Laser Ablation Research Articles

Review of melt inclusions in lunar rocks: constraints on melt and mantle composition and magmatic processes

Abstract. Mineral-hosted melt inclusions provide a window into magmatic processes and pre-eruptive liquid compositions. Because melt inclusions are small (typically < 100 µm), the study of lunar melt inclusions is enabled by advancements of microbeam instrumental techniques. In the 1970s immediately following the Apollo and Luna missions, major and minor oxide concentrations of lunar melt inclusions were measured using electron microprobes. The data were used to understand magma evolution, and they revealed the immiscibility of two silicate liquids in the late stage of lunar magma evolution. More recently, the development of secondary ion mass spectrometry as well as laser ablation–inductively coupled plasma–mass spectrometry has enabled the measurement of key volatile elements and other trace elements in lunar melt inclusions, down to about the 0.1 ppm level. The applications of these instruments have ushered in a new wave of lunar melt inclusion studies. Recent advances have gone hand in hand with improved understanding of post-entrapment loss of volatiles. These studies have provided deep insights into pre-eruptive volatiles in lunar basalts, the abundance of volatiles in the lunar mantle, the isotopic ratios of some volatile elements, and the partition of trace elements between host olivine and melt inclusions. The recent studies of lunar melt inclusions have played a critical role in establishing a new paradigm of a fairly wet Moon with about 100 ppm H2O in the bulk silicate Moon (rather than a “bone-dry” Moon) and have been instrumental in developing an improved understanding of the origin and evolution of the Moon.

Experimental studies of hydrodynamics of the «plate» type canonical region with a modified surface

The possibility of using biomimetic approaches, in particular, the "lotus leaf" effect, expressed in the superhydrophobicity of streamlined surfaces, is considered. The results are presented of experimental studies of the influence produced by various modifications of the surface of the “plate” type canonical region on its hydraulic characteristics. The plates were streamlined in a hydrodynamic tray of rectangular cross-section. Copper plates with dimensions of 200x300x1 mm were studied. Three plates were considered, identical in geometry, but with different surface conditions — one in its original state; one with surfaces modified based on a surfactant; and one with surfaces treated by laser ablation (laser formation of a multimodal relief) with subsequent modification based on surfactants. In the course of experimental studies, the velocity distribution behind streamlined plates with different surface characteristics was obtained. Based on the nature of the velocity variations of the trail behind the streamlined plates, it is concluded that the amount of hydraulic resistance decreases due to surface modification. The weighted average velocity behind the streamlined plate increased by more than 4% for a plate with a combined modified surface compared to the original one. The process of a copper plate surface modifying using laser ablation, as well as the formation of additional surfactant molecular layers in order to achieve the maximum effect of superhydrophobicity is described. The most effective technological features of the laser ablation process are determined, such as the radiation power and frequency, the most preferred relief of modified surfaces and its geometric parameters. The most characteristic features of the influence of the surface roughness on the wetting angle (θ) are considered. With the OSA 20 complex, the wetting angles were determined for all the prepared plate samples. The research results prove the prospects of this surface modification technology for use in hydraulic machines.

Sulfide compositions of young Chang’e-5 basalts and implications for sulfur isotopes in lunar basalt sources

