Probe Experiments Research Articles

Surface stress can initiate environment-assisted fracture in metals.

Controlling environmental effects in surface plasticity/fracture of metals is of interest for areas as diverse as manufacturing processes, product performance, and structural safety. The key to controlling these effects is understanding the effect of adsorbates on surface energy (γ) and surface stress (f). While γ has been well studied, the role of surface stress has received much less attention. We characterize surface stress induced in metals by adsorption of organic monolayers. Linear alkanoic acids of varying chain length (3-18) are deposited by molecular self-assembly onto one side of an aluminum cantilever, several centimeters in length. The surface stress is estimated from in situ measurement of the cantilever deflection. We find that the organic adsorbates induce large surface stress of -4 to +30N/m. Furthermore, we show that f may be tuned by varying adsorbate-molecule chain length. The stress data explain beneficial embrittlement of metal surfaces by organic adsorbates in cutting and comminution processes, and point to a critical role, hitherto ignored, for f in environment assisted cracking (EAC) phenomena. Our results suggest opportunities for utilizing controlled environment-assisted fracture as an aid-fracture as a friend-to enhance material removal processes, apart from using surface stress itself as an experimental probe to explore various manifestations of EAC.

Design and methodology for a proof of mechanism study of individualized neuronavigated continuous Theta burst stimulation for auditory processing in adolescents with autism spectrum disorder.

It has been suggested that aberrant excitation/inhibition (E/I) balance and dysfunctional structure and function of relevant brain networks may underlie the symptoms of autism spectrum disorder (ASD). However, the nomological network linking these constructs to quantifiable measures and mechanistically relating these constructs to behavioral symptoms of ASD is lacking. Herein we describe a within-subject, controlled, proof-of-mechanism study investigating the pathophysiology of auditory/language processing in adolescents with ASD. We utilize neurophysiological and neuroimaging techniques including magnetic resonance spectroscopy (MRS), diffusion-weighted imaging (DWI), functional magnetic resonance imaging (fMRI), and magnetoencephalography (MEG) metrics of language network structure and function. Additionally, we apply a single, individually targeted session of continuous theta burst stimulation (cTBS) as an experimental probe of the impact of perturbation of the system on these neurophysiological and neuroimaging outcomes. MRS, fMRI, and MEG measures are evaluated at baseline and immediately prior to and following cTBS over the posterior superior temporal cortex (pSTC), a region involved in auditory and language processing deficits in ASD. Also, behavioral measures of ASD and language processing and DWI measures of auditory/language network structures are obtained at baseline to characterize the relationship between the neuroimaging and neurophysiological measures and baseline symptom presentation. We hypothesize that local gamma-aminobutyric acid (GABA) and glutamate concentrations (measured with MRS), and structural and functional activity and network connectivity (measured with DWI and fMRI), will significantly predict MEG indices of auditory/language processing and behavioral deficits in ASD. Furthermore, a single session of cTBS over left pSTC is hypothesized to lead to significant, acute changes in local glutamate and GABA concentration, functional activity and network connectivity, and MEG indices of auditory/language processing. We have completed the pilot phase of the study (n=20 Healthy Volunteer adults) and have begun enrollment for the main phase with adolescents with ASD (n=86; age 14-17). If successful, this study will establish a nomological network linking local E/I balance measures to functional and structural connectivity within relevant brain networks, ultimately connecting them to ASD symptoms. Furthermore, this study will inform future therapeutic trials using cTBS to treat the symptoms of ASD.

Two-Step Relaxation of Non-Equilibrium Electrons in Graphene: The Key to Understanding Pump–Probe Experiments

In the majority of experiments targeting nonlinear optical phenomena, the application of high-intensity pulses drives electrons in graphene into a strongly non-equilibrium state. Under these conditions, conventional perturbation theory falls short in explaining graphene’s intricate optical response because of significant deviations in electron distribution over energy states from the equilibrium Fermi-Dirac one. In this work, we present a two-step relaxation model capable of predicting the transient dynamics of graphene’s carriers out of equilibrium, from the generation of spectrally narrow populations of non-thermalized electrons and holes to the establishment of a hot-electron gas and its subsequent cooling toward equilibrium with the crystal lattice. By comparing our model calculations to experimental results, we demonstrate its reliability and relevance to pump–probe experiments, providing insights into the pivotal role of hot electrons in comprehending ultrafast dynamics in graphene.

