Search Results (219)

This paper presents a computational model of delirium in the Intensive Care Unit (ICU), in which delirium is defined as the endpoint of a self-reinforcing cycle of predictive failure between two bidirectionally coupled agents: the patient and the ICU room environment. Drawing on the active inference framework and the free energy principle, the paper proposes that delirium is not a property of the patient in isolation but a relational phenomenon that emerges when the environment persistently fails to predict the patient’s internal state. This failure triggers a causal feedback mechanism in which desynchronization pressure progressively sharpens the patient’s prior beliefs—implementing precision rigidity in the correct active inference sense: not a brain overwhelmed by noise but a brain locked into a state that incoming observations can no longer update. The model is implemented as a two-agent POMDP in which both agents maintain generative models and continuously attempt to predict each other’s states. The room agent (R)—understood as the environment-side sensing–inference–actuation loop, whether instantiated by clinical staff or by an automated monitoring system—infers the patient (P)’s latent parameters $({\theta }_{\mathrm{cog}},{\theta }_{\mathrm{emo}})$ over time and builds a progressively personalized generative model of the patient. Synchronization is operationalized via two commensurable directional surprisal metrics: $S_{R\to P}=-ln{Q}_R\left(s^{*}\right)$, the room’s surprisal at the patient’s true state, and $S_{P\to R}=-lnP(o_R\mid Q_P)$, the patient’s surprisal at the room’s observations. A systematic ablation study across four model variants shows that room inference is the architectural component necessary to reproduce the synchronization–delirium relationship: when the room infers, the association between synchronization and declared delirium is strong and stable, whereas a non-inferring room collapses to ceiling delirium rates and a weak association. $\theta$ learning and the prior-sharpening feedback do not increase the strength of this association; instead they shape the phenotypic gradient, reducing ceiling effects in vulnerable phenotypes and amplifying the separation between them. The model is presented as a computational hypothesis generator rather than a calibrated clinical predictor, and its implications for ICU design are discussed. Full article

Sweep-field operation in a single-beam spin-exchange relaxation-free (SERF) magnetometer requires stable extraction of the dispersion zero-crossing. A frequency mismatch between the modulation signal and the demodulation references, or an unsuitable low-pass filter, can shift this zero-crossing and affect working-point determination. This paper presents a zero-crossing-stability-oriented FPGA quadrature lock-in module for SERF sweep-field demodulation. The module is designed around two requirements of sweep-field operation: maintaining a common frequency basis between the modulation output and the demodulation references, and preserving the dispersion zero-crossing when the low-pass-filter cutoff frequency is adjusted. A shared direct digital synthesizer generates both the sinusoidal modulation output and the I/Q references, keeping the excitation and demodulation signals on the same frequency basis. After quadrature multiplication, CIC decimation and a reloadable Kaiser-window FIR filter are used for low-pass processing. Board-level tests show a 1000.054 Hz spectral peak for a 1000 Hz setting and a loopback amplitude of 0.496 V, close to the ideal 0.500 V baseband amplitude. On the SERF platform, I/Q rotation reduces the quadrature residual ratio from 32.1% to 0.10%. When the FIR cutoff frequency is changed from 3 to 15 Hz, the maximum zero-crossing difference is about 0.58 ms, corresponding to 0.12% of the 2 Hz sweep period. These results show that the module supports stable zero-crossing extraction and working-point determination during sweep-field operation in a single-beam SERF magnetometer. Full article