Sulfides are accessory phases in lunar rocks butare important forunderstanding lunar interior processes as well as impacts on the lunar surface.Whether or not the lunar mantle had achieved sulfide saturation during magma ocean evolution and displays homogeneous sulfur isotopes remains under debate. TheChang’e-5 (CE-5) mission returned young (2.0 Ga) basalts from a mare terrain in thenorthern Oceanus Procellarum.Here we study chemical and sulfur isotopic compositions (δ34SV-CDT) of sulfides from CE-5 basaltic fragments and combine them with δ34S of other young (3.1–3.0 Ga) lunar low-Ti basalt (NWA 10597 and NWA 4734) and gabbro meteorites (NWA 6950) to compare them with Apollo low-Ti and high-Ti mare basalts. The sulfides in basaltic fragments of CE-5 are troilites (FeS) with lowabundances ofNi, Co, and Cu(e.g., Ni < 0.04 wt% and Ni/Co < 0.3). Textures and chemical compositions indicate that most troilites arelate-stage crystallization products fromthe highly evolvedCE-5 basalts. Several troilites occur in the matrices of impactite clasts and are intergrown with Fe–Ni metal(12–36 wt% Ni, Ni/Co of 12–39). These troilites are distinct from the major population of troilites withnoticeably higher Ni abundances (mostly > 0.2 wt% with Ni/Co of 1–3) andreconcile with the addition of meteoritic materials into the impact melts.The δ34SV-CDTof large troilite grains (>10 μm) from the CE-5 basaltic fragments and lunar meteorites were obtained by high-precision, high-spatial-resolution femtosecond laser ablation MC-ICP-MS which achieved external uncertainty (0.65 ‰, 2SD at 8-μm laser spots) like nano-SIMS. Sulfur degassing during surficial effusive lava flow likely led to a slightdecrease inδ34S (by ∼ 1 ‰) for some basaltic fragments; however, such effects were limited to the scale of bulk rock samples, consistent with previous results. The mean δ34Sof troilites in CE-5 basaltic fragments (0.35 ± 0.25 ‰, 2SE, n = 45) is similar to those of ancient (3.8–3.1 Ga old) Apollo low-Ti and high-Ti mare basalts and the young gabbro cumulate NWA 6950 (0.56 ± 0.21 ‰, 2SE, n = 10). The paired NWA 10597 and NWA 4734 show consistent δ34S, lower than most values by ∼ 0.5 ‰. Current data thus indicate that most mantle sources of lunar basalts would be homogeneous for δ34S(0.6 ± 0.3 ‰) and minor regions may be different. The overall homogenous δ34S from different mantle sources with variably low sulfur contents supports sulfide-undersaturated accumulation of the lunar magma ocean, which was inherited from strong volatile loss and evaporative fractionation during the formation of the Moon.

Comprehensive study of the cold-temperature directed energy deposition: Multi-physics modelling and experimental validation

Currently almost all the directed energy deposition (DED) processes are performed under ideal lab conditions with the room temperature close to 20 °C. By contrast, the cold-temperature DED has potentially onsite use in cold environments, such as the winter in the Northern Hemisphere, where the ambient temperatures are often near or below freezing point temperature (0 °C). However, there is a lack of study on the cold-temperature DED process due to its unique temperature conditions. To fill this gap, the authors employed both multi-physics modelling and experimental approaches to study the DED process at cold temperature (CT) −3 °C, and compare to the room temperature (RT) 20 °C DED process. Stainless Steel 316L (SS316L) was selected as powder material. The multiple physics in the DED process involving laser heat source, local melting, rapid cooling, solidification, phase change, evaporation, and fluid-gas interactions were modeled using the computational fluid dynamics (CFD) – volume of fluid (VOF) approach. To validate the model, the DED experiments were conducted using a cryogenic DED platform in which the DED process was chilled to customized low temperatures. This high-fidelity model predicted accurate thermal results and deposit geometries for both the CT and RT DED cases. The results show that under sub-freezing conditions, the deposit size of the CT-DED is ∼62.1 % bigger than the RT-DED in the mean area throughout the length of the single-track thin wall. Furthermore, the CT-DED results show a steeper thermal gradient and at the same time a lower heat flux near the substrate. This high-fidelity modelling framework can be effectively expanded to study more cold-temperature additive manufacturing cases, like the Arctic exploration and in-Space manufacturing.

