Probe Particles Research Articles

Radial dependence of solar energetic particle peak fluxes and fluences. Multispacecraft observations based on Parker Solar Probe, Solar Orbiter, and near-Earth particle detectors

We present a list of solar energetic particle (SEP) events detected by instruments on board the Solar and Heliospheric Observatory (SOHO), Parker Solar Probe (PSP), and Solar Orbiter between 2021 and 2023. The investigation focuses on identifying the peak flux and the fluence of SEP events in four energy ranges from 10.5 to 40 MeV, as observed by PSP or Solar Orbiter at heliospheric distances shorter than 1 AU and by SOHO at the Sun-Earth L1 Lagrangian point. Based on the data from these events, we conduct a statistical analysis to study the radial dependence of the SEP proton peak flux and fluence at different energies. We identified 42 SEP events with enhanced proton flux that were observed simultaneously by at least two out of three spacecraft (SOHO, PSP, and Solar Orbiter). These events were further selected based on a criterion of a difference smaller than a 30^∘ difference in longitudinal separation between the magnetic footpoints of the two spacecraft. For the selected events, we used a linear interpolation method to compute the proton peak flux and fluence in four energy ranges and quantified their radial dependence as a function of R^α, where R is the radial distance of the observer from the Sun. The peak flux and fluence of the SEP events display the following radial dependence: The average values of α across all energies range between about -3.7 and -2 for the peak fluxes and between -2.7 and -1.4 for the fluences. We also obtained the energy dependence of $|α|$, which decreases with increasing energy. Additionally, based on theoretical functions, we find that the SEP source and transport parameters may have a significant impact on α(E), and the measurement-derived $|α(E)|$ values and their distribution fall within the range of theoretical predictions. (1) Despite the uncertainties arising from the low statistics and the longitudinal influence, the radial dependence of the peak flux agrees with the upper limit R^-3 predicted by previous studies. (2) The radial dependence on the fluence R^-2 tends to be weaker than the radial decay of the peak flux. (3) As the proton energy increases, the proton mean free path increases, and the adiabatic cooling effect modifies the proton energy. As a result, the peak flux and fluence decay more significantly with increasing radial distance for lower-energy particles.

How Much Data Are Enough? Toward Statistically Robust Adhesion Experiments by Atomic Force Microscopy.

Direct force measurements by atomic force microscopy (AFM) have become an indispensable analytical tool in the last decades. Force measurements have been widely used for adhesion measurements, often in combination with the colloidal probe technique. For the latter technique, a colloidal particle is attached to the end of an AFM cantilever, proving great flexibility in terms of colloid/surface interaction to be studied. Interestingly, the question of how much data is necessary to obtain statistically reliable results has been addressed in this context only sparsely. By contrast, the value and necessity of determining and reporting distributions of adhesion forces has been widely accepted. Here, simple statistical methods of the experimental design have been applied to address this question. It has been demonstrated that it is possible to determine an optimal number of force curves even during data acquisition. This approach would be essential to prevent oversampling of data. Moreover, it allows to address questions like heterogeneity of the sample in a more reliable or less time-consuming way. In AFM measurements with colloidal probes, most statistical variation results from the surface roughness of the probe particle. In this case, the use of different colloidal particles is important, which can be achieved by techniques such as fluidic force microscopy (FluidFM). The latter enables to combine a real-time determination of the required data size and high-throughput techniques of unattended measurements, which will open new fields of analysis.

Colored Cellulose Nanoparticles with High Stability and Easily Modified Surface for Accurate and Sensitive Multiplex Lateral Flow Assay.

Decentralized testing using multiplex lateral flow assays (mLFAs) to simultaneously detect multiple analytes can significantly enhance detection efficiency, reduce cost and time, and improve analytic accuracy. However, the challenges, including the monochromatic color of probe particles, interference between different test lines, and reduced specificity and sensitivity, severely hinder mLFAs from wide use. In this study, we prepared polydopamine (PDA)-coated dyed cellulose nanoparticles (dCNPs@P) with tunable colors as the probe for mLFAs. Cellulose nanoparticles (CNPs) were synthesized with uniform spheric shapes and tunable sizes. Dye molecules were loaded on CNPs via a mature industrial dyeing method. The PDA shell provided a reactive surface for facile receptor conjugation and protected the dye from leaking. dCNPs@P displayed a higher signal intensity than gold nanoparticles. They also had higher stability to tolerate salt and varied pH. The dCNP@P-based mLFAs were successfully applied to detect multiple mycotoxins in cereals and determine the levels of inflammatory biomarkers to differentiate between viral and bacterial infections. The tests represented high specificity and accuracy and were more sensitive than the tests using gold nanoparticles. The quantified detection was accessible by measuring the intensities of the colorimetric or photothermal signals. Overall, this study provides a practical system solution for mLFAs based on colored dCNPs@P.

