Search Results (316)

The Pennes bioheat equation is the most widely used model for describing heat transfer in living tissue during thermal exposure. It is derived from the classical Fourier law of heat conduction and assumes energy exchange between blood vessels and surrounding tissues. The literature presents various numerical methods for solving the bioheat equation, with exact solutions developed for different boundary conditions and geometries. However, analytical models based on this framework are rarely reported. This study aims to develop an analytical three-dimensional model using MATHEMATICA software, with subsequent mathematical validation performed through COMSOL simulations, to characterize heat transfer in biological tissues induced by laser irradiation under various therapeutic conditions. The objective is to refine the conventional bioheat equation by introducing three key improvements: (a) incorporating a non-Fourier framework for the Pennes equation, thereby accounting for the relaxation time in thermal response; (b) integrating Dirac functions and the telegraph equation into the bioheat model to simulate localized point heating of diseased tissue; and (c) deriving a closed-form analytical solution for the Pennes equation in both its classical (Fourier-based) and improved (non-Fourier-based) formulations. This paper investigates the nuanced relationship between the relaxation time parameter in the telegraph equation and the thermal relaxation time employed in the bioheat transfer equation. Considering all these aspects, the optimal thermal relaxation time determined for these simulations was 1.16 s, while the investigated thermal exposure time ranged from 0.01 s to 120 s. This study introduces a generalized version of the model, providing a more realistic representation of heat exchange between biological tissue and blood flow by accounting for non-uniform temperature distribution. It is important to note that a reasonable agreement was observed between the two modeling approaches: analytical (MATHEMATICA) and numerical (COMSOL) simulations. As a result, this research paves the way for advancements in laser-based medical treatments and thermal therapies, ultimately contributing to more optimized therapeutic outcomes. Full article

This study explores the optical properties of a close-packed monolayer composed of core/shell-alloyed CdSeS/ZnS quantum dots (QDs) of two different sizes and compositions. The monolayers were self-assembled in a stacked configuration at the water/air interface using Langmuir–Blodgett (LB) techniques. Under continuous 532 nm laser illumination on the red absorption edge of the blue-emitting smaller QDs (QD450), the red-emitting larger QDs (QD645) exhibited oscillatory temporal dynamics in their photoluminescence (PL), characterized by a pronounced blueshift in the emission peak wavelength and an abrupt decrease in peak intensity. Conversely, excitation by a 405 nm laser on the blue absorption edge induced a drastic redshift in the emission wavelength over time. These significant shifts in emission spectra are attributed to photon- and anisotropic-strain-assisted interlayer atom transfer. The findings provide new insights into strain-driven atomic rearrangements and their impact on the photophysical behavior of QD systems. Full article

In ecotoxicological risk assessment, current methods for measuring the transfer and bioavailability of organic pollutants like polycyclic aromatic hydrocarbons (PAHs) in bioindicators are often destructive and environmentally unfriendly. These limitations are especially problematic when only small amounts of biological material are available. Here, we present a novel, high-throughput method combining laser-induced UV fluorescence spectroscopy (UV-LIF) and solid-phase spectroscopy (SPS) for rapid, in situ quantification of PAHs in land snails—a key bioindicator species. Using dual excitation wavelengths (266 nm and 355 nm), our method reliably detected pyrene and fluoranthene in snails exposed to varying concentrations, demonstrating clear dose-responses and inter-individual differences in bioaccumulation. The analysis time per sample was under four minutes. This approach allows simultaneous measurement of internal contaminant levels and health biomarkers in individual organisms and aligns with green chemistry principles. These findings establish a new, scalable tool for routine assessment of PAH transfer and bioavailability in diverse ecosystems. Full article

The motivation of this work is to enable the use of piezoelectric micromachined ultrasonic transducer (PMUT)-based implants within the human body for biomedical applications, particularly for power and data transfer for implanted medical devices. To protect surrounding tissue and ensure PMUT functionality over time, biocompatible and hermetic encapsulation is essential. This study investigates the impact of Parylene F-VT4 layers of various thicknesses as well as the effect of multilayer stacks of Parylene F-VT4 combined with atomic layer-deposited nanolayers of Al₂O₃ and HfO₂ on the mechanical and acoustic properties of PMUTs. PMUTs with various diameters (40 µm, 60 µm, and 80 µm) are fabricated and tested both as stand-alone devices and as arrays. The mechanical behavior of single stand-alone PMUT devices is characterized in air and in water using laser Doppler vibrometry (LDV), while the acoustic output of arrays is evaluated by pressure measurements in water. Experimental results reveal a non-monotonic change in resonance frequency as a function of increasing encapsulation thickness due to the competing effects of added mass and increased stiffness. The performance of PMUT arrays is clearly influenced by the encapsulation. For certain array designs, the encapsulation significantly improved the arrays’ pressure output, a change that is attributed to the change in the acoustic wavelength and inter-element coupling. These findings highlight the impact of encapsulation in modifying and potentially enhancing PMUT performance. Full article

