exhibited by chalcogenides contribute to receiving increasing attention. However, it should be noted that chalcogenides still show unsatisfactory electrochemical performance in aqueous batteries, because of their inferior chemical stability and sensitivity to pH value in aqueous media. Consequently, the application of chalcogenides in AZIBs still requires further investigation and optimization. This review offers a systematic summary of recent advancements in the rational design strategies employed to develop advanced cathode materials derived from chalcogenides. Furthermore, the review comprehensively presents the applications of various transition metal dichalcogenides, as well as sulfur (S), selenium (Se), tellurium (Te), and their corresponding solid solutions, in AZIBs. Lastly, the challenges currently confronting chalcogenides research are deliberated upon, followed by a perspective outlining future directions for practical applications of AZIBs.
Effect of zero-point motion on properties of quantum particles adsorbed on a substrate
Authors: Al-Oqali Amer D , Sakhel Roger R , Sakhel Asaad R
Published: March 2024

We qualitatively investigate the effect of zero-point motion (ZPM) on the structure and properties of a film composed of quantum particles adsorbed on a graphite substrate. The amplitude of ZPM is controlled by a change of the particle mass while keeping the interactions fixed. In that sense it is assumed that the interactions can be controlled by future doping methods. The worm-algorithm path integral Monte Carlo (WAPIMC) method is applied to simulate this system in the grand-canonical ensemble, where particles can be exchanged with the external particle reservoir. Another method, namely the multiconfigurational time-dependent Hartree method for bosons is additionally applied to verify some of the WAPIMC results and to provide further information on the entropy and the condensate fraction. Several important findings are reported. It is found that ZPM plays an important role in defining order and disorder in the crystalline structure of the adsorbed film. The total energy of the film drops with a reduction in the amplitude of ZPM, that is, it becomes more negative which is an indication to stronger adsorption. For a few particle numbers, a significant condensate fraction is detected that however drops sharply at critical values of the ZPM amplitude. Most importantly, a connection is established between chaos, in coordinate as well as momentum space, and the Heisenberg uncertainty principle. The importance of the present study lies in the fact that adsorbed two-dimensional films serve as an excellent experimental testbed for demonstrating low-dimensional quantum phenomena in the ground state. The present examination contributes also to a further understanding of the properties of heavy quantum particles adsorbed on substrates.
High harmonic generation from Kagome lattice based on multi-band semiclassical trajectory method
Authors: Li Jia , Yu Chao , Peng Yigeng , Lu Ruifeng
Published: March 2024

We develop a multi-band semiclassical trajectory (MBSCT) method for studying the high harmonic generation (HHG) from solids, which is fundamentally similar to the Boltzmann equation but describe the electron density distribution in a different way and can simulate the electron transitions between bands, thereby depicting a richer array of physical processes. Compared to other theoretical methods, such as the time-dependent Schrödinger equation, the semiconductor Bloch equation, and time-dependent density functional theory, our MBSCT method avoids issues like massive consumption of computational resources and the need for wave function phase correction. Moreover, we focus on Kagome-type materials to justify the MBSCT method and investigate the influence of flat band on HHG in strong laser fields. The simulated results show that the intensity of certain harmonic orders is suppressed by the flat band, implying harmonic spectroscopy as a potential all-optical approach for characterising nonequilibrium physics of flat-band quantum materials.
Enhancing ferroelectric performance in hafnia-based MFIS capacitor through interface passivation and bulk doping
Authors: Yang Jianxing , Xie Yufang , Zhu Chengyan , Chen Sixue , Wei Jiajing , Liu Yuan , Chen Mingming , Cao Dawei
Published: March 2024