In Situ Monitoring of Non-Thermal Plasma Cleaning of Surfactant Encapsulated Nanoparticles

Surfactants are widely used in the synthesis of nanoparticles, as they have a remarkable ability to direct their growth to obtain well-defined shapes and sizes. However, their post-synthesis removal is a challenge, and the methods used often result in morphological changes that defeat the purpose of the initial controlled growth. Moreover, after the removal of surfactants, the highly active surfaces of nanomaterials may undergo structural reconstruction by exposure to a different environment. Thus, ex situ characterization after air exposure may not reflect the effect of the cleaning methods. Here, combining X-ray photoelectron spectroscopy, in situ infrared reflection absorption spectroscopy, and environmental transmission electron microscopy measurements with CO probe experiments, we investigated different surfactant-removal methods to produce clean metallic Pt nanoparticles from surfactant-encapsulated ones. It was demonstrated that both ultraviolet-ozone (UV-ozone) treatment and room temperature O2 plasma treatment led to the formation of Pt oxides on the surface after the removal of the surfactant. On the other hand, when H2 was used for plasma treatment, both the Pt0 oxidation state and nanoparticle size distribution were preserved. In addition, H2 plasma treatment can reduce Pt oxides after O2-based treatments, resulting in metallic nanoparticles with clean surfaces. These findings provide a better understanding of the various options for surfactant removal from metal nanoparticles and point toward non-thermal plasmas as the best route if the integrity of the nanoparticle needs to be preserved.

Computation of X-ray and Neutron Scattering Patterns to Benchmark Atomistic Simulations against Experiments.

Molecular Dynamics simulations study material structure and dynamics at the atomic level. X-ray and neutron scattering experiments probe exactly the same time- and length scales as the simulations. In order to benchmark simulations against measured scattering data, a program is required that computes scattering patterns from simulations with good single-core performance and support for parallelization. In this work, the existing program Sassena is used as a potent solution to this requirement for a range of scattering methods, covering pico- to nanosecond dynamics, as well as the structure from some Ångströms to hundreds of nanometers. In the case of nanometer-level structures, the finite size of the simulation box, which is referred to as the finite size effect, has to be factored into the computations for which a method is described and implemented into Sassena. Additionally, the single-core and parallelization performance of Sassena is investigated, and several improvements are introduced.

Weyl semimetal assisted nonreciprocal modification of Flat-top optical pulses via defective photonic band-gap structures

We study the non-reciprocal modification of flat-top optical pulses via a one-dimensional photonic band-gap structure with Weyl semimetal-based defect layers due to their wide range of applications, such as high-speed communication, nonlinear optical switching, and ultrafast pump–probe experiments. We apply the transfer matrix method to obtain the transmission spectrum of the structure. Also, the Fourier transform technique is used to investigate the effect of the propagation direction of the incoming pulse on the time profile of the outgoing pulse. Then we examine the effect of the carrier frequency and duration of the incoming pulse on the length, energy, and magnetic field distribution of the outgoing pulse. It is shown that the time profile of an incoming flat-top pulse may modify to a nearly flat-top, single-peak, or oscillatory multi-peak time profile depending on the carrier frequency, length, and propagation direction of the incoming pulse.

Polarization reversal dynamics of ferroelastic nanodomains in Pb(Zr,Ti)O3 thin film

Applying an electric field along the [001] direction can drive the coupled polarization reversal in [100] oriented ferroelastic nano-sized a-domains in Pb(Zr,Ti)O3 thin film. In this study, experimental probing of nanodomain evolution in ferroelastic Pb(Zr,Ti)O3 thin films using in-situ synchrotron X-ray scattering reveals mechanisms of polarization reversal of both nanosized a-domains as well as that of matrix c-domains. Polarization reversal of a- and matrix c-domains under an electric field along the [001] direction generates the scattering intensity–electric field hysteresis loops. Both time-dependent scattering intensity and phase-field simulation reveal that the polarization reversal of nanodomains can be completed ten times faster than that of matrix c-domain owing to the ferroelastic switching mediated reversal mechanism.

