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The hypersonic airflow around a blunt cone coupled with carbonaceous surface ablation is numerically simulated to analyze the impacts of ablation on aerodynamic heating. Ablative reactions, including oxidation, nitridation, and sublimation, are found to affect aerodynamic heating mainly through the surface thermal effect (STE) and the gas-phase chemistry thermal effect (GCTE). Specifically, the sublimation reactions produce significant STE and GCTE. The STE of the sublimation reactions is not always endothermic. Downstream along the cone surface, the condensation of gas-phase C atoms on the wall leads to heat release. The GCTE is exothermic and increases the boundary layer temperature. The oxidation reaction generates weak GCTE but powerful STE, which is exothermic overall. On the contrary, nitridation reaction only leads to appreciable GCTE, characterized by releasing heat. The STE of nitridation is quite small and can be neglected. Oxidation and nitridation reactions often dominate the downstream region of the cone. In addition, in the head region where the ablation reactions are intense, ablation processes could generate considerable diffusive heat flux, increasing the total incident heat flux. Simultaneously, mass ejection can carry away much heat from the surface. [ABSTRACT FROM AUTHOR]

Human desire to explore Mars has persisted throughout history, and especially, it is required to achieve precise and safe landings on the Martian surface. The atmospheric entry phase plays a crucial role in ensuring mission success, and active research on entry guidance methods continues. This paper presents a comparative study between the two primary types of entry guidance methods: (1) path planning-tracking and (2) predictor–corrector methods by applying them to solve two distinct Mars atmospheric entry guidance problems: (a) robotic entry and (b) human entry missions. Optimization approaches are adopted for the path planning-tracking method. After generating an optimal reference trajectory based on a mission concept-defined cost function, the receding horizon control method is employed to minimize tracking errors. In the predictor–corrector method, two parameterized entry guidance approaches are explored and analyzed. A well-known numerical predictor–corrector method that utilizes a parameterized bank angle profile for entry trajectory generation is tested to demonstrate its robustness against random dispersions. On the other hand, another predictor–corrector type guidance method that assumes a polynomial shape to shape an altitude profile over range-to-go is adopted to show its range control capability. Numerical simulations reveal the pros and cons of each type of entry guidance method, and a suitable guidance method for each Mars entry mission is identified depending on the mission concept and requirements. The analysis results provide future work. • A comparative study between path planning-tracking and predictor-corrector guidance methods. • Mars atmospheric entry problem for robotic and human landing missions. • Optimization approaches for reference trajectory generation and path tracking. • Numerical predictor-corrector based on parameterized bank angle and altitude profiles. [ABSTRACT FROM AUTHOR]

With a gradual increase in breast cancer incidence and mortality rates and an urgent need to improve patient prognosis and cosmetology, magnetic resonance imaging (MRI)-guided radiofrequency ablation (RFA) therapy has attracted wide attention as a new treatment method for breast cancer. MRI-RFA results in a higher complete ablation rate and extremely low recurrence and complication rates. Thus, it may be used as an independent treatment for breast cancer or adjuvant to breast-conserving surgery to reduce the extent of breast resection. Furthermore, with MRI guidance, accurate control of RFA can be achieved, and breast cancer treatment can enter a new stage of minimally invasive, safe, and comprehensive therapy. With progress in MR thermometry technology, the applications of MRI are expected to broaden. [ABSTRACT FROM AUTHOR]

This study investigates the ablation of internal insulation induced by the deposition of an alumina film with different lateral film speeds. A sub-scale test solid rocket motor (SRM) was designed in an impinging jet configuration to form an alumina film on the sample and to encourage the lateral movement of the film by a high-speed wall jet. Fifteen static fire tests of the test SRM were conducted with six different jet velocities (Vjet = 100 m/s, 150 m/s, 200 m/s, 268 m/s, 330 m/s, and 450 m/s) that indirectly affected the velocity of the wall jet and the deposition rate of alumina droplets. The ablation velocity was deduced from the difference in the sample thickness after a test using a coordinate measuring machine. The droplet deposition mass flux and wall jet velocity were obtained via two-phase flow simulation with the same jet velocity and effective pressure. As a result, the characteristics of alumina-induced ablation and the changes in ablation with jet velocities were obtained. The area within 0.8 × jet diameter was focused upon, where the ratio of ablation velocity to incoming alumina mass was constant for each jet velocity, and showed a similarity in jet structure. When the ablation velocity was increased from 2.05 to 9.98 mm/s with increasing jet velocity, the ratio of the ablation velocity and alumina mass flux decreased from 1.07×10−4 to 0.49×10−4 m3/kg as Al2O3–C reactions became less efficient with a reduced residence time of the film. Because the decrease in residence time by the wall jet is more pronounced for slow reactions involved in Al2O3–C reactions, fast reactions in Al2O3–C reactions are less affected and result in a convergence of the volumetric rate of ablation per unit mass of alumina. [ABSTRACT FROM AUTHOR]