In recent times, there has been a notable surge of interests in hafnia (HfO2)-based ferroelectrics, primarily due to their remarkable ferroelectric properties employed in ultra-thin configurations, alongside their compatibility with the conventional CMOS manufacturing process. In order to harness the full potential of HfO2-based films for high-performance non-volatile memory applications, it is imperative to enhance their ferroelectric characteristics and durability. This study introduces a straightforward approach aimed at augmenting the ferroelectric performance of Hf
x
Zr1−x
O2 (HZO) films deposited on silicon (Si) substrates through the engineering of oxygen vacancies (V
O). The results of this endeavor demonstrate a significant enhancement in ferroelectric performance, characterized by a 2Pr value of 47 μC cm−2 and impressive endurance, enduring up to 108 cycles under an 8 MV cm−1 electric field without the need of a wake-up process. This marked improvement can be attributed to a dual-pronged approach, involving the incorporation of an Al2O3 interlayer and the introduction of Al atoms into the HZO film. The Al2O3 interlayer primarily serves to mitigate the presence of oxygen vacancies at the interface, while the introduction of Al dopants elevates the concentration of oxygen vacancies within the bulk material. This modulation of oxygen vacancy concentration proves instrumental in facilitating the formation of a ferroelectric o-III phase within the HZO-based films, thereby further augmenting their ferroelectric performance. This innovative and effective strategy offers an alternative avenue for enhancing the ferroelectric properties of materials characterized by a fluorite crystal structure.
Silicon eccentric shell nanoparticles fabricated by template-assisted deposition for Mie magnetic resonances enhanced light confinement
Authors: Yang Huan , Jiang Xinbing , Zhang Manman , Li Ben Q , Wang Jiajie , Han Yiping
Published: March 2024

We report a structure of silicon eccentric shell particles array, fabricated by the SiO2 particles monolayer array assisted deposition of amorphous Si, for high-efficiency light confinement. The SiO2 particles monolayer array is tailored to regulate its interparticle distance, followed by silicon film deposition to obtain silicon eccentric shell arrays with positive and negative off-center distance e. We studied the Mie resonances of silicon solid sphere, concentric shell, eccentric shell and observed that the eccentric shell with positive off-center e supports superior light confinement because of the enhanced Mie magnetic resonances. Spectroscopic measurements and finite difference time domain simulations were conducted to examine the optical performance of the eccentric shell particles array. Results show that the Mie magnetic resonance wavelength can be easily regulated by the size of the inner void of the silicon shell to realize tunable enhanced light confinement. It was found silicon shell with D = 460/520 nm offered high enhanced light absorption efficiency at wavelength of λ = 830 nm, almost beyond the bandgap of the amorphous silicon.
Remote photoplethysmography based on reflected light angle estimation
Authors: Fan Xuanhe , Liu Fangwu , Zhang Jinjin , Gao Tong , Fan Ziyang , Huang Zhijie , Xue Wei , Zhang JingJing
Published: March 2024

Objective. In previous studies, the factors affecting the accuracy of imaging photoplethysmography (iPPG) heart rate (HR) measurement have been focused on the light intensity, facial reflection angle, and motion artifacts. However, the factor of specularly reflected light has not been studied in detail. We explored the effect of specularly reflected light on the accuracy of HR estimation and proposed an estimation method for the direction of specularly radiated light. Approach. To study the HR measurement accuracy influenced by specularly reflected light, we control the component of specularly reflected light by controlling its angle. A total of 100 videos from four different reflected light angles were collected, and 25 subjects participated in the dataset collection. We extracted angles and illuminations for 71 facial regions, fitting sample points through interpolation, and selecting the angle corresponding to the maximum weight in the fitted curve as the estimated reflected angle. Main results. The experimental results show that higher specularly reflected light compromises HR estimation accuracy under the same value of light intensity. Notably, at a 60° angle, the HR accuracy (ACC) increased by 0.7%, while the signal-to-noise ratio and Pearson correlation coefficient increased by 0.8 dB and 0.035, respectively, compared to 0°. The overall root mean squared error, standard deviation, and mean error of our proposed reflected light angle estimation method on the illumination multi-angle incidence (IMAI) dataset are 1.173°, 0.978°, and 0.773°. The average Pearson value is 0.8 in the PURE rotation dataset. In addition, the average ACC of HR measurements in the PURE dataset is improved by 1.73% in our method compared to the state-of-the-art traditional methods. Significance. Our method has great potential for clinical applications, especially in bright light environments such as during surgery, to improve accuracy and monitor blood volume changes in blood vessels.
Self-bound liquid droplets in one-dimensional optical speckle potentials
Authors: Abbas Karima , Boudjemâa Abdelâali
Published: March 2024

