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We present quantitative motivations and assessments of various proposed and ongoing directions to further improving yields and target gain of igniting indirect-drive implosions at the National Ignition Facility (NIF). These include increasing compression and confinement time, improving hohlraum and ablator efficiency, and further increasing peak power and laser energy. 1D hydroscaled simulations, augmented by analytic 1D theory, have been used to project yield improvements for each of these implosion optimization tracks, normalized to the best current performing 4 MJ shot. At current NIF capabilities of 2.2 MJ, 450 TW, we project several paths could reach 15 MJ yield levels. We also expect several key implosion physics questions will be addressed in attempting to reach this yield level. These include demonstrating to what extent lower adiabat designs leading to higher compression will increase gain and efficiency, and whether we can reduce residual kinetic energy and ablator-fuel mix that is probably limiting the current burn-up fraction. For an envisaged NIF upgrade to EL = 3 MJ at fixed 450 TW peak power, scaling capsule size and fuel thicknesses faster than pure hydroscaling should allow for yields that could reach up to 60–80 MJ, depending on the efficiency gains realized in increasing deuterium-tritium fuel thickness, reducing hohlraum losses, and switching to lower Z ablators. The laser-plasma instability and beam transmission scaling in these larger hohlraums is shown to be favorable if the spot size is increased with hohlraum scale. [ABSTRACT FROM AUTHOR]

Double shell targets are a promising potential avenue to obtain robust neutron yield at current laser facilities. Similar to single shell designs, double shells require the symmetric implosion of an ablator in order to uniformly compress and heat a fuel volume, with the goal of achieving thermonuclear burn. Significant differences between double and single shells include the usage of an aluminum ablator as well as a reverse ramp laser pulse. In addition, double shells require a different convergence than single shells for fuel ignition. Numerical implosion studies at various energies with comparisons to experimental outcomes are required to gain confidence that simulations can capture the ablator shape from subscale to full scale. The current work builds on previous implosion experiments conducted at 1-MJ laser energy to confirm achieved ablator symmetry at 1.25 and 1.5 MJ. Average ablator P2 and P4 shapes measured in these experiments are within 5% of the simulated shape, which merits the platforms for further experimental studies. [ABSTRACT FROM AUTHOR]

Recent indirect drive inertial confinement fusion implosions on the National Ignition Facility (NIF) [Spaeth et al., Fusion Sci. Technol. 69, 25 (2016)] have crossed the threshold of ignition. However, performance has been variable due to several factors. One of the leading sources of variability is the quality of the high-density carbon (HDC) shells used as ablators in these experiments. In particular, these shells can have a number of defects that have been found to correlate with the appearance of ablator mix into the hot spot and a degradation in nuclear yield. These defects include pits on the ablator surface, voids in the ablator bulk, high-Z debris from the Hohlraum wall that adheres to the capsule surface, and finally the inherent granular micro-structure of the crystalline HDC itself. This paper summarizes high-resolution modeling of each of these mix sources in two recent high-performance NIF implosion experiments. The simulated impact from a range of individual capsule defects is found to be broadly consistent with the trends seen in experiment, lending credence to the modeling results and the details of the mixing process that they reveal. Interestingly, modeling of the micro-structure inherent to HDC shows that this perturbation source results in considerable mixing of the deuterium–tritium fuel with ablator material during the implosion. The reduction in fuel compression from this mix results in an approximately factor of two reduction in neutron yield in current implosions and emphasizes the importance of mitigating this significant performance degradation. [ABSTRACT FROM AUTHOR]

The rapid development of large heavy-duty solid rockets has placed increasing demands on the density and ablation resistance of thermal protection system (TPS) materials. Hollow microspheres (HMs) are promising reinforcing materials. However, HMs break under mechanical extrusion during material preparation, which limits their development into high-performance TPS materials. In this study, a novel preparation scheme was designed for low-damage TPS materials. High-strength HMs were selected to reduce their breakage. Moreover, a TPS material with low density and excellent ablation resistance was developed. The density reduction of the HM formulation was considerably higher than that reported in other studies. This study addressed the problem of easy HM breakage during material preparation. Consequently, HM-reinforced TPS materials with low density and excellent ablation resistance were developed to help reduce the negative mass and improve the comprehensive performance of solid rocket motors. • Hollow microsphere (HM)-reinforced thermal protection system (TPS) materials were studied. • HM breakage during material preparation was addressed. • A novel low-damage TPS material preparation scheme was designed. • The density reduction observed in this study was significantly higher than that in previous reports. • A TPS material with low density and excellent ablation resistance was developed. [ABSTRACT FROM AUTHOR]

In this study, ablative resistance of single fiber‐ and hybrid fiber‐reinforced epoxy‐modified vinyl silicone rubber (EMVSR) composites was systematically studied. Three types of fibers, namely aramid fiber (AF), basalt fiber (BF), and carbon fiber (CF), were employed as the reinforcements. The results indicated that the incorporation of fiber reinforcements effectively suppressed the expansion and strengthened the char layer. Besides, the quality of char layer was quite different when different types of fibers were used. The char layer of AF‐modified samples had more surface defects, BF‐modified samples were brittle, and CF‐filled samples were dense and flat. The use of hybrid AF/BF fibers improved the ablation and anti‐erosion performance of EMVSR. Meanwhile, the thermal insulation performance was enhanced because the back‐face temperature was the lowest with the addition of 1 phr AF and 5 phr CF. The above results indicated that the ablation and anti‐erosion resistance and the quality of char layer as well as the thermal insulation behavior of EMVSR were significantly improved by incorporating fibrillar fillers, which demonstrate practical applications as flexible anti‐ablation materials for thermal protection systems. Highlights: Epoxy‐modified vinyl silicone rubber was used for preparing ablative composites.The effect of adding different fibers on the ablation properties was studied.The presence of single fibers improved the strength of char layer.The use of hybrid fibers was found effective in enhancing the ablative properties.The intrinsic property and entanglement of fibers affected the ablative properties. [ABSTRACT FROM AUTHOR]

Lightweight phenolic ablative composites are considered to be the most reliable materials for thermal protection systems. However, improving the thermal ablation‐insulation performance of heritage phenolic aerogel‐based ablators for extremely complex environments is still necessary. Herein, from the perspective of enhancing the gas‐blocking effect, we design and fabricate a series of needle quartz fiber‐reinforced melamine‐phenolic aerogels (NQF/MPAs) composites by polycondensation of melamine and phenolic in a sol–gel process, followed by ambient drying. The effects of melamine content on the comprehensive performance are analyzed. The prepared nitrogen‐doped phenolic aerogel composites exhibit low density of 440–490 kg/m3, high tensile strength of 36.3–39.1 MPa, and low thermal conductivity of 0.041–0.043 W/(m·K) at room temperature. Simultaneously, the modified composite exhibits excellent high‐temperature insulation property with lower equivalent thermal conductivity of 0.045 W/(m·K) at 1000°C. In arc wind tunnel testing of 130 kW/m2 for 1000 s, the linear recession rates of the composites show a great improvement from 3.7 × 10−6 to 2.5 × 10−6 m/s with the proper introduction of melamine. Furthermore, a one‐dimensional finite element model is stablished, which indicate the introduction of melamine can significantly improve the mass flow rate of pyrolysis gas and the corresponding block factor is enhanced from 0.958 to 0.848. Highlights: Economic sol–gel method and ambient drying for composites production.Phenolic aerogel‐based ablative composite with enhanced gas blocking effect.The pyrolysis gas blocking effect is controllable with melamine content.Combined experimental‐simulation approach for ablators designing. [ABSTRACT FROM AUTHOR]