Single Nucleotide Polymorphism Highlighted via Heterogeneous Light-Induced Dissipative Structure.

The unique characteristics of biological structures depend on the behavior of DNA sequences confined in a microscale cell under environmental fluctuations and dissipation. Here, we report a prominent difference in fluorescence from dye-modified single-stranded DNA in a light-induced assembly of DNA-functionalized heterogeneous probe particles in a microwell of several microliters in volume. Strong optical forces from the Mie scattering of microparticles accelerated hybridization, and the photothermal effect from the localized surface plasmons in gold nanoparticles enhanced specificity to reduce the fluorescence intensity of dye-modified DNA to a few %, even in a one-base mismatched sequence, enabling us to clearly highlight the single nucleotide polymorphisms in DNA. Fluorescence intensity was positively correlated with complementary DNA concentrations ranging in several tens fg/μL after only 5 min of laser irradiation. Remarkably, a total amount of DNA in an optically assembled structure of heterogeneous probe particles was estimated between 2.36 ymol (2.36 × 10-24 mol) and 2.36 amol (2.36 × 10-18 mol) in the observed concentration range. These findings can promote an innovative production method of nanocomposite structures via biological molecules and biological sensing with simple strategies avoiding genetic amplification in a PCR-free manner.

Microrheological model for Kelvin-Voigt materials with micro-heterogeneities.

We introduce a generalization of the Kelvin-Voigt model in order to include and characterize heterogeneities in viscoelastic semisolid materials. By considering a microrheological approach, we present analytical expressions for the mean square displacement and for the time-dependent diffusion coefficient of probe particles immersed in a viscoelastic material described by this model. Besides validating our theoretical approach through Brownian dynamics simulations, we show how the model can be used to describe experimental data obtained for polyacrylamide and LAPONITE® gels.

Compton scattering from proton pairs – illustrating weak and strong measurements

Abstract Neutrons interacting with protons in Compton scattering is here chosen as an example of a non-trivial quantum measurement. It illustrates a situation where a probe particle makes an observation (a weak measurement) of the studied protons, preparing for a final state in which one of them takes up the recoil in the collision. The proton is ejected during a strong (projective) measurement that selects one particular momentum value out of the proton’s initial distribution of momentum states. This course of events in the measurement process is evidenced by the observation that destructive interference appears during the weak interaction stage which leads to a strongly reduced neutron cross section for the proton system.

Scattering and Bound Observables for Spinning Particles in Kerr Spacetime with Generic Spin Orientations.

We derive the radial action of a spinning probe particle in Kerr spacetime from the worldline formalism in the first-order form, focusing on linear in spin effects. We then develop a novel covariant Dirac bracket formalism to compute the impulse and the spin kick directly from the radial action, generalizing some conjectural results in the literature and providing ready-to-use expressions for amplitude calculations with generic spin orientations. This allows, for the first time, to find new covariant expressions for scattering observables in the probe limit up to O(G^{6}s_{1}s_{2}^{4}). Finally, we use the action-angle representation to compute the fundamental frequencies for generic bound orbits, including the intrinsic spin precession, the periastron advance, and the precession of the orbital plane.

Homogeneous turbophoresis of heavy inertial particles in turbulent flow

Heavy particles suspended in turbulent flow possess inertia and are ejected from violent vortical structures by centrifugal forces. Once piled up along particle paths, this small-scale mechanism leads to an effective large-scale drift. This phenomenon, known as ‘turbophoresis’, causes particles to leave highly turbulent regions and migrate towards calmer regions, explaining why particles transported by non-homogeneous flows tend to concentrate near the minima of turbulent kinetic energy. It is demonstrated here that turbophoretic effects are just as crucial in statistically homogeneous flows. Although the average turbulent activity is uniform, instantaneous spatial fluctuations are responsible for inertial-range inhomogeneities in the particle distribution. Direct numerical simulations are used to probe particle accelerations, specifically how they correlate to local turbulent activity, yielding an effective coarse-grained dynamics that accounts for particle detachment from the fluid and ejection from excited regions through a space- and time-dependent non-Fickian diffusion. This leads to cast fluctuations in particle distributions in terms of a scale-dependent Péclet number ${\textit {Pe}}_\ell$ , which measures the importance of turbulent advection compared with inertial turbophoresis at a given scale $\ell$ . Multifractal statistics of energy dissipation indicate that $ {\textit {Pe}}_\ell \sim \ell ^\delta /\tau _{p}$ with $\delta \approx 0.84$ . Numerical simulations support this behaviour and emphasise the relevance of the turbophoretic Péclet number in characterising how particle distributions, including their radial distribution function, depends on $\ell$ . This approach also explains the presence of voids with inertial-range sizes, and the fact that their volumes have a non-trivial distribution with a power-law tail $p(\mathcal {V}) \propto \mathcal {V}^{-\alpha }$ , with an exponent $\alpha$ that tends to 2 as ${\textit {Pe}}_\ell \to 0$ .