We present a comprehensive description of the equilibrium properties of self-bound liquid droplets in one-dimensional optical speckle potentials at both zero and finite temperatures. Using the Bogoliubov theory we calculate analytically the equation of state, fluctuations induced by disorder, and the equilibrium density. In particular, we show that the peculiar competition between the speckle disordered, the interactions and the Lee-Huang-Yang quantum fluctuations may strongly affect the stability and the formation of the self-bound droplet. We address also the static and dynamical properties of such a disordered droplet using the generalized disorder-dependent Gross-Pitaevskii equation. Notably, impacts of a weak speckle potential are treated numerically for both small droplets of an approximately Gaussian shape and large droplets with a flat-top plateau.
Controllable Floquet topological phases in the magnetic ladder system
Authors: Wang Xu-Jin , Zhang Lu , Yan Liang , Yan Jie-Yun
Published: March 2024

Utilizing both the electric and magnetic fields to manipulate electron dynamics enables the external control of topological states. This study investigates the topological characteristics of a quasi-one-dimensional ladder lattice subjected to a time-periodic electric field and a constant magnetic field. The Floquet topological phases are determined in the high-frequency approximation. In the absence of a magnetic field (φ = 0), the energy band diagram is modulated by the electric field parameter

α

/

ℏ
ω

, leading to a topological phase transition when

α

/

ℏ
ω

crosses the value of 1. When a magnetic field is present (

ϕ
=
π

), the topological phase transitions in the ladder model are influenced by both the electric field parameter

α

/

ℏ
ω

and the perpendicular hopping t
0, resulting in a diverse range of adjustable topological states. These discoveries offer promising prospects for the utilization of ladder lattice systems with externally modifiable topological properties.
Structure and magnetic properties of FeSiAl-based composites with the compound passivation agent
Authors: Tong Shanlin , Li Weijian , Qian Yuetong , Jiang Yawei , Liu Yongsheng
Published: March 2024

FeSiAl soft magnetic composites (SMCs), which are widely used in electromagnetic applications, have good electromagnetic characteristics. To reduce their core loss, the current research focuses on improving the properties of insulating coating materials. In this work, different contents of phosphoric acid and chromic acid compound passivating agents are used to prepare the insulation coating of FeSiAl powder. The results revealed that the surface film layer of the powder coating with the compound passivation agent is relatively smooth, and the film layer is too thin to be detected by XRD. With the increase of the amount of passivating agent, the permeability of powder decreases gradually and the performance of anti-DC-Bias loading improved. The core loss shows a trend that it decreases first and then increases with the increase of passivating agent dosage. If the amount of passivator is too much, the core loss will increase rapidly. When a 2% passivator is used, the magnetic permeability of the powder is 72, the DC-Bias characteristic is 51.3% with 100 Oe, and the core loss is 57 mW cm−3 at 100 kHz and 50 mT.
Characterizing SU(1,1) nonclassicality via variance
Authors: Li Huihui , Li Nan , Luo Shunlong , Zhang Yue
Published: March 2024

We quantify the nonclassicality of quantum states associated with the Lie group SU(1,1) by regarding states as observables and considering their variances in the SU(1,1) Perelomov coherent states. Combining the resolution of identity induced by the SU(1,1) Perelomov coherent states, we propose a quantifier for nonclassicality of a state based on the average uncertainty (variance) of the state (regarded as an observable) in the SU(1,1) Perelomov coherent states. This quantifier is easy to calculate and possesses several operational interpretations. We reveal its basic properties and illustrate it by several prototypical examples.
Ar plasma-engraved rGO/In2O3 hollow nanospheres with rich oxygen vacancies for enhanced triethylamine detection
Authors: Guo Lanlan , Zeng Hua , Zhao Wei , Yang Yingli , Wang Guodong , Liu Xiaolian , Wang Yan , Yang Xueli
Published: March 2024

We successfully constructed a high-performance In2O3 based triethylamine sensor using rGO combined with Ar plasma treatment (Ar-rGO/In2O3). The Ar plasma treatment and rGO doping did not cause significant changes to the crystal structure of In2O3 hollow nanospheres, but increased the content of oxygen vacancies in In2O3, while making the structure of In2O3 hollow nanospheres more porous and thin-walled. The gas sensitivity test results show that this new Ar-rGO/In2O3 based sensor has the advantages of high response (Ra/Rg = 172 to 100 ppm, 4.2 times that of pure In2O3 material), low detection limit (0.5 ppm), fast response speed (1 s), and good stability to triethylamine. It also has excellent selectivity, repeatability, and long-term stability. This work is of great significance for understanding the relationship between response and surface oxygen vacancies of sensitive materials, as well as promoting the development of new triethylamine sensors.
Thickness-related variation in the structure, morphology and optical characteristics of nickel thin films for neutral density filtering
Authors: Yadav Mini , Yadav Sandeep , Shankar Ajay , Bala Renu , Rani Mamta
Published: March 2024

