High-brightness betatron emission from the interaction of a sub picosecond laser pulse with pre-ionized low-density polymer foam for ICF research.

Direct laser acceleration (DLA) of electrons in plasmas of near-critical density (NCD) is a very advancing platform for high-energy PW-class lasers of moderate relativistic intensity supporting Inertial Confinement Fusion research. Experiments conducted at the PHELIX sub-PW Nd:glass laser demonstrated application-promising characteristics of DLA-based radiation and particle sources, such as ultra-high number, high directionality and high conversion efficiency. In this context, the bright synchrotron-like (betatron) radiation of DLA electrons, which arises from the interaction of a sub-ps PHELIX laser pulse with an intensity of 1019 W/cm2 with pre-ionized low-density polymer foam, was studied. The experimental results show that the betatron radiation produced by DLA electrons in NCD plasma is well directed with a half-angle of 100-200 mrad, yielding (3.4 ± 0.4)·1010 photons/keV/sr at 10 keV photon energy. The experimental photon fluence and the brilliance agree well with the particle-in-cell simulations. These results pave the way for innovative applications of the DLA regime using low-density pre-ionized foams in high energy density research.

P-limitation regulates the accumulation of soil aggregates organic carbon during the restoration of Pinus tabuliformis forest.

Artificial forest restoration is widely recognized as a crucial approach to enhance the potential of soil carbon sequestration. Nevertheless, there is still limited understanding regarding the dynamics of aggregate organic carbon (OC) and the underlying mechanisms driving these dynamics after artificial forest restoration. To address this gap, we studied Pinus tabuliformis forests and adjacent farmland in three recovery periods (13, 24 and 33 years) in the Loess Plateau region. Samples of undisturbed soil from the surface layer were collected and divided into three aggregate sizes: >2 mm (large aggregate), 0.25-2 mm (medium aggregate), and <0.25 mm (small aggregate). The aim was to examine the distribution of OC and changes in enzyme activity within each aggregate size. The findings revealed a significant increase in OC content for all aggregate sizes following the restoration of Pinus tabuliformis forests. After 33 years of recovery, the OC of large aggregates, medium aggregates and micro-aggregates increased by (30.23 ± 9.85)%, (36.71 ± 21.60)% and (37.88 ± 16.07)% respectively compared with that of farmland. Moreover, the restoration of Pinus tabuliformis forests lead to increased activity of hydrolytic enzymes and decreased activity of oxidative enzymes. It is noteworthy that the regulation of carbon in all aggregates is influenced by soil P-limitation. In large aggregates, P-limitation promotes the enhancement of hydrolytic enzyme activity, thereby facilitate OC accumulation. Conversely, in medium and small aggregates, P-limitation inhibits the increase in oxidative enzyme activity, resulting in OC accumulation. The results emphasize the importance of P-limitation in regulating OC accumulation during the restoration of Pinus tabulaeformis forest, in which large aggregates play a leading role.

Spatiotemporal variability and drivers of water microchemistry in the upper Nu-Salween river: With implications for fish habitat conservation.

Microchemical maps, also known as "chemoscapes", hold immense potential for reconstructing fish habitat utilization and guiding conservation efforts. This approach relies on matching the microchemical composition of fish calcified structures (e.g., otoliths) with the surrounding water's microchemistry. However, applying this method faces a major challenge: a clear understanding of the spatiotemporal variability and drivers of water microchemistry, particularly in vast, free-flowing river ecosystems like the Nu-Salween River, Southeast Asia's longest free-flowing river. We analyzed the spatiotemporal variability and influencing factors of water microchemistry (i.e., Na:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Zn:Ca, Se:Ca, Sr:Ca, and Ba:Ca) in the upper Nu-Salween River, based on a two-year sampling. Five elemental ratios (excluding Na:Ca, Mg:Ca, and Zn:Ca) in water demonstrated significant spatiotemporal variability, with Cu:Ca having the largest spatial variation, and Mn:Ca and Sr:Ca showing the greatest temporal variation. More specifically, four elemental ratios (Cu:Ca, Se:Ca, Sr:Ca, and Ba:Ca), exhibited significant variations along the longitudinal gradient, and Mn:Ca, Cu:Ca, Sr:Ca, and Ba:Ca, showed significant differences between mainstreams and tributaries. Temporally, Mn:Ca, Cu:Ca, and Ba:Ca displayed higher values and variations during the wet season, opposing the seasonal patterns of Na:Ca, Mg:Ca, and Sr:Ca. The four-element (Ba:Ca, Sr:Ca, Mg:Ca, and Mn:Ca) forest model showed the highest classification accuracy of 93%. Linear mixed-effects models showed that spatial factors have the largest influence on the variances in water microchemistry (56.36 ± 28.64%). Our study highlights the feasibility and reliability of utilizing microchemistry to reconstruct fish habitat utilization, thereby unveiling promising avenues for a more accurate understanding of fish life history in large rivers characterized by high heterogeneity in water microchemistry. By proportionally accounting for contribution of different factors to water microchemistry variability and relating them to microchemical composition of fish calcified structures, key fish habitats (e.g., spawning grounds) and migratory routes can be more precisely identified and thus protected.