In this work, we address the task of monitoring Powder Bed Fusion–Laser Beam processes for metal powders (PBF-LB/M). Two main contributions with practical merit are presented. First, we consider the comparison between a large deep neural network (VGG-19) and a small model consisting of, among others, four convolutional layers. Our study shows that the small model can compete favorably with the big model, which takes advantage of transfer learning techniques. Secondly, we present a filtering method using a semantic segmentation approach to preselect a region for the classification algorithm. The region is selected based on post-exposure images, and preselection can be easily adopted for any machine independently of the software used for the translation of process input files. To consider the task, a master dataset with over 260,000 samples was prepared, and a detailed process of preparing the training datasets was described. The study demonstrates that the classification time can be reduced by a factor of 4.51 while still maintaining the model’s necessary performance to detect errors in a PBF-LB process. Full article

This study systematically investigates for the first time the effects of dual-site co-cultivation on spectral characteristics and trace element enrichment in marine-cultured Akoya pearls from Beihai, China. Akoya pearls were cultured over a one-year period, with the final 40-day stage designated as the terminal phase. During this period, two experimental groups of pearl oysters were established: Group Y remained in Beihai for continued local cultivation and harvest, while Group B was transferred to Weihai, Shandong Province, for terminal-stage farming under different thermal conditions. A series of comparative analyses were performed using Fourier-transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, Raman spectroscopy, X-ray fluorescence (XRF), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The FTIR results revealed distinct differences between the two groups in the distribution of amide and polysaccharide functional groups, particularly around 1643 cm⁻¹ and 1100 cm⁻¹. The UV-Vis spectra of Group B displayed characteristic absorption bands at 430 nm and 460 nm, associated with the organic matrix of the nacre. Raman spectroscopy further indicated a higher abundance of organic-related vibrational features in Group B. Additionally, both XRF and LA-ICP-MS analyses consistently showed significant differences in the concentrations and distributions of trace elements, particularly copper (Cu), cobalt (Co), and zinc (Zn). The findings demonstrate that the dual-site co-cultivation mode significantly impacts both the organic composition and trace element enrichment patterns in seawater Akoya pearls. This research provides valuable references for optimizing environmental parameters in pearl cultivation processes. Full article

This study introduces an innovative analytical solution to the time-fractional Cattaneo heat conduction equation, which models photothermal transport in metallic thin films subjected to short laser pulse irradiation. The model integrates the Caputo fractional derivative of order 0 < p ≤ 1, addressing non-Fourier heat conduction characterized by finite wave speed and memory effects. The equation is nondimensionalized through suitable scaling, incorporating essential elements such as a newly specified laser absorption coefficient and uniform initial and boundary conditions. A hybrid approach utilizing the finite Fourier cosine transform (FFCT) in spatial dimensions and the Laplace transform in temporal dimensions produces a closed-form solution, which is analytically inverted using the two-parameter Mittag–Leffler function. This function inherently emerges from fractional-order systems and generalizes traditional exponential relaxation, providing enhanced understanding of anomalous thermal dynamics. The resultant temperature distribution reflects the spatiotemporal progression of heat from a spatially Gaussian and temporally pulsed laser source. Parametric research indicates that elevating the fractional order and relaxation time amplifies temporal damping and diminishes thermal wave velocity. Dynamic profiles demonstrate the responsiveness of heat transfer to thermal and optical variables. The innovation resides in the meticulous analytical formulation utilizing a realistic laser source, the clear significance of the absorption parameter that enhances the temperature amplitude, the incorporation of the Mittag–Leffler function, and a comprehensive investigation of fractional photothermal effects in metallic nano-systems. This method offers a comprehensive framework for examining intricate thermal dynamics that exceed experimental capabilities, pertinent to ultrafast laser processing and nanoscale heat transfer. Full article

