Μm Scale Research Articles

Identifying Band Structure Changes of FePS3 across the Antiferromagnetic Phase Transition.

Magnetic 2D materials enable interesting tuning options of magnetism. As an example, the van der Waals material FePS3, a zig-zag-type intralayer antiferromagnet, exhibits very strong magnetoelastic coupling due to the different bond lengths along different ferromagnetic and antiferromagnetic coupling directions enabling elastic tuning of magnetic properties. The likely cause of the length change is the intricate competition between direct exchange of the Fe atoms and superexchange via the S and P atoms. To elucidate this interplay, we study the band structure of exfoliated FePS3 by μm scale ARPES (angular resolved photoelectron spectroscopy), both, above and below the Néel temperature TN. We found three characteristic changes across TN. They involve S 3p-type bands, Fe 3d-type bands and P 3p-type bands, respectively, as attributed by comparison with density functional theory calculations (DFT + U). This highlights the involvement of all the atoms in the magnetic phase transition providing independent evidence for the intricate exchange paths.

An experimental investigation of boundary layer over permeable interfaces in Hele-Shaw micromodels

This study experimentally investigates boundary layer development over permeable interfaces using Hele-Shaw micromodels and high-resolution micro-particle image velocimetry (micro-PIV). Velocity vectors, captured at a 5 μm scale, reveal the flow behavior at the interface between free-flow and porous media with ordered structures and porosities ranging from 50% to 85%. The results show that the boundary layer streamline alignment decreases with increasing porosity, while lower permeability fosters more uniform and parallel flow near the interface. Flow channeling occurs along paths of the least resistance, with more flow directed through the Hele-Shaw free-flow region as the solid fraction of the porous material increases. The Reynolds number (0.14–0.94), based on the Hele-Shaw hydraulic diameter, has a minimal effect on the normalized velocity distribution. Furthermore, an analytical solution for the external boundary layer thickness exhibited good agreement with experimental data, confirming a thickness of 2–4 times the square root of the free-flow Hele-Shaw permeability. Additionally, a Q-criterion analysis identified, for the first time, distinct zones within the external boundary layer, capturing the balance between rotational and deformation components as a function of permeability. These findings offer insight into flow dynamics in porous media systems, with implications for both natural and industrial applications, and contribute to the improved modeling of fluid dynamics and momentum transport in coupled free-flow and porous media environments.

Cellular Characteristics and Protein Signatures of Human Adipose Tissues from Donors With or Without Advanced Coronary Artery Disease.

Background/Objectives: Perivascular adipose tissue (PVAT) exerts a paracrine effect on blood vessels and our objective was to understand PVAT molecular signatures related to cardiovascular disease. Methods: We studied two groups: those undergoing mitral valve repair/replacement (VR, n = 16) and coronary artery bypass graft (CABG, n = 38). VR donors did not have coronary artery disease, whereas CABG donors had advanced coronary artery disease. Clinical and tissue pathologies and proteomics from adipose tissue were assessed. Results: Donors undergoing VR had a lower body mass index (p = 0.01), HbA1C (p = 0.0023), and incidence of diabetes (p = 0.022) compared to CABG. VR donors were overall healthier, with higher cardiac function compared to CABG donors, based on ejection fraction. Although adipose histopathology between groups was not markedly different, PVAT had smaller and more adipocytes compared to subcutaneous adipose tissues. These differences were validated by whole specimen automated morphological analysis, and anisotropy analysis showed small (2.8-7.5 μm) and large (22.8-64.4 μm) scale differences between perivascular and subcutaneous adipose tissue from CABG donors, and small scale changes (2.8-7.5 μm) between perivascular and subcutaneous adipose tissue from VR donors. Distinct protein signatures in PVAT and subcutaneous adipose tissue include those involved in secretion, exosomes and vesicles, insulin resistance, and adipocyte identity. Comparing PVAT and subcutaneous adipose tissue from CABG donors, there were 82 significantly different proteins identified with log fold change ≥ 0.3 or ≤-0.3 (p < 0.05). Using this threshold, there were 36 differences when comparing PVAT and subcutaneous adipose tissue from VR donors, 58 differences when comparing PVAT from CABG or VR donors, and 55 when comparing subcutaneous adipose tissue from CABG vs. VR donors. Conclusions: Routine histopathology cannot differentiate between PVAT from donors with or without coronary artery disease, but multiscale anisotropy analysis discriminated between these populations. Our mass spectrometry analysis identified a cohort of proteins that distinguish between adipose depots, and are also associated with the presence or absence of coronary artery disease.

