Investigation of Projectile Impact Behaviors of Graphene Aerogel Using Molecular Dynamics Simulations

Graphene aerogel(GA),as a novel solid material,has shown great potential in engineering applications due to its unique mechanical properties.In this study,the mechanical performance of GA under high-velocity projectile impacts is thoroughly investigated using full-atomic molecular dynamics(MD)simulations.The study results show that the porous structure and density are key factors determining the mechanical response of GA under impact loading.Specifically,the impact-induced penetration of the projectile leads to the collapse of the pore structure,causing stretching and subsequent rupture of covalent bonds in graphene sheets.Moreover,the effects of temperature on the mechanical performance of GA have been proven to be minimal,thereby highlighting the mechanical stability of GA over a wide range of temperatures.Finally,the energy absorption density(EAD)and energy absorption efficiency(EAE)metrics are adopted to assess the energy absorption capacity of GA during projectile penetration.The research findings of this work demonstrate the significant potential of GA for energy absorption applications.

Robust measurement of orbital angular momentum of a partially coherent vortex beam under amplitude and phase perturbations

The ability to overcome the negative effects,induced by obstacles and turbulent atmosphere,is a core challenge of long-distance information transmission,and it is of great significance in free-space optical communication.The spatial-coherence structure,that characterizes partially coherent fields,provides a new degree of freedom for carrying information.However,due to the influence of the complex transmission environment,the spatial-coherence structure is severely damaged during the propagation path,which undoubtedly limits its ability to transmit information.Here,we realize the robust far-field orbital angular momentum(OAM)transmission and detection by modulating the spatial-coherence structure of a partially coherent vortex beam with the help of the cross-phase.The cross-phase enables the OAM information,quantified by the topological charge,hidden in the spatial-coherence structure can be stably transmitted to the far field and can resist the influence of obstructions and turbulence within the communication link.This is due to the self-reconstruction property of the spatial-coherence structure embedded with the cross-phase.We demonstrate experimentally that the topological charge information can be recognized well by measuring the spatial-coherence structure in the far field,exhibiting a set of distinct and separated dark rings even under amplitude and phase perturbations.Our findings open a door for robust optical signal transmission through the complex environment and may find application in optical communication through a turbulent atmosphere.

Analysis of Wigner’s Set Theoretical Proof for Bell-Type Inequalities

We present a detailed analysis of the set theoretical proof of Wigner for Bell type inequalities with the following result. Wigner introduced a crucial assumption that is not related to Einstein’s local realism, but instead, without justification, to the existence of certain joint probability measures for possible and actual measurement outcomes of Einstein-Podolsky-Rosen (EPR) experiments. His conclusions about Einstein’s local realism are, therefore, not applicable to EPR experiments and the contradiction of the experimental outcomes to Wigner’s results has no bearing on the validity of Einstein’s local realism.

Assessment of composite failure and ultimate strength without experiment on composite

This paper attempts to estimate the ultimate strength of a laminated composite only based on its constituent properties measured independently. Three important issues involved have been systematically addressed, i.e.,stress calculation for the constituent fiber and matrix materials, failure detection for the lamina and laminate upon the internal stresses in their constituents, and input data determination of the constituents from monolithic measurements.There are three important factors to influence the accuracy of the strength prediction. One is the stress concentration factor(SCF) in the matrix. Another is matrix plasticity. The third is thermal residual stresses in the constituents. It is these three factors, however, that have not been sufficiently well realized in the composite community. One can easily find out the elastic and strength parameters of a great many laminae and laminates in the current literature. Unfortunately, necessary information to determine the SCF, the matrix plasticity,and the thermal residual stresses of the composites is rare or incomplete. A useful design methodology is demonstrated in the paper.