The laser pulse detection probability of a scanning direct time-of-flight light detection and ranging (LiDAR) measurement is evaluated based on the optical signal distribution on a multipixel single photon avalanche diode (SPAD) array. These detectors intrinsically suffer from dead-times after the successful detection of a single photon and, thus, allow only for limited counting statistics when multiple returning laser photons are imaged on a single pixel. By blurring the imaged laser spot, the transition from single-pixel statistics with high signal intensity to multipixel statistics with less signal intensity is examined. Specifically, a comparison is made between the boundary cases in which (i) the returning LiDAR signal is focused through optics onto a single pixel and (ii) the detection is performed without lenses using all available pixels on the sensor matrix. The omission of imaging optics reduces the overall system size and minimizes optical transfer losses, which is crucial given the limited laser emission power due to safety standards. The investigation relies on a photon rate model for interfering (background) and signal light, applied to a simulated first-photon sensor architecture. For single-shot scenarios that reflect the optimal use of the time budget in scanning LiDAR systems, the lens-less and blurred approaches can achieve comparable or even superior results to the focusing system. This highlights the potential of fully solid-state scanning LiDAR systems utilizing optical phase arrays or multidirectional laser chips. Full article

Forests grow under dynamic conditions influenced by vegetation structure and environmental factors. However, empirical models to enhance growing stock volume GSV) estimation are commonly established based on structural information from airborne laser scanning (ALS) data, raising important questions regarding the models’ performance across time (temporal transferability). This study presents the integration of ALS and microclimate and site-specific data to assess the temporal transferability of GSV models at the plot level in a mixed forest located in Milicz, Poland, between 2007 (t₁) and 2015 (t₂). We compared random forest (RF), multiple linear regression (MLR), and generalized additive models (GAMs) across three modelling scenarios, ALS + site type + climate (sa), ALS only (sb), and ALS + site type (sc), and also performed internal and external validation to assess temporal transferability. Among the three modelling approaches, GAMs outperformed the MLR and RF models in internal validation, improving the R² by 6%–8% and reducing the rRMSE by 6%–12%. We found that climate was significant in GSV prediction when integrated with ALS and site conditions, with a permutation test (p ≤ 0.023) based on the rRMSE confirming climate significance. The direct contribution of climate to model performance was marginal on a broad scale. However, its influence on GSV and temporal transferability seem stronger in homogenous sites. In general, RF was the most stable in both the forward (t₁→t₂) and backward (t₂→t₁) directions in the sa scenario unlike the GAM, which was more stable in the backward direction. This study provides a framework for assessing the reliability of GSV models and addresses a critical gap in forest monitoring. Full article

To enhance the performance of state-of-the-art lithium-ion batteries, high-capacity silicon is increasingly introduced as active material for anodes. Furthermore, advanced batteries with new electrode architectures—so-called 3D architectures—can provide significantly enhanced electrochemical performance compared to state-of-the-art batteries. To facilitate and speed up the architectural development, the laser-induced forward transfer (LIFT) process was applied as a digital additive manufacturing method. As polyvinylidene fluoride (PVDF), the binder commonly used in the LIFT process, is not a suitable binder for silicon-containing electrodes due to its weak binding forces, polyacrylic acid (PAA) was introduced as a binder for use in printable electrode pastes. Since water as a solvent in such pastes evaporates quickly and the corresponding printing time would be too short, glycerol was added to the solvent mixture in different amounts. The silicon in the printed electrodes reaches a specific capacity of more than 3000 mAh$·{\mathrm{g}}^{–1}$ for most of the printed anodes. To further improve the electrochemical performance of the printed electrodes, as well as the rheology of the slurries, two different conductive additives with different particle sizes were used. Full article

High-order harmonic generation provides a powerful tool for probing ultrafast chemical dynamics, such as electron transfer, bond breaking, and molecular structural changes, with attosecond temporal resolution. The strong laser fields used in HHG can also directly influence chemical reaction pathways and rates, enabling coherent control of reaction selectivity. However, enhancing the efficiency of harmonic emission remains a critical challenge in ultrafast science. In this study, we investigate the effects of molecular size and orientation on HHG efficiency using time-dependent density functional theory simulations. By analyzing the linear molecules ${\mathrm{C}}_{18}{\mathrm{H}}_2$, ${\mathrm{C}}_2{\mathrm{H}}_2$, and C₁₀H₂ under linearly polarized laser fields, we demonstrate that larger molecular sizes significantly enhance harmonic emission intensity. Our results reveal that ${\mathrm{C}}_{18}{\mathrm{H}}_2$, with its larger spatial dimensions, exhibits substantially higher harmonic intensity compared to smaller molecules like ${\mathrm{C}}_2{\mathrm{H}}_2$. This enhancement is further supported by examining charge redistribution and bond length changes during the HHG process. Additionally, we validate our findings with C₁₀H₂, a molecule of intermediate size, confirming the correlation between molecular size and harmonic efficiency. Full article

