Search Results (289)

This paper presents a numerical investigation of the effect of rotational speed on the development of leakage flow in a low-speed axial fan equipped with a rotating shroud. Rotor deformation induced by centrifugal forces and aerodynamic loading is taken into account through a one-way coupling between steady CFD simulations and static FEM analyses. Aerodynamic and structural results obtained at four rotational speeds are validated against available experimental data collected by the same research group, and the different leakage flow patterns associated with rotor deformation are correctly reproduced. Subsequently, the deformed geometries corresponding to two rotational speeds and operating at the same non-dimensional flow coefficient are used to perform URANS simulations. The numerical results provide insight into the leakage flow behavior within the gap between the rotating shroud and the stationary casing, a region that cannot be experimentally investigated due to optical access limitations. It is shown that the leakage flow rate through the gap shows limited sensitivity to rotor deformation, as it scales with rotational speed, and it is fed by two main contributions: a flow directly extracted from the rotor outlet and a recirculating flow developing along the mounting panel. Conversely, the non-dimensional angular momentum flow rate is larger at the lower rotational speed, corresponding to the case in which the leakage flow is rapidly re-ingested by the rotor. This indicates that the centrifugal effects associated with the leakage flow swirl are not responsible for the observed change in leakage flow pattern. Finally, significant periodic and non-periodic components are identified within the leakage flow. These components are expected to contribute to the formation of the large-scale structures impinging on the rotor blades and thus generating significant noise. Full article

We present a computational framework for constructing effective, intrinsically screened heavy-particle potentials in dense plasmas from first-principles pseudopotentials. Starting from available projector-augmented-wave (PAW) data in the Unified Pseudopotential Format (UPF), the angular-momentum-dependent channel potentials (s, p, d, f) are reconstructed and mixed according to Boltzmann occupation probabilities at the plasma temperature. The intrinsic screening by thermally populated valence electrons is included through a self-consistent Hartree potential computed for each charge state, yielding element-specific temperature-dependent effective scattering potentials for neutral atoms and ions. The Saha ionisation equilibrium, corrected for ionisation-potential depression via the Stewart–Pyatt model, determines the species composition. A number-density-weighted mixture average then produces a single effective heavy-particle potential for multi-component plasmas. The procedure is implemented in D_plas_V, a C++17 code with zero external dependencies, and all methods are validated against analytical test cases. Full article

In the contemporary landscape of spacecraft engineering, reaction wheels, control moment gyros, and momentum wheels are standard tools for precise attitude control, functioning by exchanging angular momentum through the rotation of a solid mass around its major axis. The VEKTOR-FDA (Vector Fluid Dynamic Actuator) proposed in this paper offers an alternative by utilizing the principle of rotating liquid to generate angular momentum instead of relying on a solid body. Electromagnetic pumps drive and circulate the fluid, connecting to a hollow sphere via inlet and outlet channels. The fluid within the sphere is drawn into the pump through the outlet channel and reintroduced through the inlet channel. This circulation, combined with the spherical shape, generates a rotational fluid flow inside the hollow sphere, creating a rotating fluid volume and an angular momentum vector aligned with the rotation axis. By utilizing at least three pumps arranged orthogonally, simultaneous operation allows flow mixing, which can be precisely controlled by adjusting the individual flow velocities of each pump. This setup enables the rotation axis of the fluid flow to be directed in any desired orientation, allowing the rotating fluid volume and its angular momentum vector to be spatially aligned as needed. As a result, a single VEKTOR-FDA can manage attitude control across all three axes of the spacecraft, effectively functioning as a multiple-degree-of-freedom (MDOF) actuator. The electromagnetic pump drive in the VEKTOR-FDA actuator provides self-lubrication and eliminates the need for moving mechanical parts, minimizing potential damage from mechanical loads like shocks during launch. Its simple design also enables the use of commercial off-the-shelf components, ensuring cost-effective implementation. This paper provides a comprehensive overview of the motivation and concept behind the VEKTOR-FDA actuator. Additionally, this paper presents analyses and experimental results that investigate how rotating fluid flow can be generated within the sphere and examines its behavior. The study evaluates various factors influencing fluid flow inside the sphere, including configurations with variable cross-sectional shapes of the inlet and outlet channels. Furthermore, it determines the optimal positioning and arrangement of these channels to achieve efficient fluid flow volume, which is essential for maximizing angular momentum output. Full article