Indentation of elastically soft and plastically compressible solids

The effect of soft elasticity, i.e., a relatively small value of the ratio of Young's modulus to yield strength and plastic compressibility on the indentation of isotropically hardening elastic–viscoplastic solids is investigated. Calculations are carried out for indentation of a perfectly sticking rigid sharp indenter into a cylinder modeling indentation of a half space. The material is characterized by a finit strain elastic–viscoplastic constitutive relation that allows for plastic as well as elastic compressibility. Both soft elasticity and plastic compressibility significantl reduce the ratio of nominal indentation hardness to yield strength. A linear relation is found between the nominal indentation hardness and the logarithm of the ratio of Young's modulus to yield strength, but with a different coefficien than reported in previous studies.The nominal indentation hardness decreases rapidly for small deviations from plastic incompressibility and then decreases rather slowly for values of the plastic Poisson's ratio less than0.25. For both soft elasticity and plastic compressibility, the main reason for the lower values of indentation hardness is related to the reduction in the hydrostatic stress level in the material below the indenter.

3D printing of bio-instructive materials:Toward directing the cell

Fabrication of functional scaffolds for tissue engineering and regenerative medicine applications requires material systems with precise control over cellular performance.3D printing is a powerful technique to create highly complex and multicomponent structures with well-defined architecture and composition.In this review paper,we explore extrusion-based 3D printing methods(EBP,i.e.,Near Field Electrospinning(NFES),Melt Electrowriting(MEW),Fused Deposition Modeling(FDM),and extrusion bioprinting)in terms of their ability to produce scaffolds with bio-instructive properties.These material systems provide spatio-temporal guidance for cells,allowing controlled tissue regeneration and maturation.Multiple physical and biochemical cues introduced to the EBP scaffolds are evaluated in their ability to direct cell alignment,proliferation,differentiation,specific ECM production,and tissue maturation.We indicate that the cues have different impacts depending on the material system,cell type used,or coexistence of multiple cues.Therefore,they must be carefully chosen based on the targeted application.We propose future directions in bio-instructive materials development,including such concepts as metamaterials,hybrid living materials,and 4D printing.The review gathers the knowledge essential for designing new materials with a controlled cellular response,fabrication of advanced engineered tissue,and developing a better understanding of cell biology,especially in response to the biomaterial.

Engineering the Thermoelectrical Properties of PEDOT:PSS by Alkali Metal Ion Effect

Engineering the electrical properties of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)holds great potential for various applications such as sensors,thermoelectric(TE)generators,and hole transport layers in solar cells.Various strategies have been applied to achieve optimal electrical properties,including base solution post-treatments.However,the working mechanism and the exact details of the structural transformations induced by base post-treatments are still unclear.In this work,we present a comparative study on the post-treatment effects of using three common and green alkali base solutions:namely LiOH,NaOH,and KOH.The structural modifications induced in the film by the base post-treatments are studied by techniques including atomic force microscopy,grazing-incidence wide-angle X-ray scattering,ultraviolet–visible–near-infrared spectroscopy,and attenuated total reflectance Fourier-transform infrared spectroscopy.Base-induced structural modifications are responsible for an improvement in the TE power factor of the films,which depends on the basic solution used.The results are explained on the basis of the different affinity between the alkali cations and the PSS chains,which determines PEDOT dedoping.The results presented here shed light on the structural reorganization occurring in PEDOT:PSS when exposed to high-pH solutions and may serve as inspiration to create future pH-/ion-responsive devices for various applications.

Counterfactual Definiteness and Bell’s Inequality

Counterfactual definiteness must be used as at least one of the postulates or axioms that are necessary to derive Bell-type inequalities. It is considered by many to be a postulate that not only is commensurate with classical physics (as for example Einstein’s special relativity), but also separates and distinguishes classical physics from quantum mechanics. It is the purpose of this paper to show that Bell’s choice of mathematical functions and independent variables implicitly includes counterfactual definiteness. However, his particular choice of variables reduces the generality of his theory, as well as the physics of all Bell-type theories, so significantly that no meaningful comparison of these theories with actual Einstein-Podolsky-Rosen experiments can be made.

