Search Results (41,575)

Variational Quantum Eigensolvers (VQEs) have become a standard tool for use in preparing eigenstates in quantum simulations of many-body systems. In the case of the nuclear shell model, various adaptations of the VQE have been shown to be able to produce ground and excited states of nuclei. The VQE algorithm works by seeking minima in a cost function, which is often the expectation value of the energy. For a well-formulated problem, symmetries that are respected by the Hamiltonian should appear in the final converged solution provided by the VQE, even if those symmetries are broken by the wave function ansatz. We demonstrate explicit appearance of the particle–hole symmetry, and explicit recovery of angular momentum conservation due to rotational symmetry, during VQE runs in the case of the nuclear shell model. We conduct analyses of how the symmetry convergence appears in different ansatz formulations, and suggest that information obtained could be used in future VQE design. Full article

Accurate hub-height wind-speed forecasting is a prerequisite for the safe and economical integration of wind power into the electricity grid, because forecasting errors propagate directly into imbalance penalties, reserve sizing, and turbine wear, and short-term predictions (one to twenty-four hours ahead) are of direct operational value. The literature on wind-speed and, more broadly, multivariate time-series forecasting has advanced through three overlapping waves, namely classical statistical and physical models, shallow machine-learning regression, and deep sequence models, which share a common trajectory of replacing hand-crafted meteorological relationships by data-driven estimators. Four shared limits recur across this work: deep architectures treat covariates as exchangeable tokens and under-use the physically grounded relationships among synchronous variables; they optimize pure accuracy without a mechanism that keeps the forecast physically consistent with the atmosphere; evaluations concentrate on generic benchmarks where the short-term optimum is often a linear or persistence baseline, so the benefit of complex inductive biases at operational horizons is unclear; and wind-speed studies seldom isolate an explicit physical prior from the recurrent or attention backbone. This work contributes (a) a reproducible multi-site benchmark of eight forecasting strategies, namely persistence, ARIMA, gradient-boosted trees, a plain LSTM, and four further deep architectures including PatchTST, DLinear, iTransformer, and the proposed physics-informed PIV-LSTM, evaluated at five horizons on four real sites; (b) a physics-informed vector (PIV) that augments the network input with an ordinary-least-squares linear reconstruction of the target from its known covariates, and regularizes training with a decaying consistency loss, implemented on an LSTM backbone (PIV-LSTM); and (c) an ablation that quantifies where the physical prior helps and where it does not, together with an honest assessment of the results, including where a classical model remains competitive and the long-horizon regime in which every model loses skill. Full article

To address the limited source level of transducers and the insufficient signal-to-reverberation ratio (SRR) and signal-to-noise ratio (SNR) of target echoes in underwater model target-strength measurements, coherent multi-element transmission is commonly employed in lake acoustic-scattering experiments to focus the acoustic field in the target region and improve echo quality. However, because practical deployment distances do not always satisfy strict far-field conditions, the measurement configuration may deviate from the ideal plane-wave incidence and reception conditions, thereby introducing errors into target-strength measurements. In this study, an elastic spherical shell is used as a representative target for method validation. A theoretical target-strength model incorporating multi-element transmission and reception is established, and an extreme gradient boosting (XGBoost) regression model is proposed for measurement-error prediction and correction. The results show that the target-strength deviation caused by finite-aperture transmission generally increases with increasing frequency and element spacing and with decreasing transmission distance, whereas the target-strength deviation introduced by the receiving array is comparatively smaller. The developed XGBoost model captures the dependence of target-strength error on frequency and array parameters, reducing the root mean square error (RMSE) relative to the ideal plane-wave reference by 62.1% to 1.6 dB after correction. Lake experiments further show that finite-aperture transmission introduces deviations from the ideal plane-wave theoretical values, with an RMSE of 3.4 dB under finite measurement distances, highlighting the need to improve the model’s generalization capability for practical correction. Full article