Generation of High-Density High-Polarization Positrons via Single-Shot Strong Laser-Foil Interaction.

We put forward a novel method for producing ultrarelativistic high-density high-polarization positrons through a single-shot interaction of a strong laser with a tilted solid foil. In our method, the driving laser ionizes the target, and the emitted electrons are accelerated and subsequently generate abundant γ photons via the nonlinear Compton scattering, dominated by the laser. These γ photons then generate polarized positrons via the nonlinear Breit-Wheeler process, dominated by a strong self-generated quasistatic magnetic field B^{S}. We find that placing the foil at an appropriate angle can result in a directional orientation of B^{S}, thereby polarizing positrons. Manipulating the laser polarization direction can control the angle between the γ photon polarization and B^{S}, significantly enhancing the positron polarization degree. Our spin-resolved quantum electrodynamics particle-in-cell simulations demonstrate that employing a laser with a peak intensity of about 10^{23} W/cm^{2} can obtain dense (≳10^{18} cm^{-3}) polarized positrons with an average polarization degree of about 70% and a yield of above 0.1 nC per shot. Moreover, our method is feasible using currently available or upcoming laser facilities and robust with respect to the laser and target parameters. Such high-density high-polarization positrons hold great significance in laboratory astrophysics, high-energy physics, and new physics beyond the standard model.

Two new species of the bamboo-feeding subgenus Myittana (Benglebra) (Hemiptera: Cicadellidae: Deltocephalinae) from China.

Two new species of the bamboo-feeding genus Myittana (Benglebra) Mahmood & Ahmad, 1969, M. (B.) weiningensis Zhao, Luo & Chen sp. nov. and M. (B.) dongae Zhao, Luo & Chen sp. nov. from China (Guizhou and Guangxi) are described and illustrated. A key to all known species of the subgenus Myittana (Benglebra) is also given.

Target Density Effects on Charge Transfer of Laser-Accelerated Carbon Ions in Dense Plasma.

We report on charge state measurements of laser-accelerated carbon ions in the energy range of several MeV penetrating a dense partially ionized plasma. The plasma was generated by irradiation of a foam target with laser-induced hohlraum radiation in the soft x-ray regime. We use the tricellulose acetate (C_{9}H_{16}O_{8}) foam of 2 mg/cm^{3} density and 1 mm interaction length as target material. This kind of plasma is advantageous for high-precision measurements, due to good uniformity and long lifetime compared to the ion pulse length and the interaction duration. We diagnose the plasma parameters to be T_{e}=17 eV and n_{e}=4×10^{20} cm^{-3}. We observe the average charge states passing through the plasma to be higher than those predicted by the commonly used semiempirical formula. Through solving the rate equations, we attribute the enhancement to the target density effects, which will increase the ionization rates on one hand and reduce the electron capture rates on the other hand. The underlying physics is actually the balancing of the lifetime of excited states versus the collisional frequency. In previous measurement with partially ionized plasma from gas discharge and z pinch to laser direct irradiation, no target density effects were ever demonstrated. For the first time, we are able to experimentally prove that target density effects start to play a significant role in plasma near the critical density of Nd-glass laser radiation. The finding is important for heavy ion beam driven high-energy-density physics and fast ignitions. The method provides a new approach to precisely address the beam-plasma interaction issues with high-intensity short-pulse lasers in dense plasma regimes.

Multi-target object scattering imaging with intensity correlation of structured illumination.

Imaging through scattering layers based on the optical memory effect (OME) concept has been widely investigated in recent years. Among many scattering scenarios, it is very important to recover hidden targets with proper spatial distribution in the scene where multiple targets out of the OME range exist. In this Letter, we put forward a method for multi-target object scattering imaging. With the help of intensity correlation between the structured illumination patterns and recorded speckle images, the relative position of all hidden targets can be obtained and the movement of the targets within the OME range can be tracked. We experimentally implement scattering imaging with 16 targets and the motion tracking of them. Our results present a significant advance in a large field of view scattering imaging with multiple targets.