Ignition on the National Ignition Facility (NIF) provides a novel opportunity to evaluate past data to identify signatures of capsule failure mechanisms. We have used new simulations of high-yield implosions as well as some from past studies in order to identify unique signatures of different ignition failure mechanisms: jetting due to the presence of voids or defects, jetting due to the capsule fill tube, interfacial mixing due to instabilities or due to plasma transport, radiative cooling due to the presence of contaminant in the hot spot, long-wavelength drive asymmetry, and preheat. Many of these failure mechanisms exhibit unique trajectories that can be distinguished through variations in experimental observables such as neutron yield, down-scattered ratio (DSR), and burn width. Our simulations include capsules using both plastic and high-density carbon ablators and span all high-yield designs considered since the beginning of the National Ignition Campaign in 2011. We observe that the variability in trajectories through the space of neutron yield, DSR, and burn width varies little across capsule design yet are unique to the failure mechanism. The experimental trajectories are most consistent with simulated preheat and jetting due to voids and defects, which are the only failure mechanisms that are indistinguishable in our analysis. This suggests that improvements to capsule compression due to improved capsule quality or reduced preheat have played a primary role in enabling high yields on NIF. Furthermore, our analysis suggests that further improvements have the potential to increase yields further. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the long-term safety and efficacy of adjuvant intravitreal anti-VEGF therapy in juvenile Coats disease. Methods: This retrospective, observational study included a total of 62 eyes in 62 pediatric patients with juvenile Coats disease treated with intravitreal anti-VEGF agents followed for a mean of 67.08 months (ranged from 60 to 93 months). All affected eyes were managed initially with one session of ablative treatment plus adjuvant intravitreal anti-VEGF agent (0.5 mg/0.05 ml ranibizumab or conbercept). Ablative treatment was repeated if telangiectatic retinal vessels were not completely regressed or recurred. Anti-VEGF therapy was repeated if subretinal fluid or macular edema still existed. Treatments above were repeated every 2 to 3 months. We reviewed clinical and photographic records of patients including the demographics, clinical characteristics and interventions. Results: At final visit, all 62 affected eyes had partially or completely disease resolution; none progressed to advanced stage namely neovascular glaucoma or phthisis bulbi, respectively. No ocular or systemic side effects related to intravitreal injections were observed during follow-up. In terms of 42 affected eyes that could cooperate with visual examination, best corrected visual acuity improved in 14 (14/42, 33.3%) eyes, stabled in 25 (25/42, 59.5%) eyes, and worsened in 3 (3/42, 7.1%) eyes. In the field of complications, 22 (22/62, 35.5%) eyes developed cataracts; 33 (33/62, 53.2%) eyes developed vitreoretinal fibrosis, of whom 14 (14/33, 42.4%) eyes in the subgroup of stage 3B developed progressive TRD; 40 (40/62, 64.5%) eyes developed subretinal fibrosis. Multivariate regression analysis showed increased clinical stage may be associated with the development of vitreo- and subretinal fibrosis (adjusted odds ratio:16.77,17.59; 95% CI:4.50–62.53, 3.98–77.86, respectively, all P < 0.001). Conclusion: Adjuvant intravitreal ranibizumab or conbercept combined with ablative therapies may be a long-term safe and effective treatment for juvenile Coats disease. [ABSTRACT FROM AUTHOR]

Lightweight ablative materials owing to their low density, high efficiency heat insulation and excellent designability, which are considered as the most promising candidate materials in the field of aerospace ablative thermal protection. In this work, a polycarbosilane (PCS) in-situ reinforced carbon felt/phenolic (PR/C f) aerogel composite is reported. The surface of aerogel and carbon fiber was coated with PCS protective layer by sol gel method and secondary vacuum impregnation process. The aerogel composite material possesses low density (0.264–0.307 g/cm3), hydrophobic, low thermal conductivity (0.121–0.178 W/(m·K)) and significant high compressive strength (12.89 MPa). When the oxygen acetylene flame with high heat flow density ablates for 20 s, it shows high efficiency in heat protection and insulation, and the linear ablation rate is as low as 0.089 mm/s. The PL/PR/C f aerogel composite shows competitive and broad application prospects in the field of ablation heat protection in the future. [ABSTRACT FROM AUTHOR]

This paper is aimed at investigating the microstructure evolution of resin-based ablative materials under aerodynamic heating. The microstructure, morphology, material density, and thermophysical parameters at different positions of the material after aerodynamic heating were deeply studied. The changes in the microstructural characteristics of materials caused by complex reaction processes were investigated, including microstructural morphology, porosity, the overlap relationship between microstructural components, and the mutual positional relationship. The relationship between microstructural evolution and material heat transfer is discussed. By analyzing the heat transfer mechanism and heat transfer path of the microstructure, combing with the analysis results of the evolution of the microstructure and the physical properties of the material, multiscale heat transfer unit cell models were established to predict the equivalent thermal conductivity. Thereby, the evolution of physical properties and microstructure of resin-based ablative materials under aerodynamic heating and the relationship between microstructure evolution and heat transfer process are obtained. It can improve the accuracy of ablative heat transfer simulation. In addition, it can provide reference for the process design of ablative materials and promote the application and development of ablative materials in the field of aircraft. [ABSTRACT FROM AUTHOR]

The Holmium (Ho:YAG) laser is presently the most extensively employed in laser lithotripsy for the management of kidney stones. Despite its adoption as the gold standard for laser lithotripsy, Ho:YAG laser lithotripsy poses three significant challenges, namely thermal effect, insufficient stone fragmentation, and stone displacement, which have garnered increased attention from urologic surgeons. Nowadays, the femtosecond laser is regarded as a potential alternative to the Ho:YAG laser due to its capacity to ablate diverse materials with minimal thermal effect. In our ex vivo investigation, we assessed the dimensions of ablation pits, the efficacy of ablation, the degree of stone fragmentation, the alterations in water temperature surrounding stones, and the degree of tissue damage associated with Femtosecond laser lithotripsy utilizing adjustable power settings (1–50 W). Our findings indicate that the ablation pits generated by the Femtosecond laser exhibited uniform geometries, and the effectiveness of ablation and fragmentation for Femtosecond laser lithotripsy were significantly and positively correlated with laser power. When the laser power remained constant, the Femtosecond laser with higher pulse energy demonstrated superior efficiency in stone ablation, but inferior performance in stone fragmentation. Conversely, the Femtosecond laser with higher pulse frequency exhibited the opposite behavior. Furthermore, the thermal effect increased proportionally with laser power, leading to a tentative recommendation of 10W laser power for future investigations. Our in vitro findings suggest that the Femtosecond laser holds promise as a safe and effective alternative to holmium lasers. [ABSTRACT FROM AUTHOR]

Two classes of thermal protection systems composed of a carbon-fibre-reinforced (CFRP) layer and an ablative material layer joined with a thermo-resistant ceramic adhesive were developed. The two classes differ in the composition of the ablative material reinforcing compound. In the first class, the ablative material is based on micronic-sized cork granules, and in the second class, the ablative material is reinforced with carbonic felt. For both classes of thermal protection systems, the reinforcement material was impregnated in simple phenolic resin, and nanometric additive, consisting of silicon carbide nanoparticles added in two different weight contents (1 and 2% by weight) relative to the resin. The thermal conductivity for the ablative materials in the thermal protection systems structure was determined. A test facility using oxy-butane flame was developed through which the thermal protection systems developed were tested at extreme temperatures, to simulate some thermal conditions in space applications. The materials were characterised from a morphostructural point of view using optical and scanning electron microscopy after thermal testing. The TPS composed of the carbon-felt-based ablative layer showed improved behaviour compared to the cork-based ablative ones in terms of the temperature increase rate during thermal conductivity testing, mass loss, as well as morphostructural appearance and material erosion after oxy-butane testing. The nSiC-based samples in both sets of TPSs showed improved behaviour compared to the un-filled ones, considering the temperature increase, mass loss, and morphostructure of the eroded material. [ABSTRACT FROM AUTHOR]