Background/Objectives: Poor nutritional status is common among hospitalized patients and may adversely affect the response to severe acute illness. We investigated the association between nutritional status at hospital admission and clinical outcomes in patients hospitalized with COVID-19 during the first two pandemic waves in Italy. Methods: This retrospective multicenter study included 1187 patients hospitalized with COVID-19 across nine Italian centers participating in the MODIeCOSe in Italia registry. Nutritional status was assessed using the Controlling Nutritional Status (CONUT) score, the Prognostic Nutritional Index (PNI), and available anthropometric measures. The primary outcome was a composite of in-hospital death or transfer to an intensive care unit (ICU). Multivariable logistic regression was used to assess the independent association between nutritional status and outcome. Results: Overall, 275 patients (23.2%) experienced the composite adverse outcome. CONUT score was higher in patients with an adverse than in those with a favorable outcome (4.4 ± 2.3 vs. 3.4 ± 1.8; p < 0.001), whereas PNI did not differ significantly. Patients with an adverse outcome also had lower body weight, BMI, waist circumference, and waist-to-height ratio, although anthropometric data were available only in subsets of the cohort. In the main multivariable model adjusted for admission PaO₂/FiO₂ and relevant clinical covariates, higher CONUT remained independently associated with adverse outcome (OR 1.65, 95% CI 1.12–2.45 per 1-SD increase; p = 0.01). The association was similar in a sensitivity analysis excluding PaO₂/FiO₂ (OR 1.79, 95% CI 1.28–2.49; p < 0.001). Conclusions: A higher CONUT score at admission was independently associated with an increased risk of in-hospital death or ICU transfer, supporting its prognostic relevance as an immuno-nutritional index in hospitalized patients with COVID-19. Full article

Design-variable scaling is often treated as numerical preprocessing in simulation-driven optimization, although the coordinates supplied to the optimizer form part of the numerical interface to the computational model. This study quantifies the resulting implementation-level sensitivity of Nelder–Mead using two full-wave electromagnetic (EM) microwave-filter models as controlled engineering benchmarks: a three-variable low-pass filter (LPF) with comparable variable magnitudes and a five-variable band-pass filter (BPF) containing a much smaller coupling gap. For each benchmark, the physical seeds, EM model, frequency samples, sampled mask-based objective, aggregation norm, optimizer options, and evaluation budget were fixed; only the optimizer-space representation was changed. Raw physical, relative-normalized, partially scaled gap, and log-relative coordinates were compared using exact and tolerance-based success, residual violation severity, EM evaluation count, seed-level outcomes, and final-design distances. For the LPF, raw and normalized coordinates each achieved 5/15 exact successes, while log-relative coordinates achieved 4/15 with milder residual violations. For the BPF, the corresponding counts were 13/15, 13/15, 12/15, and 9/15, with the log-relative formulation producing the most severe failures. The results show that parameterization is a non-neutral component of simulation-driven optimization and should be documented and validated as part of reproducible computational-modeling workflows. Full article

A novel heuristic search algorithm, the Acoustic Diffraction Search Algorithm (ADSA), is proposed to address the global path planning problem for orchard transport robots. By simulating the diffraction characteristics of acoustic waves around obstacles, ADSA constructs a search method centered on an acoustic-wave-based search strategy, a diffraction node identification rule, and sound pressure attenuation estimation at diffraction nodes. Path-planning simulations were conducted on random grid maps of different scales and obstacle densities, and ADSA was compared with the A* algorithm, the Dijkstra algorithm, and the Jump Point Search (JPS) algorithm. The simulation results indicate that ADSA generated relatively short planned paths while maintaining relatively high search efficiency in the test scenarios. Only on the large-scale map with an obstacle density of 30% was the path generated by ADSA 0.24% longer than that generated by the Dijkstra algorithm, while its pathfinding time was only 0.18% of that of the Dijkstra algorithm. Path-planning experiments conducted on maps of the two test field sites showed that ADSA generally generated paths with shorter path lengths and smaller cumulative turning angles. Specifically, ADSA reduced the average path length by 3.95% compared with the Dijkstra algorithm and by 6.30% compared with the A* and JPS algorithms. The results show that ADSA achieved favorable overall performance in terms of path length, cumulative turning angle, and search efficiency, providing a new search approach for the global path planning of orchard transport robots in known environments. Full article