In this paper we fabricate neutral density filter (NDF) for the visible region on the Borosilicate glass substrate at room tempreature. E-Beam coating unit is used for fabrication of Nickel thin film on the Borosilicate glass substrate under high vacuum. XRD measurement examined the amorphous growth of thin film at low thickness (t = 10 nm) while higher thickness supported crystalline growth. The Crystallite size (D) and lattice strain (
ϵ
) is decreasing with increasing the thickness. Microstructural investigation by atomic force microscope (AFM) revealed that surface roughness is decreasing with increasing of thickness i.e. From 0.018 to 0.008 nm. The decreasing of roughness prevents scattering loss in neutral density filter. Optical transmittance spectra are obtained using UV–visible spectrophotometer. Nickel 70 nm thickness is an optimum thickness to achieve high optical density (OD = 2.5) but neutrality is poor for higher thickness of filter. Hence the spectral variation of thin filters in our case 10 nm has least spectral variation (ΔOD = 0.11) for stable and durable NDF.
Frequency-domain image encryption based on IWT and 3D S-box
Authors: Wen Heping , Feng Zhaoyang , Bai Chixin , Lin Yiting , Zhang Xiangyu , Feng Wei
Published: March 2024

Most of the existing spatial domain image encryption techniques suffer from the difficulty of resisting cryptographic attacks. For this reason, this paper proposes a frequency-domain based digital image encryption scheme by combining Integer Wavelet Transform (IWT), three-dimensional S-box and chaotic system. First, the plaintext image is decomposed into different frequency subbands by IWT to map the digital image from spatial domain to frequency domain. Second, the plaintext hash value is selected as the dynamic key, and dynamic chaotic pseudo-random sequences with associations are generated, which are used for the encryption of each module respectively. Then, a three-dimensional S-box is designed to encrypt the information-rich low-frequency information using ‘bit-permutation three-dimensional S-box replace ciphertext interleaved diffusion’, while the high-frequency information is encrypted using a lightweight ‘XOR-row column permutation’ operation. Finally, the secure ciphertext for public channel transmission is obtained by the reconstruction method. The scheme of this paper, the frequency domain transformation is implemented through IWT, which enhances the ability to resist attacks. In addition, the diffusion encryption modules employ the introduction of ciphertext interleaved diffusion and parallel encryption mechanisms, thus the algorithm has the ability to resist plaintext attacks. Theoretical analysis and empirical results show that the algorithm has excellent numerical statistical analysis results, which corroborate that it has good confusion, diffusion and avalanche effects, and is able to resist various common cryptographic attacks. The frequency domain image encryption scheme proposed in this paper is a preferred high-security digital image privacy protection technique, so it has good application prospects.
Bouncing pNGB dark matter via a fermion dark matter
Authors: Sáez Bastián Díaz , Contreras Patricio Escalona
Published: March 2024

In addition to the Standard Model, the introduction of a singlet complex scalar field that acquires vacuum expectation value may give rise to a cosmologically stable pseudo-Nambu-Goldstone boson (pNGB), a suitable dark matter (DM) candidate. This work extends this scenario
by including a second cosmologically stable particle: a fermion singlet. The pNGB and the new fermion can be regarded as DM candidates simultaneously, both interacting with the Standard Model through Higgs portals via two non-degenerate Higgs bosons. We explore the thermal freeze-out of this scenario, with particular emphasis on the increasing yield of the pNGB before it completely decouples (recently called Bouncing DM). We test the model under collider bounds, relic abundance, and direct detection, and we explore some indirect detection observables today.
On the absence of ghosts in quadratic bigravity
Authors: Gialamas Ioannis D. , Tamvakis Kyriakos
Published: March 2024