Templating Iron(III) Oxides on DNA Molecules.

Fe(III) oxides were prepared as free nanoparticles and on DNA templates via the precipitation of Fe(III) salts with NaOH in the presence/absence of DNA. Through control of the pH and temperature, FeOOH and Fe2O3 were synthesised. The formation of templated materials FeOOH/DNA and Fe2O3/DNA was confirmed using UV-Vis absorption and FTIR spectra. The direct optical gap of Fe2O3/DNA was estimated as 3.2 eV; the absorption by FeOOH/DNA and Fe2O3/DNA at longer wavelengths is weaker, but consistent with indirect gaps near 2 eV. X-ray photoelectron spectra confirmed the presence of Fe(III) and DNA in the templated samples. Analysis of the X-ray diffraction patterns of both templated and non-templated FeOOH and Fe2O3 demonstrated that the materials were the α-FeOOH and α-Fe2O3 polymorphs with crystallite diameters of the DNA-templated materials estimated as 7.6 nm and 6.8 nm. Transmission electron microscopy showed needle-like crystals of both FeOOH and Fe2O3, but the Fe2O3 contains some globular structures. In contrast, the morphology of FeOOH/DNA and Fe2O3/DNA consists of needle-like crystallites of the respective oxides organised into complex dendritic structures with a length on the 10 μm scale formed by the DNA molecules. Finally, scanned conductance microscopy provided evidence for the conductivity of the FeOOH/DNA after alignment via molecular combing on an Si/SiO2 substrate. Fe2O3/DNA did not exhibit any detectable conductivity.

Nanoindentation creep response of Ti–6Al–4V ELI alloy manufactured via laser powder bed fusion

The anisotropic creep response in both the XY and XZ planes of Ti–6Al–4V ELI manufactured by powder bed fusion (PBF) was examined under nanoindentation creep loading at room temperature, ranging from nm to μm scales. The stress exponent values of 4.06–4.30, rationalised through threshold stress, indicate that the creep behaviour is primarily dominated by dislocation gliding. Creep displacement results show that the anisotropic creep behaviour in the XY and XZ planes of the as-built, and heat treatment enhances the creep resistance of the XZ plane, while there is no significant difference in creep displacement between the as-built and heat-treated XY planes. Due to the higher dislocation density and compressive residual stress in the XY plane compared to the XZ plane, the creep resistance is higher in the XY plane for the as-built. It is highlighted that compressive residual stress is more relieved in the XY plane than in the XZ plane through heat treatment. The heat treatment results in improved creep resistance due to the formation of the Widmanstätten structure and β precipitates, which can impede dislocation movement under creep loading. The combination of residual stress and microstructural effects leads to anisotropic creep behaviour, suggesting that the anisotropy is inherited from the additive manufacturing process at micron scales.

An in-depth study of the synthesis of ReSe2 for anisotropic Raman characteristics

Abstract Two-dimensional transition metal dichalcogenides (TMDs) have received more interest for their potential role in future electronic and optoelectronic applications. Unlike other TMDs, Rhenium diselenide (ReSe2) stands out for its distinctive anisotropic growth characteristics. These unique features arise from its low lattice symmetry and interlayer decoupling, this has sparked significant interest among researchers. Previous research has indicated the presence of various growth patterns, including dendritic formations and structures resembling flowers. In this study, we effectively produced ReSe2 using the ‘Tilting Boat’ method to achieve growth on a 21 μm scale. Through precise manipulation of the growth conditions, we successfully attained flakes of 21 μm scale in comparison to prior findings. Moreover, we successfully produced a variety of shapes, including triangles, diamonds, and hexagons, on 1 × 1 cm2 Si/SiO2 substrates. Furthermore, we achieved the successful production of a continuous ReSe2 film on a 1 × 3 cm2 Al2O3 substrate. We verified the distinct anisotropic properties of ReSe2 via Raman Spectroscopy. Furthermore, we acquired three-dimensional visual representations of ReSe2 flakes and continuous films via SEM measurements. By employing EDS data and analysing x-ray photoelectron spectroscopy spectra, we have established a compositional ratio of 1:2 for Re and Se, which aligns with the MX2 structure. This confirmation indicates the successful synthesis of high-quality ReSe2 flakes.