Five compounds with the formula Ln₂Zr₂O₇ (Ln = La, Nd, Sm, Eu, and Gd) were investigated. These materials exhibit important physicochemical properties and find practical applications for the development of high-temperature barriers, gas traps, and the adsorption of actinides in nuclear waste. The investigations were performed using ab initio calculations within the framework of density functional theory employing the full-potential augmented plane-wave method. Quantum-mechanical calculations of the electronic structure and optical spectra of the investigated semiconductors were carried out using the exchange-correlation potential within the generalized gradient approximation (GGA), incorporating GGA + U corrections to account for strong correlations among f- and d-electrons, as well as the GGA + U + mBJ approach to obtain more realistic band gap (E_g) values. Relativistic spin–orbit coupling effects within the electronic systems of heavy-element atoms were also taken into account. The band gaps (E_g) and the complex dielectric function, from which optical properties can be derived, were calculated. A comparison of the calculated total densities of states (DOS) with experimental X-ray photoelectron spectra (XPS) demonstrated the validity of the applied exchange-correlation potential corrections and highlighted the importance of accounting for the spin–orbit splitting of atomic electronic states to accurately reproduce all features of the experimental XPS spectra. Full article

Acoustic stimulation precisely timed during sleep can enhance slow oscillations (SOs), a hallmark of deep sleep that is critical for restorative sleep. To date, this approach has largely been restricted to laboratory settings using high-density electroencephalography (EEG). Wearable EEG systems featuring closed-loop acoustic stimulation could enable scalable, home-based approaches to modulating slow-wave sleep. Here, we tested whether a real-time modeling approach (M-CLNS) could be implemented using a wireless EEG headband with forehead electrodes in healthy participants. Acoustic stimulation was delivered during a single night of sleep in alternating stimulation and sham conditions. We evaluated the accuracy of SO phase targeting utilizing the EEG headband and assessed whether it could be used to detect stimulation-induced changes in oscillatory dynamics. The findings were validated against simultaneous polysomnographic (PSG) recordings as an independent reference. We found that SO phase was targeted consistently near the intended phase using the headband, despite reduced amplitude and signal quality compared with simultaneous PSG. Acoustic stimulation produced an immediate enhancement of SO dynamics, as well as sustained increases in SO density and power spectral density within the SO and delta frequency range (0.75–5 Hz) during deep sleep. These effects were apparent both in the EEG headband and PSG signals. These results demonstrate the feasibility of closed-loop acoustic stimulation using a wireless EEG headband, providing a foundation for future home-based and clinical applications. Full article

Under combined wind-wave, wind-ice, and wave-whipping loads, the stress responses of ship and offshore structures often exhibit bimodal characteristics. Frequency-domain fatigue assessment methods, which directly evaluate damage using stress power spectral density functions, offer high computational efficiency. However, because the available methods differ in accuracy, a systematic comparison is needed to select the most suitable method for different operational conditions. In this study, based on time-domain simulation results from 400 bimodal rectangular spectra that span a wide range of Wirsching spectral width parameters from 0.0586 to 0.9922, the existing methods are categorized into four groups: narrow-band correction factor methods, rainflow cycle approximation methods, independent summation of combined fatigue damage methods, and nonlinear combination methods for decomposed broadband spectra. Sixteen typical methods are selected, and their prediction accuracies are quantitatively evaluated under three fatigue strength exponents (m = 3, 4 and 5), using the ratio of frequency-domain damage to time-domain damage as the evaluation metric. The results indicate that the Tovo–Benasciutti, Dirlik and Low methods all possess good engineering applicability. Among them, the Tovo–Benasciutti method provides the highest accuracy, the Dirlik method is more suitable for bilinear S–N curves, and the Low method is more robust in engineering applications. Full article