Fabrication and structural modification of graphene oxide-tetraethyl orthosilicate solution via liquid-phase pulsed laser ablation

Liquid-phase pulsed laser ablation (LP-PLA) is a physical deposition technique to fabricate micro- and nanoscale particles of polymer, glass, and ceramic materials. In this work, graphene oxide (GO) that was immersed in tetraethyl orthosilicate (TEOS) and ethanol was used to fabricate the graphene-silicone polymer using the LP-PLA technique. The GO-TEOS solution was ablated with different fluences of the laser. The ablated GO-TEOS solution was characterized by Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive x-ray, and ultraviolet-visible (UV-Vis) spectroscopy to study the graphene-silicone polymer properties. The FTIR result shows that the laser ablation has provided sufficient laser energy to create or break the chemical species of GO and TEOS compounds as observed on Si–O and C–O bonds. The Raman result shows the changes in the intensity in the D band, which suggests that the carbon atom of the GO has been functionalized with other compounds. Several large flakes were observed in the SEM images, representing the silicon polymer with the GO aggregation. The particle size in the range of 3–8 and 66–110 μm was formed due to the presence of uniformly sized nanoparticles of the GO-TEOS mixture and aggregation of the GO-TEOS nanoparticles into clusters. The zeta potential results indicated that the stability of the GO-TEOS mixture decreases after laser ablation. The UV-Vis result shows a broad absorption band with center at 492 and 532 nm with increasing absorbance at low fluence then saturated and decreased at maximum laser fluence. From the results above, several chemical interactions between GO and TEOS were observed, and the data suggested the laser fluence as the major source to cause both photothermal and photochemical reactions on the samples. In short, laser ablations provide sufficient energy to induce chemical bonding, which further allows structural modification of materials.

Plasmonic Nanocomposites of ZnO-Ag Produced by Laser Ablation and Their Photocatalytic Destruction of Rhodamine, Tetracycline and Phenol.

Hydrosphere pollution by organic pollutants of different nature (persistent dyes, phenols, herbicides, antibiotics, etc.) is one of the urgent ecological problems facing humankind these days. The task of water purification from such pollutants can be effectively solved with the help of modern photocatalytic technologies. This article is devoted to the study of photocatalytic properties of composite catalysts based on ZnO modified with plasmonic Ag nanoparticles. All materials were obtained by laser synthesis in liquid and differed by their silver content and preparation conditions, such as additional laser irradiation and/or annealing of produced powders. The prepared ZnO-Ag powders were investigated by electron microscopy, X-ray diffraction and UV-Vis spectroscopy. Photocatalytic tests were carried out with well- known test molecules in water (persistent dye rhodamine B, phenol and common antibiotic tetracycline) using LED light sources with wavelengths of 375 and 410 nm. The introduction of small concentrations (up to 1%) of plasmonic Ag nanoparticles is shown to increase the efficiency of the ZnO photocatalyst by expanding its spectral range. Both the preparation conditions and material composition were optimized to obtain composite photocatalysts with the highest efficiency. Finally, the operation mechanisms of the material with different distribution of silver are discussed.

Thermal stress coupling mechanism during nanosecond impulse delay for the synergistic study of continuous-nanosecond combined laser removal of the rubber layer on a concrete surface.

Based on the principle of laser ablation and elastic vibration effect, a model of continuous nanosecond combined laser removal of rubber marks on a concrete surface was established. The model can explain the evolution of temperature, stress, and removal depth on time and laser energy density during laser cleaning. The results show that the theoretical adsorption force between the rubber layer and the concrete base is approximately 3.88×10-9 N. The continuous laser cleaning threshold is 561.31J/c m 2. In the combined laser, the continuous laser is 534.41J/c m 2, and the nanosecond laser is 0.35J/c m 2. As the delay time between the 2ns laser beams increases, the maximum peak in the temperature curve gradually decreases. The optimal cleaning delay was obtained as Δ t=0.65S. The peak temperature at the characteristic position (0µm, 0µm) is 592.13K, which is lower than the vaporization temperature of the rubber layer. The thermal stress values generated at this characteristic position exceed the adsorption stress values, indicating that the elastic removal mechanism is the main removal mechanism at the junction between the rubber layer and the concrete substrate.