An extension of the bimetric theory of gravity is considered that includes quadratic Ricci
curvature terms associated with each metric. The issue of the Boulware-Deser ghost is
analyzed. The Hamiltonian constraint is derived and the existence of a secondary constraint is
shown, proving that the theory is ghost-free.
Magnetism, heat capacity, magnetocaloric effect, and magneto-transport properties of heavy fermion antiferromagnet CeGaSi
Authors: Zhang 张 Li-Bo 黎博 , Dong 董 Qing-Xin 庆新 , Bai 白 Jian-Li 建利 , Liu 刘 Qiao-Yu 乔宇 , Cheng 程 Jing-Wen 靖雯 , Li 李 Cun-Dong 存东 , Liu 刘 Pin-Yu 品宇 , Sun 孙 Ying-Rui 英睿 , Huang 黄 Yu 宇 , Ren 任 Zhi-An 治安 , Chen 陈 Gen-Fu 根富
Published: March 2024

We synthesize high-quality single crystal of CeGaSi by a Ga self-flux method and investigate its physical properties through magnetic susceptibility, specific heat and electrical resistivity measurements as well as high pressure effect. Magnetic measurements reveal that an antiferromagnetic order develops below T
m ∼ 10.4 K with magnetic moments orientated in the ab plane. The enhanced electronic specific heat coefficient and the negative logarithmic slope in the resistivity of CeGaSi indicate that the title compound belongs to the family of Kondo system with heavy fermion ground states. The max magnetic entropy change

−
Δ

S
M

max

(μ
0
H⊥c, μ
0
H = 7 T) around T
m is found to reach up to 11.85 J⋅kg−1⋅K−1. Remarkably, both the antiferromagnetic transition temperature and −lnT behavior increase monotonically with pressure applied to 20 kbar (1 bar = 105 Pa), indicating that much higher pressure will be needed to reach its quantum critical point.
NSTX-U research advancing the physics of spherical tokamaks
Authors: Berkery J.W. , Adebayo-Ige P.O. , Al Khawaldeh H. , Avdeeva G. , Baek S-G. , Banerjee S. , Barada K. , Battaglia D.J. , Bell R.E. , Belli E. , Belova E.V. , Bertelli N. , Bisai N. , Bonoli P.T. , Boyer M.D. , Butt J. , Candy J. , Chang C.S. , Clauser C.F. , Corona Rivera L.D. , Curie M. , de Vries P.C. , Diab R. , Diallo A. , Dominski J. , Duarte V.N. , Emdee E.D. , Ferraro N.M. , Fitzpatrick R. , Foley E.L. , Fredrickson E. , Galante M.E. , Gan K.F. , Gerhardt S. , Goldston R. , Guttenfelder W. , Hager R. , Hanson M.O. , Jardin S.C. , Jenkins T.G. , Kaye S.M. , Khodak A. , Kinsey J. , Kleiner A. , Kolemen E. , Ku S. , Lampert M. , Leard B. , LeBlanc B.P. , Lestz J.B. , Levinton F.M. , Liu C. , Looby T. , Lunsford R. , Macwan T. , Maingi R. , McClenaghan J. , Menard J.E. , Munaretto S. , Ono M. , Pajares A. , Parisi J. , Park J-K. , Parsons M.S. , Patel B.S. , Petrov Y.V. , Podestà M. , Poli F. , Porcelli M. , Rafiq T. , Sabbagh S.A. , Sánchez Villar Á. , Schuster E. , Schwartz J. , Sharma A. , Shiraiwa S. , Sinha P. , Smith D. , Smith S. , Soukhanovskii V.A. , Staebler G. , Startsev E. , Stratton B. , Thome K.E. , Tierens W. , Tobin M. , Uzun-Kaymak I.U. , Van Compernolle B. , Wai J. , Wang W. , Wehner W. , Welander A. , Yang J. , Zamkovska V. , Zhang X. , Zhu X.L. , Zweben S.
Published: March 2024