Growth, Characterizations of Aspartame-ASP Crystals for Mechano, Spectral, Photonic, Opto-Electronic and Sensor Applications

The organic crystal has prevalent outcome and Aspartame-ASP crystal which is in anhydrate form is of 160–200 times sweeter than the sucrose and the single crystalline X-ray diffraction (XRD) data for ASP are a, b, c in Å as 19.4077, 4.9604, 15.6547, and alpha and gamma as 90°, beta as 94.877° and system is monoclinic, the space group is P21. The XRD reveals the monoclinic arrangement of the ASP crystal, the UV effect with Tauc’s plot for lower frequency cut off at 295 nm and band gap as 4.203 eV, morphology by scanning electron microscopy study in μm scaling, Vicker’s proviso by hardness profile, basic functional groups by Fourier transform infrared and basic examinations, excitation—emission by PhotoLuminescence-PL peak at 513 nm, electronic sort of ASP filters in 4.3275 microns, electric depiction by dielectric study and mechano use by hardness profile of ASP are studied and reported. Hardness coefficient by Vicker’s intended for ASP with n as 2.91. The NLO-SHG is of 1.76 times KDP with phase matched effect of ASP is reported. Also, the room-temperature sensor study of ASP is measured and compliance by red light-emitting diode source.

Microstructure modification and mechanical reinforcement in sub-10 μm scale Cu/Sn–Ag/Cu microbump joints via Co-addition of Zn and Ni in Cu substrates

The trend towards miniaturization of solder joints addresses the need for high-density interconnections in microelectronics. Excessive intermetallic compounds (IMC) and phase transformations cause internal stresses, leading to voiding and cracking in conventional microbumps. Therefore, advanced microbump design must focus on IMC suppression and phase stabilization. This study explores Cu–26Zn–18Ni/Sn-3.5Ag/Cu–26Zn–18Ni microbumps, comparing them to conventional Cu/Sn-3.5Ag/Cu under various reflow times. High-field emission electron probe micro-analysis and transmission electron microscopy reveal improved microstructures. Electron backscatter diffraction confirms the (Cu,Ni)6(Sn,Zn)5 grain size of several hundreds of nanometers. Fracture modes were established based on the correlation between shear testing and fracture surfaces. Cu–26Zn–18Ni/Sn-3.5Ag/Cu–26Zn–18Ni microbumps enhanced shear strength (19.6 %–97.8 %) and failure toughness (10.6 %–132.1 %) compared to Cu/Sn-3.5Ag/Cu. The solid solution strengthened and refined (Cu,Ni)6(Sn,Zn)5 combined with tough bulk (Cu,Ag)5(Sn,Zn)8 in Cu–26Zn–18Ni/Sn-3.5Ag/Cu–26Zn–18Ni microbumps, demonstrate a tough microstructure. These findings provide insights into the design of microbumps with a bonding height in sub-10micron scales.

Kidney stone growth through the lens of Raman mapping

Bulk composition of kidney stones, often analyzed with infrared spectroscopy, plays an essential role in determining the course of treatment for kidney stone disease. Though bulk analysis of kidney stones can hint at the general causes of stone formation, it is necessary to understand kidney stone microstructure to further advance potential treatments that rely on in vivo dissolution of stones rather than surgery. The utility of Raman microscopy is demonstrated for the purpose of studying kidney stone microstructure with chemical maps at ≤ 1 µm scales collected for calcium oxalate, calcium phosphate, uric acid, and struvite stones. Observed microstructures are discussed with respect to kidney stone growth and dissolution with emphasis placed on < 5 µm features that would be difficult to identify using alternative techniques including micro computed tomography. These features include thin concentric rings of calcium oxalate monohydrate within uric acid stones and increased frequency of calcium oxalate crystals within regions of elongated crystal growth in a brushite stone. We relate these observations to potential concerns of clinical significance including dissolution of uric acid by raising urine pH and the higher rates of brushite stone recurrence compared to other non-infectious kidney stones.