Inherent defect of easy oxidation limited further application of carbon fiber/phenolic resin composites in hostile environments. Herein, a combined strategy of matrix modification and fiber coating was proposed to fabricate a novel ceramizable composite containing Al-coated carbon fibers and Ti 3 SiC 2 toward thermal protection materials (TPM), which offered a promising solution to challenge facing long-term thermal protection and load-bearing subject to severe oxidation corrosion and ablation in hypersonic vehicle applications. Oxidation resistance, mechanical strength evolution, phase evolution, microstructure evolution and mechanical strength failure mechanism at elevated temperatures were studied based on thermogravimetric analysis, static ablation test, mechanical test, X-ray diffraction analysis, and scanning electron microscopy coupled with energy dispersive X-ray analysis. The resulting composites exhibited outstanding oxidation resistance, with residue yield at 1600 °C and flexural strength at 1400 °C as high as 87.7% and 31.7 MPa, respectively. It was found that dense multiphase ceramics formed by reactions between Ti 3 SiC 2 , O 2 , pyrolytic carbon (PyC) and N 2 , acted as oxygen barriers and self-healing agents during static ablation. Besides, the resulting composites exhibited satisfactory ablation resistance and the linear ablation rate was as low as 0.00853 mm/s. Furthermore, ablation mechanisms were revealed based on phase identification, microstructure characterization and thermodynamic calculation analysis. It was revealed that multiphase ceramics composed of PyC, Al coatings, Ti 3 SiC 2 , TiC, Al 2 OC and AlB 2 contributed great to the ablation resistance during oxyacetylene ablation. [Display omitted] • A combined strategy of matrix modification and fiber coating was proposed to prepare a novel ceramizable composite containing boron phenolic resin, Al-coated carbon fibers and Ti 3 SiC 2. • The resulting composites exhibited outstanding oxidation resistance, with the residue yield at 1600 °C and flexural strength at 1400 °C as high as 87.7% and 31.7 MPa, respectively, and satisfactory ablation resistance, with the linear ablation rate as low as 0.00853 mm/s. • Readily oxidized pyrolytic carbon was fixed by a carbothermal reduction-nitridation reaction with TiO 2 and N 2 to yield refractory TiC 0.7 N 0.3 during static ablation. • Multiphase ceramics composed of PyC, Al coatings, Ti 3 SiC 2 , TiC, Al 2 OC and AlB 2 contributed great to the ablation resistance during oxyacetylene ablation. [ABSTRACT FROM AUTHOR]

Irreversible electroporation (IRE) is a recent and minimally invasive method of partial prostate ablation. However, knowledge of the essential landmarks of prostate anatomy is crucial to achieving safe and effective partial ablation by IRE. High-quality imaging of the prostate is essential before the procedure. The individual morphological pattern of the prostate must be taken into account and detailed mapping with measurement of the lesion is necessary to determine optimal needle placement. The entire tumour volume must be covered while ensuring the safety of critical anatomical structures such as the rectum, urethra, nerve bundles and sphincter muscle. [ABSTRACT FROM AUTHOR]

For the problem of power generation turbine blade ablation in hypersonic vehicles, hydrocarbon fuel carried by the vehicle is used to cool the turbine blades. In order to fully utilize the cooling capacity of hydrocarbon fuel, the structure of the cooling channels needs to be optimized. In this study, a variable clearance hydrocarbon fuel cooling channel is applied for the first time to the rotating turbine blades of a hypersonic vehicle to enhance the heat transfer ability of hydrocarbon fuel. The effect of clearance size on the heat transfer performance of hydrocarbon fuel under rotating conditions is investigated. The accuracy of the calculations is verified by comparison with experimental data. The results of the study show that the heat transfer performance can be significantly improved by changing the clearance of the turning section. The clearance size 2.5 D channel has the highest thermal performance with a maximum improvement of 1.8 times. The law of change of thermal performance is affected by crossing the critical temperature point, as it is different before and after the crossing. Thermal performance changes from decreasing then increasing to increasing then decreasing as the clearance size increases for high rotation speed conditions as the temperature of the entrance straddles the critical temperature. The Nusselt number first increases and then decreases for all channels with different clearance sizes with an increasing rotational speed. The friction factor changes from first increasing and then decreasing to decreasing and then increasing as the clearance size increases for high rotation speed conditions as the temperature of the entrance straddles the critical temperature. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ordnance Equipment Engineering is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Considerable advancements in nonfluoroscopic localization techniques, including substantial improvements in electroanatomic mapping (EAM) systems have been reported over the last two decades. Combining the use of a navigation software and a mapping catheter, EAM has been shown to increase the success rate for complex procedures by recording electrical activation within the myocardium to determine the origin of an arrythmia, map cardiac chamber geometry in three dimensions, delineate areas of anatomic interest, and facilitate catheter positioning and manipulation. Multielectrode catheters have greatly improved the accuracy of EAM with high density maps identifying critical channels in dense substrates for better delivery of ablation therapy. Recently, the OCTARAY Mapping Catheter (OCT), a novel catheter with eight splines and 48 mapping electrodes, was introduced to allow higher number of bipolar electrograms recording at each beat with an overall higher mapping density. In this review, we discuss the basic structure and functionality of OCT and compare its mapping ability and resolution with other commercially mapping catheters currently used in electrophysiology laboratories. [ABSTRACT FROM AUTHOR]

Uncontrolled atmospheric entry of meteors, satellites, and spacecraft components often leads to their partial or complete demise. In this destructive process, driven by hypersonic ablation, reentry objects fragment, interact, and alter each other's aerothermal environment. The effect of these interactions on the heat transfer to the fragments has not been investigated, despite the heat transfer's importance in hypersonic ablation and reentry demise. This study focuses on the numerical investigation of heat transfer to proximal circular cylinders in a thermochemically frozen flow and in two dimensions. First, binary body configurations at Mach numbers 2, 4, and 8 revealed that the heat load and peak heat transfer can be augmented for either or both proximal bodies by +20% to −90% of an isolated body. Second, different clusters of five proximal bodies showed that the heat load to any given body can range from +40% to −90% of an isolated body. Moreover, the average heat load in a cluster is found to vary between +20% and −60% of an isolated body. Intuitively, clusters which are thin in the direction perpendicular to free-stream velocity and long in the direction parallel to the free-stream velocity have their cluster-averaged heat load reduced. In contrast, thick and thin clusters, in directions perpendicular and parallel to the free-stream velocity, are subject to an increased cluster-averaged heat load. [ABSTRACT FROM AUTHOR]