The objectives of NSTX-U research are to reinforce the advantages of STs while addressing the challenges. To extend confinement physics of low-A, high beta plasmas to lower collisionality levels, understanding of the transport mechanisms that set confinement performance and pedestal profiles is being advanced through gyrokinetic simulations, reduced model development, and comparison to NSTX experiment, as well as improved simulation of RF heating. To develop stable non-inductive scenarios needed for steady-state operation, various performance-limiting modes of instability were studied, including MHD, tearing modes, and energetic particle instabilities. Predictive tools were developed, covering disruptions, runaway electrons, equilibrium reconstruction, and control tools. To develop power and particle handling techniques to optimize plasma exhaust in high performance scenarios, innovative lithium-based solutions are being developed to handle the very high heat flux levels that the increased heating power and compact geometry of NSTX-U will produce, and will be seen in future STs. Predictive capabilities accounting for plasma phenomena, like edge harmonic oscillations, ELMs, and blobs, are being tested and improved. In these ways, NSTX-U researchers are advancing the physics understanding of ST plasmas to maximize the benefit that will be gained from further NSTX-U experiments and to increase confidence in projections to future devices.
Numerical investigations on the effect of asymmetric inlet conditions on the performance variations of centrifugal compressor
Authors: Li Xing , Huang Ning , Zhang Jie , Zhang Yanli , Tong Ding , Zhao Yang
Published: March 2024

The high adoption frequency of inlet bent pipes result in variations between the operating performance and design value. In this paper, the performance of centrifugal compressor while adopting two inlet bent pipes, i.e., Pz and Pu, are simulated through the verified simulation method, respectively, and the flow field characteristics of inlet pipes are analyzed and quantitatively characterized. The analysis shows that centrifugal compressor’s performance with Pz and Pu both decrease to a certain degree. The flow field of symmetric swirling distribution both occurred on the outlet plane of Pz and Pu, and the circumferential distortion degree of plane (PCD) with Pz and Pu shows an increasing trend as the flow rate increases. The PCD of Pz with different rotational speed are always higher than that of Pu. The degradation degree of centrifugal compressor’s performance of Pz and Pu both increase with the increasing of PCD, and it is higher by adopting Pz, the pressure ratio degradation degree reaches 6.82% while it reaches 7.38% in efficiency degradation degree. It is found that there is a power law relation between the degradation degree of pressure ratio and PCD, and an exponential relationship between the efficiency degradation degree and PCD.
Experimental investigation of flow instability evolution in a low-speed two-stage axial compressor
Authors: He Rong , Dou Xiangyuan , Liu Yongwen , Wang Tong
Published: March 2024

A low-speed two-stage axial flow compressor with inlet guided vane was tested. Based on its performance, the near-stall condition was determined. The transient pressure signals on the casing wall were obtained along the circumferential and axial directions. Data statistics method was applied to analyze the features of the pressure signals on the working conditions. The variance of pressure increased along streamwise direction under the large flow rate condition. Meanwhile, it was influenced by the interaction between the stator and the rotor at the inlet of the second stage as well. On the near-stall condition, a modal wave like signal was found in time domain, whose frequency was about 47% of the impeller rotation frequency, accompanied with a broad-band feature in the low-frequency region. The first-stage rotor was found to stall with the analysis on the variance of the pressure. While there was no obvious unstable character observed in the second stage, the parameter at the inlet of the second stage revealed that the disturbance generated in the first stage was suppressed by the second stage. These signals’ features could be used to predict the appearance of instability in the two-stage axial flow compressor.
Study on cavitation performance improvement of high-power centrifugal pump impeller
Authors: Zheng Yang , Meng Long , Wang Xin , Xue Peng , Zhang Chiye , Tian Yajuan
Published: March 2024

High power centrifugal pump is frequently used in large project for water resources allocation. Cavitation phenomenon causes noise and vibration and affects the centrifugal pump unit stability. The impeller model was used an initial impeller to be developed, and the impeller geometry, the blade profile, blade inlet edge were optimized by design method based on numerical simulation technique to improve cavitation performances. The 3D model with the initial and optimized impeller were simulated to obtain cavitation characteristic. The results of optimization impeller are compared and verified by model test. The numerical simulation results show that the pressure distribution is distributed on the blade surface is uniform and the location of lowest pressure is reasonable. The test results show that the optimized design significantly increases the ratio of plant cavitation coefficient σp to incipient cavitation coefficient σi and critical cavitation coefficient σ1 of the impeller under normal operation conditions, the safety margin of cavitation is increased. It was confirmed from numerical simulation and model test results that the impeller blade optimization is a reasonable and effective method for cavitation performance improvement. The study results provides design reference for the cavitation performance improvement and safe operation of high power centrifugal pump.
Numerical investigation of vortex structure and unsteady evolution in multi-stage double-suction centrifugal pump
Authors: Zhao Jiantao , Pei Ji , Yuan Jianping , Wang Wenjie
Published: March 2024