We study the response of a system consisting of a neutral heat bath (liquid or gaseous) that contains a charged Brownian particle (BP) to an external static magnetic field. The bath particles do not interact directly with the magnetic field, but it affects them due to their interaction with the BP. We obtain the equations of motion for the particles of the system within the framework of the generalized Zwanzig–Caldeira–Leggett model. Based on this theory, the motion of the BP is described by the original or generalized Langevin stochastic equations with memory effects. For memoryless overdamped dynamics, we find that individual bath particles acquire a nonzero mean angular momentum, while the collective angular momentum of the bath grows linearly with time; at the same time, their mean kinetic energy obeys equipartition. Closed-form analytical solutions are obtained for the individual bath particles and for the entire bath if the dynamics of the BP is overdamped. The problem offers several possibilities for further generalizations. Full article

This paper investigates the constrained particle dynamics on rotational surfaces within the 4-dimensional pseudo-Euclidean space $E_2^4$, characterized by its second-order metric signature of index 2. A comprehensive Lagrangian and Hamiltonian formulation is developed to construct the specific energy and specific angular momentum as conserved Noetherian charges along timelike geodesics. By integrating Clairaut’s theorem into the geodesic flow equations, explicit analytical expressions for these fundamental physical invariants are obtained. This work explores the structural relationship between the surface’s continuous rotational symmetries and the mechanical stability of the geodesic flow. A mathematical resolution for the signature transitions manifested via the appearance of the imaginary unit i on elliptic surfaces is provided through analytic continuation and distinct coordinate charts. Furthermore, by reducing the second-order geodesic flow to a one-dimensional energy balance equation, the exact effective potentials ($V_{eff}$) are derived, and the local orbital stability zones are analytically verified via second-order radial derivatives (${\partial }_s^2{V}_{eff}>0$). These embedded geometric configurations are shown to share qualitative features with the equatorial slices of rotating relativistic spacetimes. Consequently, they can serve as potential geometric toy-models for studying the dynamics of photon spheres, ergosphere oscillations, and innermost stable circular orbits in extreme gravitational fields. Full article

Universal Time (UT1) is a core component of the Earth orientation parameters (EOP). High-precision UT1 predictions are essential for satellite navigation, deep-space exploration, and the maintenance of national standard time. Although effective angular momentum (EAM) information can improve UT1 predictions, the impacts of different angular momentum combinations on prediction performance have not yet been systematically investigated. To improve the prediction accuracy of the National Time Service Center (NTSC) UT1 products, we constructed four prediction schemes: Case 1 uses only atmospheric angular momentum (AAM) data; Case 2 uses AAM + oceanic angular momentum (OAM) data; Case 3 uses AAM + OAM + hydrological angular momentum (HAM) data; and Case 4 uses the full EAM datasets combining AAM, OAM, HAM, and sea-level angular momentum (SLAM) data. The input UT1 series is from the NTSC EOP products, and the 10-day angular momentum forecasts are provided by the German Research Centre for Geosciences (GFZ). The rolling forecast evaluation was conducted from June 2024 to September 2025. The results show that Case 2 performs best for short-term UT1 predictions over 1–12 days, improving the mean prediction accuracy by 10.7%, 10.0%, and 52.0% relative to the predictions using Case 4, IERS finals.daily, and the original NTSC predictions, respectively. For medium- and long-term UT1 predictions over 13–90 days, Case 1 performs best, with corresponding mean improvements of 9.8%, 50.7%, and 61.3%, respectively. These results indicate that incorporating more angular momentum components does not necessarily lead to better UT1 predictions, i.e., Case 2 is preferable for short-term UT1 predictions, whereas Case 1 is more suitable for medium- and long-term UT1 predictions. These findings provide empirical evidence and practical guidance for optimizing UT1 prediction models. Full article