High-speed turbulence is generated when hypersonic vehicles fly in the atmosphere, which can create aero-optical effects and interfere with optical navigation and guidance systems. At the same time, the front end and optical window of hypersonic vehicles are exposed to an aerodynamic heating environment, leading to the head ablation and thermal deformation of the optical window. This further aggravates the turbulent transition process and makes the error of the aero-optical effects more difficult to predict. In this paper, the aero-optical effects under the condition of high-temperature ablation were analyzed. Ablation deformation models of both the head and optical window were established. Then, a high-speed flow field was simulated under different flight conditions. The distortion characteristics of the aero-optical effects were obtained through the photon transmission theory. The simulation results show that the ablation deformation of hypersonic vehicles under an aerodynamic heating environment aggravates the disturbance error of the aero-optical effects. Moreover, with the increase in the flight speed and the decrease in the flight altitude, the ablation deformation of the hypersonic vehicles and the aero-optical effects distortion both gradually increase. The research in this paper provides a reference for the prediction of aero-optical distortion in an aerothermal environment. [ABSTRACT FROM AUTHOR]

We have developed a system for remote Raman spectra detection in hypersonic wind tunnel, which can be used in extreme environments such as ultra‐high temperature, high pressure, and complex airflow to measure in situ Raman spectra of ceramic matrix composites during oxidation, phase transformation or ablation. The designed system avoids stray light generated by windows and airflow through oblique incidence of excitation light. The time‐resolved method combined with pulsed laser and intensified charge‐coupled device (ICCD) was used to reduce the thermal emission background. An optical structure design based on fiber bundle is adopted to suppress the influence of aero‐optical effects and mechanical vibration on Raman spectrum acquisition. We demonstrated the feasibility of in situ Raman spectra detection in a Mach 5 combustion wind tunnel system. The design of anti‐interference prevents Raman spectra intensity from the influence of wind tunnel testing conditions. [ABSTRACT FROM AUTHOR]

Background: Pulmonary vein isolation (PVI) is used for treating atrial fibrillation, and high-power, short-duration (HP-SD) radiofrequency ablation is considered effective. The depth of myocardial scar in HP-SD ablation is shallower than that in conventional-power, conventionalduration (CP-CD) ablation, and this can be a possible limitation. Hence, the current study aimed to investigate the differences between CP-CD and HP-SD ablation. Methods: Retrospective analyses were performed on patients who received PVI at Fujigaoka Hospital between May 2018 and June 2020. All electroanatomic mapping was performed using EnSite-PrecisionTM cardiac mapping system (Abbott). In both methods, PVI was performed under the same lesion size index (LSI) guidance. The pulmonary veins (PVs) on both sides were divided into six segments (anterior, posterior, roof, bottom, and anterior and posterior parts of the carina). The characteristics of patients and procedures, remnant conduction and early reconnections of the PV after the initial PVI, and clinical outcomes were compared between the CP-CD and HP-SD groups. Results: 200 consecutive patients who underwent same lesion size index-guided PVI were enrolled. The first half of consecutive patients (n = 100) underwent CP-CD ablation, and the second half (n = 100) underwent HP-SD ablation. The CP-CD group had a significantly longer procedure time than the HP-SD group. The remnant conduction and early reconnections in the right anterior carina were significantly less common in the CP-CD group than in the HP-SD group. The 2-year cumulative recurrence rate of all types of atrial fibrillation was comparable between the CP-CD and HP-SD groups. Conclusions: CP-CD and HP-SD radiofrequency ablation had distinct features. Combined CP-CD and HP-SD based on the PV segment, particularly the right PV anterior carina, might be a reasonable approach. [ABSTRACT FROM AUTHOR]

In this study, C/C–SiC and C/C–SiC–ZrC composites were prepared via chemical vapor infiltration and polymer infiltration pyrolysis, and the ablation mechanism under hypersonic oxygen-rich environmental conditions was investigated. The C/C–SiC composites demonstrate an excellent ablation resistance in a hypersonic oxygen-rich environment with a relatively low temperature and speed of approximately 1800 K and 1100 m/s, respectively. It is only in the ablation center area with higher temperatures that a certain degree of thermochemical ablation was observed. The mass and linear ablation rates of C/C–SiC composites (0.027 g/s and 0.117 mm/s, respectively) showed a significant increase in a hypersonic oxygen-rich environment with a temperature and velocity of approximately 2050 K and 2000 m/s, respectively. The high-temperature ablation resistance of ZrC-modified C/C–SiC–ZrC composites improved significantly. However, the ZrC ceramic component had a considerable impact on the ablation resistance of the material. The structural integrity of C/C–20SiC–30ZrC composites was relatively high in hypersonic oxygen-rich environments with a jet temperature and velocity of 2050 K and 2000 m/s, respectively, and mass and linear ablation rates were 0.012 g/s and 0.015 mm/s, respectively. When the ZrC content increased by 40%, the ablation resistance of the composite reduced significantly, whereas the mass and linear ablation rates increased to 0.043 g/s and 0.130 mm/s, respectively. [ABSTRACT FROM AUTHOR]

The continuous fiber reinforced porous resin‐based composites with integrated gradient fabric (CPIGF) were successfully prepared. From the bottom to the top surface, the fiber volume fraction of the integrated fabric gradually increased, as well as the fabric architecture changed, meanwhile the porosity of the resin gradually decreased. The temperature in the inner composite increased quite slowly during ablation, and the linear ablation rate ranged from 0.019 mm/s to 0.029 mm/s. The simulation results showed that the good heat insulation capacity of CPIGFs was attributed to the anisotropy properties of the fabric architecture. The microstructure analysis showed that the good ablation resistance came from both the thermal expansion of the integrated gradient fabric and the densification of the zone with 3D orthogonal woven fabric. This work is helpful for designing thermal protection materials having both heat insulation and ablation resistance for hypersonic aircrafts. [ABSTRACT FROM AUTHOR]

Microwave ablation (MWA) is based on localized heating of biological tissues, enabled by an electric field. Antennas for ablation are commonly designed in a forward approach to generate a temperature profile specific to the design. The concept of an inversely-designed MWA antenna, consisting of printed dipoles, is presented herein. This design can be configured to synthesize a desired target temperature profile by controlling and optimizing its current distribution, as demonstrated by simulations. This concept provides the functionality of a phased array on the tip of an interstitial device. [ABSTRACT FROM AUTHOR]