Vacuum on-load tap-changers (OLTC) for converter transformers have a much higher number of breakings than conventional circuit breakers. Contact ablation after several breakings will affect the stability and life of the device. This paper establishes the electromagnetic thermal multi-physical field coupling model of the vacuum interrupter for OLTC based on the finite element analysis method. The thermal field distribution of normal and ablative contact materials during the breaking process was analyzed. The key parameters affecting the contact temperature under the cumulative number of breakings are analyzed and the optimized design is completed. The simulation results show that the contact surface reaches a maximum temperature of 1390 K at 8 ms. There is a significant increase in the area of the high-temperature area on the contact surface. The possibility of re-ignition of the interrupter is increased. Based on the judgment matrix method, the key influencing parameters of the contact temperature rise are analyzed. The final parameters are selected as follows: contact material—CuCr8 alloy, contact seat thickness—2 mm, contact thickness—10 mm, and contact diameter—40 mm. [ABSTRACT FROM AUTHOR]

We studied the behavioral characteristics of a newly developed dual-layer ablator, which uses carbon-phenolic as a recession layer and silica-phenolic as an insulating layer. The ablator specimens were tested in a 0.4 MW supersonic arc-jet plasma wind tunnel, employing two different shapes (flat-faced and hemispherical-faced) and varying thicknesses of the carbon-phenolic recession layer. The specimens underwent two test conditions, namely, stationary tests (7.5 MW/m2, ~40 s) and transient tests simulating an interplanetary spacecraft re-entry heat flux trajectory (6.25↔9.4 MW/m2, ~108 s). During the stationary tests, stagnation point temperatures of the specimens were measured. Additionally, internal temperatures of the specimens were measured at three locations for both stationary and transient tests: inside the carbon-phenolic recession layer, inside the silica-phenolic insulating layer, and at the recession layer–insulating layer intersection. The hemispherical-faced specimen surface temperatures were about 3000 K, which is about 350 K higher than those of flat-faced specimens, resulting in higher internal temperatures. The recession layer internal temperatures rose more exponentially when moved closer to the specimen stagnation point. Layer interaction and insulating layer internal temperatures were found to be dependent on both the recession layer thickness and the exposed surface shape. The change in exposed surface shape increased mass loss and recession, with hemispherical-faced specimens showing ~1.4-fold higher values than the flat-faced specimens. [ABSTRACT FROM AUTHOR]

Space exploration missions rely on ablative heat shields for the thermal protection of spacecraft during atmospheric entry flights. While dedicated research is needed for future missions, the scientific community has limited access to ablative materials typically used in aerospace. In this paper, we report the development of the HEFDiG Ablation-Research Laboratory Experiment Material (HARLEM), a carbon–phenolic ablator designed to supply the need for ablative materials in laboratory experiments. HARLEM is manufactured using polyacrylonitrile-based carbon fiber preforms and a simplified processing route for phenolic impregnation. We characterized the thermal protection performance of HARLEM in arcjet experiments conducted in the plasma wind tunnel PWK1 of the Institute of Space Systems at the University of Stuttgart. We assessed the performance of the new material by measuring surface recession rate and temperature using photogrammetry and thermography setups during the experiments, respectively. Our results show that HARLEM's thermal protection performance is comparable to legacy carbon–phenolic ablators that have been validated in different arcjet facilities or in-flight, as demonstrated by calculations of the effective heat of ablation and scanning electron microscopy of as-produced samples. In-house manufacturing of carbon–phenolic ablators enables the addition of embedded diagnostics to ablators, allowing for the acquisition of data on internal pressure and more sophisticated pyrolysis analysis techniques. [ABSTRACT FROM AUTHOR]

The silicon carbide (SiC) ceramic material was prepared by powder metallurgy processing route using spark plasma sintering (SPS) technique without any sintering additives. The effects of the SiC surface ablation by fiber laser and subsequent superficial incorporation of graphene nanoplatelets (GNPs) into the created microcraters were investigated in terms of their influence on the resulting tribological (i.e., friction and wear) behavior of the created SiC-graphene composite surfaces. It was clearly shown that the used laser treatment with the pulse duration in ms range led to desirable surface morphological changes, i.e., the creation of SiC ablated microrelief, suitable for GNPs incorporation. The friction and wear behavior of produced SiC-graphene composite surfaces was studied using translational ball-on-disc nanotribometer at room temperature and applied loading up to 1000 mN. The results showed that at all normal loads the wear rates of laser ablated surface materials were gradually decreasing as a result of frictional coefficient reduction. The observations of wear track topography indicated abrasive wear to be the dominant wear mechanism of the sintered SiC material. However, by incorporation of GNPs, the abrasive wear was significantly reduced by the graphene friction film created on the ablated SiC-graphene composite surfaces. [ABSTRACT FROM AUTHOR]

We developed and tested two carbon–phenolic-based ablators for future Korean spacecraft heat shield applications. The ablators are developed with two layers: an outer recession layer, fabricated from carbon–phenolic material, and an inner insulating layer, fabricated either from cork or silica–phenolic material. The ablator specimens were tested in a 0.4 MW supersonic arc-jet plasma wind tunnel at heat flux conditions ranging from 6.25 MW/m2 to 9.4 MW/m2, with either specimen being stationary or transient. Stationary tests were conducted for 50 s each as a preliminary investigation, and the transient tests were conducted for ~110 s each to stimulate a spacecraft's atmospheric re-entry heat flux trajectory. During the tests, each specimen's internal temperatures were measured at three locations: 25 mm, 35 mm, and 45 mm from the specimen stagnation point. During the stationary tests, a two-color pyrometer was used to measure specimen stagnation-point temperatures. During the preliminary stationary tests, the silica–phenolic-insulated specimen's reaction was normal compared to the cork-insulated specimen; hence, only the silica–phenolic-insulated specimens were further subjected to the transient tests. During the transient tests, the silica–phenolic-insulated specimens were stable, and the internal temperatures were lower than 450 K (~180 °C), achieving the main objective of this study. [ABSTRACT FROM AUTHOR]

Background: Chemical peeling is the controlled wounding of the epidermis and dermis for skin rejuvenation, involving the application of ablative agents to induce keratolysis and regeneration of damaged cell layers. Prolonged erythema is one complication of this procedure. We report the prevalence and probable etiology of prolonged facial erythema in a cohort of patients treated with medium‐depth chemical peels. Materials and Methods: A retrospective audit was conducted of all medium‐depth facial chemical peels performed at two major teaching hospitals. All patients had severe facial photodamage affecting at least 75% surface area of the face. The occurrence of prolonged erythema following this peel was then identified and analyzed. Results: Of our treatment cohort (n = 82, 51 women, 31 men) with 60 years mean (61.3 years for women, 56.7 years for men), 10 patients (12%; eight women, two men) experienced prolonged erythema beyond a month of treatment. Facial psoriasis was not apparent at the time of chemical peel but manifested as prolonged erythema beyond the expected timeframe following the procedure. Conclusion: When patients experience prolonged erythema beyond a month of treatment and fail to respond to standard treatments, clinicians should examine carefully for extra‐facial psoriasis prior to this procedure, and also consider facial psoriasis a possible cause of prolonged post‐peel erythema. [ABSTRACT FROM AUTHOR]