Inclusive tourism research has examined visitor-facing inclusion separately from workplace conditions under which frontline employees enact inclusive service. This separation leaves uncertainty about whether employees who experience workplace exclusion can perform inclusive service behaviors and whether such behaviors shape tourists’ perceptions. This study examined how workplace discrimination, psychological safety, identity concealment, and LGBTQ+-inclusive organizational climate are associated with inclusive service behavior among gay men employed in tourism and hospitality in Ecuador, and tested whether identity recognition and active intervention influence tourist identity safety and service equity. A sequential multimethod design combined a two-wave survey of gay men in customer-facing roles (N = 450 at Wave 1; N = 350 matched at Wave 2) and a randomized 2 × 2 video-vignette experiment with sexual- and gender-minority tourists (N = 480). Study 1 showed configurational heterogeneity in workplace discrimination. Greater discrimination was associated with lower psychological safety and greater identity concealment; psychological safety was positively associated with inclusive service behavior, whereas concealment was negatively associated with it. Study 2 showed that identity recognition and active intervention increased identity safety and service equity. Overall, the findings provide functionally and conceptually convergent evidence consistent with an inside-out framework, without establishing a complete organizational-to-customer causal chain. Full article

In this paper, we study the energy decay rate for a porous-elastic system with fractional infinite memory, which acts on the material displacement equation. Using the frequency domain method, we show that the energy decay rate of the system depends on the order $\theta$ of the fractional operator and the wave speeds ${\displaystyle \frac{\mu }{\rho }}$ and ${\displaystyle \frac{\delta }{J}},$ where $\theta \in [0,1].$ Specifically, the energy of the system decays exponentially when $\theta =1$ and ${\displaystyle \frac{\mu }{\rho }}={\displaystyle \frac{\delta }{J}}.$ The energy of the system decays polynomially when $\theta \in [0,1)$ and ${\displaystyle \frac{\mu }{\rho }}={\displaystyle \frac{\delta }{J}}$ or $\theta \in [0,1]$ and ${\displaystyle \frac{\mu }{\rho }}\ne {\displaystyle \frac{\delta }{J}}.$ In addition, we also show that the polynomial decay rates obtained are optimal in some sense. Full article

The traditional control approach for piston-type wave makers is reduced to a piston position tracking problem based on open-loop wave-maker theory; however, due to hydrodynamic loading, nonlinear effects, and propagation delays, the target wave condition at the measurement section cannot be guaranteed. This experimental study involves controllers tuned offline through numerical simulations and validated in real time on a 24 m wave channel. The novelty of this work is a two-layer field-programmable gate array (FPGA) cascade that regulates the measured wave height in closed loop, not just the piston position. In the inner layer, the hydraulic servo cylinder position is controlled within a 1 ms cycle using a proportional–integral (PI) or a Takagi–Sugeno (T–S) fuzzy controller; the outer layer, in a 20 ms cycle, updates the position reference via real-time wave height feedback. Controller parameters were tuned using three meta-heuristic algorithms under the integral of time-weighted absolute error criterion, and a similarity-based rule reduction reduced the T–S consequent parameters from 27 to 9, yielding 66.7% and 62.5% reductions in FPGA execution time and digital signal processing slice usage with tracking-error changes of only 2.2–2.3%. Experiments confirm high-accuracy position tracking and steady-state wave height regulation, verified by fast Fourier transform analysis. Full article