The influence of different background gases and substrate heating on the plasma plume dynamics from silver ablation is investigated by species selected time and space resolved imaging. The results provide a time-resolved understanding on how those process parameters affect the expansion: from a free expansion in vacuum with velocities exceeding 20 000 m/s to a very slow expansion in Ar at 1×10-1 mbar with arrival velocities of 280 m/s. In addition, we observe a rebound of the ablated material on the substrate holder leading to a re-coating of the ablated target. At 1×10-1 mbar, it seems that the expansion of the plasma plume displaces a considerable portion of the background gas and traps it against the frontal area of the substrate holder. This leads to a transient high local pressure just above the substrate. In the case of Ar, the rebound is enhanced due to inelastic scattering, whereas for an O2 background, an area of high reactivity/emission in addition to the rebound is created. Imaging of selected species shows that the light emission in this area is mainly due to excited Ag and metal oxygen species. There is a clear influence of substrate heating on the plasma expansion due to the background gas density gradients, reducing the stopping ability of the background gas and already detectable 2 cm away from the substrate. Both rebound and excitation effects are reduced in intensity due to the substrate heating. [ABSTRACT FROM AUTHOR]

INTRODUCTION: The current therapy of neoplastic Barrett's esophagus (BE) consists of endoscopic resection plus ablation, with radiofrequency ablation as the best studied technique. This prospective trial assesses a potential alternative, namely hybrid argon plasma ablation. METHODS: Consecutive patients with neoplastic BE undergoing ablation after curative endoscopic resection (89.6%) or primarily were included into this prospective trial in 9 European centers. Up to 5 ablation sessions were allowed for complete eradication of BE (initial complete eradication of intestinal metaplasia [CE-IM]), by definition including BE-associated neoplasia, documented by 1 negative endoscopy with biopsies. The main outcome was the rate of initial CE-IM in intention-to-treat (ITT) and per-protocol (PP) samples at 2 years. The secondary end points were the rate of recurrence-free cases (sustained CE-IM) documented by negative follow-up endoscopies with biopsies and immediate/delayed adverse events. RESULTS: One hundred fifty-four patients (133 men and 21 women, mean age 64 years) received a mean of 1.2 resection and 2.7 ablation sessions (range 1–5). Initial CE-IM was achieved in 87.2% of 148 cases in the PP analysis (ITT 88.4%); initial BE-associated neoplasia was 98.0%. On 2-year follow-up of the 129 successfully treated cases, 70.8% (PP) or 65.9% (ITT) showed sustained CE-IM; recurrences were mostly endoscopy-negative biopsy-proven BE epithelium and neoplasia in 3 cases. Adverse events were seen in 6.1%. DISCUSSION: Eradication and recurrence rates of Barrett's intestinal metaplasia and neoplasia by means of hybrid argon plasma coagulation at 2 years seem to be within expected ranges. Final evidence in comparison to radiofrequency ablation can only be provided by a randomized comparative trial. [ABSTRACT FROM AUTHOR]

Pulsed beams containing O and O 2 with incident velocities of ∼7900 m s−1 were directed at a carbon fiber preform network (FiberForm) at temperatures in the range, 1023–1823 K, and the products that scattered from the network were detected with a rotatable mass spectrometer as a function of their velocities and scattering angles. A beam containing pure Ar atoms was also directed at the network, allowing multiple-bounce effects in the absence of reaction to be characterized. Scattered O, O 2 , and Ar exhibited the dynamical characteristics of impulsive (non-thermal) scattering and thermal desorption (TD). On the other hand, CO and CO 2 exhibited only TD dynamics. The fluxes of all products were quantified as a function of sample temperature and, for two focus temperatures, as a function of scattering angle. CO was the dominant reactive product. A temperature dependent hysteresis in the CO flux was quantified, and a comparison was made between the hysteresis on the carbon fiber network and on a planar vitreous carbon surface. The new results may be used to increase the fidelity of oxygen-carbon ablation models for hypersonic flight. [Display omitted] [ABSTRACT FROM AUTHOR]

Background and Objectives: The aim of the present study was to report the safety and efficacy of percutaneous navigation under local anesthesia for computed tomography-guided microwave ablation of malignant liver lesions located in the hepatic dome. Patients with primary and secondary malignant liver lesions located in the hepatic dome who underwent percutaneous computed tomography-guided microwave ablation using a computer-assisted navigation system under local anesthesia were prospectively evaluated. The primary objective was technical success. Materials and Methods: The sample consisted of 10 participants (16 lesions) with a mean age of 60.60 years (SD = 9.25 years) and a mean size of 20.37 ± 7.29 cm, and the mean follow-up time was 3.4 months (SD = 1.41) months. Results: Primary technical success was 93.75%. Tumor remnant was noticed at one month follow-up in a single metastatic lesion, which was re-treated with an ablation session, and no tumor remnant was depicted in the subsequent imaging follow-up (secondary technical success 100%). Grade I self-limited complications (according to the CIRSE classification system) included small pleural effusion (n = 1) and minor bleeding post antenna removal (n = 1) requiring nothing but observation. Conclusions: the findings of the present study indicate that percutaneous navigation under local anesthesia is a safe and efficacious approach for computed tomography-guided microwave ablation of malignant liver lesions located in the hepatic dome. Large randomized controlled studies are warranted to observe treatment effectiveness and compare the results with those of other options. [ABSTRACT FROM AUTHOR]

The plume expansion dynamics strongly affects the growth and the chemistry of pulsed laser deposited thin films. The interaction with the background gas determines the kinetic energy of the species impinging on the substrate, their angular broadening, the plasma chemistry, and eventually the cations stoichiometric ratio in oxide films. Here, we exploit two-dimensional, spectrally resolved plume imaging to characterize the diverse effects of the oxygen background pressure on the expansion dynamics of La, Ga, and LaO species during pulsed laser deposition of LaGaO3. The propagation of the ablated species towards the substrate is studied for background oxygen pressures ranging from high vacuum up to ≈10-1 mbar. Our experimental results show specie-dependent effects of the background gas on the angular distribution of the precursors within the plume. These findings suggest that even in the presence of a stoichiometric ablation and of a globally stoichiometric plume, cations off-stoichiometry can take place in the forefront portion of the plume impinging on the substrate. We show that such effect can be compensated by a proper choice of process parameters. [ABSTRACT FROM AUTHOR]