Preparation and Preliminary Analysis of Several Nanoformulations Based on Plant Extracts and Biodegradable Polymers as a Possible Application for Chronic Venous Disease Therapy.

Nanotechnology is one of the newest directions for plant-based therapies. Chronic venous disease often predisposes to long-term and invasive treatment. This research focused on the inclusion of vegetal extracts from Sophorae flos (SE), Calendulae flos (CE), and Ginkgo bilobae folium (GE) in formulations with PHB and PLGA polymers and their physicochemical characterization as a preliminary stage for possible use in the development of a complex therapeutic product. The samples were prepared by an oil-water emulsification and solvent evaporation technique, resulting in suspensions with high spreadability and a pH of 5.5. ATR-FTIR analysis revealed bands for stretching vibrations (O-H, C=O, and C-H in symmetric and asymmetric methyl and methylene) in the same regions as the base components, but switched to high or low wavenumbers and absorbance, highlighting the formation of adducts/complexes between the extracts and polymers. The obtained formulations were in the amorphous phase, as confirmed by XRD analysis. AFM analysis emphasized the morphological peculiarities of the extract-polymer nanoformulations. It could be noticed that, in the case of SE-based formulations, the dominant characteristics for SE-PHB and SE-PLGA composition were the formation of random large (SE-PHB) and smaller uniform (SE-PLGA) particles; further on, these particles tended to aggregate in the case of SE-PHB-PLGA. For the CE- and GE-based formulations, the dominant surface morphology was their porosity, generally with small pores, but larger cavities were observed in some cases (CE- and GE-PHB). The highest roughness values at the (8 µm × 8 μm) scale were found for the following samples and succession: CE-PHB < SE-PLGA < SE-PHB-PLGA. In addition, by thermogravimetric analysis, impregnation in the matrix of compression stockings was evaluated, which varied in the following order: CE-polymer > SE-polymer > GE-polymer. In conclusion, nine vegetal extract-polymer nanoformulations were prepared and preliminarily characterized (by advanced physicochemical methods) as a starting point for further optimization, stability studies, and possible use in complex pharmaceutical products.

Chemistry in Retrieved Ryugu Asteroid Samples Revealed by Non-Invasive X-ray Microanalyses: Pink-Beam Fluorescence CT and Tender-Energy Absorption Spectroscopy

The Hayabusa2 space mission recently retrieved 5.4 g of material from asteroid Ryugu, providing the first direct access to pristine material from a carbonaceous asteroid. This study employs a novel combination of non-invasive synchrotron X-ray techniques to examine microscale chemistry (elemental distributions and element-specific chemical speciation and local structure) inside Ryugu grains without physically cutting the samples. Manganese primarily occurs in carbonate: Mn-bearing dolomite with minor earlier ankerite. Iron sulfides present as large single grains and as smaller particles in the finer-grained matrix are both predominantly pyrrhotite. At the 5 μm scale, Fe sulfides do not show the mineralogical heterogeneity seen in many carbonaceous meteorites but exhibit some heterogeneous localized oxidation. Iron is present often as intergrowths of oxide and sulfide, indicating incomplete replacement. Trace selenium substitutes for S in pyrrhotite. Copper is present as Fe-poor Cu sulfide. These results demonstrate multiple episodes of fluid alteration on the parent body, including partial oxidation, and help constrain the sequence or evolution of fluids and processes that resulted in the current grain-scale mineralogical composition of Ryugu materials.