Experimental observation of the electron beam focusing effect induced by plasma currents with opposite directions.

We report on the experimental observation of the focusing effect of a 50MeV accelerator electron beam in a gas-discharge plasma target. The plasma is generated by igniting an electric discharge in two collinear quartz tubes, with the currents up to 1.5kA flowing in opposite directions in either of the two tubes. In such plasma current configuration, the electron beam is defocused in the first discharge tube and focused with a stronger force in the second one. With symmetric plasma currents, asymmetric effects are, however, induced on the beam transport process and the beam radius is reduced by a factor of 2.6 compared to the case of plasma discharge off. Experimental results are supported by two-dimensional particle-in-cell simulations.

Au L-shell x-ray emission induced by 154.3-423.9 MeV/u C6+ ions.

The L-shell x-ray emissions of gold are investigated for the bombardment of high energy C6+ ions in the high energy region of 154.3-423.9 MeV/u. Due to the multiple ionization of outer-shell electrons at the movement of L x-ray emission, the blue shift of the experimental x-ray energy and an enhancement of the relative intensity ratios of Lι, Lß-Lα x rays are observed. Using the improved thin target formula and considering the effect of multiple ionization on atomic parameters, the L-subshell x-ray production cross sections are extracted from the counts and compared with the theoretical estimations of BEA, PWBA and ECPSSR. It is found that the relative corrections of ECPSSR on PWBA can be ignored in the present experimental energy region. The calculations of PWBA and ECPSSR are almost identical and both are larger than the experimental results. The BEA is in better agreement with the experiment as a whole.

Triple ionization and fragmentation of benzene trimers following ultrafast intermolecular Coulombic decay.

Intermolecular interactions involving aromatic rings are ubiquitous in biochemistry and they govern the properties of many organic materials. Nevertheless, our understanding of the structures and dynamics of aromatic clusters remains incomplete, in particular for systems beyond the dimers, despite their high presence in many macromolecular systems such as DNA and proteins. Here, we study the fragmentation dynamics of benzene trimer that represents a prototype of higher-order aromatic clusters. The trimers are initially ionized by electron-collision with the creation of a deep-lying carbon 2s-1 state or one outer-valence and one inner-valence vacancies at two separate molecules. The system can thus relax via ultrafast intermolecular decay mechanisms, leading to the formation of C[Formula: see text]C[Formula: see text]C[Formula: see text] trications and followed by a concerted three-body Coulomb explosion. Triple-coincidence ion momentum spectroscopy, accompanied by ab-initio calculations and further supported by strong-field laser experiments, allows us to elucidate the details on the fragmentation dynamics of benzene trimers.

Brilliant circularly polarized γ-ray sources via single-shot laser plasma interaction.

Circularly polarized (CP) γ-ray sources are versatile for broad applications in nuclear physics, high-energy physics, and astrophysics. The laser-plasma based particle accelerators provide accessibility for much higher flux γ-ray sources than conventional approaches, in which, however, the circular polarization properties of the emitted γ-photons are usually neglected. In this Letter, we show that brilliant CP γ-ray beams can be generated via the combination of laser plasma wakefield acceleration and plasma mirror techniques. In a weakly nonlinear Compton scattering scheme with moderate laser intensities, the helicity of the driving laser can be transferred to the emitted γ-photons, and their average polarization degree can reach ∼61% (20%) with a peak brilliance of ≳1021 photons/(s · mm2 · mrad2 · 0.1% BW) around 1 MeV (100 MeV). Moreover, our proposed method is easily feasible and robust with respect to the laser and plasma parameters.

Multiple ionization of iodine for 2.5-5.0 MeV I22+ ions impacting on Fe target.

The L-shell X-ray emissions of iodine are investigated as a function of the incident energy for I22+ ions impacting on Fe target in the energy region near the Bohr velocity. Six distinct L-subshell X-rays, Lι, Lα1, 2, Lß1, 3, 4, Lß2, 15, Lγ1 and Lγ2, 3, 4, 4', are observed. Compared to the atomic data, the energy of the experimental X ray shifts to the higher energy side. The relative intensity ratios of Lι, Lß1, 3, 4, Lß2, 15, to Lα1, 2, Lι to Lß2, 15 and Lγ2, 3, 4, 4/ to Lγ1 are enhanced, but has no obvious change with the increase of projectile energy in the present energy region. That is interpreted by the multiple ionization effect of the M-, N- and O-shell electrons.