Fluoranthene degradation in a persulfate system activated by sulfidated nano zero-valent iron (S-nZVI): performance and mechanisms.

Fluoranthene (FLT) has received mounting focus due to its hazardous properties and frequent occurrence in groundwater. In this study, sulfidated nano zero-valent iron (S-nZVI) was selected as an efficient catalyst for activating persulfate (PS) to degrade FLT. The effects of reagent doses, various water conditions (pH, anions, and humic acid), and the presence of surfactants on FLT degradation were investigated. Radical probe experiments, electron paramagnetic resonance (EPR) spectrum detection, and scavenging tests were performed to identify the major reactive oxygen species (ROS) in the system. The results showed that in the PS/S-nZVI system, 96.2% of FLT was removed within 120 min at the optimal dose of PS = 0.07 mM and S-nZVI = 0.0072 g L-1. S(-II) in the S-nZVI surface layer promoted Fe(II) regeneration. Furthermore, HO• and SO4-• were identified as the main contributors to FLT degradation. The intermediates of FLT degradation were detected by gas chromatograph-mass spectrometry (GC-MS) and a possible FLT degradation pathway was proposed. Finally, the effective degradation of two other common polycyclic aromatic hydrocarbons (PAHs) (naphthalene and phenanthrene) demonstrated the broad-spectrum reactivity of the PS/S-nZVI process. In conclusion, these findings strongly demonstrate that the PS/S-nZVI process is a promising alternative for the remediation of PAH-contaminated groundwater.

Registration of Phytoplankton Fluorescence Using an Experimental Sounding Probe

The main optical characteristics of phytoplankton and colored dissolved organic matter are described. The necessity of simultaneous registration of fluorescence of phytoplankton pigments and colored dissolved organic matter in seawater in situ is substantiated. Commercial recording devices, realizing registration of signals of phytoplankton fluorescence intensity in situ, are considered. This paper presents the developed experimental probing autonomous multichannel multichannel meter of fluorescence and light scattering in seawater (FR1). The paper presents the functional scheme of the developed meter, describes its main assemblies and principles of its operation. The developed meter allows quasi-simultaneous registration of a large set of parameters: excitation spectra of phytoplankton fluorescence, fluorescence intensity of phytoplankton pigments (chlorophyll-a, phycoerythrin, phycocyanin, β-carotene), as well as fluorescence intensity of colored dissolved organic matter and spectra of light scattering index at an angle of 90°. Registration of all these parameters is carried out from one measuring volume, where the same composition of suspended matter is located in the process of probing at each specific moment of time. The paper presents the results of approbation of the developed meter and suggests the direction of further research using it.

Large Thermal Hall Effect in Spinel FeCr2$_2$S4$_4$

AbstractThe thermal Hall effect (THE) is an important experimental probe of band topology and elementary excitations. Here, a large thermal Hall angle (THA) κxy/κxx ≈ 7 × 10−3 discovered so far in ferrimagnetic spinel FeCr2S4 and a large thermal Hall conductivity (κxy) discovered first in spinel structure and reaching a magnitude of at 50 K with a small magnetic field of 0.1 T are reported. These results suggest the emergence of nontrivial topological excitations in FeCr2S4. A large THA in spin caloritronics devices means that a small number of excitations can produce a large transverse signal. FeCr2S4 is therefore a potential platform for spintronics‐magnonics applications, and may enhance the knowledge of the thermal Hall effect.