We explore the generation of photon blockade effect in a Laguerre–Gaussian optorotational system where a Gaussian beam exchanges orbital angular momentum with a rotating spiral phase mirror. In addition to the typical optorotational coupling, we consider the existence of cross-Kerr nonlinearity between the cavity mode and the rotating mirror. We investigate the statistical characteristics of photons by numerically and analytically calculating the second-order correlation function. In particular, we find that the antibunching effect of photons is dominated by the cooperative operation between the optorotational coupling and the cross-Kerr coupling instead of any individual part. The optimal single photon blockade can be achieved in a moderate coupling regime and enhanced due to the presence of cross-Kerr nonlinearity. The dependence of photon blockade effect on the different system parameters is discussed in detail. Our work provides an alternative way to manipulate the photon quantum behaviors in Laguerre–Gaussian optorotational systems, which may find potential applications in quantum information processing and optical communication utilizing the optical orbital angular momentum. Full article

We demonstrate optomechanical spatial projection of azimuthally structured optical beams. The system is based on an ultra-low loss circular membrane integrated into an interferometric setup, which exploits the spatial analogies between the mechanical modes and the structured optical fields. A slight geometric asymmetry, originating from a tiny ellipticity introduced during microfabrication, lifts the degeneracy of the membrane modes, producing a spectrally resolved mechanical doublet composed of two orthogonal eigenmodes. Crucially, this doublet provides a phase-sensitive mechanical reference where the spatial orientation of the optical mode is mapped to a distinct resonance frequency, effectively acting as an optical-spatial-to-mechanical spectral projector. Petal-shaped optical intensity distributions, formed by coherent superpositions of orbital-angular-momentum eigenstates with opposite topological charges and generated via a q-plate, are used to probe the membrane in a readout-only regime, where the motion is thermally excited. By rotating the azimuthal orientation of the optical pattern, we observe a controlled redistribution of spectral weight between the two members of the mechanical doublet. The split doublet, therefore, acts as a two-channel mechanical spatial analyzer for azimuthal quadratures. This mechanism yields maximum sensitivity for a topological charge of $\mathsf{\ell }=1$, as its two-lobed intensity distribution matches well the fundamental azimuthal mechanical modes. Overall, the system provides a wavelength-independent platform for the projection and processing of structured optical fields. Since the analyzer relies on spatial mode matching rather than optical spectral properties, the system can interface with a wide range of optical sources and channels, making it a potentially relevant platform for future structured-light communication architectures. Full article

Space inertial actuators, represented by reaction wheels, momentum wheels, flywheels, and control moment gyroscopes, are indispensable angular-momentum exchange devices in spacecraft attitude determination and control systems. Owing to their non-consumable operation, high reliability, and precise torque-generation capability, these actuators are widely employed for attitude stabilization, rapid attitude maneuvering, payload disturbance mitigation, and precision pointing in modern satellites and space vehicles. With the rapid growth of high-resolution Earth observation missions, deep-space exploration programs, and large-scale commercial satellite constellations, the performance requirements imposed on inertial actuators are becoming increasingly stringent. This paper systematically reviews the current state of the art in space inertial actuator technologies by integrating peer-reviewed research with publicly available industrial product information, and summarizes recent research progress, representative products, and development strategies in the United States, Europe, Russia, and China. By comparing the technical characteristics and evolutionary pathways of mainstream reaction wheel, momentum wheel, flywheel, and control moment gyroscope systems, the study identifies the principal technological drivers shaping future development. The analysis reveals five dominant trends: extended operational lifetime, higher control accuracy, greater torque and angular-momentum density, reduced micro-vibration disturbance, and scalable, cost-effective manufacturing. These findings provide a systematic technical reference for future research, engineering design, and industrial development of advanced space inertial actuator systems in China and internationally, particularly for next-generation spacecraft requiring long service life, high pointing accuracy, low disturbance, and scalable production. Full article

