Temperature and structure measurements of heavy-ion-heated diamond using in situ X-ray diagnostics

We present in situ measurements of spectrally resolved X-ray scattering and X-ray diffraction from monocrystalline diamond samples heatedwith an intense pulse of heavy ions.In this way,we determine the samples’heating dynamics and their microscopic and macroscopic structuralintegrity over a timespan of several microseconds.Connecting the ratio of elastic to inelastic scattering with state-of-the-art density functionaltheory molecular dynamics simulations allows the inference of average temperatures around 1300 K,in agreement with predictions fromstopping power calculations.The simultaneous diffraction measurements show no hints of any volumetric graphitization of the material,butdo indicate the onset of fracture in the diamond sample.Our experiments pave the way for future studies at the Facility for Antiproton andIon Research,where a substantially increased intensity of the heavy ion beam will be available.

National Forest Inventories capture the multifunctionality of managed forests in Germany

Background:Forests perform various important ecosystem functions that contribute to ecosystem services.In many parts of the world,forest management has shifted from a focus on timber production to multi-purpose forestry,combining timber production with the supply of other forest ecosystem services.However,it is unclear which forest types provide which ecosystem services and to what extent forests primarily managed for timber already supply multiple ecosystem services.Based on a comprehensive dataset collected across 150 forest plots in three regions differing in management intensity and species composition,we develop models to predict the potential supply of 13 ecosystem services.We use those models to assess the level of multifunctionality of managed forests at the national level using national forest inventory data.Results:Looking at the potential supply of ecosystem services,we found trade-offs(e.g.between both bark beetle control or dung decomposition and both productivity or soil carbon stocks)as well as synergies(e.g.for temperature regulation,carbon storage and culturally interesting plants)across the 53 most dominant forest types in Germany.No single forest type provided all ecosystem services equally.Some ecosystem services showed comparable levels across forest types(e.g.decomposition or richness of saprotrophs),while others varied strongly,depending on forest structural attributes(e.g.phosphorous availability or cover of edible plants)or tree species composition(e.g.potential nitrification activity).Variability in potential supply of ecosystem services was only to a lesser extent driven by environmental conditions.However,the geographic variation in ecosystem function supply across Germany was closely linked with the distribution of main tree species.Conclusions:Our results show that forest multifunctionality is limited to subsets of ecosystem services.The importance of tree species composition highlights that a lack of multifunctionality at the stand level can be compensated by managing forests at the landscape level,when stands of complementary forest types are combined.These results imply that multi-purpose forestry should be based on a variety of forest types requiring coordinated planning across larger spatial scales.

Utilization of nonlinear vibrations of soft pipe conveying fluid for driving underwater bio-inspired robot

Creatures with longer bodies in nature like snakes and eels moving in water commonly generate a large swaying of their bodies or tails,with the purpose of producing significant frictions and collisions between body and fluid to provide the power of consecutive forward force.This swaying can be idealized by considering oscillations of a soft beam immersed in water when waves of vibration travel down at a constant speed.The present study employs a kind of large deformations induced by nonlinear vibrations of a soft pipe conveying fluid to design an underwater bio-inspired snake robot that consists of a rigid head and a soft tail.When the head is fixed,experiments show that a second mode vibration of the tail in water occurs as the internal flow velocity is beyond a critical value.Then the corresponding theoretical model based on the absolute nodal coordinate formulation(ANCF)is established to describe nonlinear vibrations of the tail.As the head is free,the theoretical modeling is combined with the computational fluid dynamics(CFD)analysis to construct a fluid-structure interaction(FSI)simulation model.The swimming speed and swaying shape of the snake robot are obtained through the FSI simulation model.They are in good agreement with experimental results.Most importantly,it is demonstrated that the propulsion speed can be improved by 21%for the robot with vibrations of the tail compared with that without oscillations in the pure jet mode.This research provides a new thought to design driving devices by using nonlinear flow-induced vibrations.