Spectral micro-CT for simultaneous gold and iodine detection, and multi-material identification

Multiple energy bin spectral micro-CT (SμCT) is an advanced imaging technique that allows multi-material decomposition according to their specific absorption patterns at a sub-100 μm scale. Typically, iodine is the preferred CT contrast agent for cardiovascular imaging, while gold nanoparticles have gained attention in recent years owing to their high absorption properties, biocompatibility and ability to target tumors.In this work, we demonstrate the potential for multi-material decomposition through SμCT imaging of a test sample at the PEPI lab of INFN Trieste. The sample, consisting of gold, iodine, calcium, and water, was imaged using a Pixirad1/PixieIII chromatic detector with multiple energy thresholds and a wide spectrum (100 kV) produced by a micro-focus X-ray tube. The results demonstrate the simultaneous detection and separation of the four materials at a spatial scale of 35 μm, suggesting the potential of this technique in improving material detectability and quantification in a range of pre-clinical applications, including cardiovascular and oncologic imaging.

Scope and Limitations of Using Microemulsions for the Covalent Patterning of Graphene.

Patterning of graphene (functionalizing some areas while leaving others intact) is challenging, as all the C atoms in the basal plane are identical, but it is also desirable for a variety of applications, like opening a bandgap in the electronic structure of graphene. Several methods have been reported to pattern graphene, but most of them are very technologically intensive. Recently, we reported the use of microemulsions as templates to pattern graphene at the μm scale. This method is very simple and in principle tunable, as emulsions of different droplet size and composition can be prepared easily. Here, we explore in detail the scope of this methodology by applying it to all the combinations of four different emulsions and three different organic reagents, and characterizing the resulting substrates exhaustively through Raman, SEM and AFM. We find that the method is general, works better when the reactive species are outside the micelles, and requires reactive species that involve short reaction times.

Investigation of the Impact of Temporal Dose Delivery Patterns of Ion Irradiation with the Local Effect Model.

We present an extension of the Local Effect Model (LEM) to include time-dose relationships for predicting effects of protracted and split-dose ion irradiation at arbitrary LET. With this kinetic extension, the spatial and temporal induction and processing of DNA double strand breaks (DSB) in cellular nuclei can be simulated for a wide range of ion radiation qualities, doses and dose rates. The key concept of the extension is based on the joint spatial and temporal coexistence of initial DSB, leading to the formation of clustered DNA damage on the µm scale (as defined e.g., by the size scale of Mbp chromatin loops), which is considered to have an increased cellular lethality as compared to isolated, single DSB. By simulating the time dependent induction and repair of DSB and scoring of isolated and clustered DSB upon irradiation, the impact of dose rate and split dose on the cell survival probability can be computed. In a first part of this work, we systematically analyze the predicted impact of protraction in dependence of factors like dose, LET, ion species and radiosensitivity as characterized by the photon LQ-parameters. We establish links to common concepts that describe dose rate effects for low LET radiation. We also compare the model predictions to experimental data and find agreement with the general trends observed in the experiments. The relevant concepts of our approach are compared to other models suitable for predicting time effects. We investigate an apparent analogy between spatial and temporal concentration of radiation delivery, both leading to increased effectiveness, and discuss similarities and differences between the general dependencies of these clustering effects on their impacting factors. Finally, we conclude that the findings give additional support for the general concept of the LEM, i.e. the characterization of high LET radiation effects based on the distinction of just two classes of DSB (isolated DSB and clustered DSB).

Synergistic effect between CoSx and MoS2 at the micrometer scale: Considerable promotion of the hydrodesulfurization of DBT

The future implementation of ultralow sulfur fuel regulations requires researchers to have an excellent understanding of the mechanism of the synergistic effect between the Co(Ni) and (Mo)W sulfides in supported Co(Ni)Mo(W)S hydrodesulfurization (HDS) catalysts. This synergistic effect occurs when the distance between two metals is on the mm or nm scale. To investigate the promotion of HDS on the µm scale, a series of Co and Mo multilayer flake catalysts with a thickness of 1 mm were prepared by laminate molding. The distance between CoSx and MoS2 in these specially structured catalysts was adjustable on the µm scale by controlling the order and quality of the catalyst powder. The results for the HDS of dibenzothiophene (DBT) demonstrate that there is an obvious synergistic effect between CoSx and MoS2 on the µm scale. The results of pyridine IR spectroscopy indicate that this synergy is due to CoSx and MoS2 synergistically generating more coordinatively unsaturated sites (CUSs) and -SH active sites at the μm scale, thus increasing the HDS activity. Moreover, the catalyst activity increases as the distance between CoSx and MoS2 decreases, and the fact that the feed comes into contact with CoSx first greatly improves the activity.