Advances in Diagnosis and Treatment of Basal Cell Carcinoma.

Basal cell carcinoma (BCC) is one among the most prevalent malignant neoplasms that has exhibited a notable surge in global incidence over recent decades. This slow-growing malignancy is typified by its localized invasiveness while demonstrating an exceedingly rare metastatic proclivity. It predominantly afflicts the sun-exposed skin of aging individuals, with a heightened predilection for the maxillofacial region. Scraping cytology offers numerous benefits, including the potential for an earlier diagnosis and the absence of scarring, as opposed to a biopsy. The cytodiagnosis of BCC proves to be straightforward with various techniques, making it highly advantageous in an outpatient environment as a swift diagnostic method when planning a surgical excision. Our study sought to scrutinize the clinicopathological facets of BCC within the maxillofacial region. We compared advanced cytological techniques for diagnosis, including scraping, scratching, and imprinting using Papanicolau and Diff-Quick stains. In addition, we evaluated the therapeutic effectiveness of diode lasers operating at wavelengths of 940nm and 980n. A retrospective analysis was undertaken, encompassing facial BCC lesions smaller than 2.5cm in diameter that underwent treatment through diode laser ablation between September 2021 and August 2023 at Ramadi Teaching Hospital and a private clinic in Ramadi City, Iraq. Among the cohort of 48 patients with BCC, a majority (58%) were 50 years of age or older, with a predominance of males (62%). The mean duration of lesion existence exceeded 4 months. The anatomical region most commonly involved was the middle 1/3 of the face, accounting for 34% of cases. Intriguingly, the therapeutic approach of diode laser ablation yielded exceptional esthetic and functional outcomes, which were consistently observed throughout the follow-up period post-healing. The occurrence of complications following diode laser ablation was relatively infrequent. This investigation revealed that cytological examination is easily conducted, eliminating the need for local anesthesia, saving time, being more cost-effective than a conventional biopsy, and delivering swift diagnoses. The process of smear-taking for cytology is well-tolerated, inflicting minimal trauma or discomfort on the patient. BCC predominantly afflicts elderly males and most frequently affects the middle third of the face. Notably, nodular BCC emerged as the prevailing histological subtype. The use of diode laser ablation exhibited a commendable track record, producing exemplary functional and esthetic outcomes over a 6-month follow-up period.

Removal mechanism on 4H–SiC single crystal by picosecond laser ablation-assisted chemical mechanical polishing (CMP)

The properties of the single-crystal 4H–SiC are complex and difficult to understand. Consequently, determining the effect of the surface and subsurface structures and composition changes of picosecond laser ablation (PLA) on the material removal mechanism during the CMP stage is challenging. In this study, we used PLA of 4H–SiC surfaces to investigate the mechanism underlying the effect of PLA-assisted CMP, which is considerably larger than the laser ablation threshold, on the removal of 4H–SiC to improve the material removal rate and surface quality of CMP. The TEM and contact angle detection results indicated that the reduction in the fracture strength and increase in the surface energy of high-power PLA contributed to the removal form and chemical action of CMP. Subsequent experimental results showed that the contact angle and hardness of the PLA-treated surfaces in the hydrophilic range were reduced by 45% and 48.6%, respectively. The material removal rate (MRR) of PLA-CMP (alumina slurry) at 45 min was 3.67 μm/h that was a 70% improved CMP removal relative to no picosecond laser ablation (NPLA). The mechanism of PLA-assisted CMP removal was revealed to be related to the plastic cutting of the abrasive and high pressure and temperature, leading to the softening-removal-softening cycle of the material. This study provides a new perspective on the ultraprecise and high-efficiency fabrication of high-quality single-crystal 4H–SiC.

Micro-distribution of arsenic in toenail clippings using laser ablation inductively coupled plasma mass spectrometry: implications for biomonitoring.