The electronic spectra of trivalent lanthanide ions constitute one of the most extensively characterised manifestations of partially filled 4f shells. Conventional rare-earth spectroscopy provides a detailed microscopic description based on assigned multiplets, angular-momentum structure, crystal-field effects and transition probabilities. Here, we examine a complementary question: whether information associated with the underlying 4f electronic architecture remains detectable after the spectroscopic labels normally used to identify it are deliberately removed. Using the multiplet-centre energies of Ln³⁺ ions in LaF₃, each ion was represented as an energy-only spectral manifold, $M_n=\left\{E_i\right\}$, obtained after removing term identity, angular-momentum labels and transition assignments. The resulting manifolds were analysed through a controlled information-reduction sequence involving spectral occupancy and four complementary descriptors: spectral entropy $S$, compactness $C$, mean manifold energy ${\mu }_E$ and spectral dispersion ${\sigma }_E$. The results show that the reduced manifolds do not collapse into featureless collections of energies. Instead, they retain structured organisation across the lanthanide series, with distinctive behaviour associated with the shell-edge configurations Ce³⁺ ($4f^1$) and Yb³⁺ ($4f^{13}$), and with the half-filled-shell configuration Gd³⁺ ($4f^7$). A blind reconstruction test provides the strongest internal validation: when Gd³⁺ is excluded from the reference evolution and subsequently reintroduced, it emerges as the dominant positive deviation of the mean manifold-energy coordinate. This demonstrates that the $4f^7$ signature is not encoded only in explicit term labels or selected multiplets but leaves a measurable fingerprint in the collective energy distribution. The comparison of normalised descriptor responses further indicates that electronic shell information is distributed across state occupation, compactness, energetic displacement and spectral spreading. These results suggest that lanthanide spectra can be analysed not only as collections of assigned transitions, but also as collective spectral manifolds whose global organisation preserves physically meaningful information about shell filling. This approach does not replace conventional rare-earth spectroscopy; rather, it provides a complementary framework for testing which aspects of electronic structure remain accessible after microscopic spectroscopic identity has been removed. Full article

The effective-one-body (EOB) formalism accurately describes the conservative dynamics of general binary orbits, but current implementations of radiation reaction remain largely limited to quasi-circular inspirals. Extending EOB to eccentric orbits currently requires the corresponding post-Newtonian (PN) energy fluxes in EOB coordinates, which are only known to 1PN order. In this paper, we compute the instantaneous gravitational-wave energy flux in EOB coordinates to 2PN accuracy using a systematic coordinate transformation between the Arnowitt–Deser–Misner (ADM) and EOB phase-space variables. We derive the 2PN-accurate transformation laws for the relative coordinates and velocities between the two coordinate systems and re-express the 2PN instantaneous energy flux entirely in EOB variables. Working within the EOB test-particle framework (with finite mass ratio $\nu$) for an equatorial elliptic orbit, we adopt a Keplerian reparameterization in terms of the semilatus rectum p, eccentricity e, and two phase variables $(\xi ,\varphi )$ associated with the radial and azimuthal motion, which makes the calculations more transparent and facilitates the subsequent computation of gravitational waveforms. Using the conservative orbital angular frequency, we compute the orbit-averaged energy flux. In addition to the energy flux, we also compute the corresponding 2PN angular momentum flux in EOB coordinates using the same transformation method. Our results, expressed in gauge-invariant variables $x={\left(M\omega \right)}^{2/3}$ and eccentricity $e_t$, agree with known PN results and show improved accuracy compared to the 1PN EOB fluxes of Hinderer and Babak. Full article