Relaxor ferroelectric and dielectric properties of(1-x)Ba(Zr_(1/3)Ti_(2/3))O_(3)-xBaMg_(0.1)Ta_(0.9))O_(3)ceramics

The environmentally-friendly(1-x)Ba(Zr_(1/3)Ti_(2/3))O_(3)-xBaMg_(0.1)Ta_(0.9))O_(3)(x=0,0.02,0.04,0.06,0.08)relaxor ferroelectric ceramics were prepared by the conventional solid-state method and sintered in air at 1400°C for 2 h.SEM and XRD analyses were utilized to study the surface morphologies and the crystalline structures,respectively.The effects of BaMg_(0.1)Ta_(0.9))O_(3)on the phase transformation,dielectric and ferroelectric properties of Ba(Zr_(1/3)Ti_(2/3))O_(3)ceramics were also investigated.It is found that the average grain size of(1-x)Ba(Zr_(1/3)Ti_(2/3))O_(3)-xBaMg_(0.1)Ta_(0.9))O_(3)(BZT-BMT)perovskite single-phase ceramics decreases as the content of BaMg_(0.1)Ta_(0.9))O_(3)(BMT)increases.The relaxor ferroelectric behavior with diffuse phase transition and well-defined frequency dispersion of dielectric maximum temperature is found for the ceramic with increasing x values.0.98BZT-0.02BMT ceramic shows very good dielectric properties with the relative permittivity and the dielectric loss,measured at 100 k Hz as 6034 and 0.01399 respectively at room temperature.Both remnant polarization and coercive field decreased with increasing BMT content,indicating a transition from the ferroelectric phase to the paraelectric phase at room temperature.

Synchronized off-harmonic probe laser with highly variable pulse duration for laser-plasma interaction experiments

This paper presents the development and experimental utilization of a synchronized off-harmonic laser system designed as a probe for ultra-intense laser±plasma interaction experiments. The system exhibits a novel seed-generation design,allowing for a variable pulse duration spanning over more than three orders of magnitude, from 3.45 picoseconds to 10 nanoseconds. This makes it suitable for various plasma diagnostics and visualization techniques. In a side-view configuration, the laser was employed for interferometry and streaked shadowgraphy of a laser-induced plasma while successfully suppressing the self-emission background of the laser±plasma interaction, resulting in a signal-to-self-emission ratio of 110 for this setup. These properties enable the probe to yield valuable insights into the plasma dynamics and interactions at the PHELIX facility and to be deployed at various laser facilities due to its easy-to-implement design.

Novel C_(sf)/SiBCN composites prepared by densifying C_(sf)/MA-SiBCN with the PIP process:Oxidation behavior and damage mechanism

To improve the oxidation resistance of short carbon fiber(C_(sf))-reinforced mechanically alloyed SiBCN(MA-SiBCN)(C_(sf)/MA-SiBCN)composites,dense amorphous C_(sf)/SiBCN composites containing both MA-SiBCN and polymer-derived ceramics SiBCN(PDCs-SiBCN)were prepared by repeated polymer infiltration and pyrolysis(PIP)of layered C_(sf)/MA-SiBCN composites at 1100℃,and the oxidation behavior and damage mechanism of the as-prepared C_(sf)/SiBCN at 1300–1600℃ were compared and discussed with those of C_(sf)/MA-SiBCN.The C_(sf)/MA-SiBCN composites resist oxidation attack up to 1400℃ but fail at 1500℃ due to the collapse of the porous framework,while the PIP-densified C_(sf)/SiBCN composites are resistant to static air up to 1600℃.During oxidation,oxygen diffuses through preexisting pores and the pores left by oxidation of carbon fibers and pyrolytic carbon(PyC)to the interior of the matrix.Owing to the oxidative coupling effect of the MA-SiBCN and PDCs-SiBCN matrices,a relatively continuous and dense oxide layer is formed on the sample surface,and the interfacial region between the oxide layer and the matrix of the as-prepared composite contains an amorphous glassy structure mainly consisting of Si and O and an incompletely oxidized but partially crystallized matrix,which is primarily responsible for improving the oxidation resistance.

Composition-dependent structural characteristics and mechanical properties of amorphous SiBCN ceramics by ab-initio calculations