Recently, endoscopic ultrasound (EUS)‐guided ablation therapy has been reported as a less invasive therapy for patients with pancreatic neoplasms. Some ablation techniques, including injective ablation (using ethanol or other ablative agents), radiofrequency ablation (RFA), photodynamic therapy, and laser ablation, have been described in the literature. Among these, injective ablation and RFA are more frequently used for treating pancreatic neoplasms. Few studies have evaluated the effectiveness of EUS‐guided ethanol ablation (EUS‐EA) for potentially malignant solid neoplasms (neuroendocrine neoplasms or solid pseudopapillary neoplasms) and have reported a complete response (CR) rate of 60–80%. In addition, the CR rate after EUS‐RFA for these lesions has been reported to be 55–100%, with no additional procedure‐related adverse events (AEs). Regarding the amelioration of the symptoms of an insulinoma, the success rates of both the therapies were found to be excellent. Regarding complete tumor ablation, EUS‐RFA appeared to be superior to EUS‐EA. Although EUS‐RFA has been reported as a safe treatment for pancreatic cancers, its effectiveness remains inadequate. Some studies have examined the effectiveness of EUS‐guided injection ablation therapy for pancreatic cystic neoplasms (PCNs) and have reported CR rates that range from 35% to 79%. Alcohol‐free chemotherapeutic agent ablation appears to be effective, with a low risk of AEs. However, studies on the effectiveness of EUS‐RFA for PCNs are limited. In the future, EUS‐guided ablation therapy could become a more widely used approach for potentially malignant and malignant pancreatic lesions. [ABSTRACT FROM AUTHOR]

Recently, much effort has been dedicated to the high-density carbon ablator coated fuel capsule in indirect drive inertial confinement fusion experiments due to its higher density compared to other ablators. By using detailed radiation hydrodynamic simulations over a broad range of drive and target parameters, a thorough analysis is performed on shock speed, shock breakout, and maximum preheating temperature in pure and tungsten doped high density carbon foils. The ablators are irradiated by a non-equilibrium x-ray temperature drive consisting of the usual Planckian plus an additionally imposed Gaussian distribution lying in the high frequency M-band region of the incident spectrum. All variables have shown a complex interdependence on strength of the drive, its spectral distribution, and the thickness of the target. Maximum preheating temperature, an important parameter in designing experiments, reduces up to 34% for thicker high-density carbon (HDC) foils, whereas a mere 0.44% doping of tungsten in pure HDC is able to reduce preheating up to 17% for extreme drive conditions. The results are explained on the basis of variation of average albedo/wall loss behavior in foils, an outcome of the interplay between total extinction coefficient and spectral intensity variation with photon energy. For a better understanding and comparison among different types of ablators, multi-parameter scaling relations are proposed for above-mentioned variables, which govern the dynamics of shock propagation and preheating phenomena in HDC based foils. [ABSTRACT FROM AUTHOR]

In this review, all available publications on the polymerization of all isomers of bifunctional diethynylarenes due to the opening of C≡C bonds were considered and analyzed. It has been shown that with the use of polymers of diethynylbenzene, heat-resistant and ablative materials, catalysts, sorbents, humidity sensors, and other materials can be obtained. Various catalytic systems and conditions of polymer synthesis are considered. For the convenience of comparison, the publications considered are grouped according to common features, including the types of initiating systems. Critical consideration is given to the features of the intramolecular structure of the synthesized polymers since it determines the entire complex of properties of this material and subsequent materials. Branched and/or insoluble polymers are formed as a result of solid-phase and liquid-phase homopolymerization. It is shown that the synthesis of a completely linear polymer was carried out for the first time by anionic polymerization. The review considers in sufficient detail publications from hard-to-reach sources, as well as publications that required a more thorough critical examination. The review does not consider the polymerization of diethynylarenes with substituted aromatic rings because of their steric restrictions; the diethynylarenes copolymers with complex intramolecular structure; and diethynylarenes polymers obtained by oxidative polycondensation. [ABSTRACT FROM AUTHOR]

Purpose: The objective of this study is to examine the safety and efficacy of ablative therapy for hepatocellular carcinoma (HCC). Methods: A retrospective review of 419 consecutive patients diagnosed with HCC, treated with percutaneous ablation at a tertiary academic medical center from June 2015 to June 2022, was conducted. Data evaluated included demographics, disease and tumor burden scores, and functional status. Procedural outcomes included procedural course, complication rates, biochemical and radiologic response, survival, and functional status. Results: A total of 419 patients, including 313 males (74.7%) and 106 females (25.3%) with a mean age of 63.8 ± 6.64 years, made up the study cohort. 120 patients (28.6%) presented with solitary lesions and 299 patients (71.4%) had multifocal involvement, with a mean tumor size of 2.3 ± 0.92 cm. A majority of the interventions performed were microwave ablations (n = 413, 98.3%), with 6 radiofrequency ablations (1.4%). Treatment response was radiographically assessed up to 6 months post-ablation and graded as complete response (96.2%), partial response (2.6%), stable disease (0%), and progressive disease (1.2%). 97 (23.2%) of the treated patients went on to receive liver transplant. The average progression-free survival in the study population was 24 months with a survival of 85.9% (n = 360), 67.8% (n = 284), and 63.2% (n = 265) at 1 year, 3 years, and 5 years respectively. Functional outcomes, as defined by ECOG scores, were maintained or improved in 383 patients (91.4%) and 349 patients (83.3%) at 6 months and 12 months respectively. Conclusions: This large institutional experience demonstrated safety and efficacy of ablation therapies for treatment of HCC with promising tumor response rates and enduring clinical outcomes including prolonged survival and preserved functional status. [ABSTRACT FROM AUTHOR]

Analyses of thermal protection system response to atmospheric entry are generally performed in a decoupled manner where some terms in the surface balance equations are simplified. In such an approach, surface fluxes are calculated using a fluid dynamics solution of the hypersonic flowfield. These are nondimensionalized for use by a material response code, where correction terms are applied to account for the missing physics. A new method is presented here that directly includes ablation physics, thus removing the need for correction models. This approach includes the diffusion processes of ablative species in the boundary layer and nonequilibrium surface chemistry. The new approach is compared to the heritage methodology using a trajectory designed to allow molecular dissociation and vibrational energy contribution. The new methodology predicts surface temperatures with the same qualitative trend, with the largest disagreements in areas of the trajectory where nonequilibrium effects are expected to occur. The solid ablation flux and subsequent recession behavior are consistently lower for the new method, but this discrepancy in surface thermochemistry can be decreased by adopting kinetic models with more aggressive oxidation mechanisms. It is found that a large difference in computed recession does not necessarily equate to the largest difference in heat shield sizing. [ABSTRACT FROM AUTHOR]

Although chemotherapy constitutes of the first-line standard therapy for unresectable extrahepatic cholangiocarcinoma, the treatment outcomes are unsatisfactory. In recent years, local ablative therapy, which is delivered to the cholangiocarcinoma lesion via the percutaneous or endoscopic approach, has garnered attention for the treatment of unresectable, extrahepatic cholangiocarcinoma. Local ablative therapy, such as photodynamic therapy and radiofrequency ablation, can achieve local tumor control. A synergistic effect may also be expected when local ablative therapy is combined with chemotherapy. However, it is a long way from being entrenched as an established therapeutic technique, and several unresolved problems persist, including the paucity of evidence comparing photodynamic therapy and radiofrequency ablation. Clinical application of photodynamic therapy and radiofrequency ablation requires sound comprehension and assimilation of the available evidence to truly benefit each individual patient. In this study, we reviewed the current status, issues, and future prospects of photodynamic therapy and radiofrequency ablation for extrahepatic cholangiocarcinoma, with a special focus on their combination with chemotherapy. [ABSTRACT FROM AUTHOR]