This work characterises thermal properties of a typical epoxy-based carbon-fibre-reinforced polymer used in aircraft construction, but with an out-of-plane fibre orientation, and assesses its potential as a structural ablative material. Samples of the commercially available Hexply® 8552/IM7 are prepared with out-of-plane angles up to 90°, with a focus on 0° to 15°, enhancing thermal conductivity through the thickness of the panel. Ablation processes are simulated by a hot-air blower at 580 °C, and examined in detail by ultrasonic testing and microfocused computed X-ray tomography afterwards. Matrix degradation is characterised by infrared spectroscopy and mass loss. To assess structural properties, tensile, compression, and bending tests are performed. The results show a loss in mechanical performance with an increasing fibre angle, which may be negligible for angles lower than ~5° in the initial state. Composite material with an out-of-plane fibre orientation is deeply penetrated concerning matrix degradation by thermal loading, but it is held together by the fibres fixed in the intact matrix underneath. This type of material shows a high potential for structural components in single-use, high-temperature, ablative applications with a focus on saving weight. [ABSTRACT FROM AUTHOR]

Copyright of Systems Engineering & Electronics is the property of Journal of Systems Engineering & Electronics Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The presented study addresses the characterization of nanometer sized defects acting as damage precursors in nanosecond laser pulse duration regime. Two approaches are used to extract distributions of localized damage precursors, namely, damage probability and damage density measurements. Testing is performed on uncoated and SiO2 monolayer film deposited fused silica substrate exposed with pulsed UV irradiation (355 nm, 4.8 ns). Then, a direct comparison of damage precursor ensembles obtained from both methods is carried out. Our analysis indicates apparent differences between both methods that are discussed in detail. Contamination by ablation products is identified as one of the key factors that influence damage density measurements. [ABSTRACT FROM AUTHOR]

In this work, chemical properties, surface modification, and micro structures formation on ablated polyallyl di-glycol carbonate (CR-39) polymer by ArF laser irradiation (k=193 nm) at various fluences and pulse number were investigated. CR-39 samples have been irradiated with an ArF laser (λ=193 nm) at a repetition rate of 1 Hz. Threshold fluence of ablation and effective absorption coefficient of CR-39 were determined. Conical microstructures (Taylor cone) formed on laser-ablated CR-39 exhibit: smooth, Taylor cone shape walls and sharp tips together with interference and well defined fringe-structure with a period of 230 nm, around cone base. Mechanism of cone formation and cone evolution of CR-39 ablated surface were investigated by change of fluences (at a given pulse number) and pulse number (at a given fluence). Cone height, cone base, and region of interface were increased in micrometer steps by increasing the total fluence. Depression on the base of the cone and the circular fringe were simulated. FTIR spectra were measured and energy dispersive x-ray analysis of irradiated and un-irradiated samples was performed. [ABSTRACT FROM AUTHOR]

In multi-pulse laser damage and ablation experiments, the laser-induced damage threshold (LIDT) usually changes with the number of pulses in the train, a phenomenon known as incubation. We introduce a general incubation model based on two physical mechanisms-pulse induced change of (i) absorption and (ii) critical energy that must be deposited to cause ablation. The model is applicable to a broad class of materials and we apply it to fit data for dielectrics and metals. It also explains observed changes of the LIDT as a function of the laser repetition rate. We discuss under which conditions the crater-size method to determine LIDTs can be applied in multi-pulse experiments. [ABSTRACT FROM AUTHOR]

As two prominent natural hazards, tropical cyclone (TC) and heat compound events seem irrelevant on most occasions. TC generally leads to cooling, but could induce extreme heat days (EHD) and heat compound hazard under certain circumstances. An EHD along the southeastern coast of China (SECC) associated with Typhoon Lekima (2019) is documented with its major contributing factors. The formation and intensity of the EHD were found to be closely related to the outer circulation of Lekima by comparing a series of WRF simulations. Via a boundary layer heat budget, we found local sensible heat flux was a necessary, but not sufficient condition for this EHD. Aided by a backward trajectory analysis, we found that upstream surface sensible heat flux, subsidence induced by Typhoon Lekima, and foehn effect due to local topography played approximately equal roles to the occurrence of the EHD. The retreat of regional land‐sea breeze circulation was also beneficial to the appearance of the EHD. Such TC‐heat events might be more overwhelming due to more vigorous TCs with warming in the future. Plain Language Summary: Tropical cyclone (TC) and heat compound events pose a severe threat to human health and natural ecosystems. This paper documents an extreme heat days (EHD) along the southeastern coast of China associated with Typhoon Lekima (2019). Through a series of WRF simulations, we found that the formation and intensity of the EHD are closely related to the outer circulation of Lekima. The local sensible heat flux was necessary, but insufficient for the formation of the EHD. The upstream surface sensible heat flux, subsidence induced by Typhoon Lekima, and foehn effect due to local topography were the key factors to the occurrence of the EHD and the contributions of these three factors were approximately equal. Regional land‐sea breeze circulation influenced by Lekima was also beneficial for the EHD. Such TC‐heat events can be more widespread and severe due to increased intensity of tropical cyclones with warming. Key Points: An extreme heat event along the southeastern coast of China was closely related to the outer circulation of Typhoon Lekima (2019)Upstream surface sensible heat flux, subsidence induced by Typhoon Lekima, and foehn effect due to local topography played approximately equal roles for the eventRetreat of regional land‐sea breeze circulation also favored the event [ABSTRACT FROM AUTHOR]