Urban shrinkage has evolved from a localized phenomenon into a systemic challenge within China’s rapid urbanization, rendering traditional growth-oriented planning paradigms increasingly obsolete. However, existing research often treats shrinkage as either a passive outcome or an isolated shock, lacking a holistic perspective on how complex urban systems can adapt and reorganize under prolonged decline. This study constructs a coupling framework integrating urban shrinkage with Social–Ecological System (SES) resilience to bridge this theoretical gap. Drawing on a systematic literature review of 76 peer-reviewed articles following the PRISMA guidelines, we identify six core dimensions that drive this coupling. These dimensions consist of distinct physical and social elements. Our analysis reveals that the interactions between rigid physical environments and highly fluid social elements trigger nonlinear cascading feedback loops. While demographic contraction amplifies systemic risks, the subsequent structural release provides crucial spatial and institutional room for right-sizing. To translate these mechanisms into actionable governance strategies within the Chinese context, we propose a dual-track paradigm. Regionally, strategies emphasize collaborative risk monitoring, cross-boundary factor substitution, and industrial functional complementarity to mitigate vulnerability spillover. Locally, planning needs to pivot toward systemic downsizing and social empowerment, integrating proactive spatial reduction with agile service provision and community capacity-building. Ultimately, integrating structural reconfiguration with grassroots social learning enables shrinking cities to establish a new resilient equilibrium. While anchored in the Chinese context, this dual-track governance paradigm offers transferable insights for global shrinking cities seeking to overcome structural lock-in and foster adaptive SES resilience. Full article

Vortex-induced vibration (VIV) is the main cause of fatigue failure in steel catenary risers (SCRs). This study developed a fluid–structure interaction (FSI) model, combining Reynolds-Averaged Navier–Stokes (RANS)-based computational fluid dynamics (CFD) with the Newmark-β algorithm, to simulate VIV responses under ocean currents and platform heave motion. First, the FSI model analyzed SCR behaviors under steady currents, then was adapted to oscillatory flow mimicking heave motion. A finite element model (FEM) was built, using the simulated VIV response as displacement boundary conditions to compute the equivalent stress time history along the riser. Finally, Miner’s rule was applied to quantify fatigue damage in three scenarios: current-only, heave-only, and the combined action of both factors. The results indicate that, in the South China Sea’s 10-year return period sea state, the SCR experiences a broad vortex-induced resonance interval under ocean current loads, with a maximum vibration amplitude of 0.7D. At the associated resonant height, platform heave motion triggers near-complete lock-in of the SCR’s VIV. The peak fatigue damage induced by ocean currents alone, platform heave motion alone, and their combined action all concentrates at the riser touchdown point (TDP). Over the 600 s VIV response duration, fatigue damage from platform heave motion alone constitutes 8.48% of that caused by ocean currents alone, while the combined action results in fatigue damage 1.847 times that of ocean currents alone. Thus, the combined action significantly amplifies both the magnitude and spatial non-uniformity of VIV-induced fatigue damage in SCRs. Full article

Underwater acoustic monitoring is a critical technology for marine resource development and modern aquaculture. The performance of acoustic sensors directly determines the effectiveness of biological behavior tracking in complex marine environments. This paper presents the design, fabrication, and characterization of a custom hydrophone utilizing a polyvinylidene fluoride (PVDF) piezoelectric film configured in a biomimetic tympanic cavity structure. Operating on the direct piezoelectric effect, the device employs a pre-tensioned PVDF diaphragm integrated with a dedicated charge amplifier circuit to condition high-impedance signals. Laboratory calibrations demonstrate a stable frequency response (with a sensitivity variation within ±1 dB) in the low-frequency range (1–200 Hz) with an average acoustic pressure sensitivity of approximately −206 dB (re 1 V/μPa), providing a higher relative voltage gain compared to a commercial reference hydrophone with a nominal sensitivity of −210 dB (re 1 V/μPa). Furthermore, extensive field evaluations were conducted in a marine net pen to analyze acoustic data across multiple fish feeding scenarios (baseline, pre-feeding, active feeding, and post-feeding). The proposed custom hydrophone exhibited a superior dynamic range and successfully locked onto a 24.4 Hz Golden Pompano (Trachinotus blochii) bioacoustic signature, maintaining remarkable feature stability even after active feeding ceased. This study validates the efficacy of the biomimetic PVDF hydrophone for low-frequency acoustic detection, providing a robust hardware foundation for automated behavioral recognition systems in aquaculture. Full article