Toenails are a common monitoring tool for arsenic exposure, but the risk of external contamination of toenails has cast doubt on its usefulness. The main objective of this study is to investigate the micro-distribution of arsenic through the dorsoventral plane of nail clippings to understand endogenous vs exogenous sources. We used laser-ablation inductively coupled plasma mass spectrometry to measure arsenic through a dorsoventral cross-section of the nail plate collected from reference (N = 17) and exposed individuals (N = 35). Our main results showed (1) bulk toenail concentrations measured using ICP-MS in this study ranged from 0.54 to 4.35µg/g; (2) there was a double-hump pattern in arsenic concentrations, i.e., dorsal and ventral layers had higher arsenic than the inner layer; (3) the double-hump was more pronounced in the exposed group (ventral: 6.25μg/g; inner: 0.75μg/g; dorsal: 0.95μg/g) than the reference group (ventral: 0.58μg/g; inner: 0.15μg/g; dorsal: 0.29μg/g) on average; (4) the distribution was, in part, associated with different binding affinity of nail layers (i.e., ventral > dorsal > inner); (5) most individuals in the higher exposure group showed > 25% contamination in ventral and dorsal nail layers; and (6) there were no statistically significant correlations between LA-ICP-MS arsenic with either bulk toenail arsenic or urine arsenic from the same individuals. Our results on micro-distribution and binding affinity provide insight into the impact of external contamination on arsenic concentrations and show how LA-ICP-MS can access the protected inner nail layer to provide a more accurate result.

Mechanical Abrasion of Laser‐Machined Highly Hydrophobic Stainless Steel Surface Depending on Surface Topography

Stainless steel (SST) is an important material for a variety of applications including construction, food, and medical. Highly hydrophobic wetting properties enhance the surface properties of SST to support processes such as self‐cleaning . However, applications also require long‐term stability of such properties against chemical and mechanical influences from the environment or technical processes. Therefore, the reduction of highly hydrophobicity of chemically modified, laser‐textured SST surfaces is investigated in relation to abrasive wear using hierarchical structures, micro‐/nanotextured surface, and support structures that shield the highly hydrophobic pattern. Surface textures comprising ridges, grooves (size: 50–500 μm; depth: up to 100 μm), and a nanostructured grooves bottom are machined by infrared ultrashort pulse laser ablation into SST and are subsequently chemically modified by a self‐assembled monolayer of a fluorinated, phosphonic acid‐modified alkane. Abrasive wear tests of these surfaces show decreasing water contact angles with increasing wear of the modified surface of the support structures. However, there is good stability of the highly hydrophobic properties due to the protection of modified areas at the groove bottom. The proposed wetting model for such designed functionalized laser textures shows possibilities for further optimization of such robust highly hydrophobic surfaces and adaptation to specific applications.

Development of ZnO and Si semiconductor-based ultraviolet photodetectors enhanced by laser-ablated silver nanoparticles

The present study employs a cost-effective laser ablation technique in combination with the RF sputtering method to successfully synthesize silver nanoparticles encapsulated by zinc oxide on a silicon (Si) substrate. This synthesis approach aims to enhance the efficiency of photodetector devices while concurrently reducing material expenses, thereby promoting advancements in photodetector applications. The incorporation of various plasmonic nanoparticles (NPs) into the photodetector's architecture is demonstrated as a means to substantially improve the photoresponse of UV photodetectors. Three distinct samples, denoted as AgNPs/Si, AgNPs/ZnO/Si, and ZnO/AgNPs/Si, underwent comprehensive analysis and characterization of their morphological attributes, crystal structures, elemental composition, and optical properties. The UV photodetection efficacy of these samples was evaluated by subjecting them to 385 nm UV light at different bias voltages. The current-voltage (I-V) characteristics of the ZnO/AgNPs/Si photodetector revealed significantly enhanced conductivity in comparison to the AgNPs/Si and AgNPs/ZnO/Si counterparts. Remarkably, the ZnO/AgNPs/Si photodetector exhibited the highest responsivity value of 132 A/W, accompanied by quantum efficiency of 429.88, sensitivity of 31,400%, gain of 315, detectivity of 18 × 1010 Jones, and a noise equivalent power (NEP) of 0.556 × 10–13 W. These findings underscore the efficacy of our innovative broadband photodetector, highlighting its potential for practical implementation. This research offers valuable insights into the enhancement of photodetector performance and its applicability in real-world scenarios.