We present a novel method for deriving radially resolved dynamical chronometers from galaxy rotation curves, allowing galaxy assembly histories to be reconstructed directly from kinematic data. In the Nexus Paradigm, the baryonic Tully–Fisher relation is used to estimate the dynamical mass profile. We compare this profile with independently derived intrinsic baryonic mass distributions obtained from stellar Sérsic fits and gas surface-density measurement yields. This yields a radial ratio that maps to formation redshift with radial resolution. Inverting this ratio within a standard cosmological framework produces a radial lookback-time profile, representing the time since each radial shell last experienced dynamical reconfiguration. Applying the method to a pilot sample of seven SPARC galaxies, including both high- and low-surface-brightness systems as well as the Milky Way, reveals diverse age structures: stratified profiles associated with inside-out growth and flatter profiles consistent with coherent disk assembly. The method requires no dark-matter halo fitting and offers a kinematic chronometer that complements stellar population and chemical evolution approaches. The NP rotation-curve parameters were determined by minimizing the chi-squared statistic between the observed and predicted velocities using a two-stage optimization consisting of a global differential-evolution search followed by nonlinear least-squares refinement. Observational uncertainties were taken from the published rotation-curve data, supplemented by a 5 km s⁻¹ systematic error floor added in quadrature to account for non-circular motions and other unresolved systematics. We also show that the governing dynamical equation admits a gravitoelectromagnetic interpretation, in which a velocity-dependent term generates disk-wide torques that regulate angular momentum transport. This leads to a unified stability framework in which galaxy morphology emerges from a single parameter regime: balanced conditions favor a coherent spiral structure, whereas dynamically hot regimes naturally produce diffuse and ultra-faint systems. The cosmological scaling of the effective gravitomagnetic field further suggests that the spiral structure is partly regulated by cosmic time. Although the inferred ages depend on the accuracy of the baryonic mass reconstruction and on the local validity of the evolving baryonic Tully–Fisher relation, our results show that rotation curves encode time-resolved dynamical information. This establishes the radial dynamical chronometer as a new observable for studying galaxy evolution and testing gravitational frameworks. Full article

This study investigates a polymorphic underwater vehicle designed to combine long-range cruising with stable underwater operation, reducing dependence on surface support vessels. By introducing a foldable polymorphic structure, the vehicle can switch configurations, including serial and parallel. However, underwater environments often contain obstacles, and the vehicle may collide with them during the folding process. To prevent collisions between the vehicle and surrounding obstacles during the folding process, this paper investigates the motion envelope of the vehicle and examines how motion parameters and mass distribution influence the motion envelope. In this work, the polymorphic underwater vehicle is modeled as a multibody system operating under a neutrally buoyant condition. Based on space robot modeling methodologies and the linear and angular momentum theorems, the equations of motion of the polymorphic underwater vehicle are derived and verified using the Adams software 2020. In summary, the present study establishes a clear relationship between motion parameters, mass distribution, hydrodynamic effects, and the resulting motion envelope of a polymorphic underwater vehicle. The results show that the attitude of the vehicle during the folding process is uniquely determined by the joint angles, and a larger relative speed between the outer and inner folding motions produces a more compact attitude during the folding process. Mass distribution further influences the motion envelope of the vehicle: concentrating mass toward the center of the vehicle shifts the overall motion envelope upward, whereas concentrating mass toward both ends of the vehicle shifts it downward. In addition, hydrodynamic forces introduce an upward velocity component of the vehicle in the vertical direction during the folding process, which leads to an upward shift in the overall center of mass of the vehicle. Full article

Permalloy (Py) is a crucial component in spin nano-oscillators due to its excellent soft magnetic properties. Due to orbital angular momentum quenching, Py exhibits very low magnetic damping. It reduces intrinsic energy dissipation during precession, which is beneficial for lowering operational power consumption and enhancing the thermal stability of certain memory devices. But lower magnetic damping limits its application in fast-switching spintronic devices. Thus, in this work, the rare earth element Gd is introduced into Py to further enhance the spintronic performance of Py_100−xGd_x alloys. Through spin-torque ferromagnetic resonance measurements (ST-FMRs), the maximum spin Hall angle of the system was calculated to be 0.149 when x = 20, significantly exceeding that of 0.042 in the pure Py sample. Additionally, Gd doping significantly enhances the ability to modulate the magnitude of the linewidth. Also, as the Gd content in the alloy increased, the magnetic damping coefficient of the device gradually rose, reaching a peak in the sample with 17% Gd content. The maximum magnetic damping coefficient of the Py-Gd alloy was 0.051, representing an approximate 2.4-fold increase compared to that of pure Py. The findings of this study confirm that the use of rare-earth elements is highly effective in tuning the performance of spintronic devices and provide support for the development of highly efficient SOT devices. It is noted that the regulation of magnetic damping by Py-Gd holds significant implications for enhancing the magnetization switching speed of SOT devices and reducing the drive current density for microwave emission in spin nano-oscillators. Full article