Accurate and stable measurement of carbon dioxide (CO₂) concentrations in industrial flue gases is critical for emissions monitoring and carbon management. The present study developed a wavelength-modulated tunable diode laser absorption spectroscopy (WMS-TDLAS) system for measuring high-concentration carbon dioxide (CO₂) in flue gases, covering a range of 3–20% (by volume). To mitigate optical intensity fluctuations caused by particle scattering and detector gain drift in harsh flue gas environments, a normalized second harmonic (2f/1f) detection scheme based on a single-harmonic peak was employed. A digital phase-locked amplification algorithm replaces the conventional hardware lock-in amplifier, enabling simultaneous demodulation of multiple harmonic components and enhancing system integration. A comparison of the digital locking method with a commercial lock-in amplifier reveals that the former demonstrates comparable or superior stability, with relative standard deviations of 0.04% for the 2f signal and 0.02% for the first-harmonic signal. In order to address the sensitivity degradation of WMS-TDLAS at elevated CO₂ concentrations, a pressure control strategy was introduced. Maintaining the measurement cell pressure at 70 ± 0.005 kPa resulted in a 2.74-fold enhancement in system sensitivity at 13.01% CO₂ and a more than one-order-of-magnitude increase at 20.01% CO₂ compared to operation at atmospheric pressure. Concentration measurement error under reduced pressure also decreased from 1.101% to 0.075%. The system exhibited 0.6% repeatability in high-concentration CO₂ measurements, signifying its aptitude for industrial flue gas monitoring applications. Full article

Accurately identifying damage in beam structures remains a tough challenge, the global trend of wavelet coefficients easily swallows faint local defect signatures, and high-dimensional model updating is computationally inefficient. To tackle these problems, this paper introduces a robust two-stage framework for damage identification that combines a residual-based wavelet strategy with an Improved t-distribution Dung Beetle Optimizer (ITDBO). Rather than relying on guesswork for wavelet selection, we introduce the Residual-based Wavelet Contrast Index (RWCI). By actively stripping away the global trend embedded within the wavelet coefficients, RWCI isolates the pure residual data, drastically amplifying the contrast between genuine stiffness loss and ambient noise for precise damage localization. With the search zone narrowed down, we deploy the ITDBO to quantify the severity. Powered by Bernoulli chaotic mapping and a t-distribution perturbation mechanism, ITDBO effectively bypasses the curse of dimensionality and entirely avoids the premature convergence traps that plague standard metaheuristics. Validated through both numerical simulations and physical experiments on a one-dimensional fixed-fixed steel beam, this hybrid approach proves its mettle. The framework not only accurately flags the defects through heavy noise but also locks onto the exact damage severity with unprecedented efficiency and stability. Full article

Differential light shift (DLS) is an important error term that limits the atom interferometer’s measurement precision, especially for the case of the electro-optic modulator (EOM)-based scheme, where multiple laser sidebands exist, and their ratios are hard to control synchronously. This article carried out an experimental and theoretical study on this subject. By conducting long-term gravity measurement, we find that the gravity exhibits drifts of about 13.13 μGal, and is strongly correlated to the Raman laser’s sidebands. A model of the DLS-induced gravity error is established and a DLS compensation method is proposed to suppress the gravity drift to 2.54 μGal. Besides the compensation method, we propose a Dual-Sideband Ratio Locking scheme to more robustly eliminate the gravity measurement drift. By feeding back to both the EOM microwave power and the tapered amplifier’s temperature, this method locks both the ±1 order sideband to a stability level of ${10}^{-5}$, which corresponds to a gravity error of less than 0.1 μGal. Long-term gravity measurement is carried out after the locking method, showing a long-term stability of 1.6 μGal. The proposed methods will benefit the suppression of the DLS effect for high-precision atom interference measurement. Full article