Band Gap Opening of Graphene by Noncovalent π-π Interaction with Porphyrins

Graphene has been recognized as a promising 2D material with many new properties. However, pristine graphene is gapless which hinders its direct application towards graphene-based semiconducting devices. Recently, various ways have been proposed to overcome this problem. In this study, we report a robust method to open a gap in graphene via noncovalent functionalization with porphyrin molecules. Two type of porphyrins, namely, iron protoporphyrin (FePP) and zinc protoporphryin (ZnPP) were independently physisorbed on graphene grown on nickel by chemical vapour deposition (CVD) resulting in a bandgap opening in graphene. Using a statistical analysis of scanning tunneling spectroscopy (STS) measurements, we demonstrated that the magnitude of the band gap depends on the type of deposited porphyrin molecule.The π-π stacking of FePP on graphene yielded a considerably larger band gap value (0.45 eV) than physisorbed ZnPP (0.23 eV). We proposed that the origin of different band gap value is governed due to the metallic character of the respective porphyrin.

Photoexcitation dynamics in solution-processed formamidinium lead iodide perovskite thin films for solar cell applications

Formamidinium lead iodide(FAPbI3)is a newly developed hybrid perovskite that potentially can be used in high-efficiency solution-processed solar cells.Here,the temperature-dependent dynamic optical properties of three types of FAPbI3 perovskite films(fabricated using three different precursor systems)are comparatively studied.The time-resolved photoluminescence(PL)spectra reveal that FAPbI3 films made from the new precursor(a mixture of formamidinium iodide and hydrogen lead triiodide)exhibit the longest lifetime of 439 ns at room temperature,suggesting a lower number of defects and lower non-radiative recombination losses compared with FAPbI3 obtained from the other two precursors.From the temperature-dependent PL spectra,a phase transition in the films is clearly observed.Meanwhile,exciton-binding energies of 8.1 and 18 meV for the high-and lowtemperature phases are extracted,respectively.Importantly,the PL spectra for all of the samples show a single peak at room temperature,whereas at liquid-helium temperature the emission features two peaks:one in higher energy displaying a fast decay(0.5 ns)and a second red-shifted peak with a decay of up to several microseconds.These two emissions,separated by~18 meV,are attributed to free excitons and bound excitons with singlet and triplet characters,respectively.

Atomistic fracture in bcc iron revealed by active learning of Gaussian approximation potential

The prediction of atomistic fracture mechanisms in body-centred cubic(bcc)iron is essential for understanding its semi-brittle nature.Existing atomistic simulations of the crack-tip under mode-I loading based on empirical interatomic potentials yield contradicting predictions and artificial mechanisms.To enable fracture prediction with quantum accuracy,we develop a Gaussian approximation potential(GAP)using an active learning strategy by extending a density functional theory(DFT)database of ferromagnetic bcc iron.We apply the active learning algorithm and obtain a Fe GAP model with a converged model uncertainty over a broad range of stress intensity factors(SIFs)and for four crack systems.The learning efficiency of the approach is analysed,and the predicted critical SIFs are compared with Griffith and Rice theories.The simulations reveal that cleavage along the original crack plane is the atomistic fracture mechanism for{100}and{110}crack planes at T=0 K,thus settling a long-standing issue.Our work also highlights the need for a multiscale approach to predicting fracture and intrinsic ductility,whereby finite temperature,finite loading rate effects and pre-existing defects(e.g.,nanovoids,dislocations)should be taken explicitly into account.

Nanostructure and thermal power of highly-textured and single-crystal-like Bi_(2)Te_(3) thin films

Bi_(2)Te_(3)-based alloys are known to have outstanding thermoelectric properties.Although structure–property relations have been studied,still,detailed analysis of the atomic and nano-scale structure of Bi_(2)Te_(3)thin film in relation to their thermoelectric properties remains poorly explored.Herein,highly-textured(HT)and single-crystal-like(SCL)Bi_(2)Te_(3)films have been grown using pulsed laser deposition(PLD)on Si wafer covered with(native or thermal)SiOx and mica substrates.All films are highly textured with c-axis out-of-plane,but the in-plane orientation is random for the films grown on oxide and single-crystal-like for the ones grown on mica.The power factor of the film on thermal oxide is about four times higher(56.8μW·cm^(−1)·K^(−2))than that of the film on mica(12.8μW·cm^(−1)·K^(−2)),which is comparable to the one of the polycrystalline ingot at room temperature(RT).Reduced electron scattering in the textured thin films results in high electrical conductivity,where the SCL film shows the highest conductivity.However,its Seebeck coefficient shows a low value.The measured properties are correlated with the atomic structure details unveiled by scanning transmission electron microscopy.For instance,the high concentration of stacking defects observed in the HT film is considered responsible for the increase of Seebeck coefficient compared to the SCL film.This study demonstrates the influence of nanoscale structural effects on thermoelectric properties,which sheds light on tailoring thermoelectric thin films towards high performance.