Multi-stage double-suction centrifugal pump is constructed to handle situations with large flow rates and high head. However, due to the complex internal flow structure, the pump can experience hydraulic excitation caused by the presence of numerous vortical structures. Such excitation can lead to unstable pump operation and increased energy losses. In this study, we aim to analyze the multi-stage double-suction centrifugal pump by combining numerical simulation using detached eddy simulation (DES) and experiments to accurately capture the vortical structure and elucidate the mechanism of the rotor-stator interaction (RSI) formation. The results indicate that the omega vortex identification method can accurately capture the vortex structure in the pump, irrespective of the threshold value and without the influence of wall shear layers. Additionally, based on this identification method, we have analyzed the unsteady evolution characteristics of the vortex structure in the pump. Specifically, we have focused on the shedding of wake vortices and their collision with the tongue. The findings suggest that the rotor-stator interaction primarily arises from the periodic shedding of wake vortices near the impeller outlet. In summary, this study provides valuable insights into the flow dynamics of multi-stage turbomachines.
Comparative study on stator corner separation vortex characteristics in axial-flow pump and tubular pump: To understand the effects of guide-vane cone diffusion on horn-like vortices
Authors: Wang B H , Wang F J , Wang C Y , Wang H , Yao Z F , Xiao R F
Published: March 2024

The guide-vane cone diffusion is a typical structural difference between an axial-flow pump and a tubular pump, which is shown as low diffusivity and high diffusivity respectively, but it is still unclear how this structural difference affects the vortex characteristics in stator corner separation flows. In this paper, a comparative study of stator corner separation flows in an axial-flow pump and a tubular pump was conducted, and the effects of guide-vane cone diffusion on vortical structures were clarified. Firstly, for the apparent vortical features, compared with the guide-vane of axial-flow pump with low diffusivity, the horn-like vortex in the guide-vane of tubular pump with high diffusivity has the features of smaller scale, weaker swirling strength, shorter evolution cycle and lower pressure fluctuations. Secondly, for the vortex dynamics mechanism, the guide-vane cone diffusion of tubular pump can cause additional pressure energy recovery, which leads to higher adverse pressure gradients, so it is easier to induce additional shroud backflow near the suction surface. In this coupled flow field of main flow, namely hub corner separation flow and shroud backflow, the streamwise periodic oscillation of the pressure function gradient
ωS

·▽(▽p/ρ) is found, and it induces the unique vortex-street-like distributions of the deformational vorticity
ωS

and the rigid vorticity
ωR

. This physical effect causes a mutual competition between the horn-like vortex near the hub corner and the opposite backflow vortex near the shroud side. It is this competition effect originating from the guide-vane cone diffusion that greatly suppresses the development of the horn-like vortex in a tubular pump.
A numerical study on the unsteady flow in the guide vane of a water-jet propulsion mixed-flow pump
Authors: Sun C , Wang L Y , Dai Y X
Published: March 2024

Mixing and dissipation of the complex vortices in the water-jet propulsion mixed-flow pump is an important source of flow loss. Furthermore, some vortices have strong unstable feature, which adversely affect vibration and noise. The unsteady flow in the guide vane of a mixed-flow pump is studied by numerical methods. Through the spectral results of hydrodynamic excitation and the instantaneous flow field of the mix-flow pump, the basic unsteady features of the unsteady flow are obtained. Peak frequency of approximately 1.68 rotation frequency is found as the dominant frequency of the excitation in the guide vane. Dynamic mode decomposition (DMD) is then used to extract the key flow modes in the guide vane. The results illustrate the dominant flow structure in the guide vane, including upstream sweeping structures, the separate vortex structures, and large-scale passage vortex structure. The upstream sweeping wake caused the fluctuation in the boundary layer and induced flow separation. Following the separation, passage vortices are induced which has the dominant frequency 1.68 rotation frequency.
Study on the experiment and numerical simulation of cavitation flow mechanisms at different flow rates in water-jet propulsion pumps
Authors: Kaixuan Zheng , Yun Long , Qingjiang Xiang , Changjian Xu , Jianping Chen , Dezhong Wang
Published: March 2024