BPR has been widely used as ablative material for thermal protection on aircraft surface. In this study, model-free method was employed to study the kinetic models of BPR and ZrSi2/B4C-Ph composite. In addition, the thermal stability, chemical reaction and structure evolution during pyrolysis of ZrSi2/B4C-Ph composite were characterized by TGA, XRD, XPS, GC–MS and TG-MS. The results indicated that the pyrolysis of BPR includes three consecutive and overlapping stages. And the kinetic mechanism function f(α), apparent activation energy Ea and pre-exponential factor A of each stage were confirmed. Besides, the high char yield of ZrSi2/B4C-Ph composite is mainly attributed to the reaction of ZrSi2 and B4C with gases released during BPR pyrolysis, which formed solid phases such as amorphous carbon, ZrO2, SiO2 and B2O3. [ABSTRACT FROM AUTHOR]

The ablative properties of epoxy-modified vinyl silicone rubber (EMVSR) composites containing hexaphenoxycyclotriphosphonitrile (HPCTP) have been systematically studied. The strength of the ablation char layer was greatly enhanced with the addition of HPCTP, which induced the formation of a more complete, denser, and thicker char during oxyacetylene ablation tests. Moreover, the HPCTP-containing EMVSR composites demonstrated lower thermal conductivity and pyrolysis rate when compared with those without HPTCP. At the same time, the thermal insulation properties of HPCTP-filled composites were improved under low heat flow ablation scenarios. The reduction of graphitic carbon content, the formation of phosphate-like crystals as well as the increase of SiC content contributed to strengthening the char layer, which was critical for improving the ablation properties. The optimum char layer strength and thermal insulation properties were achieved when the content of HPCTP was 15 phr, whereas an optimum ablation resistance was achieved at 25 phr HPCTP. This suggests that HPCTP-modified EMVSR composites can be used for thermal protection purposes, especially in the fields of aerospace and aeronautics. [ABSTRACT FROM AUTHOR]

Effect of highly-porous and lightweight carbon nanotube sponges on the high-power continuous wave laser ablation resistance of the sandwich panel was investigated experimentally. As a comparison, thermal responses of monolithic plate, carbon nanotube film filled sandwich panel, unfilled sandwich panel and carbon nanotube sponge filled sandwich panel subjected to continuous wave laser irradiation were analyzed. Experimental results showed that the laser resistance of the carbon nanotube filled sandwich panel is obviously higher than the unfilled structure. The added failure time of the sandwich panel by filling the cores with the carbon nanotube sponge of unit mass was about 18 times and 33 times longer than that by filling with the conventional ablative and insulated material. It could be understood by the high thermal diffusion coefficient and latent heat of sublimation of the carbon nanotube sponge. During ablation by the continuous wave, the carbon nanotube sponge not only fast consumed the absorbed laser energy through phase change of a large-area material due to its high latent heat of sublimation, but also quickly dispersed the heat energy introduced by the continuous wave laser due to its high thermal diffusion coefficient, leading to the extraordinary laser ablation resistance. [ABSTRACT FROM AUTHOR]

The ablation of fused silica and sapphire is investigated from the perspective of laser micromachining. In this study, dielectric rods are machined using a 12 ps pulsed laser at 1064 nm wavelength. The machining of the rods is a calibration method to determine process parameters for an analytical ablation model. More specifically, the ablation threshold fluence and effective penetration depth are determined under process-relevant conditions due to the removal of macroscopic volumes, which leads to a higher accordance. The introduced ablation model predicts macroscopic ablation volumes and ablation efficiencies of dielectric materials as a function of the angle of incidence. Originally, the ablation process model was developed for metals under the normal incidence, but this work extends its applicability to dielectrics. In contrast to metals, the optical penetration depth should be independent of the angle of incidence. Altogether, the presented model is universally applicable and can be seen as a first step toward computer-aided 3D-manufacturing using ultrashort pulsed lasers. The ability to predict ablation volumes and machine heat-sensitive tool materials with high accuracy and precision is demonstrated by the fabrication of end mills made of fused silica and sapphire with a diameter of 1 mm. This shows that picosecond lasers are well suited for the fabrication of such microcutting tools. In particular, the ability of ultrashort pulses to ablate materials independent of their hardness and without any wear makes this technology highly promising for the tooling industry. [ABSTRACT FROM AUTHOR]

Carbon‐phenolic ablators are very efficient heat shields for atmospheric reentry vehicles: they are able to protect a capsule from hyper thermal environments characterized by intense heat fluxes (>1 MW/m2) and very high temperature (also exceeding 300°C). Ablative materials can be modified by the addition of nano‐fillers in order to improve their performance: small amounts of nano‐fillers (in the order of 2–5 wt%) are able to enhance the matrix material properties, guarantying a weight saving too. In this work, three different kinds of ceramic nano‐particles (ZrO2, SiC, and MgO) were tested as fillers for a phenolic resin and for a carbon‐phenolic ablator: the variation in the mechanical properties and ablative performances were verified through mechanical tests and oxyacetylene flame exposure. The influence of the nano‐particles in the composite materials properties and the phenomena connected to their presence in the ablative material were deeply investigated with scanning electron microscope, EDS, XRD, and FTIR analysis. [ABSTRACT FROM AUTHOR]

Previously, hydrodynamic simulations [Clark et al., Phys. Plasmas 23, 072707 (2016)] suggested that precisely tailoring the capsule ablator thickness (shimming) could counterbalance cylindrical Hohlraum Legendre P4 drive asymmetries at the capsule in laser indirect drive implosions. As a result, the stagnated deuterium–tritium (DT) fuel areal density P4 asymmetry is reduced, potentially resulting in a nuclear yield increase. Inflight radiographs of various level of shimmed capsules with plastic (CH) ablators showed that shims can indeed control the in-flight capsule shell P4 asymmetry, with a linear sensitivity to shim amplitude that is close to analytic estimates and simulations. Furthermore, the stagnated DT fuel areal density P4 asymmetry inferred from downscattered neutron imaging was reduced when the capsule shim was applied, in agreement with simulations matching the inflight shell asymmetry. A nuclear yield improvement via shim was not observed, as predicted, likely due to implosion instabilities and as built capsule shim deviations from an ideal P4 shape. [ABSTRACT FROM AUTHOR]

Porous carbon ablators offer cost-effective thermal protection for aerospace vehicles during re-entry into planetary atmospheres. However, the exploration of more distant planets requires the development of ablators that are able to withstand stronger thermal radiation conditions. Here, we report the development of bio-inspired porous carbon insulators with pore sizes that are deliberately tuned to enhance heat-shielding performance by increasing scattering of high-temperature thermal radiation. Pore size intervals that promote scattering are first estimated using an established model for the radiative contribution to the thermal conductivity of porous insulators. On the basis of this theoretical analysis, we identify a polymer additive that enables the formation of pores in the desired size range through the polymerization-induced phase separation of a mixture of phenolic resin and ethylene glycol. Optical and electron microscopy, porosimetry and mechanical tests are used to characterize the structure and properties of porous insulators prepared with different resin formulations. Insulators with pore sizes in the optimal scattering range reduce laser-induced damage of the porous structures by up to 42%, thus offering a promising and simple route for the fabrication of carbon ablators for enhanced thermal protection at high temperatures. [Display omitted] [ABSTRACT FROM AUTHOR]