Background/Objectives: The COVID-19 pandemic disrupted youth movement behaviours and mental health, but evidence on post-pandemic trends remains limited. Therefore, this study examined differences in compliance with the 24-hour movement behaviour guidelines and their association with mental health outcomes among Portuguese children and adolescents between 2022 and 2024. Methods: This repeated cross-sectional study included two independent samples of Portuguese children and adolescents from the 2022 and 2024 waves of the Health Behaviour in School-aged Children study (2022: n = 2775; 2024: n = 2381). The 24-hour movement behaviours (physical activity, sleep and screen time) and mental health outcomes, assessed by Depression Anxiety Stress Scales—21 (DASS-21), were self-reported. Prevalences of attaining the 24-hour movement guidelines and DASS-21 categories were calculated and compared between 2022 and 2024 using chi-square tests. Adjusted logistic regression models were used to examine the associations between movement behaviour compliance and mental health outcomes. Results: From 2022 to 2024, the proportion meeting physical activity (7.5% to 13.7%; p < 0.001) and screen-time (12.8% to 28.2%; p < 0.001) guidelines increased, while adherence to sleep recommendations did not differ significantly (42.4% to 41.2%; p = 0.365). The proportion meeting two or more guidelines was also higher in 2024 (9.5% to 20.1%; p < 0.001). The prevalence of mild-to-extremely severe symptoms was lower in 2024 than in 2022 for depression (34.2% to 43.9%; p < 0.001), anxiety (38.1% to 43.2%; p = 0.001) and stress (23.6% to 31.0%; p < 0.001). Meeting screen-time and sleep guidelines was associated with at least 31% lower odds of having depressive, anxiety and stress symptoms (p < 0.001). Conclusions: More favourable prevalence estimates for movement behaviours and mental health outcomes were observed in 2024 than in 2022. Compliance with screen-time and sleep guidelines was associated with lower odds of depressive, anxiety and stress symptoms. Full article

Rural labor out-migration and low comparative returns to grain challenge food security in China. This study examines the association between agricultural machinery services (AMS) and the allocation of sown land between grain and economic crops, and whether farmland rent is linked to a countervailing pattern. Using data from the 2021 China Household Finance Survey (CHFS) for 421 villages and 5496 farming households, supplemented by the 2019 wave for the instrumental-variable analysis and additional diagnostics, we estimate province fixed-effects and instrumental-variable models. Greater AMS coverage is associated with a lower economic-crop share. Grain-specific service intensity is positively associated with relative gross sales revenue from grain and with farmland rent. Higher rent is positively associated with the economic-crop share in villages with active rental markets, but the estimated rent-related indirect association is imprecise: its bootstrap confidence interval includes zero. The data do not provide robust evidence that the rent association diminishes at higher rent levels. The association between AMS coverage and the economic-crop share is more negative in villages with better irrigation. These findings suggest that machinery services are linked to grain-oriented cropping, while the possible land-market feedback requires further investigation. Full article

Objective: Existing computational reconstruction methods for plane-wave ultrasound imaging (PWI) often neglect the interference of strong tissue signals with weak flow-related scattering signals in microflow imaging. This study aims to develop a multi-frame computational ultrasound reconstruction technique that integrates multi-frame sparse constraints with RF signal preprocessing strategies to facilitate the suppression of tissue signals and background noise. Methods: We propose multi-frame reconstruction of contrast-enhanced ultrasound microflow imaging. First, to prevent tissue signals from diluting the sparsity of multi-frame data, we apply singular value decomposition directly to the raw radio-frequency data, attenuating tissue-dominated components before beamforming. This yields sparser data and increases the relative contribution of flow-related components in the optimization. Results: The method was evaluated in contrast-enhanced microflow simulations and an exploratory in vivo experiment involving one rabbit. Under the tested conditions, VrUSi reduced background signals and produced narrower apparent intensity profiles than delay-and-sum and single-frame computational reconstruction. In the single-rabbit experiment, VrUSi yielded higher image-domain BCR values and smaller apparent-profile FWHM values across the analyzed temporal windows. These metrics are interpreted as background suppression and apparent profile compactness under the tested conditions, rather than as evidence of improved physical contrast or spatial resolution. The findings support feasibility only for visualizing flow-related structures in the tested rabbit lower-limb acquisition. Full article