Characterization of hydrogen traps in a co-precipitation steel investigated by atom probe experiments without cryogenic transfer

Hydrogen (H) embrittlement in high-strength steels can be mitigated by introducing H traps into the microstructure. The co-precipitation model steel in this work contains intermetallic ß-NiAl and secondary Cr-carbides, which provide abundant trapping sites. Needle-shaped specimens are prepared for atom probe tomography (APT) and electro-chemically charged in a solution of 0.1 M NaOH in D2O to introduce deuterium (D). D is located at the finely dispersed Cr-carbides even after specimen transfer at room temperature (RT), which shows that nano-sized Cr-carbides are strong H traps. This is in contrast to previous studies of weak traps where cryogenic transfer was needed to detect any D.

Time-resolved photoelectron diffraction imaging of methanol photodissociation involving molecular hydrogen ejection.

Imaging ultrafast atomic and molecular hydrogen motion with femtosecond time resolution is a challenge for ultrafast spectroscopy due to the low mass and small scattering cross section of the moving neutral hydrogen atoms and molecules. Here, we propose time- and momentum-resolved photoelectron diffraction (TMR-PED) as a way to overcome limitations of existing methodologies and illustrate its performance using a prototype molecular dissociation process involving the sequential ejection of a neutral hydrogen molecule and a proton from the methanol dication. By combining state-of-the-art molecular dynamics and electron-scattering methods, we show that TMR-PED allows for direct imaging of hydrogen atoms in action. More specifically, the fingerprint of hydrogen dynamics reflects the time evolution of polarization-averaged molecular-frame photoelectron angular distributions (PA-MFPADs) as would be recorded in X-ray pump/X-ray probe experiments with few-femtosecond resolution. We present the results of two precursor experiments that support the feasibility of this approach.

RNA Secondary Structure Modeling Following the IPANEMAP Workflow.

The structure of RNA molecules and their complexes are crucial for understanding biology at the molecular level. Resolving these structures holds the key to understanding their manifold structure-mediated functions ranging from regulating gene expression to catalyzing biochemical processes. Predicting RNA secondary structure is a prerequisite and a key step to accurately model their three dimensional structure. Although dedicated modelling software are making fast and significant progresses, predicting an accurate secondary structure from the sequence remains a challenge. Their performance can be significantly improved by the incorporation of experimental RNA structure probing data. Many different chemical and enzymatic probes have been developed; however, only one set of quantitative data can be incorporated as constraints for computer-assisted modelling. IPANEMAP is a recent workflow based on RNAfold that can take into account several quantitative or qualitative data sets to model RNA secondary structure. This chapter details the methods for popular chemical probing (DMS, CMCT, SHAPE-CE, and SHAPE-Map) and the subsequent analysis and structure prediction using IPANEMAP.

The effect of confinement on the phase behavior of propane in nanoporous media: an experimental study probing capillary condensation, evaporation, and hysteresis at varying pore sizes and temperatures.

Fundamental understanding of the phase behavior and properties of fluids under confinement is of great significance for multiple fields of engineering and science, as well as for many practical industrial applications. In particular, unconventional geological systems, such as shale reservoirs, possess nanometer-scale pores, which impose nanoconfinement on the fluid molecules. In large pores, the bulk phase behavior of fluids can be modeled by the well-established methods, such as equation of state (EOS) approaches. However, under confinement the thermodynamic properties of fluids deviate significantly from those in the bulk, thus rendering the traditional EOS methods ineffective in predicting the phase behavior of confined fluids. Recently, the PC-SAFT/Laplace EOS has been developed to better represent the fluid phase equilibria in nanopores, which incorporates a new parameter that needs to be determined from experimental data. In this study, a new dataset is presented to reflect the phase properties of propane confined within the MCM-41 pores, with the aim to improve both the general understanding of the phase behavior of hydrocarbons under confinement and to parameterize the PC-SAFT/Laplace EOS for the nanoconfined propane. For this purpose, propane adsorption and desorption isotherms are determined experimentally for a wide range of temperatures (-27 to 20 °C) in MCM-41 of three different pore sizes (nominal pore diameters of 60, 80, and 100 Å). The effects of temperature and pore diameter on the capillary condensation and evaporation pressures are discussed in detail. Furthermore, the adsorption-desorption hysteresis behavior and its progression for different pore sizes were discussed. The experimental data are modeled using the parameterized PC-SAFT/Laplace EOS, which accurately captured the effects of confinement on the capillary condensation of propane in MCM-41. In addition, this study enriches the field of nanoconfinement research by providing a new dataset exemplifying the thermodynamic characteristics of hydrocarbons in nanopores.