• Innovatively introduce the molecular structure of ceramic precursor into the molecular chain of silicone rubber. • Detailed analyzed the pyrolysis process and mechanism of PCS and silicone rubber. • Modification of liquid silicone rubber through blending and molecular modification and comparison of performance differences. • Developed high-performance flexible ablation materials. High ablation-resistant silicone rubber exhibits a significant role in the thermal protection of space vehicles. However, its limited by the low mechanical strength in practical heat protection applications. Herein, a novel molecular network structure is proposed, which links polycarboxysilane (PCS) rigid molecules onto polydimethylsiloxane molecular chains. The use of PCS rigid chains enhances the heat resistance while reducing the material's mass ablation rate. The addition of a small quantity of PCS (0.406 mmol) increases the tensile strength of the material by 10.4 % and augmentes the static ablation residual weight by 32.8 % compared with polydimethylsiloxane. Additionally, PCS molecular modification of polydimethylsiloxane is beneficial for maintaining the stability of the char layer after oxygen acetylene ablation, making the char layer denser, and improving the interface bonding between the ceramic layer, pyrolysis layer and matrix, ultimately improving the ablation performance of polydimethylsiloxane. This work provides a new approach for development of high-performance flexible ablative materials. [ABSTRACT FROM AUTHOR]

C f /SiC composites are regarded as difficult-to-machine aerospace materials. A low-damage surface machining of C f /SiC composite by laser-ablating assisted grinding (LAAG) was conducted, and investigated the effects of laser-ablating depth and grinding modes on surface/subsurface damages. The results showed that ablated material depth reached 420 μm after 1200 times scanning, while the effective ablating rate was inhibited by the depth. Compared with down grinding, the grinding forces and temperatures were substantially higher in up grinding, with a maximum increase of 123.5 % and 140 % in normal and tangential grinding forces, respectively; however, micro brittle fracture and ductile removal were remarkably enhanced in normal and transverse fibers, and surface macroscopic damage has been suppressed; subsurface damage remained insignificant, mainly exhibited in internal micro cracks and minor interfacial debonding. It was attributed to cutting characteristics of up grinding. Furthermore, as grinding depth increased, the material removal behavior underwent a brittle-ductile transition and the surface roughness grew accordingly. Moreover, a laser scanning angle of 0° and up grinding facilitated the occurrence of longitudinal fiber debonding, producing larger sized fiber bundle chips. Combining up grinding with 90° scanning angle at low grinding depth was an effective method to improve the surface quality of C f /SiC composite. [ABSTRACT FROM AUTHOR]

In order to solve the dual uncertainty problem between heat flux and thermophysical properties in the identification of the heat flux of charring ablative materials, a dynamic Bayesian network (DBN) based on multisource information fusion is proposed. The method is divided into two stages, with thermophysical properties identified in the former stage and the heat flux identified in the latter stage. A one-dimensional pyrolysis layer model is adopted to characterize the ablation process of materials. In the DBN, the multisource information of surface recession and temperature history data are considered as observation nodes. Sensitivity analysis is used to determine the key parameters in each time step in the DBN, and only key parameters are identified in the corresponding time step. Thus, with the increase of types of information and the decrease of the number of simultaneous identification parameters, the identification accuracy can be improved. The method was verified by numerical and experimental cases. In the numerical cases with noise and experimental cases, the maximum error of using the proposed method was 3.27% and 2.55%, respectively. Compared with only considering the temperature information, the relative errors of the identification results considering multisource information fusion were reduced by 83.95% and 47.53%, respectively. • A Bayesian method based on multisource information is proposed to solve the IHCP. • The surface recession of the ablation process was obtained by photographic method. • The introduction of multisource information improves the identification accuracy. [ABSTRACT FROM AUTHOR]

[Display omitted] • An optimized manufacturing strategy with PVP addition allowed to obtain micro/nano structured carbon-phenolic ablators. • FTIR analysis enlightens hydrogen bonds between PVP and phenolic resin. • Oxyacetylene flame torch exposure shows that the PVP-enriched ablators have superior performances than the standard ones. • Microstructures and porosities were analyzed with SEM and XRM analysis. • Compression tests enlighten superior mechanical properties for charred PVP-enriched ablators. Carbon-phenolic ablators can efficiently protect space vehicles from the extreme temperatures typical of the reentry phase in a planet's atmosphere. Their performances are attributed to the low thermal conductivity and to the decomposition of the phenolic resin. These phenomena are strongly influenced by the materials microstructure. In the present work, standard and polyvinylpyrrolidone (PVP)-modified carbon-phenolic ablators were manufactured and characterized: the influence of PVP on the final microstructure and chemistry of the ablators was studied through SEM-EDS, X-ray Microscopy (XRM) analysis and FTIR technique; the mechanical properties were evaluated through compression tests on virgin and charred samples while ablative performance of the ablators were evaluated with an oxyacetylene flame exposure test. Weak bonds between phenolic resin chains and PVP were observed. The microstructure of the ablators, both before and after the exposure to the oxyacetylene flame, is strongly influenced by the PVP addition, furthermore the addition of 10 and 20 %wt of PVP can guarantee a reduction of about 30 % of the back temperature during the oxyacetylene flame test with respect to the standard carbon-phenolic ablator. Compression tests on the manufactured ablators enlighten also an improvement in the mechanical properties for PVP-enriched ablators, in particular considering their charred state. [ABSTRACT FROM AUTHOR]

In this study, the CW laser is used as a local heat source to simulate the extreme thermal environment generated by shock wave interference at discontinuities in spacecraft. The ablation behavior of the thermal protection material (C/SiC) is investigated under the combined impact of high-temperature airflow and the local extreme heat source. A novel multi-field coupling numerical computation software was presented to examine this strong coupling process of fluid-solid-thermal-ablation. The program was modified using the ALE + umeshmotion ablation calculation method in the ABAQUS software to mimic the process of the material's ablative boundary retreating under the action of the CW laser until the target was perforated. ANSYS Fluent software was used to do the numerical analysis of the high-speed airflow. The results of wind tunnel experiments and numerical simulations indicate that, compared to the effect of local heat sources in static air, irregular ablation pits are formed on the material surface under the action of local heat sources in high-temperature flow fields, resulting in higher ablation rates due to mechanical denudation effects. Analysis of the localization characteristics of the flow field near the ablation pit reveals that the shock wave generated downstream of the ablation pit leads to an increase in gas temperature, pressure, and density. When the ablation amount reaches a certain threshold, the gas in the ablation pit forms vortices, leading to an increase in local heat flow and pressure. [ABSTRACT FROM AUTHOR]

• Advanced thermal protection system suitable for various ablative environments. • Importance of low-temperature oxidation protection is emphasized for the first time. • B 2 O 3 reinforced materials show comprehensive and superior ablation resistance. • The reinforcement mechanism of B 2 O 3 on the ablation resistance was revealed. • This work opens a new avenue for the design of high-performance ablative materials. Solid rocket motors (SRMs) have multiple working states, and thermal protection system (TPS) materials used in their combustion chambers must possess high ablation resistance in different ablation environments. However, the currently utilized TPS materials do not fully satisfy this requirement. In this study, the importance of the thermal oxidation protection of a char layer at low temperatures was established for the first time. This was achieved via B 2 O 3 addition, which produced a B 2 O 3 liquid film that considerably improved the char layer performance and ablation resistance of the TPS materials. Typical ablation tests were conducted to demonstrate the superior ablation resistance of B 2 O 3 formulations, and char layer characteristics were analyzed to elucidate the B 2 O 3 reinforcement mechanism. This work opens a new avenue for the design of high-performance TPS materials and presents novel B 2 O 3 -reinforced TPS materials with excellent ablation performance, which can help improve the comprehensive performances of TPSs and SRMs. [Display omitted] [ABSTRACT FROM AUTHOR]

