Search Results (698)

Under accelerating global warming, the northern slope of the Middle Kunlun Mountains in Xinjiang, China, has seen a marked rise in extreme rainfall, posing increasing challenges for flood risk management and water resources. To improve our predictive capabilities and deepen our understanding of the driving mechanisms, we combine the European Centre for Medium-Range Weather Forecasts Reanalysis-5 (ERA5) reanalysis, regional observations, and high-resolution Weather Research and Forecasting model (WRF) simulations to dissect the 14–17 June 2021, extreme rainfall event. A deep Siberia–Central Asia trough and nascent Central Asian vortex established a coupled upper- and low-level jet configuration that amplified large-scale ascent. Embedded shortwaves funnelled abundant moisture into the orographic basin, where strong low-level moisture convergence and vigorous warm-sector updrafts triggered and sustained deep convection. WRF reasonably replicated observed wind shear and radar echoes, revealing the descent of a mid-level jet into an ultra-low-level jet that provided a mesoscale engine for storm intensification. Momentum–budget diagnostics underscore the role of meridional momentum transport along sloping terrain in reinforcing low-level convergence and shear. Together, these synoptic-to-mesoscale interactions and moisture dynamics led to this landmark extreme-precipitation event. Full article

We report a computational investigation on the reachability of the molecular similarity index (MSI) approach for predicting the relative drug strength of methylcarbamate derivatives. Traditional MSI values have been obtained by calculating the overlap integral of total electron momentum densities between one molecule and another. Furthermore, we have proposed and tested orbital-specific MSI (OS-MSI) values, obtained by doing the same but with electron momentum densities of a selected molecular orbital (MO) such as the highest occupied MO (HOMO) and the lowest unoccupied MO (LUMO). In the calculations, a Boltzmann-weighted electron momentum density estimated by a theoretical probability distribution of rotamers was used, while the solvation effect was considered using the polarizable continuum model. It is shown that the traditional MSI values as well as the OS-MSI values for the HOMO do not have any correlation with experimental relative toxicity of the methylcarbamate derivatives. In contrast, it has been observed and found that the OS-MSI values for the LUMO exhibit a noticeable correlation with the experimental data. The reason behind this observation is discussed in relation to the drug reaction mechanism of the methylcarbamate derivatives. Full article

We analyze the high-order above-threshold ionization (HATI) process of a small polyatomic molecule with C₃ symmetry, which is induced by a bicircular strong laser field. This field consists of two coplanar, counter-rotating, circularly polarized components with frequencies $r\omega$ and $s\omega$ where r and s are integers. In our study, we use an improved molecular strong-field approximation to obtain electron energy-angle-resolved and momentum spectra of the BF₃ molecule. We analyze the contributions of individual atoms as well as the impact of molecular symmetries on these spectra. We find that these spectra are significantly affected by the characteristics of the molecule and the laser-field parameters. Furthermore, we observe pronounced interference minima in the HATI spectra. We demonstrate that these minima result from the destructive interference of rescattered wave packets from different atomic centers, and we determine the conditions under which they occur, including two-, three-, and four-center interference. Full article

The quantum states of a spin $\frac{1}{2}$ (a qubit) are parametrized by the space ${\mathbf{CP}}^1\sim S^2$, the Bloch sphere. A spin j for a generic j (a $2j+1$-state system) is represented instead by a point in a larger space, ${\mathbf{CP}}^{2j}$. Here we study the state of a single angular momentum/spin in the limit $j\to \infty$. A special class of states, $|j,\mathbf{n}⟩\in {\mathbf{CP}}^{2j}$, with spin oriented towards definite spatial directions, $\mathbf{n}\in S^2$, i.e., $(\widehat{\mathbf{J}}·\mathbf{n})|j,\mathbf{n}⟩=j|j,\mathbf{n}⟩$, are found to behave as classical angular momenta, $j\mathbf{n}$, in this limit. Vice versa, general spin states in ${\mathbf{CP}}^{2j}$ do not become classical, even at a large j. We study these questions by analyzing the Stern–Gerlach processes, the angular momentum composition rule, and the rotation matrix. Our observations help to better clarify how classical mechanics emerges from quantum mechanics in this context (e.g., with the unique trajectories of a particle carrying a large spin in an inhomogeneous magnetic field) and to make the widespread idea that large spins somehow become classical more precise. Full article