Contrasting evolution of beach gold on two sides of an active orogen, Southern Alps, New Zealand

ABSTRACT Placer gold on beaches on either side of a major active mountain belt has strongly contrasting compositions and morphologies. Pleistocene-Holocene beach gold placers have formed along the West Coast where silver (Ag)-bearing gold has been eroded from mountains via steep rivers and glaciers, followed by rapid burial in the abundant associated coastal sediments. Deformation along transport pathways has produced flattened gold flakes, but some primary crystalline shapes are preserved. Internal deformation of particles has caused recrystallisation to fine-grained (µm scale) grain structures including mylonitic banding. However, only minor localised (µm scale) Ag leaching has occurred on some particle margins. In contrast, Pleistocene beach placers formed on the southern side of the mountains contain flattened gold particles with a complex transport history involving long-distance (hundreds of km) fluvial transport since Cretaceous. Most primary Ag has been leached from this gold during transport-related recrystallisation to fine (5–20 µm) internal grains. Sand-blasting on the southern beaches with low sediment supply has resulted in further deformation and leaching of Ag to form toroidal shapes with Ag-free delicate extremities. Placer gold which has undergone rapid transport and deposition is useful as a prospecting tool for bedrock deposits in glaciated terranes around the world.

Hydrogen generation and heterogeneity of the serpentinization process at all scales: Turon de Técouère lherzolite case study, Pyrenees (France)

Hydrogen (H 2 ) emanations have been recognized in the south and north of the Pyrenees fold belt, within its two forelands. The proposed source is a mantle wedge quite close to the surface that is currently undergoing serpentinization. The migration pathway seems to be the deep rooting faults, as the H 2 content is higher where the faults reach the surface. The zone of current H 2 generation is around 10 km deep. It is evident from filed observations that kilometric pieces of mantle have been incorporated into the thrusts and outcrop in a few areas along the mountain belt. We studied the Turon de Tecouère, one of these mantle-derived bodies, using various field and laboratory tools that focused on the characterization of its alteration, the degree of serpentinization and its heterogeneity at the kilometre scale. Accordingly, the magnetic field and magnetic susceptibility were mapped, classical optical observations and 3D scans of some samples were performed, and H 2 soil gas content mapping was carried out. The results show a heterogenous degree of serpentinization ranging from 3 to 62% at the kilometre to the micrometre scale. As the temperature and burial history are the same throughout the Turon de Tecouère, these factors were not sufficient to characterize the level of transformation in the H 2 -generating rock. The soil gas measurements show current H 2 emanations in and around the Turon de Tecouère. Near-surface H 2 production of this mantle body is unlikely, based on the current knowledge of H 2 generation kinetics. To explain these emanations, we favour a preferential migration pathway within the root of the Turon and the surrounding faults. Thematic collection: This article is part of the Hydrogen as a future energy source collection available at: https://www.lyellcollection.org/topic/collections/hydrogen

Enhanced RBE of Particle Radiation Depends on Beam Size in the Micrometer Range.