The atomic structural features and the mechanical properties of amorphous silicoboron carbonitride ceramics with 13 different compositions in the Si–BN–C phase diagram are investigated employing ab-initio calculations.Both chemical bonds and local structures within the amorphous network relate to the elemental composition.The distribution of nine types of chemical bonds is composition-dependent,where the B–C,Si–N,Si–C,and B–N bonds hold a large proportion for all compositions.Si prefers to be tetrahedrally coordinated,while B and N prefer sp^(2)-like trigonal coordination.In the case of C,the tetrahedral coordination is predominant at relatively low C contents,while the trigonal coordination is found to be the main feature with the increasing C content.Such local structural characteristics greatly influence the mechanical properties of SiBCN ceramics.Among the studied amorphous ceramics,SiB_(2)C_(3)N_(2) and SiB_(3)C_(2)N_(3) with low Si contents and moderate C and/or BN contents have high elastic moduli,high tensile/shear strengths,and good debonding capability.The increment of Si,C,and BN contents on this basis results in the decrease of mechanical properties.The increasing Si content leads to the increment of Si-contained bonds that reduce the bond strength of SiBCN ceramics,while the latter two cases are attributed to the raise of sp^(2)-like trigonal configuration of C and BN.These discoveries are expected to guide the composition-tailored optimization of SiBCN ceramics.

Microstructure and evolution of hafnium carbide whiskers via polymer-derived ceramics:A novel formation mechanism

Polymer-derived ultra-high-temperature ceramic(UHTC)nanocomposites have attracted growing attention due to the increasing demands for advanced thermal structure components in aerospace.Herein,hafnium carbide(HfC)whiskers are successfully fabricated in carbon fiber preforms via the polymer-derived ceramic(PDC)method.A novel carbon nanotube(CNT)template growth mechanism combined with the PDC method is proposed in this work,which is different from the conventional vapor–liquid–solid(VLS)mechanism that is commonly used for polymer-derived nanostructured ceramics.The CNTs are synthesized and proved to be the templates for fabricating the HfC whiskers,which are generated by the released low-molecular-weight gas such as CO,CO_(2),and CH4 during the pyrolysis of a Hf-containing precursor.The formed products are composed of inner single crystal HfC whiskers that are measured to be several tens of micrometers in length and 100–200 nm in diameter and outer HfC/HfO_(2)particles.Our work not only proposes a new strategy to prepare the HfC whiskers,but also puts forward a new thinking of the efficient utilization of a UHTC polymer precursor.

Zernike-coefficient extraction via helical beam reconstruction for optimization(ZEHBRO) in the far field

The spatial distribution of beams with orbital angular momentum in the far field is known to be extremely sensitive to angular aberrations,such as astigmatism,coma and trefoil.This poses a challenge for conventional beam optimization strategies when a homogeneous ring intensity is required for an application.We developed a novel approach for estimating the Zernike coefficients of low-order angular aberrations in the near field based solely on the analysis of the ring deformations in the far field.A fast,iterative reconstruction of the focal ring recreates the deformations and provides insight into the wavefront deformations in the near field without relying on conventional phase retrieval approaches.The output of our algorithm can be used to optimize the focal ring,as demonstrated experimentally at the 100 TW beamline at the Extreme Light Infrastructure-Nuclear Physics facility.

Tailoring magnetic hysteresis of additive manufactured Fe-Ni permalloy via multiphysics-multiscale simulations of process-property relationships

Designing the microstructure of Fe-Ni permalloy produced by additive manufacturing(AM)opens new avenues to tailor its magnetic properties.Yet,AM-produced parts suffer from spatially inhomogeneous thermal-mechanical and magnetic responses,which are less investigated in terms of process modeling and simulations.We present a powder-resolved multiphysics-multiscale simulation scheme for describing magnetic hysteresis in AM-produced material,explicitly considering the coupled thermal-structural evolution with associated thermo-elasto-plastic behaviors and chemical order-disorder transitions.The residual stress is identified as the key thread in connecting the physical processes and phenomena across scales.By employing this scheme,we investigate the dependence of the fusion zone size,the residual stress and plastic strain,and the magnetic hysteresis of AM-produced Fe_(21.5)Ni_(78.5) on beam power and scan speed.Simulation results also suggest a phenomenological relation between magnetic coercivity and average residual stress,which can guide the magnetic hysteresis design of soft magnetic materials by choosing appropriate processing parameters.

Ta_(4)HfC_(5)-Si_(2)BC_(3)N复相陶瓷的界面结构和晶粒生长行为

超高温陶瓷(UHTC)Ta_(4)HfC_(5)因其优异的热物理和热机械性能而成为适用于高超音速飞行器最有前途的候选材料之一.然而,较差的烧结能力限制了其潜在的使用.为了克服该障碍,采用Si_(2)BC_(3)N陶瓷对钽-铪碳化物固溶体进行了致密化处理.通过热压烧结合成了致密的Ta_(4)HfC_(5)-Si_(2)BC_(3)N陶瓷,所得复相陶瓷由Ta_(4)HfC_(5),SiC和BN(C)相组成.在2100℃下,随着晶粒的快速生长,陶瓷内形成了“蝌蚪”状的SiC和BN(C)连接相,断裂韧性提高到3.47±0.12 MPa m^(1/2).随着烧结温度的升高,Ta_(4)HfC_(5)晶粒的生长活化能从112.4 kJ mol^(−1)增加到250.7±29.3 kJ mol^(−1).