We combine corrected Gaia DR3 astrometry with non-conservative MESA modelling to retrace the evolution of the FS-CMa binary MWC 728. The revised parallax sets the distance at $d=1.2\pm 0.1$ kpc, leading—after Monte-Carlo error propagation—to luminosities of $log{(L/L_{\odot })}_{\mathrm{acc}}=2.6\pm 0.1$ and $log{(L/L_{\odot })}_{\mathrm{don}}=1.5\pm 0.1$, corresponding to the accretor and donor, respectively. A fiducial binary track that starts with $M_{\mathrm{don}}=3.6\pm 0.1M_{\odot }$, $M_{\mathrm{acc}}=1.8\pm 0.1M_{\odot }$, and $P_0=21.0\pm 0.2$ d reproduces the observations provided the Roche-lobe overflow, which is moderately non-conservative: only $39\%$ of the transferred mass is retained by the accretor, while the remainder leaves the system via (i) a fast isotropic wind from the donor ($\alpha =0.01$), (ii) isotropic re-emission near the accretor ($\beta =0.45$), and (iii) outflow into a circumbinary torus ($\delta =0.15$, lever arm $\gamma =1.3$). These channels remove sufficient angular momentum to expand the orbit to the observed $P_{\mathrm{obs}}=27.5\pm 0.1$ d while sustaining the dusty circumbinary outflow. At $t\simeq 223$ Myr, the model matches every current observable: $M_{\mathrm{don}}=1.30\pm 0.05M_{\odot }$, $M_{\mathrm{acc}}=2.67\pm 0.05M_{\odot }$, mass ratio $q=2.0\pm 0.1$, and an ongoing transfer rate of $\dot{M}\simeq (1\pm 0.3)\times {10}^{-6}{M}_{\odot }{\mathrm{yr}}^{-1}$. MWC 728 thus serves as a benchmark intermediate-mass binary for testing how non-conservative outflows regulate angular-momentum loss and orbital growth. Full article

Be stars are characterized by the presence of a circumstellar Keplerian disk formed from material ejected from the rapidly rotating stellar surface. This article presents recent observational and theoretical progress on two central aspects of this phenomenon: the mechanisms driving mass loss, and the fate of the ejected material. Using simultaneous TESS photometry and ground-based spectroscopy, we examine the short-term variability associated with discrete mass ejection events, or “flickers”, and review strong evidence linking them to pulsational activity near the stellar surface. Complementary 3D hydrodynamic simulations reproduce key observational signatures and establish that disk formation requires compact and asymmetric ejection sites with sufficient angular momentum to overcome re-accretion. In systems with binary companions, new high-resolution simulations resolve the outer disk for the first time and identify five dynamically distinct regions, including a circumsecondary disk and a circumbinary spiral outflow. Together, these results provide a coherent framework that traces the full life cycle of disk material from pulsation-driven ejection near the stellar surface to its final destination, whether re-accreted by the companion or lost from the system entirely. Full article

Water vapor plays a crucial role in maintaining global energy balance and water cycle, and it is closely linked to various meteorological disasters. Precipitable water vapor (PWV), as an indicator of variations in atmospheric water vapor content, has become a key parameter for meteorological and climate monitoring. However, due to limitations in observation costs and technology, traditional atmospheric monitoring techniques often struggle to accurately capture the distribution and variations in space–time water vapor. With the continuous advancement of Global Navigation Satellite System (GNSS) technology, ground-based GNSS monitoring technology has shown rapid development momentum in the field of meteorology and is considered an emerging monitoring tool with great potential. Hence, based on the GNSS observation data from July 2023, this study retrieves PWV using the Global Pressure and Temperature 3 (GPT3) model and evaluates its application performance in the “7·31” extremely torrential rain event in Beijing in 2023. Research has found the following: (1) Tropospheric parameters, including the PWV, zenith tropospheric delay (ZTD), and zenith wet delay (ZWD), exhibit high consistency and are significantly affected by weather conditions, particularly exhibiting an increasing-then-decreasing trend during rainfall events. (2) Through comparisons with the PWV values through the integration based on fifth-generation European Centre for Medium-Range Weather Forecasts (ERA-5) reanalysis data, it was found that results obtained using the GPT3 model exhibit high accuracy, with GNSS PWV achieving a standard deviation (STD) of 0.795 mm and a root mean square error (RMSE) of 3.886 mm. (3) During the rainfall period, GNSS PWV remains at a high level (>50 mm), and a strong correlation exists between GNSS PWV and peak hourly precipitation. Furthermore, PWV demonstrates the highest relative contribution in predicting extreme precipitation, highlighting its potential value for monitoring and predicting rainfall events. Full article