Development of matrix-specific standards for LA-ICP-MS zinc analysis in sand flathead (Platycephalus bassensis)

The use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to analyse soft tissues is limited because of the lack of suitable certified reference materials resulting in difficulties with calibration. In this study, several laboratory-prepared thin agarose sections were tested as matrix-specific standards. Our results showed 1 mm thin agarose sections were suitable as calibration standards for LA-ICP-MS Zn analyses in fish muscle, especially when the signal intensity of 66Zn was normalised to 13C. The thin agarose standard sections were used for LA-ICP-MS Zn analyses in the muscle of melanised and non-melanised sand flathead collected from a polluted estuary and assigned with different melanisation scores. Zn levels in melanised regions of fish muscle were determined to be significantly higher than non-melanised regions across all melanisation scores, though Zn levels in the melanised regions of muscle were not significantly different between sand flathead with different melanisation scores. In non-melanised regions of muscle from fish with melanisation and fish unaffected by melanisation, Zn levels were around baseline levels. Overall, this study has successfully developed matrix-specific standards for LA-ICP-MS analysis of soft tissues, thus allowing broader application of this analytical technique in future environmental pollution studies.

Detection of gold alloy elements by target-enhanced orthogonal triple-pulse laser-induced breakdown spectroscopy with improved sensitivity and minimal sample ablation

In order to realize more sensitive elemental analysis of precious samples under minimal sample ablation, target-enhanced orthogonal triple-pulse laser-induced breakdown spectroscopy (TEOTP-LIBS) was first developed. In this technique, a pre-ablation laser with adequate interpulse delay was introduced in reheating target-enhanced orthogonal double-pulse laser-induced breakdown spectroscopy (TEODP-LIBS); the pre-ablation laser was collinearly propagated with the reheating laser and both interacted with a solid KHCO3 target. 5–7 folds signal enhancement caused by the pre-ablation laser could be observed. A maximum of 256 folds total signal enhancement has been achieved for Au I 267.595 nm transition line while analyzing an 18 K gold sample, if comparing TEOTP-LIBS with single-pulse LIBS using equal pulse energy for the ablation laser. 5.4–11.3 folds total improvement on the signal-to-noise ratio could be observed. The mechanism of the signal enhancement contributed by the pre-ablation laser was also discussed. It was demonstrated that TEOTP-LIBS was able to provide a better solution on the sensitive elemental analysis of precious samples under minimal sample ablation than TEODP-LIBS.

Comparative efficacies and safeties of cylindrical interstitial laser ablation and radiofrequency ablation on swine pancreas.

Laser ablation (LA) has been evaluated for the minimally invasive thermal treatment of various cancers, but conventional unidirectional endoscopic ultrasound (EUS)-guided LA has limitations. Therefore, we developed a cylindrical laser diffuser to overcome the limitations of unidirectional EUS-guided LA. The purpose of this study was to compare the efficacies and safeties of EUS-guided LA using a novel cylindrical laser diffuser and radiofrequency ablation (RFA) in vivo in swine pancreas. EUS-guided RFA (15 W, 30s, 450J) and cylindrical interstitial LA (CILA) (5 W, 90s, 450J) were applied to normal pancreatic tissue in six anesthetized pigs (three per group). Laboratory tests were performed at baseline, immediately after ablation (day 0), and 2days after procedures (day 2). Two days after procedures, all pigs were sacrificed, and histopathological safety and efficacy assessments were performed. Technically, EUS-guided RFA and CILA were performed successfully in all cases. No major complications, including perforation or acute pancreatitis, occurred during the experiment in either group. All animals remained in excellent condition throughout the experimental period, and laboratory tests provided no evidence of a major complication. Average necrotic volumes in the RFA and CILA groups were 424.2 mm3 and 3747.4 mm3, respectively, and average necrotic volume was significantly larger in CILA group (p < 0.001). EUS-guided RFA and CILA had acceptable safety profiles in the normal swine pancreas model. Our findings indicate EUS-guided CILA has potential for the effective local treatment of pancreatic cancer as an alternative to EUS-guided RFA.