Neutron star collapse from accretion: A probe of massive dark matter particles

We explore the multi-scatter capturing of the massive dark matter (DM) particle inside the neutron star via a momentum-dependent dark matter-nucleon scattering cross-section. We find that the capturing enhanced for the positive velocity and momentum transfer dependent DM-nucleon scattering in comparison with the constant cross-section case. Further, a large capture of the DM particles can be thermalized and lead to black hole formation and, therefore, destroy the neutron star. Using the observation of the old neutron star in the DM-dominated region, we obtain strong constraints on massive DM parameters.

Sequence-Encoded Spatiotemporal Dependence of Viscoelasticity of Protein Condensates Using Computational Microrheology.

Many biomolecular condensates act as viscoelastic complex fluids with distinct cellular functions. Deciphering the viscoelastic behavior of biomolecular condensates can provide insights into their spatiotemporal organization and physiological roles within cells. Although there is significant interest in defining the role of condensate dynamics and rheology in physiological functions, the quantification of their time-dependent viscoelastic properties is limited and is mostly done through experimental rheological methods. Here, we demonstrate that a computational passive probe microrheology technique, coupled with continuum mechanics, can accurately characterize the linear viscoelasticity of condensates formed by intrinsically disordered proteins (IDPs). Using a transferable coarse-grained protein model, we first provide a physical basis for choosing optimal values that define the attributes of the probe particle, namely, its size and interaction strength with the residues in an IDP chain. We show that the technique captures the sequence-dependent viscoelasticity of heteropolymeric IDPs that differ in either sequence charge patterning or sequence hydrophobicity. We also illustrate the technique's potential in quantifying the spatial dependence of viscoelasticity in heterogeneous IDP condensates. The computational microrheology technique has important implications for investigating the time-dependent rheology of complex biomolecular architectures, resulting in the sequence-rheology-function relationship for condensates.

Composition Variation of the 2023 May 16 Solar Energetic Particle Event Observed by SolO and PSP

In this study, we employ the combined charged particle measurements from Integrated Science Investigation of the Sun on board the Parker Solar Probe (PSP) and Energetic Particle Detector on board the Solar Orbiter (SolO) to study the composition variation of the solar energetic particle (SEP) event occurring on 2023 May 16. During the event, SolO and PSP were located at a similar radial distance of ∼0.7 au and were separated by ∼60° in longitude. The footpoints of both PSP and SolO were west of the flare region, but the former was much closer (18° versus 80°). Such a distribution of observers is ideal for studying the longitudinal dependence of the ion composition with the minimum transport effects of particles along the radial direction. We focus on H, He, O, and Fe measured by both spacecraft in sunward and antisunward directions. Their spectra are in a double power-law shape, which is fitted best by the Band function. Notably, the event was Fe rich at PSP, where the mean Fe/O ratio at energies of 0.1–10 Mev nuc−1 was 0.48, higher than the average Fe/O ratio in previous large SEP events. In contrast, the mean Fe/O ratio at SolO over the same energy range was considerably lower at 0.08. The Fe/O ratio between 0.5 and 10 MeV nuc−1 at both spacecraft is nearly constant. Although the He/H ratio shows energy dependence, decreasing with increasing energy, the He/H ratio at PSP is still about twice as high as that at SolO. Such a strong longitudinal dependence of element abundances and the Fe-rich component in the PSP data could be attributed to the direct flare contribution. Moreover, the temporal profiles indicate that differences in the Fe/O and He/H ratios between PSP and SolO persisted throughout the entire event rather than only at the start.

Study on Measurement Method of Three-dimensional Position of Unlabeled Microspheres under Bright Background

Abstract: Using computer vision technology to obtain the position and trajectory data of particle probe microspheres from microscope images has significance and value in the molecular field. However, most of the existing microsphere measurement methods are based on transmission, which can only be measured under transparent samples and substrates and are not suitable for the application scenario of living cell measurement. In this paper, a method based on reflectivity imaging is proposed to measure the three-dimensional position of the dark microspheres in the bright field. Based on the outermost ring radius method, the relationship between the inner ring radius of the microsphere spot and the out-of-focus distance was explored to measure the coordinates in the Z direction. Cardiomyocytes were combined with 10um size silica microspheres. Experiments show that in a bright field with a high perturbation environment, it can achieve high precision measurement of dark microspheres and achieve three-dimensional position measurement with an accuracy of 50nm in XY direction and 100nm in Z direction.