The research reviews and contrasts two studies based on the gas-phase reaction OH + D₂(v, j). In these studies, Quasi-Classical Trajectory (QCT) calculations and the Gaussian Binning (GB) technique were used on the Wu–Schatz–Lendvay–Fang–Harding (WSLFH) potential energy surface. Large sample sizes allow for precise energy state distribution analysis across translational, vibrational, and rotational components in the products. A key observation is the influence of the vibrational and rotational excitation of D₂ on the total angular momentum (J′) of the HOD* product. This study reveals that increasing the vibrational level, vD₂, significantly shifts P(J′) distributions toward higher values, broadening them due to increased isotropy. In contrast, increasing the rotational level, jD₂, results in a smaller shift but introduces greater anisotropy, leading to a more selective distribution of J′ values. The dual Gaussian Binning selection—Vibrational-GB followed by Rotational-GB—further highlights a preference for either odd or even J′ values, depending on the specific excitation conditions. These findings have implications for the development of chemical lasers, as the excitation and emission properties of HOD* can be leveraged in the laser design. Future research aims to extend this study to a broader range of initial conditions, refining the understanding of reaction dynamics in controlled gas-phase environments. Full article

This study employs Direct Numerical Simulation (DNS) to investigate the flow and heat transfer characteristics in a compressor blade passage at five Reynolds numbers ($Re=1.091\times {10}^5$, $1.229\times {10}^5$, $1.367\times {10}^5$, $1.506\times {10}^5$, and $1.645\times {10}^5$). A recent method based on local inviscid velocity reconstruction is applied to define and calculate boundary layer parameters, whereas the Rortex vortex identification method is used to analyze turbulent vortical structures. Results indicate that $Re$ significantly affects separation bubble size, transition location, and reattachment behavior, thereby altering wall heat transfer characteristics. On the pressure surface, separation and early transition are observed at higher $Re$, with the Nusselt number ($Nu$) remaining high after transition. On the suction surfaces, separation occurs such that large-scale separation at low $Re$ reduces $Nu$, while reattachment combined with turbulent mixing at high $Re$ significantly increases $Nu$. Turbulent vortical structures enhance near-wall fluid mixing through induced ejection and sweep events, thereby promoting momentum and heat transport. As $Re$ increases, the vortical structures become denser with reduced scales and the peaks in heat flux move closer to the wall, thus improving convective heat transfer efficiency. Full article

Robotic positioning accuracy is critically affected by both geometric and non-geometric errors. To address this dual error issue comprehensively, this paper proposes a novel two-stage compensation framework. First, a Memory based red billed blue magpie optimizer (MRBMO) is employed to identify and compensate for geometric errors by optimizing the geometric parameters based on end-effector observations. This memory-guided evolutionary mechanism effectively enhances the convergence accuracy and stability of the geometric calibration process. Second, a tuned graph neural network (AMPSO-GNN) is developed to model and compensate for non-geometric errors, such as cable deformation, thermal drift, and control imperfections. The GNN architecture captures the topological structure of the robotic system, while the adaptive momentum PSO dynamically optimizes the network’s hyperparameters for improved generalization. Experimental results on a six-axis industrial robot demonstrate that the proposed method significantly reduces residual positioning errors, achieving higher accuracy compared to conventional calibration and compensation strategies. This dual-compensation approach offers a scalable and robust solution for precision-critical robotic applications. Full article