Experimental study on femtosecond laser ablation of 4H–SiC substrate

Silicon carbide (SiC) is an ideal substrate for manufacturing high-power electronic devices and microwave devices and has broad application prospects. The surface treatment of SiC wafers plays a critical role and faces challenges in the semiconductor industry. Among the multiple treatment methods, the laser-based method has gradually attracted the attention of scholars. Therefore, this research uses a femtosecond laser to ablate 4H–SiC sliced wafers and analyzes the influence of key parameters, such as laser pulse energy, defocus amount, repetition frequency, and scanning intervals, on the laser ablation depth, width, and surface morphology. Scanning electron microscopy and laser coherence-focused microscopy were used to characterize the laser ablation surface. When the defocus amount was 6 mm, the microgroove profile formed by the laser was U-shaped. The scanning interval parameters had to be optimized to obtain the optimized surface roughness. The results show that the optimized surface roughness (Sa ) was 0.267 μm, and brittle fracture areas such as microcracks and pits on the original surface were removed. Effective removal facilitates further material surface processing, which provides valuable insights for similar researchers and benefits for the semiconductor industry.

New possibilities of overcoming pharmacoresistance in epilepsy

Despite the presence of antiepileptic drugs with different mechanisms of action and application points, almost a third of patients still remain resistant to drug therapy. In such patients, the risk of physical and mental injuries, depression, premature death increases, and the quality and standard of living decreases.Objective. To study the mechanisms of formation of pharmacoresistance in epilepsy and to evaluate possible ways to overcome it based on the analysis of current scientific publications containing information on this topic.Results. The proposed pathophysiological mechanisms of the formation of drug resistance reflect the target hypothesis, the carrier hypothesis, pharmacokinetic theory and neural network theory. However, they are based on preclinical studies and do not have a comprehensive explanation for the appearance of this phenomenon. Surgical treatment remains the most studied and most commonly used approach. Both the usual resection of the epileptogenic part of the brain and new less crippling interventions are used: laser ablation and stereotactic radiosurgery. As an alternative, polytherapy schemes, invasive and non-invasive neurostimulation techniques, and diet therapy can be considered.Conclusions. Insensitivity to antiepileptic drugs remains a major problem in epileptology, and to overcome it, new methods are being sought and developed to influence the presumed pathogenetic targets of pharmacoresistant epileptogenesis. Vagus, deep, transcranial neurostimulation, stereotactic surgery, and laser ablation should be considered as new safe and potentially effective techniques.

Femtosecond laser ablation (fs-LA) XPS – A novel XPS depth profiling technique for thin films, coatings and multi-layered structures

Sputter depth profiling has been employed for XPS/AESdepth profilingsincethe late 1960s. However, for many materials, ion beam induced damage distorts the chemical state information and chemical composition, limiting the value of the analysis. A novelmethodology is presented in which XPS depth profiles are generated using a 160 fs pulse length, 1030 nm peak wavelength femtosecond laser in place of the traditional ion gun. Femtosecond laser ablation (fs-LA) XPS depth profiles are compared with argon monatomic and cluster ion beam depth profilesfor different classes of materials, including ceramics, semiconductors, polymers and metals. In all cases, the XPS spectra recorded following femtosecond laser ablation are fully representative of the original chemical composition and chemical state, with no ablation induced damage. The technique is also shown to be very versatile with ablation rates of <20 nm per pulse being achieved for thin films but profiles to depths of >30 μm are also realisable in practical time scales.fs-LA XPS depth profiling promises to be a very exciting new methodology for the XPS community, complementing sputter depth profiling but avoiding the chemical damage induced by ion beams and offering valuable new depth profiling capabilities.