Non-monotonic dynamic correlation explored via active microrheology

Abstract In the study of local and heterogeneous structures in supercooled liquids, microrheology plays a crucial role, offering a closer examination of the mechanical properties at a local level. We concentrate on active microrheology, where an external force drives a probe particle. This technique is employed in the study of a Kob–Andersen mixture, using extensive molecular dynamics simulations. Through active microrheology, we analyze the positional dependence of viscosity, observing how probe particles respond to activation velocity. Utilizing advanced stochastic analysis, we disentangle the deterministic and stochastic components of the local viscosity time series, characterizing its nonlinear and intermittent properties, which indicate heterogeneity. We construct a Langevin equation to model the dynamics of local viscosity and derive its drift and diffusion coefficients from simulation data. Additionally, we investigate the temperature-dependent variations of viscosity dynamics, unveiling their multiplicative and nonlinear nature. We elaborate on how the existence of multiplicative dynamics in viscosity results in the characteristic emergence of heterogeneity within viscosity dynamics. We derive a dynamic correlation length from local viscosity. Moreover, this correlation length shows a non-monotonic dependence on temperature with a maximum at about the Kauzmann temperature.

Dynamic Light Scattering Microrheology of Phase-Separated Poly(vinyl) Alcohol–Phytagel Blends

In this investigation, we explored the microrheological characteristics of dilute hydrogels composed exclusively of Poly(vinyl) alcohol (PVA), Phytagel (PHY), and a blend of the two in varying concentrations. Each of these polymers has established applications in the biomedical field, such as drug delivery and lens drops. This study involved varying the sample concentrations from 0.15% to 0.3% (w/w) to assess how the concentration influenced the observed rheological response. Two probe sizes were employed to examine the impact of the size and verify the continuity hypothesis. The use of two polymer blends revealed their immiscibility and tendency to undergo phase separation, as supported by the existing literature. Exploring the microrheological structure is essential for a comprehensive understanding of the molecular scale. Dynamic light scattering (DLS) was chosen due to its wide frequency range and widespread availability. The selected dilute concentration range was hypothesized to fall within the transition from an ergodic to a non-ergodic medium. Properly identifying the sample’s nature during an analysis—whether it is ergodic or not—is critical, as highlighted in the literature. The obtained results clearly demonstrate an overlap in the results for the storage (G’) and loss moduli (G″) for the different probe particle sizes, confirming the fulfillment of the continuum hypothesis.

Harmonic chain driven by active Rubin bath: transport properties and steady-state correlations

Characterizing the properties of an extended system driven by active reservoirs is a question of increasing importance. Here, we address this question in two steps. We start by investigating the dynamics of a probe particle connected to an ‘active Rubin bath’: a linear chain of overdamped run-and-tumble particles. We derive exact analytical expressions for the effective noise and dissipation kernels, acting on the probe and show that the active nature of the bath leads to a modified fluctuation–dissipation relation. In the next step, we study the properties of an activity-driven system, modelled by a chain of harmonic oscillators connected to two such active reservoirs at the two ends. We show that the system reaches a non-equilibrium stationary state (NESS), remarkably different from that generated due to a thermal gradient. We characterize this NESS by computing the kinetic temperature profile, spatial and temporal velocity correlations of the oscillators, and the average energy current flowing through the system. It turns out that the activity drive leads to the emergence of two characteristic length-scales, proportional to the activities of the reservoirs. Strong signatures of activity are also manifest in the anomalous short-time decay of the velocity autocorrelations. Finally, we find that the energy current shows a non-monotonic dependence on the activity drive and reversal in direction, corroborating previous findings.

Nonlinear Langevin functionals for a driven probe.