Marine atmospheric boundary-layer height (MABLH) is crucial for ocean heat, momentum, and substance transfer, affecting ocean circulation, climate, and ecosystems. Due to the unique geographical location of the South China Sea (SCS), coupled with its complex atmospheric environment and sparse ground-based observation stations, accurately determining the MABLH remains challenging. Coherent Doppler wind lidar (CDWL), as a laser-based active remote sensing technology, provides high-resolution wind profiling by transmitting pulsed laser beams and analyzing backscattered signals from atmospheric aerosols. In this study, we developed a stacking optimal ensemble model (SOEM) to estimate MABLH in the vicinity of the site by integrating CDWL measurements from a representative SCS site with ERA5 (fifth-generation reanalysis dataset from the European Centre for Medium-Range Weather Forecasts) data from December 2019 to May 2021. Based on the categorization of the total cloud cover data into weather conditions such as clear/slightly cloudy, cloudy/transitional, and overcast/rainy, the SOEM demonstrates enhanced performance with an average mean absolute percentage error of 3.7%, significantly lower than the planetary boundary-layer-height products of ERA5. The SOEM outperformed random forest, extreme gradient boosting, and histogram-based gradient boosting models, achieving a robustness coefficient ($R^2$) of 0.95 and the lowest mean absolute error of 32 m under the clear/slightly cloudy condition. The validation conducted in the coastal city of Qingdao further confirmed the superiority of the SOEM in resolving meteorological heterogeneity. The predictions of the SOEM aligned well with CDWL observations during Typhoon Sinlaku (2020), capturing dynamic disturbances in MABLH. Overall, the SOEM provides a precise approach for estimating convective boundary-layer height, supporting marine meteorology, onshore wind power, and coastal protection applications. Full article

We study the impact on the cosmic microwave background (CMB) landscape of peculiar rotational general relativistic effects. These effects, on galactic scales, do not possess a Newtonian analogue, and therefore could a priori impact CMB analysis. We find that the velocity inferred from the CMB dipole, under the kinematic interpretation, coincides with that measured by a stationary observer within the Milky Way and not with the one measured by the zero angular momentum observer. We show that the galaxy peculiar frame-dragging effects do not impact the standard CMB analysis, as these modify the multipole coefficients only at higher orders with respect to the dominant terms. Moreover, we prove that no general relativistic framework at the galactic scale patched within the standard cosmological model can account for the current tension on the CMB quadrupole amplitude. Full article

Sprinkler system performance enhancement has been a key area of research due to concerns about water shortages and rising energy costs. This study evaluated the hydraulic performance of the newly designed Spiral Fluidic Sprinkler (SFS) with various nozzles under different operating pressures. MATLAB R2020b software was used to simulate sprinkler uniformities under various operating pressures and the droplet diameter, velocity, and kinetic energy were measured using a 2DVD video raindrop spectrometer. The results showed that larger nozzle sizes generally improved application uniformity and efficiency. The 4 mm nozzle at 200 kPa achieved the lowest coefficient of variation (CV) at 6.2%, while the 3 mm nozzle showed a higher CV of 10.4%. Under 200 and 250 kPa of pressure, a statistically significant difference (p < 0.05) was observed between the CVs for the 4 mm nozzle. Droplet size distributions revealed that over 90% of droplets produced by the 4 mm nozzle were under 3 mm in diameter across all pressures. Kinetic energy analysis indicated that droplet momentum increased with pressure, enhancing coverage but potentially increasing drift at higher levels. Overall, the SFS demonstrated strong potential for water conservation and improved irrigation efficiency in controlled agricultural environments. Full article

The interaction between particles and their surrounding medium can induce a squeezed back-to-back correlation between particles and antiparticles. In this paper, the squeezed fermion back-to-back correlation (fBBC) for expanding sources is studied. The formulas of the fBBC correlation function of fermion–antifermion pairs for expanding sources are given. The expanding flow leads to a decrease in the fBBC of proton–antiproton pairs and $\Lambda$-$\overline{\Lambda }$ pairs in the high-momentum region, an increase in the fBBC in the low-momentum region, and a narrowing width of the fBBC varies with in-medium mass in the low-momentum region. Even though the expanding flow influences fBBC, the fBBC of proton–antiproton pairs and $\Lambda$-$\overline{\Lambda }$ pairs can still offer possible observation signals as the collision energy varies from a few GeV to 200 GeV. Full article

In 2019, the Event Horizon Telescope (EHT) released the first image of a black hole, sparking huge interest in the study of black-hole images. We present analytical solutions to the null geodesic equations for Kerr–Newman–de Sitter black holes derived using Jacobi elliptic functions. Using these solutions, we have performed an analytic ray-tracing simulation to model direct images, lensing rings, and photon rings, considering standard observers and zero angular momentum observers (ZAMOs). Additionally, we have derived analytic expressions for the critical parameters governing the structure of the photon ring and analyzed them in detail. From the foregoing, an increase in charge leads to a decrease in both time delay and Lyapunov exponent, while the change in azimuthal angle is insignificant. These findings improve our understanding of the effects of charge on black-hole photon rings and provide a foundation for future studies. Full article