Millijoule ultrafast optical parametric amplification as replacement for high-gain regenerative amplifiers

We report on the development of an ultrafast optical parametric amplifier front-end for the Petawatt High Energy Laser for heavy Ion eXperiments(PHELIX)and the Petawatt ENergy-Efficient Laser for Optical Plasma Experiments(PEnELOPE)facilities.This front-end delivers broadband and stable amplification up to 1 mJ per pulse while maintaining a high beam quality.Its implementation at PHELIX allowed one to bypass the front-end amplifier,which is known to be a source of pre-pulses.With the bypass,an amplified spontaneous emission contrast of 4.9×10^(−13)and a pre-pulse contrast of 6.2×10^(−11)could be realized.Due to its high stability,high beam quality and its versatile pump amplifier,the system offers an alternative for high-gain regenerative amplifiers in the front-end of various laser systems.

Versatile tape-drive target for high-repetition-rate laser-driven proton acceleration

We present the development and characterization of a high-stability,multi-material,multi-thickness tape-drive target for laser-driven acceleration at repetition rates of up to 100 Hz.The tape surface position was measured to be stable on the sub-micrometre scale,compatible with the high-numerical aperture focusing geometries required to achieve relativistic intensity interactions with the pulse energy available in current multi-Hz and near-future higher repetition-rate lasers(>kHz).Long-term drift was characterized at 100 Hz demonstrating suitability for operation over extended periods.The target was continuously operated at up to 5 Hz in a recent experiment for 70,000 shots without intervention by the experimental team,with the exception of tape replacement,producing the largest data-set of relativistically intense laser–solid foil measurements to date.This tape drive provides robust targetry for the generation and study of high-repetitionrate ion beams using next-generation high-power laser systems,also enabling wider applications of laser-driven proton sources.

Automated control and optimization of laser-driven ion acceleration

The interaction of relativistically intense lasers with opaque targets represents a highly non-linear,multi-dimensional parameter space.This limits the utility of sequential 1D scanning of experimental parameters for the optimization of secondary radiation,although to-date this has been the accepted methodology due to low data acquisition rates.High repetition-rate(HRR)lasers augmented by machine learning present a valuable opportunity for efficient source optimization.Here,an automated,HRR-compatible system produced high-fidelity parameter scans,revealing the influence of laser intensity on target pre-heating and proton generation.A closed-loop Bayesian optimization of maximum proton energy,through control of the laser wavefront and target position,produced proton beams with equivalent maximum energy to manually optimized laser pulses but using only 60%of the laser energy.This demonstration of automated optimization of laser-driven proton beams is a crucial step towards deeper physical insight and the construction of future radiation sources.

质子磁荷半径:新疑难?

The electric radius,rE,and the magnetic radius,rM,of the proton are fundamental quantities of low-energy QCD,as they are a measure of the probe-dependent size of the proton.

Micro/nano multiscale reinforcing strategies toward extreme high-temperature applications:Take carbon/carbon composites and their coatings as the examples

Carbon fiber reinforced carbon composites(C/Cs),are the most promising high-temperature materials and could be widely applied in aerospace and nucleation fields,owing to their superior performances.However,C/Cs are very susceptible to destructive oxidation and thus fail at elevated temperatures.Though matrix modification and coating technologies with Si-based and ultra-high temperature ceramics(UHTCs)are valid to enhance the oxidation/ablation resistance of C/Cs,it’s not sufficient to satisfy the increasing practical applications,due to the inherent brittleness of ceramics,mismatch issues between coatings and C/C substrates,and the fact that carbonaceous matrices are easily prone to high-temperature oxidation.To effectively solve the aforementioned problems,micro/nano multiscale reinforcing strategies have been developed for C/Cs and/or the coatings over the past two decades,to fabricate C/Cs with high strength and excellent high-temperature stability.This review is to systematically summarize the most recent major and important advancements in some micro/nano multiscale strategies,including nanoparticles,nanowires,carbon nanotubes/fibers,whiskers,graphene,ceramic fibers and hybrid micro/nano structures,for C/Cs and/or the coatings,to achieve high-temperature oxidation/ablation-resistant C/Cs.Finally,this review is concluded with an outlook of major unsolved problems,challenges to be met and future research advice for C/Cs with excellent comprehensive mechanical-thermal performance.It’s hoped that a better understanding of this review will be of high scientific and industrial interest,since it provides unusual and feasible new ideas to develop potential and practical C/Cs with improved high-temperature mechanical and oxidation/ablation-resistant properties.