This paper proposes two compact, efficient, and lightweight heat exchangers based on triply periodic minimal surfaces (TPMSs). Designed in an annular configuration, the heat exchangers meet the requirements of micro gas turbines for compactness. Two prototypes of Diamond and Gyroid modular TPMS heat exchangers were fabricated using selective laser melting (SLM) with stainless steel. The flow and heat transfer experimental results indicate that, within a Reynolds number range of 200 to 800, the effectiveness of both heat exchangers remained above 0.62, and the average Nusselt numbers of the Diamond and Gyroid structures reached 3.60 and 4.06 times that of the printed circuit heat exchanger (PCHE), respectively. Although both heat exchangers exhibited relatively high friction factors, their overall performance surpassed that of conventional heat exchangers. Additionally, performance comparisons with existing TPMS heat exchangers revealed that smaller lattice sizes contribute to improved volume-based power density, although they result in increased pressure loss. Simulation results indicated that the “merge–split” effect present in both structures enhances heat transfer between the fluid and the wall. Furthermore, the complex channels of the TPMS structures ensure that the fluid maintains strong turbulence intensity throughout the heat exchanger. This study demonstrates that stainless steel TPMS structures can serve as excellent candidates for applications in micro gas turbines. Full article

In the rapidly advancing era of intelligent technology, flexible strain sensors are emerging as a key component in wearable electronics. Laser-induced graphene (LIG) stands out as a promising fabrication method due to its rapid processing, environmental sustainability, low cost, and superior physicochemical properties. However, the stretchability and conformability of LIG are often limited by the substrate material, hindering its application in scenarios requiring high deformation. To address this issue, we propose a high-performance flexible and stretchable strain sensor fabricated by generating graphene on a polyimide (PI) substrate using laser induction and subsequently transferred onto a polydimethylsiloxane (PDMS). The resultant sensor demonstrates an ultra-low detection limit (0.1%), a rapid response time (150 ms), a wide strain range (40%), and retains stable performance after 1000 stretching cycles. Notably, this sensor has been successfully applied to the real-time monitoring of civil aviation test pilots during flight for the first time, enabling the accurate detection of physiological signals such as pulse, hand movements, and blink frequency. This study introduces a unique and innovative solution for the real-time health monitoring of civil aviation test pilots, with significant implications for enhancing flight safety. Full article

The present paper deals with the study of the fluence rate over both healthy and tumor tissues in the presence of focal laser ablation (FLA). We propose new analytical solutions for a coupled partial differential equation (PDE) system, which includes the transport equation modeling of light penetration into biological tissue, the bioheat equation modeling the heat transfer, and its respective damage. The present work could be the first step toward knowledge of the mathematical framework for biothermophysical problems, as well as the main key to simplify the numerical calculations due to its zero cost. We derive exact solutions and simulate results from them. We discuss the potential physical contributions and present respective conclusions about the following: (1) the validity of the diffusion approximation of the radiative transfer equation; (2) the local behavior of the source of scattered photons; (3) the unsteady state of the fluence rate; and (4) the boundedness of the critical time of the thermal damage to the cancerous tissue. We also discuss some controversial and diverging hypotheses. Full article

Laser weeding is an innovative, environmentally friendly method for intra-row weed control. However, its effectiveness depends on accurate weed identification and an efficient control system. This study developed an intra-row laser weeding system for lettuce, combining deep learning and laser technology. The system consisted of three modules: perception, decision, and execution. It used an MV-UB130GM industrial camera to capture images, which are transmitted to a computer for processing. A target detection algorithm located weeds by calculating the central coordinates of anchor frames. The multi-task learning (MTL) decision system then planned the weeding path, generated instructions, and controlled the laser for weeding tasks. The YOLOv8 model, enhanced with an attention mechanism, formed the foundation of target detection. To compress the model, a class knowledge distillation method based on transfer learning was applied, resulting in a lightweight YOLOv8s-CBAM model with a mAP@0.5 of 98.9% and a size of just 6.2 MB. A simulation prototype of the laser weeding system was built, and initial experiments demonstrated that a 450 nm blue semiconductor laser effectively kills weeds in 1 s with 30 W output. Experimental results showed that the system detected and eliminated 100% of weeds in low-density scenes and achieved an 88.9% detection rate in high-density areas. The real-time detection speed reached 21.27 FPS, and the overall weeding success rate was 76.9%. This study provides valuable insights for the development of intra-row weed control systems based on laser technology, contributing to the advancement of precision agriculture. Full article