Cavitation is an important factor causing vibration and noise of water-jet pump. High-performance ships require water-jet pumps with high efficiency and low noise at high speeds. At present, the cavitation flow phenomenon and interference mechanism of the water-jet pump under different flow rates are not clear enough. This paper takes the mixed-flow water jet propulsion pump as the research object. The flow structure of the cavitation vortex of the water-jet pump under different flow rates was obtained by high-speed photography (HSP). Through comparison of numerical simulation and test results, the cavitation performance curves and cavitation flow structures of the water jet pump under five different flow rates were obtained. The influence of cavitation vortex structure on the performance of water-jet pump under different flow rates was obtained. The correlation between cavitation performance and cavitation vortex structure under different flow rates was established. This research work will help to understand the impact of the cavitation vortex structure of the water-jet pump under different flow rates and capture the evolution law of the cavitation vortex structure of the water-jet pump under different flow rates. And provide reference for improving the cavitation performance of water-jet pumps.
Hydraulic structure optimization of centrifugal pump based on orthogonal test
Authors: Li Wei , Pu Wei , Ji Leilei , Zhang Xing , He Xinrui
Published: March 2024

To reduce global carbon emissions and reduce the energy consumption of pumps, it is necessary to continuously improve the performance efficiency of pumps. In this paper, the blade wrapping angle, inlet mounting angle and outlet mounting angle are selected as the design variables, and the hydraulic structure of the pump is orthogonally optimized. Through experiments and simulations, the internal flow bonding and external energy characteristics of the centrifugal pump under different orthogonal test combinations were compared, and finally the impeller wrapping angle was 130 degrees, the outlet installation angle was 20 degrees, and the inlet installation angle was 40 degrees. It is found that compared with the original design scheme, the efficiency of the optimized scheme under the design flow rate is increased by 2.775%, and the hydraulic loss in the impeller is reduced by 1.18%. The main and secondary orders of influence of parameter factors on lift and efficiency are impeller wrapping angle, impeller outlet mounting angle, and impeller inlet mounting angle. The internal flow of the optimized impeller is significantly improved, and the flow loss is reduced. The research results provide a design basis for further improving the hydraulic performance of centrifugal pumps.
Effect of different blade number and thickness on performance of micro-turbine
Authors: Chen Jianchong , Zhou Qiwei , Zhu Chenbing , Yang Xuelong
Published: March 2024

At present, due to its special operating environment and operating conditions, there are few relevant theoretical studies and numerical simulation studies on micro-turbines. Therefore, the use of simulation technology to explore the internal flow law of micro-turbines is of great significance for the design optimization guidance of micro-turbines. The research method of this paper is through CFD software, using SST k-ω algorithm model. This paper studies the efficiency and output of micro-turbine with 8 blade numbers of 13,15,17,19,21,23,25 and 28, as well as the efficiency and output of micro-turbine with thickness of 12mm, 12.5mm, 13mm, 13.5mm and 14mm. The internal flow field characteristics, the pressure pulsation characteristics of impeller region and tip clearance region and the power loss distribution diagram are studied and analyzed. The results show that the maximum efficiency is 22.42% when the number of blades is 15, and 23.92% when the thickness is 10.5mm.
Study on the energy conversion characteristics in the impeller of ultra-low specific speed pump as turbine
Authors: He Jiawei , Si Qiaorui , Wang Peng , Wan Bochen , Wang Chenguang
Published: March 2024

With the increasing attention to micro-hydropower generation, pump as turbine (PAT) has broad prospects in the field of micro-hydropower generation due to low price and easy maintenance. The ultra-low specific speed has the advantage of large output power under a small flow rate and is widely used in remote areas to realize micro-hydropower generation. In this paper, With the goal of maximizing the output power at a small flow rate, an ultra-low specific speed pump as turbine (USSPAT) of 16.52 is designed. The energy characteristics inside the impeller are studied by means of experimental and simulation. It is found that the main output area in the impeller located in the inlet area of impeller and near Span0.6 area. In addition, it is found that the high-speed jet caused by RSI inside the impeller and the secondary circulation at the outlet area are the main flow structures that hinder the work of the impeller.