Collective energy-spectrum broadening of a proton beam in a gas-discharge plasma.

An accurate understanding of ion-beam transport in plasmas is crucial for applications in inertial fusion energy and high-energy-density physics. We present an experimental measurement on the energy spectrum of a proton beam at 270 keV propagating through a gas-discharge hydrogen plasma. We observe the energies of the beam protons changing as a function of the plasma density and spectrum broadening due to a collective beam-plasma interaction. Supported by linear theory and three-dimensional particle-in-cell simulations, we attribute this energy modulation to a two-stream instability excitation and further saturation by beam ion trapping in the wave. The widths of the energy spectrum from both experiment and simulation agree with the theory.

Observation of a high degree of stopping for laser-accelerated intense proton beams in dense ionized matter.

Intense particle beams generated from the interaction of ultrahigh intensity lasers with sample foils provide options in radiography, high-yield neutron sources, high-energy-density-matter generation, and ion fast ignition. An accurate understanding of beam transportation behavior in dense matter is crucial for all these applications. Here we report the experimental evidence on one order of magnitude enhancement of intense laser-accelerated proton beam stopping in dense ionized matter, in comparison with the current-widely used models describing individual ion stopping in matter. Supported by particle-in-cell (PIC) simulations, we attribute the enhancement to the strong decelerating electric field approaching 1 GV/m that can be created by the beam-driven return current. This collective effect plays the dominant role in the stopping of laser-accelerated intense proton beams in dense ionized matter. This finding is essential for the optimum design of ion driven fast ignition and inertial confinement fusion.

Haptic Rendering of Diverse Tool-Tissue Contact Constraints During Dental Implantation Procedures.

Motor skill learning of dental implantation surgery is difficult for novices because it involves fine manipulation of different dental tools to fulfill a strictly pre-defined procedure. Haptics-enabled virtual reality training systems provide a promising tool for surgical skill learning. In this paper, we introduce a haptic rendering algorithm for simulating diverse tool-tissue contact constraints during dental implantation. Motion forms of an implant tool can be summarized as the high degree of freedom (H-DoF) motion and the low degree of freedom (L-DoF) motion. During the H-DoF state, the tool can move freely on bone surface and in free space with 6 DoF. While during the L-DoF state, the motion degrees are restrained due to the constraints imposed by the implant bed. We propose a state switching framework to simplify the simulation workload by rendering the H-DoF motion state and the L-DoF motion state separately, and seamless switch between the two states by defining an implant criteria as the switching judgment. We also propose the virtual constraint method to render the L-DoF motion, which are different from ordinary drilling procedures as the tools should obey different axial constraint forms including sliding, drilling, screwing and perforating. The virtual constraint method shows efficiency and accuracy in adapting to different kinds of constraint forms, and consists of three core steps, including defining the movement axis, projecting the configuration difference, and deriving the movement control ratio. The H-DoF motion on bone surface and in free space is simulated through the previously proposed virtual coupling method. Experimental results illustrated that the proposed method could simulate the 16 different phases of the complete implant procedures of the Straumann® Bone Level(BL) Implants Φ4.8-L12 mm. According to the output force curve, different contact constraints could be rendered with steady and continuous output force during the operation procedures.

Ab initio Molecular Dynamics Simulation Study of Dissociation Electron Attachment to Lactic Acid and Isomer.

Dissociation processes of lactic acid and its isomer formed by low-energy dissociation electron attachment (DEA) in the gas phase are investigated by using ab initio molecular dynamics (MD) simulations. The ab initio MD simulations using an atom-centered density matrix propagation (ADMP) method are carried out to investigate the DEA dissociation process of lactic acid and its isomer. The analysis of the simulated dissociation trajectories of lactic acid and its isomer indicates that the C-C, C-H, and C-O bonds are cleaved within femtoseconds of the simulation time scale in the DEA dissociation process, and the difference in dissociation trajectory depends on the size of the three basis sets. The simulation results enable us to gain insights into the DEA dissociation process of lactic acid and its isomer. In this work, we present a comparative study of the 6-31 + G(d,p), 6-311++G(2d,2p), and Aug-cc-pVDZ basis sets of the DEA dissociation simulation of lactic acid and its isomer. The comparative study results indicate that the 6-311++G(2d,2p) is an excellent basis set for the ADMP trajectory simulation of lactic acid and its isomer in the DEA dissociation process. The natural bond orbital (NBO) analysis is carried out to characterize variation in the charge population and charge transfer accompanied by the C-C, C-H, and C-O bond dissociation processes for lactic acid and its isomer in the ADMP trajectory simulation. ADMP simulation and NBO analysis of the dissociation trajectory is considered an important initial and decisive step in DEA dissociation dynamics for lactic acid and its isomer.