Compared with ordinary metal structures, advanced composite materials have the characteristics of high strength, high rigidity, and light weight. The use of composite materials in aircraft structures is currently a hot research topic. This research mainly discusses the optimization design of the composite wing structure of the DF-2 light sports aircraft. This article takes the DF-2 light sports aircraft planned to be produced by the company as the source. Based on its overall design basis, aerodynamic requirements, and the original wing structure design, according to the composite material aircraft structure design theory and method, the aircraft wing structure is carried out. Composite materials are materials with new properties that are composed of two or more materials with different properties at the macroscale by physical and chemical methods. Composite materials can be divided into functional composite materials and structural composite materials according to the nature of the application. Functional composites are materials with special functions, such as conductive composites, ablative materials, and frictional composites. At present, the main research is on structural composite materials, which are composed of two components: matrix material and reinforcing material. The new structural scheme design and structural strength analysis are designed to meet the structural strength requirements of the wing and the lightest weight. In this paper, according to the force transmission characteristics of different structural types of the wing, the characteristics of the load transmission are analyzed, and the shape parameters and load parameters of the wing structure design are used as initial conditions, and the quantitative analysis model of the wing structure is constructed according to the requirements of strength, stiffness, and stability. Through rapid mathematical modeling and analysis of the wing structure, the weight and efficiency of different configurations can be evaluated. Through the quantitative analysis model of the wing, the wing structure type can be quickly determined according to the wing parameters in the preliminary design, which makes the basis for the selection of the wing structure type. After optimization, the weight of the wing structure decreased from 0.966 kg to 0.803 kg, a decrease of 16.87%. The designability of composite materials is one of its major characteristics. By optimizing the layup angle, layup sequence, and dropout area, the performance indicators of the structure are finally improved. This research will promote the further development of the aerospace field. [ABSTRACT FROM AUTHOR]

In low environmental disturbances, secondary mechanisms play a crucial role in flow instability and transition. Over the years, researchers have shown the existence of secondary waves prior to nonlinear breakdown and turbulence. In high-speed flows, the vehicles are subjected to extreme thermal loads, and usually, an ablative heat shield is used for protection. The ablative materials eject gaseous products upon heating, significantly affecting flow stability. Mass injection through the surface in the boundary layer loosely replicates the ablation process. Its effect on stability and transition has been explored earlier using experiments, numerical simulation, and Linear Stability Theory (LST). However, the effect of the surface injection on secondary instability, the most viable path to transition, remains uncertain. The present work studies the secondary instability of a hypersonic boundary over a 7° half-angle blunt cone in the presence of mass injection through the surface of the boundary layer. Mean flow over the cone is solved using a high-order shock fitting direct numerical simulation code. Primary instability is studied using the LST, and secondary instability is studied using the secondary instability theory based on the Floquet model. Computations are carried out for different injection rates, and it is found that instability increases with mass injection rate. The mass injection has increased the primary and secondary growth rates. Fundamental modes are more dominant than subharmonic and detuned modes at higher primary wave amplitudes. The mass injection has increased the primary and secondary N-factor, and transitioning behavior is observed at the maximum injection rate. [ABSTRACT FROM AUTHOR]

The thermal protection system is essential for the safe and reliable flying of any high-speed aircraft. A carbon fiber-reinforced phenolic resin (PR) composite is one of the most important matrix candidates for ablative materials, and the microscopic understanding of the pyrolysis process of PR, however, still remains poor. The usual numerical approach is based on volumetric pyrolysis while neglecting the influence of external hyperthermal surroundings. A surface-volume coupled reactive molecular dynamics model is established in this work to simulate complicated heat/mechanics/chemistry multi-physical field coupled pyrolysis problems. The pyrolysis process of the carbon fiber-PR composite is investigated in the presence of vacuum and hyperthermal gas impacts and compared with the volumetric pyrolysis simulation only. The consideration of the surface–volume coupling reveals many unique features beyond the volumetric pyrolysis, which include the generation of different pyrolysis products and the dependence of the effective mass diffusivity of pyrolysis gases on impinging gases in the presence of the hyperthermal non-equilibrium environment. With the detailed revelation of the evolutions of PR solid phase and pyrolysis gaseous products, the work is of great help in improving the microscopic pyrolysis mechanisms, especially the "blowing gas effect," a key phenomenon for improved understanding of the complicated hypersonic boundary layer flow. [ABSTRACT FROM AUTHOR]

The characteristics of x-ray radiation of a target that is bombarded by a beam of accelerated electrons ejected by a low-power vacuum discharge with laser ignition are studied. It is shown that the maximum radiation energy exceeds the applied potential difference across the discharge gap by almost an order of magnitude and is inversely proportional to the mass of the cathode material ablated by laser radiation. The energy spectrum of x-ray radiation reconstructed from the radiation attenuation curve by filters-absorbers of various thicknesses showed that in the maximum acceleration mode the average energy of the main part of the spectrum is more than four times higher than the voltage across the discharge gap at the moment of beam emission. Possible mechanisms providing anomalous acceleration of electrons in the discharge are considered. [ABSTRACT FROM AUTHOR]

Detailed investigations are carried out on shock, preheat, and ablation characteristics in x-ray driven beryllium based targets, a candidate ablator material for many inertial confinement fusion studies due to its high mass ablation rate. The study involves extensive radiation hydrodynamic simulations performed on pure and 1% copper doped beryllium foils irradiated by a temperature drive source consisting of both Planckian and Gaussian distributions with peaks lying in soft and hard x-ray regions, respectively. The results of steady state x-ray driven ablation and radiant heat exchange in a sub-critical shock are extended to a non-Planckian source. Based on that, new scaling relations are proposed for shock velocity, shock breakout temperature, maximum preheat temperature, and mass ablation rate with the temperature (120 − 200 eV) and the fraction of total energy density due to Gaussian distribution (0 − 0.25) of the incident drive. All parameters increase with drive temperature strength, but the presence of hard x rays does not affect them uniformly. Among all, preheat and shock breakout temperature exhibit a strong dependence on fraction of hard x rays present in the drive spectrum. The effect of doping translates into a pronounced decrease in preheat and shock breakout temperature, while mass ablation rate reduces marginally. The resulting variations in different parameters are explained on the basis of distribution of total extinction coefficient over the spectral form of an incident drive source. [ABSTRACT FROM AUTHOR]

At present, the use of microstructure to change the optical properties and wetting properties of the material itself has become the main means to improve the utilization rate of materials in the manufacturing industry. Due to the hydrophilicity of the material surface can achieve underwater self-cleaning, directional transportation function, it becomes an indispensable part of surface modification. Water jet-guide laser processing can significantly reduce the formation of the heat-affected zone and crack, and can clearly ablate the material, with higher precision and resolution. In this experiment, the effects of scan spacing, laser output power and channel aspect ratio are examined and processing conditions for achieving near superhydrophilicity are provided. Owing to the anaerobic processing environment, the surface chemical composition of the material does not change, and the hydrophilicity is increased by 8% to 43% compared with that before. Increasing the aspect ratio can increase the wettability, when the aspect ratio is more than 1.63, the wettability begins to rebound, and the wettability becomes worse. Using small laser power and multiple scanning processing scheme can make the surface covered with tiny small pillars of micro-nano particles layer beneficial to increase the droplet adhesion, and the minimum contact angle can reach 37.2°. [ABSTRACT FROM AUTHOR]