High-linear energy transfer (LET) radiation, such as heavy ions is associated with a higher relative biological effectiveness (RBE) than low-LET radiation, such as photons. Irradiation with low- and high-LET particles differ in the interaction with the cellular matter and therefore in the spatial dose distribution. When a single high-LET particle interacts with matter, it results in doses of up to thousands of gray (Gy) locally concentrated around the ion trajectory, whereas the mean dose averaged over the target, such as a cell nucleus is only in the range of a Gy. DNA damage therefore accumulates in this small volume. In contrast, up to hundreds of low-LET particle hits are required to achieve the same mean dose, resulting in a quasi-homogeneous damage distribution throughout the cell nucleus. In this study, we investigated the dependence of RBE from different spatial dose depositions using different focused beam spot sizes of proton radiation with respect to the induction of chromosome aberrations and clonogenic cell survival. Human-hamster hybrid (AL) as well as Chinese hamster ovary cells (CHO-K1) were irradiated with focused low LET protons of 20 MeV (LET = 2.6 keV/µm) beam energy with a mean dose of 1.7 Gy in a quadratic matrix pattern with point spacing of 5.4 × 5.4 µm2 and 117 protons per matrix point at the ion microbeam SNAKE using different beam spot sizes between 0.8 µm and 2.8 µm (full width at half maximum). The dose-response curves of X-ray reference radiation were used to determine the RBE after a 1.7 Gy dose of radiation. The RBE for the induction of dicentric chromosomes and cell inactivation was increased after irradiation with the smallest beam spot diameter (0.8 µm for chromosome aberration experiments and 1.0 µm for cell survival experiments) compared to homogeneous proton radiation but was still below the RBE of a corresponding high LET single ion hit. By increasing the spot size to 1.6-1.8 µm, the RBE decreased but was still higher than for homogeneously distributed protons. By further increasing the spot size to 2.7-2.8 µm, the RBE was no longer different from the homogeneous radiation. Our experiments demonstrate that varying spot size of low-LET radiation gradually modifies the RBE. This underlines that a substantial fraction of enhanced RBE originates from inhomogeneous energy concentrations on the µm scale (mean intertrack distances of low-LET particles below 0.1 µm) and quantifies the link between such energy concentration and RBE. The missing fraction of RBE enhancement when comparing with high-LET ions is attributed to the high inner track energy deposition on the nanometer scale. The results are compared with model results of PARTRAC and LEM for chromosomal aberration and cell survival, respectively, which suggest mechanistic interpretations of the observed radiation effects.

Bottom-to-top modeling of epoxy resins: From atomic models to mesoscale fracture mechanisms.

We outline a coarse-grained model of epoxy resins (bisphenol-F-diglycidyl-ether/3,5-diethyltoluene-2,4-diamine) to describe elastic and plastic deformation, cavitation, and fracture at the μm scale. For this, molecular scale simulation data collected from quantum and molecular mechanics studies are coarsened into an effective interaction potential featuring a single type of beads that mimic 100nm scale building blocks of the material. Our model allows bridging the time-length scale problem toward experimental tensile testing, thus effectively reproducing the deformation and fracture characteristics observed for strain rates of 10-1 to 10-5s-1. This paves the way to analyzing viscoelastic deformation, plastic behavior, and yielding characteristics by means of "post-atomistic" simulation models that retain the molecular mechanics of the underlying epoxy resin at length scales of 0.1-10 µm.

Ion acceleration from the interaction of ultrahigh-intensity laser pulses with near-critical density, nonuniform gas targets

Using one-dimensional, long-timescale particle-in-cell simulations, we study the processes of ion acceleration from the interaction of ultraintense (1020 W cm−2), ultrashort (30 fs) laser pulses with near-critical, nonuniform gas targets. The considered initially neutral, nitrogen gas density profiles mimic those delivered by an already developed noncommercial supersonic gas shock nozzle: they have the generic shape of a narrow (20 μm wide) peak superimposed on broad (∼1 mm, ∼180 μm scale length), exponentially decreasing ramps. While keeping its shape constant, we vary its absolute density values to identify the interaction conditions leading to collisionless shock-induced ion acceleration in the gas density ramps. We find that collisionless electrostatic shocks (CES) form when the laser pulse is able to shine through the central density peak and deposit a few 10% of its energy into it. Under our conditions, this occurs for a peak electron density between 0.35 nc and 0.7 nc. Moreover, we show that the ability of the CES to reflect the upstream ions is highly sensitive to their charge state and that the laser-induced electron pressure gradients mainly account for shock generation, thus highlighting the benefit of using sharp gas profiles, such as those produced by shock nozzles.