Probing of nucleic acid compaction using low-frequency Raman spectroscopy.

Compaction of nucleic acids, namely DNA and RNA, determines their functions and involvement in vital cell processes including transcription, replication, DNA repair and translation. However, experimental probing of the compaction of nucleic acids is not straightforward. In this study, we suggest an approach for this probing using low-frequency Raman spectroscopy. Specifically, we show theoretically, computationally and experimentally the quantifiable correlation between the low-frequency Raman intensity from nucleic acids, magnitude of thermal fluctuations of atomic positions, and the compaction state of biomolecules. Noteworthily, we highlight that the LF Raman intensity differs by an order of magnitude for different samples of DNA, and even for the same sample in the course of long-term storage. The feasibility of the approach is further shown by assessment of the DNA compaction in the nuclei of plant cells. We anticipate that the suggested approach will enlighten compaction of nucleic acids and their dynamics during the key processes of the cell life cycle and under various factors, facilitating advancement of molecular biology and medicine.

High-Frequency Linear Array (20 MHz) Based on Lead-Free BCTZ Crystal.

Centimeter-sized BaTiO3-based crystals grown by top-seeded solution growth from the BaTiO3-CaTiO3-BaZrO3 system were used to process a high-frequency (HF) lead-free linear array. Piezoelectric plates with (110)pc cut within 1° accuracy were used to manufacture two 1-3 piezo-composites with thicknesses of 270 and [Formula: see text] for resonant frequencies in air of 10 and 30 MHz, respectively. The electromechanical characterization of the BCTZ crystal plates and the 10-MHz piezocomposite yielded the thickness coupling factors of 40% and 50%, respectively. We quantified the electromechanical performance of the second piezocomposite (30 MHz) according to the reduction in the pillar sizes during the fabrication process. The dimensions of the piezocomposite at 30 MHz were sufficient for a 128-element array with a 70- [Formula: see text] element pitch and a 1.5-mm elevation aperture. The transducer stack (backing, matching layers, lens, and electrical components) was tuned with the characteristics of the lead-free materials to deliver optimal bandwidth and sensitivity. The probe was connected to a real-time HF 128-channel echographic system for acoustic characterization (electroacoustic response and radiation pattern) and to acquire high-resolution in vivo images of human skin. The center frequency of the experimental probe was 20 MHz, and the fractional bandwidth at -6 dB was 41%. Skin images were compared against those obtained with a lead-based 20-MHz commercial imaging probe. Despite significant differences in sensitivity between elements, in vivo images obtained with a BCTZ-based probe convincingly demonstrated the potential of integrating this piezoelectric material in an imaging probe.

Adsorption and vibrational spectroscopy of CO on the surface of MgO from periodic local coupled-cluster theory.

The adsorption of CO on the surface of MgO has long been a model problem in surface chemistry. Here, we report periodic Gaussian-based calculations for this problem using second-order perturbation theory (MP2) and coupled-cluster theory with single and double excitations (CCSD) and perturbative triple excitations [CCSD(T)], with the latter two performed using a recently developed extension of the local natural orbital approximation to problems with periodic boundary conditions. The low cost of periodic local correlation calculations allows us to calculate the full CCSD(T) binding curve of CO approaching the surface of MgO (and thus the adsorption energy) and the two-dimensional potential energy surface (PES) as a function of the distance from the surface and the CO stretching coordinate. From the PES, we obtain the fundamental vibrational frequency of CO on MgO, whose shift from the gas phase value is a common experimental probe of surface adsorption. We find that CCSD(T) correctly predicts a positive frequency shift upon adsorption of +14.7 cm-1, in excellent agreement with the experimental shift of +14.3 cm-1. We use our CCSD(T) results to assess the accuracy of MP2, CCSD, and several density functional theory (DFT) approximations, including exchange correlation functionals and dispersion corrections. We find that MP2 and CCSD yield reasonable binding energies and frequency shifts, whereas many DFT calculations overestimate the magnitude of the adsorption energy by 5-15 kJ mol-1 and predict a negative frequency shift of about -20 cm-1, which we attribute to self-interaction-induced delocalization errors that are mildly ameliorated with hybrid functionals. Our findings highlight the accuracy and computational efficiency of the periodic local correlation for the simulation of surface chemistry with accurate wavefunction methods.