In this study, an ultrashort pulse laser is used to investigate the removal efficiency and the ablation quality of stainless steel. The employed solid state laser is capable of varying the pulse duration from 0.27 to 10 ps and generates bursts with an intraburst pulse repetition frequency of 65 MHz with up to nine pulses per burst. Depending on the fluence per pulse, the pulse duration, and the number of pulses per burst, the removal efficiency and the ablation quality are presented and discussed based on the depth of the ablation structures and the surface roughness of the structured bottoms. The results prove that compared to pulse durations in the picosecond regime, the ablation efficiency in the femtosecond regime is significantly higher. The removal efficiency per burst is not affected by an increase in the number of pulses in the burst, but a smoothing effect can be identified for a certain number of pulses in the burst depending on the fluence and the pulse duration, which has a positive effect on the ablation quality. The temperature distribution and the heat accumulation induced by the high intraburst pulse repetition frequency are calculated with a semiempirical two-temperature model. The simulation results demonstrate that the melting film depth has a major influence on the smoothing effect caused by the burst mode. [ABSTRACT FROM AUTHOR]

The InSightec Exablate system is the standard of care used for transcranial focused ultrasound ablation treatments in the United States. The system calculates phase corrections that account for aberrations caused by the human skull. This work investigates whether skull aberration correction can be improved by comparing the standard of care InSightec ray tracing method with the hybrid angular spectrum (HAS) method and the gold standard hydrophone method. Three degassed ex vivo human skulls were sonicated with a 670 kHz hemispherical phased array transducer (InSightec Exablate 4000). Phase corrections were calculated using four different methods (straight ray tracing, InSightec ray tracing, HAS, and hydrophone) and were used to drive the transducer. 3D raster scans of the beam profiles were acquired using a hydrophone mounted on a 3-axis positioner system. Focal spots were evaluated using six metrics: pressure at the target, peak pressure, intensity at the target, peak intensity, positioning error, and focal spot volume. For three skulls, the InSightec ray tracing method achieved 52 ± 21% normalized target intensity (normalized to hydrophone), 76 ± 17% normalized peak intensity, and 0.72 ± 0.47 mm positioning error. The HAS method achieved 74 ± 9% normalized target intensity, 81 ± 9% normalized peak intensity, and 0.35 ± 0.09 mm positioning error. The InSightec-to-HAS improvement in focal spot targeting provides promise in improving treatment outcomes. These improvements to skull aberration correction are also highly relevant for the applications of focused ultrasound neuromodulation and blood brain barrier opening, which are currently being translated for human use. [ABSTRACT FROM AUTHOR]

Carbonaceous chondritic meteorites are primordial Solar System materials and a source of water delivery to Earth. Fluid flow on the parent bodies of these meteorites is known to have occurred very early in Solar System history (first <4 million years). We analyze short-lived uranium isotopes in carbonaceous chondrites, finding excesses of 234-uranium over 238-uranium and 238-uranium over 230-thorium. These indicate that the fluid-mobile uranium ion U6+ moved within the past few 100,000 years. In some meteorites, this time scale is less than the cosmic-ray exposure age, which measures when they were ejected from their parent body into space. Fluid flow occurred after melting of ice, potentially by impact heating, solar heating, or atmospheric ablation. We favor the impact heating hypothesis, which implies that the parent bodies still contain ice. [ABSTRACT FROM AUTHOR]

We present the studies of the high-order harmonic generation of 802-nm, 64-fs pulses in the extended plasmas contained the carbon-based clusters (fullerenes, nanofibers, nanoparticles, and nanotubes). Our studies show that the 11th-19th harmonics in the 15-33 eV range may originate from the low-sized nanoparticles produced during ablation of large clusters and agglomerates. The conversion efficiency of the 11th harmonic generated from the 5-mm-long fullerene plasma was estimated to be 2 x 10-5. [ABSTRACT FROM AUTHOR]

Molecular beam-surface scattering experiments were used to obtain fundamental data on gas-surface interactions that are central to the ablation of carbon during hypersonic flight through air. Continuous beams containing O or N atoms with incident velocities of ∼2000 m s−1 were directed at a vitreous carbon surface at temperatures in the range, 800–1873 K, and the products that desorbed from the surface were detected with a rotatable mass spectrometer detector as a function of their velocity and scattering angle. All products exhibited the dynamical characteristics of thermal desorption. The efficiencies of the gas-surface interactions, both reactive and non-reactive, were quantified as a function of surface temperature. In addition to reacting with carbon to produce CO 2 (minor product) and CO (major product), oxygen atoms may recombine on the surface to produce O 2 with an efficiency that is somewhat lower than that to produce CO. Nitrogen atoms may recombine on the surface to produce N 2 or react to produce CN. The recombination efficiency of N atoms is generally more than an order of magnitude higher than the reaction efficiency to produce CN. The quantitative reaction efficiencies reported here are useful for the development of air-carbon models for hypersonic ablation. Image 1 [ABSTRACT FROM AUTHOR]

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The increasingly serious service condition in aerospace industry has posed a higher requirement to the ablation resistance of hypersonic vehicle structural carbon fabric-reinforced phenolic composites. To further enhance the ablation resistance of the composite, different contents of TaSi2-modified carbon fabric-reinforced phenolic composites were successfully prepared. The ablation behavior and mechanism of these composite were investigated. Results showed that the ablation resistance of the modified composite was significantly improved due to the addition of the TaSi2. When the mass fraction of TaSi2 on the matrix resin was 50 wt%, the mass and liner ablation rate of the modified composites were 30% and 12% lower than those of the unmodified composites, respectively. The formed double-layer structural residue acted as an insulating layer and effectively obstructed the flame flow and oxygen to the inner material. Moreover, the occurrence of the endothermic reactions and the evaporation of the reaction gases further dissipated the heat energy. The multi-effect synergy mechanism effectively reduced the thermal oxidative ablation degree of the modified composites. All these results confirmed that the TaSi2-modified composite exhibits excellent oxidative ablation resistance, which provided a basis for the application of composite to more serious service environments. [ABSTRACT FROM AUTHOR]