We demonstrate an all-polarization-maintaining (PM) mode-locked thulium-doped fiber laser operating in the net-normal-dispersion regime based on a figure-9 nonlinear amplifying loop mirror (NALM) configuration. A chirped fiber Bragg grating (CFBG) and a commercial PM dispersion-compensating fiber (PM-DCF) are incorporated into the figure-9 cavity, providing a large normal net dispersion and enabling stable dissipative-soliton mode-locking. Under stable dissipative-soliton operation, the laser delivers a maximum output power of 53.6 mW at a repetition rate of 12.31 MHz, corresponding to a pulse energy of 4.3 nJ. The output spectrum has a central wavelength of ~1952 nm with a 3 dB bandwidth of ~11 nm. The all-PM laser oscillator directly generates a fs pulse without extra-cavity compression, achieving a pulse duration of 545 fs at the CFBG arm. Moreover, stable fundamental mode-locking is verified by a high radio-frequency signal-to-noise ratio (SNR) exceeding 82 dB and a long-term root-mean-square (RMS) power fluctuation of 0.45% over two hours. To the best of our knowledge, this represents the highest output power generated from an all-PM-fiber figure-9 laser oscillator in the 2 μm band, alongside fs-pulse operation. This high-power, compact, stable and environment-insensitive fs-pulsed laser source shows great potential as an ideal seed for biomedical imaging and mid-infrared frequency combs. Full article

We have demonstrated a high-power, polarization-maintaining all-fiber amplifier operating at a repetition rate of 1 MHz. The seed laser is a Semiconductor Saturable Absorber Mirror (SESAM) mode-locked oscillator with an 18.1 nm full width in half-maximum (FWHM) spectrum. The pulse duration is stretched to 1.1 ns using temperature-controlled chirped fiber Bragg gratings (TCFBGs) and subsequently amplified in a 40 µm core Yb-doped fiber, achieving a maximum output power of 37 W. The amplified laser exhibits excellent beam quality with an M² factor of 1.04. The pulse duration is compressed to 207 fs in a single-grating compressor with 86% efficiency, yielding an average power of 32 W, a pulse energy of 32 µJ, and a peak power of 154.6 MW. This high-power all-fiber femtosecond laser is a promising source for scientific and industrial applications. Full article

This paper proposes a method to generate a low-noise 10.23 MHz time-frequency reference signal based on high-order harmonic locking of the repetition rate (f_r) of an optical frequency comb (OFC). An all-polarization-maintaining (PM) Erbium-doped fiber laser with a 122.76 MHz f_r is constructed using the nonlinear amplifying loop mirror (NALM) principle. By applying a feedback control to the intracavity piezoelectric actuator (PZT) and electro-optic modulator (EOM), the 10th harmonic of f_r is phase-locked to a high-performance rubidium atomic clock (Rb clock), achieving low-noise conversion from the Rb clock to the target signal. Experimental results show that the generated 10.23 MHz signal exhibits residual phase noise of −123.4 dBc/Hz at 1 Hz offset and −158 dBc/Hz at 1 MHz offset, and achieves a residual frequency stability of 3.52 × 10⁻¹³ @ 1 s and 3.65 × 10⁻¹⁵ @ 10,000 s. This harmonic locking scheme validates the advantages of photonic microwave generation in achieving ultra-low phase noise while preserving the long-term stability of atomic clocks, providing a strategic solution for next-generation BeiDou Navigation Satellite System (BDS) time-frequency payloads. Full article

Background: Resting-state functional MRI (rs-fMRI) studies typically rely on linear Pearson correlation to characterize brain connectivity, potentially overlooking the distributional characteristics of functional networks. This study introduces a kernel-transformed functional connectivity (FC) entropy framework to quantify network dedifferentiation in bipolar disorder (BD). Methods: We utilized a Gaussian kernel function to execute a nonlinear similarity transformation (referred to as reweighting) on standard linear correlation matrices. This approach acts as a functional filter to amplify the contrast between strong and weak connections. Multiscale entropy (global, modular, and nodal) was subsequently calculated to characterize the uniformity of connectivity weight distributions. Results: Compared to Normal Controls (NCs), patients with BD exhibited significantly higher entropy at the global level and within the Default Mode, Salience, and Somatosensory-Motor networks, indicating widespread network dedifferentiation (distributional flattening). These alterations were robust across different kernel widths and remained significant after rigorously controlling for head motion (Mean FD). Furthermore, manic symptom severity (YMRS) was negatively correlated with global entropy, suggesting a pathological “locking-in” or rigidity of specific neural circuits during manic states. Conclusions: The kernel-transformed FC entropy serves as a distribution-sensitive complement to conventional linear metrics. Our findings highlight network dedifferentiation as a key pathophysiological feature of BD and suggest this framework as a promising candidate metric for characterizing network dysregulation. Full article