Quantifying the refractive index dispersion of a pigmented biological tissue using Jamin–Lebedeff interference microscopy

Jamin–Lebedeff polarizing interference microscopy is a classical method for determining the refractive index and thickness of transparent tissues.Here,we extend the application of this method to pigmented,absorbing biological tissues,based on a theoretical derivation using Jones calculus.This novel method is applied to the wings of the American Rubyspot damselfly,Hetaerina americana.The membranes in the red-colored parts of the damselfly’s wings,with a thickness of 2.5 μm,contain a pigment with maximal absorption at 490 nm and a peak absorbance coefficient of 0.7 μm^(-1).The high pigment density causes a considerable and anomalous dispersion of the refractive index.This result can be quantitatively understood from the pigment absorbance spectrum by applying the Kramers–Kronig dispersion relations.Measurements of the spectral dependence of the refractive index and the absorption are valuable for gaining quantitative insight into how the material properties of animal tissues influence coloration.

Nonreciprocal coherent coupling of nanomagnets by exchange spin waves

Nanomagnets are widely used to store information in non-volatile spintronic devices.Spin waves can transfer information with low-power consumption as their propagations are independent of charge transport.However,to dynamically couple two distant nanomagnets via spin waves remains a major challenge for magnonics.Here we experimentally demonstrate coherent coupling of two distant Co nanowires by fast propagating spin waves in an yttrium iron garnet thin film with sub-50 nm wavelengths.Magnons in two nanomagnets are unidirectionally phase-locked with phase shifts controlled by magnon spin torque and spin-wave propagation.The coupled system is finally formulated by an analytical theory in terms of an effective non-Hermitian Hamiltonian.Our results are attractive for analog neuromorphic computing that requires unidirectional information transmission.

Synthesis of ultra-narrow PbTe nanorods with extremely strong quantum confinement

Monodisperse, high-quality, ultra-narrow PbTe nanorods were synthesized for the first time in a one-pot, hot-injection reaction using trans-2-decenoic acid as the agents for lead precursors and tris(diethylamino)phosphine telluride together with free tris(diethylamino)phosphine as the telluride precursors. High monomer reactivity, rapid nucleation and fast growth rate derived from the new precursors led to the anisotropic growth of PbTe nanocrystals at low reaction temperatures(<150℃). In addition, the aspect ratio of PbTe nanorods could be largely adjusted from 4 to 15 by tuning the Pb to Te precursor molar ratio and reaction temperatures. Moreover, the synthesized ultra-narrow PbTe nanorods exhibited extremely strong quantum confinement and presented unique optical properties. We revealed that the diameter and length of PbTe nanorods could significantly affect their optical properties, which potentially offer them new opportunities in the application of optoelectronic and thermoelectric devices and make them desired subjects for multiple exciton generation and other fundamental physics studies.