Irreversible electroporation (IRE) is a non-thermal ablation modality that has been shown to be safe and effective in its application to tumors that are close to risky areas. This study aims to assess the safety and efficacy of IRE for unresectable hilar cholangiocarcinoma. Nine patients from two medical centers in Asia received IRE treatment between June 2015 and July 2017. Before IRE treatment, percutaneous biliary decompressions had been performed on eight patients, and internal stenting had been performed on one patient. All patients tolerated the procedure well without high-grade complications. The ablated tumors had constant size without contrast enhancement for more than three months in eight patients and the level of CA19-9 decreased significantly in all patients. The percutaneous biliary drainage tube was removed from two patients with recanalization of the bile duct. The internal stent in one patient was removed without further stenting. The median overall survival period was 26 months, and the progression-free survival was 18 months. Bile ducts remained narrow in the majority (2/3) of the treated patients. Nevertheless, IRE ablation of unresectable hilar cholangiocarcinoma involving vital structures is a safe and feasible primary treatment for local tumor control and is effective in prolonging survival. [ABSTRACT FROM AUTHOR]

Validation of one-dimensional aerodynamic heating and ablation prediction program, AeroheataBS to calculate transient skin temperatures and heat fluxes for high-speed vehicles has been performed. In the tool shock relations, flat plate convective heating expressions, Eckert's reference temperature method and modified Newtonian flow theory are utilized to compute local heat transfer coefficients. Corresponding governing equations are discretized explicitly and numerically solved. Time varying flight conditions including velocity, altitude and angle of attack serve as input to the program. In order to examine the accuracy of aerodynamic heating capabilities of AeroheataBS, calculated temperature histories are compared with flight data of the X-15 research vehicle, a modified von-Karman nose shaped body, cone-cylinder-flare configuration and results of conjugate computational fluid dynamics studies. Comparative studies show that computed values are in good agreement with the reference data and prove that methodology established in AeroheataBS is appropriate for estimating aerodynamic heating and structural thermal response. [ABSTRACT FROM AUTHOR]

Ice thickness has a great influence on glacial movement and ablation. Over the course of the change in thickness, area and external climate, the dynamic process of how glaciers change and whether a glacier's changes in melting tend to be stable or irregular is a problem that needs to be studied in depth. In our study, the changes in the dynamic process of the No. 8 Glacier in Hei Valley (H8) under the conditions of different thicknesses in 1969 and 2009 were simulated based on the Full-Stokes code Elmer/Ice (http://www.csc.fi/elmer/). The results were as follows: (1) The thickness reduction in glaciers would lead to a decrease in ice surface tension and basal pressure and friction at the bottom, and the resulting extensional and compressional flow played an important role in the variations in glacial velocity. (2) The force at the bottom of the glacier was key to maintaining the overall stress balance, and the glaciers that often melted and collapsed in bedrock were more easily destroyed by the overall force balance and increased change rate of glacial thaw. (3) Temperature changes at different altitudes affected the ice viscous force. The closer the ice surface temperature was to the melting point, the greater the influence of temperature changes on the ice viscous force and ice surface velocity. Finally, we used the RCP 4.8 and 8.5 climate models to simulate the changes in H8 over the next 40 years. The results showed that with some decreases in ice surface compression and tension, the gravity component changes caused by local topography begin to control the ice flow movement on the surface of glacier, and melting of the glacial surface will appear as an irregular change. The simulation results further confirmed that the fluctuation in glacial dynamic characteristics could be attributed to the change in the gravity component caused by ablation. [ABSTRACT FROM AUTHOR]

In this paper, we study the ablation phenomena associated with the operation of a capillary discharge for an electrothermal gun. Electrothermal-chemical (ETC) guns are used for enhancement of ignition and combustion of an energetic propellant. One of the major components of the ETC system is a plasma source based on a capillary discharge. In this paper, a model of the capillary discharge is developed. In this model, primary attention is paid to the ablation phenomenon. Different characteristic subregions near the ablated surface, namely, a space-charge sheath, a Knudsen layer, and a hydrodynamic layer, are considered. In this formulation, the ablation rate is determined by the parameters at the edge of the Knudsen layer. The kinetic approach is used to determine the parameters at the interface between the kinetic Knudsen layer and the hydrodynamic layer. Coupling the solution of the nonequilibrium Knudsen layer with the hydrodynamic layer provides a self-consistent solution for the ablation rate. According to the model predictions, the peak electron temperature is about 1.4 eV, the polyethylene surface temperature is about 700 K, and the pressure is about 10 MPa. It is found that the ablation rate increases with the capillary length. The ablated mass and the predicted total pressure agree with previous experimental observations. [ABSTRACT FROM AUTHOR]

We discuss the ablation of aluminum plasma using picosecond pulsed laser in vacuum and in ambient atmosphere of nitrogen. The plume dynamics of picosecond and nanosecond laser-ablated plumes in ambient atmosphere is discussed. The degree of polarization is measured using optical emission spectroscopy for the Al III transition 4s 2S1/2-4p 2P3/2o at 569.6 nm. Strong anisotropy is observed using picosecond laser pulse as compared to nanosecond laser pulse. [ABSTRACT FROM AUTHOR]

Several interrelated phenomena near the surface ablated into a discharge plasma, such as ablation and ionization in accelerated plasma are studied. Two characteristic ablation modes are identified, namely, ablation mode with a velocity at the Knudsen layer edge smaller than the local sound speed and a velocity at the Knudsen layer edge close to the sound speed. The existence of these two ablation modes is determined by the current density in the acceleration region. The nonequilibrium ionization region in the presence of strong electromagnetic plasma acceleration is studied. In the subsonic regime, the ionization region thickness is proportional to the ionization rate and inversely proportional to the magnetic field. Conditions for ionization equilibrium in the accelerating plasma are determined. The specific example of a micropulsed plasma thruster is considered. It is concluded that both the equilibrium and nonequilibrium ionization regimes occur in this device. [ABSTRACT FROM AUTHOR]