To address the issue of low closed-loop feedback bandwidth caused by the long latency of Carrier-Envelope Phase (CEP) measurement systems for amplified femtosecond laser pulses, and to meet the requirements for real-time single-shot measurement in 10 kHz repetition rate systems, this paper proposes a microsecond-level low-latency CEP measurement technique based on a Field-Programmable Gate Array (FPGA). To tackle the problem of non-uniform spectral sampling resulting from nonlinear wavelength-frequency mapping, the system implements a real-time linear interpolation algorithm for the interference spectrum. This approach effectively suppresses computational spurious peaks introduced by non-uniform sampling and significantly reduces measurement errors. Adopting a fully pipelined parallel processing architecture, the system achieves a CEP processing latency of approximately 89 μs, representing an improvement of 2–3 orders of magnitude compared to traditional Central Processing Unit (CPU)-based solutions. Hardware-in-the-loop testing, conducted by injecting a known sinusoidal phase modulation into the interference spectrum of a 10 kHz laser amplification system, demonstrates that the computational error of the proposed algorithm is less than 30 mrad. This work paves the way for achieving single-shot CEP feedback locking in high-repetition-rate laser amplification systems. Full article

Cancer metastasis, the spread of tumour cells from the primary site to distant organs, is responsible for over 90% of cancer deaths, yet effective treatments remain elusive due to incomplete understanding of the molecular drivers involved. Podocalyxin (PODXL), a protein overexpressed in many aggressive cancers, links the cell membrane to the internal skeleton through its interaction with Ezrin, an actin cytoskeleton cross-linker. Despite its therapeutic relevance, the PODXL–Ezrin interface remains structurally uncharacterised and pharmacologically intractable. Here, we employed an integrated computational approach combining protein–protein docking, molecular dynamics (MD) simulations, and virtual screening to investigate the structural basis of the PODXL–Ezrin interaction. Using AlphaFold-predicted structures, we modelled PODXL and Ezrin complexes, revealing that PODXL’s cytoplasmic domain stabilises upon Ezrin binding, with Arg495 mediating temporally distinct electrostatic interactions essential for initial complex assembly. Particularly, we characterised the R495W missense mutation in PODXL’s Ezrin-binding domain, demonstrating that substitution of arginine with bulky, hydrophobic tryptophan may allosterically destabilise Ezrin’s dormant conformation. This mutation slightly increases the intramolecular distance between the F3 subdomain and C-terminal domain from 2.59 Å to 3.40 Å, thus leading to potential partial unmasking of the Thr567 phosphorylation site that could plausibly prime Ezrin for activation. Molecular dynamics simulations in the WT state with a total simulation time of 100 ns revealed enhanced structural rigidity and reduced radius of gyration fluctuations in the mutant complex, consistent with a potential “locked,” activation-prone state that amplifies oncogenic signalling. Through virtual screening, we identified NSC305787 as a selective destabiliser of the R495W mutant complex by disrupting key Trp495–pre-C-terminal loop Ezrin interactions and causing steric hindrance to PIP2 recruitment. Our findings identified mutation-dependent changes in drug binding that can guide the development and repurposing of compounds for targeting PODXL-related cancers and improve patient outcomes in PODXL-altered malignancies. Full article

In this work, a carrier-free photoacoustic spectroscopy system is developed for the detection of trace acetylene gas in insulating oil. The photoacoustic cell was integrated with an oil–gas separator, allowing dissolved gases in oil to be introduced into the cell through free diffusion. The oil–gas separator is a custom-fabricated AF2400-coated ceramic membrane, and its spin-coating process was carefully designed to enable rapid oil–gas separation and achieve high film flatness. Using a resonant photoacoustic cell and a low-noise lock-in amplifier, the sensitivity of the system was improved to 6.90 mV/ppm, with a repeatability error less than 1.65%. Calibration experiments demonstrated that continuous detection of dissolved gas in oil could be achieved, with a response time T₉₀ of less than 72.5 min. Compared to traditional photoacoustic spectroscopy, the continuous measurement capability of this method is expected to enable earlier fault diagnosis, thus having greater potential in industrial fields. Full article