Multiple ionization state of Arq+ ions during collisions near the Bohr velocity.

In order to clarify the mechanism and the influence of the initial charge state and target atomic parameters for the formation of L-shell multiple ionization state of Arq+ ions produced by the collisions near the Bohr velocity, the k-shell x-ray emission of Ar is measured for 1.2 MeV Arq+(q=4, 6, 8, 9, 11, 12) ions impacting on V target and 3 MeV Ar11+ ions interacting with selected targets (Z2 = 23, 26, 27, 28, 29, 30). It is found that the measured Ar Kα and Kß x-ray energies shift to the high energy side, and the relative intensity ratios of Kß/Kα are enlarged than the atomic data, owing to the presence of out-shell multiple vacancies. The multiple ionization is almost independence of the projectile charge state, but is diminished with increasing target atomic number.

Damaging Intermolecular Energy and Proton Transfer Processes in Alpha-Particle-Irradiated Hydrogen-Bonded Systems.

Although the biological hazard of alpha-particle radiation is well-recognized, the molecular mechanisms of biodamage are still far from being understood. Irreparable lesions in biomolecules may not only have mechanical origin but also appear due to various electronic and nuclear relaxation processes of ionized states produced by an alpha-particle impact. Two such processes were identified in the present study by considering an acetylene dimer, a biologically relevant system possessing an intermolecular hydrogen bond. The first process is the already well-established intermolecular Coulombic decay of inner-valence-ionized states. The other is a novel relaxation mechanism of dicationic states involving intermolecular proton transfer. Both processes are very fast and trigger Coulomb explosion of the dimer due to creation of charge-separated states. These processes are general and predicted to occur also in alpha-particle-irradiated nucleobase pairs in DNA molecules.

Isotopic analysis on nanogram quantities of carbon from dissolved insect cuticle: a method for paleoenvironmental inferences.

RATIONALE: Carbon isotope (δ13 C ) data from arthropod cuticles provide invaluable information on past and present biogeochemical processes. However, such analyses typically require large sample sizes that may mask important variation in δ13 C values within or among species. METHODS: We have evaluated a spooling-wire microcombustion (SWiM) device and isotope ratio mass spectrometry (IRMS) to measure the δ13 C values of carbon dissolved from the cuticle of chitinous aquatic zooplankton. The effects of temperature, pH, and reaction time on the δ13 C values of acid-dissolved bulk cuticle and purified chitin fractions obtained from a single species of chironomid from four commercial suppliers were assessed. These results were compared with baseline δ13 C values obtained on solid cuticle using conventional EA (elemental analyzer)/IRMS. RESULTS: The results indicate differential, time-dependent dissolution of chitin, lipid and protein fractions of cuticle concomitant with slow depolymerization and deacetylation of chitin. Isotopic offsets between dissolved bulk head capsules and a purified chitin fraction suggest the contributions of other isotopically lighter components of the bulk head capsules to bulk chitin extracts. The SWiM/IRMS δ13 C results obtained on dissolved cuticle using a treatment of 4 N HCl at 25 °C for 24 h produced generally stable δ13 C values, large sample/blank CO2 yields and a positive correlation with conventional EA/IRMS results on unprocessed cuticle. CONCLUSIONS: The SWiM/IRMS system offers a reliable method to determine δ13 C values on nanogram quantities of carbon from dissolved insect cuticle, thus reducing sample size requirements and providing new opportunities to use δ13 C variation among/within species for reconstructing paleo-biogeochemical processes.

Temperature and energy effects on secondary electron emission from SiC ceramics induced by Xe17+ ions.

Secondary electron emission yield from the surface of SiC ceramics induced by Xe17+ ions has been measured as a function of target temperature and incident energy. In the temperature range of 463-659 K, the total yield gradually decreases with increasing target temperature. The decrease is about 57% for 3.2 MeV Xe17+ impact, and about 62% for 4.0 MeV Xe17+ impact, which is much larger than the decrease observed previously for ion impact at low charged states. The yield dependence on the temperature is discussed in terms of work function, because both kinetic electron emission and potential electron emission are influenced by work function. In addition, our experimental data show that the total electron yield gradually increases with the kinetic energy of projectile, when the target is at a constant temperature higher than room temperature. This result can be explained by electronic stopping power which plays an important role in kinetic electron emission.