We have calculated the concentration of ions in the plasma produced upon ablation of LiNbO[sub 3] with a low fluence ArF excimer laser in vacuum and different gas environments (Ar and O[sub 2]). The model shows that Li and Nb ions (with the amount of Li ions being greater than that of Nb ions) are the most abundant in the plasma with their concentrations being always above their corresponding neutral densities. In addition, we show that the concentration of excited Nb ions is relatively important while no excited Li ions are predicted. We found that the concentration of both Li and Nb ions in O[sub 2] is slightly higher than in Ar and vacuum. Moreover, the calculated spatial evolution of the ionic species suggests that a significant fraction of the predicted ion concentration is not produced by electron–atom ionization events within the plasma; on the contrary, they might have been produced in the LiNbO[sub 3] crystal through a nonthermal mechanism and then ejected from the target after the laser pulse. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Investigates the properties of the ablation products from intense-pulsed ion beam impact on solid targets. Discussion on intense ion beams; Experimental configurations; Characterization of beam and plume; Description of the beam-target interaction model; Results.

We have conducted beam-surface scattering experiments with the intent of identifying the reaction mechanisms that are relevant to the ablation of carbon by N atoms at surface temperatures relevant to hypersonic flight. A pulsed molecular beam containing N and N 2 with translational energies of 460 and 808 kJ mol-1, respectively, was directed at a vitreous carbon surface held at temperatures in the range 1023–1923 K. Time-of-flight distributions were collected for scattered products with fixed incidence and final angles of θ i = θ f = 45°. Inelastically scattered N and N 2 and reactively scattered CN were the only products observed. The scattering dynamics of N and N 2 were independent of surface temperature and were indicative of purely impulsive scattering. The scattering dynamics of CN suggested that this reaction product is formed by a mechanism that occurs in thermal equilibrium with the surface – i.e., a Langmuir-Hinshelwood mechanism. The reaction probability to produce CN has an Arrhenius temperature dependence with an activation energy of 207 kJ mol-1. The relevance of the current results to the hypersonic ablation of carbon in the presence of dissociated air is discussed. Image 1086731 [ABSTRACT FROM AUTHOR]

The persistent two‐peaked vertical structure of the Martian ionosphere is created by extreme and far ultraviolet radiation whose energies, respectively, determine their ionization altitude. A third low‐altitude transient layer (previously referred to as M3 or Mm) has been observed by radio occultation techniques and attributed to meteor ablation. However, recent remote sensing and in situ observations disfavor a meteoric origin. Here we propose an alternative hypothesis for these apparent layers associated with impact ionization from penetrating solar wind ions, previously observed as proton aurora. Localized ionization, occurring nonglobally at a given altitude range, breaks the symmetry assumed by the radio occultation technique, and creates electron layers apparently lower in the ionosphere than their true altitude. This may occur when the upstream bow shock is altered by a radial interplanetary magnetic field configuration, which allows the solar wind to penetrate directly into the thermosphere. This localized ionization hypothesis provides an explanation for apparent layers' wide variation in heights and their transient behavior. Moreover, this hypothesis is testable with new observations by the Mars Atmospheric and Volatile EvolutioN Radio Occultation Science Experiment in future Mars years. This hypothesis has implications for the ionospheres of Venus and Titan, where similar transient layers have been observed. Plain Language Summary: The ionosphere of a planet couples the neutral atmosphere to the exosphere and solar wind. Created by solar ionizing radiation, the ionosphere on the dayside of planet is expected to be hemispherically symmetric. When Mars Express discovered transient low‐altitude ionospheric layers in 2005, they were initially predicted to be due to meteor ablation. However, recent observations indicate that they are due to a geometric observational effect related to local, not hemispheric, ionization. Observations from three instruments on Mars Atmospheric and Volatile EvolutioN are used concurrently to understand this phenomenon. These transient layers have been observed at Venus and Titan as well, and this hypothesis indicates novel physics for those ionospheric systems. Key Points: Low‐altitude transient ionospheric layers may be explained by a geometric observational effect from localized, not hemispheric, ionizationA radio occultation of a transient ionospheric layer was obtained with observations of variable proton aurora and penetrating solar windTransient layers observed at Mars, Venus, and Titan are consistent with the presence of solar wind impact ionization at those planets [ABSTRACT FROM AUTHOR]

Abstract Char layer erosion due to gas flow is an important part of the ablation process for insulation materials used in solid rocket motors (SRMs) or rocket ramjets. However, the current understanding of the erosion pattern is very limited. This paper reports on an experimental study on the erosion characteristics of the char layer of ethylene propylene diene monomer (EPDM) composite. First, the charring samples were prepared using a special ablation motor. A cold flow erosion test device was then developed, and the erosion experiments on the charring samples under cold airflow conditions were conducted. The experimental results show that under a pressure of 0.5 MPa, when the airflow velocity is lower than or equal to 180 m/s, the char layer erosion is largely in the form of wear; when the airflow velocity reaches 200 m/s, the large pieces of the char layer are peeled off; when the airflow velocity reaches 230 m/s, the entire char layer is peeled off. The tensile and shear strength of the char layer under cold conditions were tested using a simple method. It was found that the shear stress of the airflow when the char layer is peeled off is significantly lower than the shear strength of the char layer. The failure of the char layer is not only due to the pure shear force of the airflow. The local cracking, warping, and delamination not only reduce the char layer strength, but also enhance the destructive force of the airflow. This was the main cause of the char layer erosion due to airflow. Highlights • Developed cold flow erosion device, shear/tensile strength method to char layer. • Flow velocity increase caused 3 gas erosion modes: wear, local, whole peeling. • Shear stress of airflow significantly lower than that of char layer. • Local cracking, warping, and delamination reduced local strength of char layer. • These phenomena also enhanced destructive force of the airflow. [ABSTRACT FROM AUTHOR]