Micro-Raman Study of Thermal Transformations of Sulfide and Oxysalt Minerals Based on the Heat Induced by Laser

The minerals in the hydrothermal and cold seep system form at different temperatures and show responses to the laser power to varying degrees. Here, we focus on the heat-induced by laser to study thermal transformations of the chalcopyrite, covellite, pyrite, barite, and aragonite based on Raman spectroscopy. Chalcopyrite mainly transforms into hematite, and covellite mainly transforms into chalcocite with the increase of laser power. Interestingly, comparing with the previous study, the pyrite can transform to the marcasite firstly, and form hematite finally. We also find that high-temperature opaque chalcopyrite is more likely to occur thermal transformations due to the smaller absolute energy difference (|ΔE1|) based on the frontier orbital theory. In contrast, the oxysalt minerals won’t transform into new components under high laser power. However, the structure of the barite has been destroyed by the high laser power, while the more transparent aragonite is not affected by the high laser power due to the laser penetrates through the transparent aragonite crystal and causes little heat absorption. Finally, we established the minimum laser power densities for thermal transformations of these minerals formed under different environments. The above study provides a simple way to study the thermal transformations of minerals by the local heat-induced by laser and also enlightens us to identify the minerals phases precisely.

Preoperative Magnetic Resonance Imaging Based Predictive Modeling of Brain Tumor Laser Ablation

INTRODUCTION Laser interstitial thermal therapy (LITT) yields precise lesions under magnetic resonance imaging (MRI) thermometry guidance and is revolutionizing brain tumor management. However, one limitation is the inability to preoperatively predict how tumors will respond to thermal energy. Our study assessed whether preoperative variables correlated with intraoperative LITT ablation dynamics were capable of predicting how ablations progressed. METHODS Pixels indicating irreversible damage were quantified as a function of time for 101 brain tumor patients treated with LITT. Ablation dynamics were determined using pixel counts modeled with first-order dynamics and related to independent preoperative variables using stepwise regression. The resulting models were evaluated for predictive accuracy using leave-one-out cross-validation analysis. RESULTS Total pixels ablated is larger for LITT performed at a high laser power and for a long duration and for lesions with a low T1 GAD signal. The rate of pixel increase is elevated with high laser power and for lesions with a low T2 signal and prior radiotherapy. Pixel counts are well modeled with first-order dynamics. Scale factor (C) is positively related to perfusion, laser power, and T2 signal and negatively related to T1 signal. Time constant (t) is positively related to T2 signal and perfusion. Tshift is negatively related to T2 signal and laser power. Pathology did not impact ablation dynamics, although the presence of radiation necrosis resulted in faster and larger ablations. A predictive model based on the independent variables accounts for 77% of the variance in ablation pixel counts. CONCLUSION Preoperative MRI features correlate with brain tumor LITT ablation dynamics. Predictive models based on these features may eventually be used to guide the planning and delivery of LITT.

PENGARUH JARAK LASER HEAD TERHADAP DIAMETER SPOT PADA PEMOTONGAN POLYMETHYL METHACRYLATE MENGGUNAKAN MESIN LASER CUTTING

Laser cutting is one of the processes used as an alternative to conventional machinery that has goodcutting qualities and minimizes product damage. The workings of laser cutting is to direct the output of high laser power on the material to be cut, the material then melts, burns, evaporates by gas, and produces edges with a good quality surface. This study aims to determine the effect of laser head distance from the laser cutting machine on the spot diameter produced on the polymethyl methacrylate (PMMA) material. This study used a laser machine with 60 watts of power and variation of laser head distance with an interval of 1 mm at a distance of 1-28 mm. Spot diameter value was gained measurement from using stereo zoom microscope with 30 X magnification and mapping. The result shows that the spot diameter was 0,229 - 0,990 mm. The factors that affect the value of spot diameter is the laser power used and laser head distance from the material.