Design of molecule-based magnetic conductors

在工艺的设备启用讲道理地设计的薄电影的使用是在材料科学的一个公认的目标。然而，与控制得好的尺寸和生长方向用高度订的超分子的体系结构构造如此的薄电影留下了一逃犯目标。这里，我们介绍一个 layer-by-layer 协议种包括 arachidic 酸和施主二度(ethylenedioxy ) 的基于分子的磁性的售票员的混合薄电影 tetrathiafulvalene (BEDO-TTF ) 作为器官的部件和 Cu/Gd 建筑群作为无机的部件。分层的混合薄电影的构造被采用 Langmuir-Blodgett 方法以周围的条件完成，它在电影厚度上提供好控制并且在单层分子收拾行李。是由 X 光检查衍射示威了，这些电影与不同器官、无机的 sublattices 是水晶的，在 BEDO-TTF 分子的层与无机的层被连接的地方。由于 Langmuir-Blodgett 免职技术的灵活性，这结果与各种各样的功能向秩序井然的电影的准备显示一条线路，自愿与 BEDO-TFF 的单位被相结合的无机的混合物的决定了。而且，在许多底层上扔电影的能力在便宜底层上为降低费用的设备制造建立潜力。

Transport receptor occupancy in nuclear pore complex mimics

Nuclear pore complexes(NPCs)regulate all molecular transport between the nucleus and the cytoplasm in eukaryotic cells.Intrinsically disordered Phe-Gly nucleoporins(FG-Nups)line the central conduit of NPCs to impart a selective barrier where large proteins are excluded unless bound to a transport receptor(karyopherin;Kap).Here,we assess“Kap-centric”NPC models,which postulate that Kaps participate in establishing the selective barrier.We combine biomimetic nanopores,formed by tethering Nsp1 to the inner wall of a solid-state nanopore,with coarse-grained modeling to show that yeast Kap95 exhibits two populations in Nsp1-coated pores:one population that is transported across the pore in milliseconds,and a second population that is stably assembled within the FG mesh of the pore.Ionic current measurements show a conductance decrease for increasing Kap concentrations and noise data indicate an increase in rigidity of the FG-mesh.Modeling reveals an accumulation of Kap95 near the pore wall,yielding a conductance decrease.We find that Kaps only mildly affect the conformation of the Nsp1 mesh and that,even at high concentrations,Kaps only bind at most 8%of the FG-motifs in the nanopore,indicating that Kap95 occupancy is limited by steric constraints rather than by depletion of available FG-motifs.Our data provide an alternative explanation of the origin of bimodal NPC binding of Kaps,where a stable population of Kaps binds avidly to the NPC periphery,while fast transport proceeds via a central FG-rich channel through lower affinity interactions between Kaps and the cohesive domains of Nsp1.

Anisotropic magnetoresistance:A 170-year-old puzzle solved

Thomson[1],the later Lord Kelvin,reported an increased electric resistance in iron and nickel when the magnetization is parallel rather than normal to the current direction,an effect now called anisotropic magnetoresistance(AMR).The AMR allows sensing magnetic fields by simply measuring the resistance change when the magnetization realigns.While the magnetoresistance of magnetic tunnel junctions is larger,AMR sensors are attractive by their simplicity and robustness.

Long-range current-induced spin accumulation in chiral crystals

Chiral materials,similarly to human hands,have distinguishable right-handed and left-handed enantiomers which may behave differently in response to external stimuli.Here,we use for the first time an approach based on the density functional theory(DFT)+PAOFLOW calculations to quantitatively estimate the so-called collinear Rashba–Edelstein effect(REE)that generates spin accumulation parallel to charge current and can manifest as chirality-dependent charge-to-spin conversion in chiral crystals.Importantly,we reveal that the spin accumulation induced in the bulk by an electric current is intrinsically protected by the quasi-persistent spin helix arising from the crystal symmetries present in chiral systems with the Weyl spin–orbit coupling.In contrast to conventional REE,spin transport can be preserved over large distances,in agreement with the recent observations for some chiral materials.This allows,for example,the generation of spin currents from spin accumulation,opening novel routes for the design of solid-state spintronics devices.

Event-by-Event Simulation of the Hanbury Brown-Twiss Experiment with Coherent Light

We present a computer simulation model for the Hanbury Brown-Twiss experiment that is entirely particle-based and reproduces the results of wave theory. Themodel is solely based on experimental facts, satisfies Einstein’s criterion of local causality and does not require knowledge of the solution of a wave equation. The simulationmodel is fully consistent with earlier work and provides another demonstration thatit is possible to give a particle-only description of wave phenomena, rendering theconcept of wave-particle duality superfluous.