It has long been recognized that high compression, and hence good confinement, is essential to achieving high yields in inertial confinement fusion implosions. In pursuit of multi-megajoule yields on the National Ignition Facility (NIF), a new campaign has begun aimed at testing the hypothesis that controlling hydrodynamic stability is key to achieving effective higher compression with the high density carbon ablators currently fielded on NIF. This campaign is built around a new implosion design, called SQ-n, that is derived from the uniquely stable Bigfoot design tested on NIF in 2016–2019. While very stable and with performance that was quite close to one-dimensional expectations, Bigfoot was a relatively high adiabat, and consequently lower compression design. The goal of SQ-n is then to evolve Bigfoot toward a higher compression design but without compromising its unique stability characteristics. Specifically, SQ-n adopts a ramped foot pulse shape to minimize early time Richtmyer–Meshkov instability growth and uses an ablator dopant distribution extending all of the way to the fuel–ablator interface that simulations suggest further reduces perturbation growth. This paper describes the design philosophy pursued with SQ-n, the results of instability modeling of the candidate design, and the experimental campaign planned to test these ideas in the near future. [ABSTRACT FROM AUTHOR]

Background: Orthotopic liver transplantation (OLT) is the accepted treatment in patients with unresectable, early-stage hepatocellular carcinoma (HCC) in the setting of cirrhosis. Due to increasing waitlist demand for OLT, determining optimal groups for transplant is critical. Elderly patients are known to have poorer postoperative outcomes. Considering the effectiveness of liver-directed therapies for HCC, we sought to determine whether elderly patients received survival benefit from OLT over liver-directed therapy alone.Study Design: The National Cancer Database participant use file was used to analyze data between 2004 and 2017. Only patients ≥70 years of age who received OLT or liver-directed therapy alone were included. Patients with alpha-fetoprotein >500 ng/mL or missing alpha-fetoprotein values were excluded. Baseline demographic variables, model for end-stage liver disease score, and overall survival from time of diagnosis were collected. Descriptive statistics, Kaplan-Meier survival, Cox proportional hazards model, and propensity score matching were used.Results: A total of 2,377 patients received ablative therapy alone, and 214 patients received OLT. Multivariable analysis and Kaplan-Meier showed that OLT conferred a significant survival benefit compared to liver-directed therapy alone. Age was also associated with a yearly 3% increase in risk of mortality. Propensity-matched analysis adjusting also demonstrated a significant survival benefit for elderly patients receiving OLT compared to liver-directed therapy alone.Conclusion: Despite increased age and associated comorbidities being factors associated with poor outcomes, OLT confers a survival advantage compared to liver-directed ablative therapies alone in selected elderly patients with HCC. OLT should be offered in medically appropriate elderly patients with HCC. [ABSTRACT FROM AUTHOR]

Neutron, gamma-ray, and x-ray imaging are important diagnostic tools at the National Ignition Facility (NIF) for measuring the two-dimensional (2D) size and shape of the neutron producing region, for probing the remaining ablator and measuring the extent of the DT plasmas during the stagnation phase of Inertial Confinement Fusion implosions. Due to the difficulty and expense of building these imagers, at most only a few two-dimensional projections images will be available to reconstruct the three-dimensional (3D) sources. In this paper, we present a technique that has been developed for the 3D reconstruction of neutron, gamma-ray, and x-ray sources from a minimal number of 2D projections using spherical harmonics decomposition. We present the detailed algorithms used for this characterization and the results of reconstructed sources from experimental neutron and x-ray data collected at OMEGA and NIF. [ABSTRACT FROM AUTHOR]

Ethylene–propylene–diene monomer (EPDM) composites were usually enhanced with ablative additives to protect solid rocket motor (SRMs) casings. However, the poor thermal insulation caused by the high thermal conductive ablative fillers can lead to rocket motor failure. Herein, the novel EPDM composites containing alternating layers of ablative EPDM (AM) and heat-insulated EPDM (HM) were prepared through layer-multiplying extrusion. Compared with conventional EPDM ablative material, the multilayer composites showed enhanced thermal insulation and mechanical properties that could be further improved by tuning the number of layers. The ablation and thermal insulation properties possessing in AM and HM layers could be combined by forced assembly during co-extrusion, and the alternating multilayer composite was capable of showing the effect of each component. In particular, compared with AM, the maximum back-face temperature with 40 alternating layers of AM/HM decreased from 96.2 °C to 75.6 °C during oxyacetylene test, while the good ablation properties were preserved in the AM component. This significant improvement was attributed to the planar orientation and densification of ablative additives, and the interruption of conductive pathways in the through-plane direction of AM/HM alternating laminate. The anisotropic EPDM composites featuring mechanical robustness, good ablative resistance and thermal insulation suggest considerable potential application in the aerospace industry. [ABSTRACT FROM AUTHOR]

High-yield implosions on the National Ignition Facility rely on maintaining low entropy in the deuterium–tritium fuel, quantified by its adiabat, in order to efficiently couple energy to the hot spot through high compression of the fuel layer. We present very-high-resolution xRAGE simulation results that study the impacts of interfacial mixing and the jetting of materials due to surface defects, defects on internal interfaces, voids, and engineering features on fuel layer compression. Defects and voids are typically neglected in implosion simulations due to their small size and three-dimensional geometry. Our results showed that supersonic jets of material arise through weak spots in the shell at peak implosion velocity that prevent uniform compression of the fuel layer even when they do not introduce contaminant into the hot spot. This occurs despite maintaining low fuel entropy, since the formation of the weak spots involves nonradial displacement of fuel mass. In contrast, simulations show that fuel–ablator mixing due to interfacial instabilities has a much smaller impact on compression. We show that defects on interior interfaces of plastic capsules decrease compression by 15% to 25% and interfacial mixing between the ablator and fuel decreases compression by less than 1% for implosions with plastic or high-density carbon (HDC) ablators. For low adiabat implosions, the impact of jetting seeded by the support tent can also decrease the compression by 25%. We demonstrate that the inclusion of interior defects in simulations can explain the inferred compression in two fielded plastic capsule implosions and that the inclusion of voids, for which available characterization has large uncertainties, in simulations of HDC capsule implosions has a qualitatively consistent impact. This mechanism offers a potential explanation for persistently overestimated fuel compression in design simulations of layered implosions on the National Ignition Facility. [ABSTRACT FROM AUTHOR]

High silicon oxygen/phenolic aldehyde (VSF/PR) ablative heat-proof material is widely used as resin-based heat-proof system for long-term aircraft. Understanding the generation and flow process of the surface droplets during high temperature is key to improving the thermal stability, and prior to which, a direct visualization of the surface evolution is required. Here we use optical imaging technique to in-situ and real time record the surface evolution of a flat plate subjected to thermal ablation at 1700 °C in wind tunnel. Based on the experimental results processed using image processing method and by combining the fluid theory in high temperature wind tunnel, we explained the distribution of the surface temperature and surface liquid droplets, the velocity field, and the movement of the liquid droplets on the plate surface. Results show that the distribution of the liquid droplets was correlated to the temperature distribution. A verification experiment for the merging process of two liquid droplets shows that droplet with high viscosity would generate a great friction force and cause the droplet to move forward in a rolling manner. The chasing and merging process of the liquid droplets with high viscosity is rather an entrainment process than a spontaneous merging process normally induced by surface tension. These findings help to understand the flow behavior of the liquid droplets during thermal ablation. [ABSTRACT FROM AUTHOR]