Most preclinical positron emission tomography (PET) systems are designed for small-animal imaging and offer a limited axial field of view (FOV). The step-and-shoot (S S) acquisition mode is employed for whole-body imaging of larger animals. However, the reduced axial sensitivity at the edges of the FOV may lead to increased noise at the image boundaries. Continuous bed motion (CBM) acquisition mode is an efficient whole-body imaging protocol available on some clinical PET systems. This study aims to evaluate and implement the CBM acquisition mode on the preclinical digital PET/CT system RAYCAN Discoverist 180 (D180) and to compare its performance with the S S mode. The CBM acquisition mode enables imaging by mapping the normalized events into the virtual system, followed by random and attenuation correction. In addition, the effects of different virtual crystal sizes on image quality were evaluated. The mode was first validated via Monte Carlo simulations and subsequently implemented in the D180 system for real imaging. In contrast with the S S acquisition mode, the CBM acquisition mode demonstrates more consistent axial noise levels. Adjusting the virtual crystal size can improve the axial spatial resolution in CBM acquisition mode while maintaining its benefit in axial noise uniformity. The CBM acquisition mode reduces scanning complexity and maintains axial noise uniformity, making it an attractive alternative to the S S acquisition mode for imaging larger animals in preclinical PET systems.
Chiral molecules exhibit enantiosensitive light-matter interactions, with photoelectron circular dichroism (PECD) serving as a sensitive probe of molecular chirality through the asymmetry in the photoelectron wave-packet amplitude. Here, we theoretically demonstrate a photoelectron interferometric approach to access the phase of the photoelectron wave packet and uncover attosecond dynamics in chiral molecule photoionization. Using circularly polarized attosecond extreme ultraviolet (XUV) pulse trains synchronized with infrared (IR) fields, we reveal distinct time delays between forward- and backward-ejected photoelectrons in a randomly oriented ensemble of chiral molecules. Moreover, we predict a pronounced enhancement of PECD due to the interference of the two photoionization pathways. The forward-backward time delay difference and the PECD are more prominent when the IR field counter-rotates with the XUV field. These results imply the counter-rotating IR field is more efficient in generating odd-parity photoelectron wave packets in continuum-continuum transitions, highlighting the critical role of long-range chiral potential. We demonstrate a way of coherent control over the chiral photoelectron wave packets, providing a route to enhance chiral signals and manipulate ultrafast chiral dynamics on attosecond time scales.
On-demand laser opens new possibilities for customizing laser mode at source, where arbitrary-profile beams have been achieved via intra-cavity digital modulators facilitated by self-imaging degenerate structure, position-dependent loss engineering, and so on. However, obtaining complete mode-discrimination ability solely through lossless holographic approaches within non-degenerate cavities still lacks a benchmark-level design paradigm and remains a practical problem. To bridge this gap, we propose an inverse Fox-Li design framework to construct an on-demand holographic cavity (HoloCavity). By proactively tailoring the wavefront with cascaded pure-phase holograms and modulating diffractive loss during long-distance free-space propagation, we realize the simultaneous self-reproduction and suppression of multiple chiral modes without any auxiliary non-planar optical elements. Continuous mode evolution is visualized with the tomographic reconstruction of the intra-cavity complex amplitude, whereas corresponding various structured beams are directly generated in experiment using HoloCavity. The design scheme of HoloCavity can serve as a generalizable strategy in the solid-state, thin-disk, and micro-ring laser regimes, also with potential applications spanning optical communications, trapping, and microscopy.
While spiking neural networks (SNNs) have demonstrated remarkable efficiency in neuromorphic computing by emulating biological neuronal dynamics, their learning capabilities remain constrained by predominant focus on synaptic plasticity. This limitation overlooks critical neurobiological evidence showing that intrinsic neuronal plasticity, particularly dynamic threshold adaptation, plays an essential role in balancing neural responsiveness and signal fidelity. Inspired by two neurophysiological principles governing threshold regulation: 1) the inverse correlation between spiking thresholds and preceding depolarization rates, and 2) the proportional relationship between thresholds and average membrane potentials, we propose a Membrane Potential-Driven Adaptive Threshold Plasticity (MPD-ATP) framework. This biologically grounded mechanism establishes a dual-pathway control system where instantaneous depolarization rates and sustained membrane potential states jointly modulate neuronal thresholds through an adaptive scaling factor. The instantaneous depolarization rate dynamically lowers thresholds during strong input bursts, while the sustained average membrane potential adjusts the baseline threshold to stabilize firing during sparse input. This complementary regulation improves precision and robustness. Extensive evaluations on static (CIFAR-10/100) and neuromorphic (CIFAR10-DVS, DVSGesture) benchmarks demonstrate that MPD-ATP-enhanced networks achieve superior classification accuracy with enhanced noise robustness. Systematic ablation studies reveal that the coordinated interaction between depolarization-sensitive and membrane potential-proportional threshold adjustments is critical for preventing signal saturation in high-activity networks while mitigating under-activation in sparse-input scenarios.
We propose a compact LIBS system with micro-spectrometers and optical filters, achieving a reduction in size and cost for water heavy metal detection while enhancing sensitivity and portability.