Si-based polymer-derived ceramics for energy conversion and storage

Since the 1960s,a new class of Si-based advanced ceramics called polymer-derived ceramics(PDCs)has been widely reported because of their unique capabilities to produce various ceramic materials(e.g.,ceramic fibers,ceramic matrix composites,foams,films,and coatings)and their versatile applications.Particularly,due to their promising structural and functional properties for energy conversion and storage,the applications of PDCs in these fields have attracted much attention in recent years.This review highlights the recent progress in the PDC field with the focus on energy conversion and storage applications.Firstly,a brief introduction of the Si-based polymer-derived ceramics in terms of synthesis,processing,and microstructure characterization is provided,followed by a summary of PDCs used in energy conversion systems(mainly in gas turbine engines),including fundamentals and material issues,ceramic matrix composites,ceramic fibers,thermal and environmental barrier coatings,as well as high-temperature sensors.Subsequently,applications of PDCs in the field of energy storage are reviewed with a strong focus on anode materials for lithium and sodium ion batteries.The possible applications of the PDCs in Li–S batteries,supercapacitors,and fuel cells are discussed as well.Finally,a summary of the reported applications and perspectives for future research with PDCs are presented.

Ultra-compact post-compressor on-shot wavefront measurement for beam correction at PHELIX

In order to reach the highest intensities,modern laser systems use adaptive optics to control their beam quality.Ideally,the focal spot is optimized after the compression stage of the system in order to avoid spatio-temporal couplings.This also requires a wavefront sensor after the compressor,which should be able to measure the wavefront on-shot.At PHELIX,we have developed an ultra-compact post-compressor beam diagnostic due to strict space constraints,measuring the wavefront over the full aperture of 28 cm.This system features all-reflective imaging beam transport and a high dynamic range in order to measure the wavefront in alignment mode as well as on shot.

Constrained crystals deep convolutional generative adversarial network for the inverse design of crystal structures

Autonomous materials discovery with desired properties is one of the ultimate goals for materials science,and the current studies have been focusing mostly on high-throughput screening based on density functional theory calculations and forward modeling of physical properties using machine learning.Applying the deep learning techniques,we have developed a generative model,which can predict distinct stable crystal structures by optimizing the formation energy in the latent space.It is demonstrated that the optimization of physical properties can be integrated into the generative model as on-top screening or backward propagator,both with their own advantages.Applying the generative models on the binary Bi-Se system reveals that distinct crystal structures can be obtained covering the whole composition range,and the phases on the convex hull can be reproduced after the generated structures are fully relaxed to the equilibrium.The method can be extended to multicomponent systems for multi-objective optimization,which paves the way to achieve the inverse design of materials with optimal properties.

3D non-isothermal phase-field simulation of microstructure evolution during selective laser sintering

During selective laser sintering(SLS),the microstructure evolution and local temperature variation interact mutually.Application of conventional isothermal sintering model is thereby insufficient to describe SLS.In this work,we construct our model from entropy level,and derive the non-isothermal kinetics for order parameters along with the heat transfer equation coupled with microstructure evolution.Influences from partial melting and laser-powder interaction are also addressed.We then perform 3D finite element non-isothermal phase-field simulations of the SLS single scan.To confront the high computation cost,we propose a novel algorithm analogy to minimum coloring problem and manage to simulate a system of 200 grains with grain tracking algorithm using as low as 8 non-conserved order parameters.Specifically,applying the model to SLS of the stainless steel 316L powder,we identify the influences of laser power and scan speed on microstructural features,including the porosity,surface morphology,temperature profile,grain geometry,and densification.We further validate the first-order kinetics of the transient porosity during densification,and demonstrate the applicability of the developed model in predicting the linkage of densification factor to the specific energy input during SLS.