Defining the Parameters for Endovenous Microwave Ablation to Achieve Equivalence With Endovenous Laser Ablation, Using the Porcine Liver Model.

Endovenous microwave ablation (EMWA) is an endovenous thermoablation (EVTA) system to ablate incompetent truncal veins. Early results suggest that EMWA uses more power than endovenous laser ablation (EVLA) to get the same results. We aimed to define the parameters for EMWA, which give the same tissue ablation as EVLA, using the validated porcine liver model. EVLA (1470nm 600micron radial fibre) treatments were performed at 6W, 8W and 10W, at pullback speeds of 6, 7, 8 and 9s/cm, giving Linear Endovenous Energy Densities (LEEDs) between 36 - 90J/cm. Each combination of power and pullback was repeated 5 times. We then used EMWA in the same model. Powers of 35-75W and pullback speeds of 4-9s/cm were used (LEEDs 140-675J/cm). Ablation tracts from both devices were analysed by 2 blinded observers, noting thermal spread and carbonisation. For each commonly used parameter for EVLA, we identified a range of parameters for EMWA that produced similar tissue ablation in the porcine liver model. To keep the pullback speeds within the usual range, powers of 35-75W were needed with EMWA, with mean EMWA LEEDs 3.9 - 5.8 times higher than EVLA LEEDs. We found the quicker the pullback speed, the higher the multiple of EMWA LEED we needed to get the same effect. We have identified parameters for EMWA that gave equivalent tissue ablation in the porcine liver model to commonly used parameters used for EVLA. These need to be validated clinically, but as the model used has already been validated against clinical outcome in endovenous thermal ablation, there is little reason to suspect that these results would not be valid. As the power during EMWA is higher than EVLA, EVMA LEEDs are approximately 4-6 times higher than EVLA LEEDs to achieve the same thermal effect on the tissues.

Predictors of fetal death, neonatal survival and neurological outcomes in severe twin-twin transfusion syndrome treated by laser ablation of placental vessels.

To identify predictors of outcomes in severe twin oligo-polyhydramnios sequence (TOPS) with or without twin anemia-polycythemia sequence (TAPS) and/or selective fetal growth restriction (SFGR) treated by laser ablation of placental vessels (LAPV). Analysis of cases treated from 2011 to 2022. Variables evaluated Prenatal predictors: stages of TOPS, presence of TAPS and/or SFGR; pre-LAPV fetal ultrasound parameters; peri-LAPV variables. Perinatal predictors: GA at birth; birthweight; Apgar scores; transfontanellar ultrasonography (TFUS). fetal death, neonatal survival, infant's neurodevelopment. Binary logistic regression analyses were performed to detect predictors of outcomes. 265 cases were included. Predictors of post-LAPV donor fetus' death were delta EFW (p:0.045) and absent/reverse end-diastolic flow in the umbilical artery (AREDF-UA) (p<0.001). The predictor of post-LAPV recipient fetus' death was hydrops (p:0.009). Predictors of neonatal survival were GA at birth and Apgar scores. Predictors of infant's neurodevelopment were TFUS and pre-LAPV middle cerebral artery Doppler (MCAD) for the donor twin; and pre-LAPV ductus venosus' flow and MCAD for the recipient twin. Prediction of fetal death, neonatal survival and infant's neurodevelopment is possible in cases of TOPS associated or not with SFGR and/or TAPS that were treated by LAPV.