Catalytic Synthesis of Carbon Nanotubes and Hydrogen Gas from Waste Plastics Using LaNiO3 Perovskite Catalyst

Using waste plastic syngas to prepare carbon nanotubes (CNTs) and hydrogen-rich gas is a clean and efficient recycling method for waste plastics, and it is very important to find out how to improve its yield and quality. In this work, CNTs and hydrogen-rich gas were prepared by LaNiO3 perovskitetype catalysts from waste plastic syngas model compound in laboratory. The LaNiO3 catalysts, carbon nanotubes and gas fractions produced at different temperatures were characterized and compared with the supported catalyst Ni/ZSM-5. The main conclusions were as follows: 650 °C catalytic temperature had maximum carbon nanotubes yield of 5.84 gCNTs/gCatalyst and H2 content of 44 Vol.%, which was 4.44 times the carbon nanotubes yield from the Ni/ZSM-5 catalyst at the same temperature case. A bottom growth pattern of carbon nanotubes produced on the LaNiO3 catalyst was observed by high resolution transmission electron microscopy (HRTEM). The X-ray crystal diffractometer (XRD) analysis revealed that the interaction force between Ni and the carrier was stronger in LaNiO3 than that of the Ni/ZSM-5 catalyst, resulting in two different growth patterns of carbon nanotubes. The present experiments probe that the LaNiO3 catalysts have a greater prospect of application in the preparation of CNTs and hydrogen-rich gas from waste plastic syngas.

STAR Overview

The STAR experiment covers a wide range of energies and collisions thanks to RHIC’s versatility and STAR’s recent detector upgrades. In this contribution to the proceedings of the 2023 QuarkMatter conference, we highlight our new results from the Beam Energy Scan, system-size scans at top RHIC energies using a broad range of experimental probes.

Magnetically separable CuFe2O4/ZnIn2S4 heterojunction photocatalyst for simultaneous removal of Cr(VI) and CIP

Although photocatalytic has been widely applied for wastewater treatment, there is still a need to develop highly efficient materials capable of simultaneous removal of pollutants and heavy metal ions. This study used a combination of electrospinning and solvothermal methods to prepare CuFe2O4/ZnIn2S4 (CFO/ZIS) heterojunction photocatalysts, and studied their photocatalytic performance in a Cr(VI)-Ciprofloxacin (CIP) coexisting pollutant system. Under simulated sunlight irradiation, the optimal ratio of CFO/ZIS composites (CFO/ZIS-2) achieved a reduction rate of about 99% for Cr(VI) within 20 min, and a degradation rate of about 73% for CIP within 60 min. In addition, even under real sunlight or lake water conditions, CFO/ZIS-2 has the ability to simultaneously remove Cr(VI) and CIP. Most importantly, after the completion of the photoreaction, the magnetism of CFO/ZIS-2 itself can be easily separated with a magnet, indicating that CFO/ZIS-2 has certain practical application capabilities. In addition, cyclic experiments have shown that CFO/ZIS-2 has a certain degree of repeatability and demonstrated that the formation of heterojunctions inhibits photo-corrosion of the catalyst. The formation of heterojunctions in CFO/ZIS-2 was demonstrated through free radical capture experiments and molecular probe experiments, which reduced the recombination of photo-generated electron-holes and enhanced light absorption. This work will provide a new avenue for designing novel magnetic separation and photo-corrosion-resistant photocatalysts to cope with complex wastewater environments.