When a probe particle immersed in a fluid with nonlinear interactions is subject to strong driving, the cumulants of the stochastic force acting on the probe are nonlinear functionals of the driving protocol. We present a Volterra series for these nonlinear functionals by applying nonlinear response theory in a path integral formalism, where the emerging kernels are shown to be expressed in terms of connected equilibrium correlation functions. The first cumulant is the mean force, the second cumulant characterizes the non-equilibrium force fluctuations (noise), and higher order cumulants quantify non-Gaussian fluctuations. We discuss the interpretation of this formalism in relation to Langevin dynamics. We highlight two example scenarios of this formalism. (i) For a particle driven with the prescribed trajectory, the formalism yields the non-equilibrium statistics of the interaction force with the fluid. (ii) For a particle confined in a moving trapping potential, the formalism yields the non-equilibrium statistics of the trapping force. In simulations of a model of nonlinearly interacting Brownian particles, we find that nonlinear phenomena, such as shear-thinning and oscillating noise covariance, appear in third- or second-order response, respectively.

Effect of particle size, probe type, position and glassware geometry on laboratory-scale ultrasonic extraction of Citrus maxima flavedo

Laboratory-scale ultrasonic extraction efficiency can be improved by selecting appropriate substrate size, glassware type and hardware configurations. For the first time, effects of using different common glassware shapes and geometries with two common ultrasonic probes on phytochemical extractability in 80 % ethanol were investigated. Citrus maxima peel powder was the model substrate. Smaller particles of 100–150 μm yielded higher mass (51.26 ± 0.25 %), however not consistently enhancing phenolic and flavonoid content owing to thermal effects. 300–500 μm particles exhibited higher antioxidant activities (92.38 ± 0.50 % DPPH reduction and 2.81 ± 0.05 mM/g FRAP). A 3 mm diameter probe gave superior yield (>43 %) and quality (>40 % TPC; >35 % TFC and >28 % FRAP) over a 13 mm probe. Deeper probe placements (50–70 mm) enhanced cavitation effects, improving extraction efficiency and bioactivity (>20 % yield; >10 % TPC and TFC; >21 % FRAP respectively). Curved vessel base was found to be appropriate for generating efficient cavitation effects and extraction zones. Narrow-bodied test tube and falcon tube outperformed wider beakers and conical flasks. Improvements up to 43 %, 40 %, 38 % and 28 % in yield, TPC, TFC and FRAP respectively were achieved in them. Principal component analysis highlighted the synergistic effects. Schemes of ultrasonic activities within the selected set-ups were hence theorized from this study.

Sequence-encoded Spatiotemporal Dependence of Viscoelasticity of Protein Condensates Using Computational Microrheology.

Many biomolecular condensates act as viscoelastic complex fluids with distinct cellular functions. Deciphering the viscoelastic behavior of biomolecular condensates can provide insights into their spatiotemporal organization and physiological roles within cells. Though there is significant interest in defining the role of condensate dynamics and rheology in physiological functions, the quantification of their time-dependent viscoelastic properties is limited and mostly done through experimental rheological methods. Here, we demonstrate that a computational passive probe microrheology technique, coupled with continuum mechanics, can accurately characterize the linear viscoelasticity of condensates formed by intrinsically disordered proteins (IDPs). Using a transferable coarse-grained protein model, we first provide a physical basis for choosing optimal values that define the attributes of the probe particle, namely its size and interaction strength with the residues in an IDP chain. We show that the technique captures the sequence-dependent viscoelasticity of heteropolymeric IDPs that differ either in sequence charge patterning or sequence hydrophobicity. We also illustrate the technique's potential in quantifying the spatial dependence of viscoelasticity in heterogeneous IDP condensates. The computational microrheology technique has important implications for investigating the time-dependent rheology of complex biomolecular architectures, resulting in the sequence-rheology-function relationship for condensates.

Recovering the activity parameters of an active fluid confined in a sphere.

The properties of an active fluid, for example, a bacterial bath or a collection of microtubules and molecular motors, can be accessed through the dynamics of passive particle probes. Here, in the perspective of analyzing experimental situations of confinement in droplets, we consider the kinematics of a negatively buoyant probe particle in an active fluid, both confined within a spherical domain. The active bath generates a fluctuating flow that pushes the particle with a velocity that is modeled as a colored stochastic noise, characterized by two parameters, the intensity and memory time of the active flow. When the particle departs a little from the bottom of the spherical domain, the configuration is well approximated by a particle in a two-dimensional harmonic trap subjected to the colored noise, in which case an analytical solution exists, which is the base for quantitative analysis. We numerically simulate the dynamics of the particle and use the planar, two-dimensional mean square displacement to recover the activity parameters of the bath. This approach yields satisfactory results as long as the particle remains relatively confined; that is, as long as the intensity of the colored noise remains low.

Jet quenching of the heavy quarks in the quark-gluon plasma and the nonadditive statistics

Using the Plastino-Plastino (PP) equation, we calculate transport coefficients of the heavy-quarks traversing inside the quark-gluon plasma, and generalize their relationship with differential energy loss. The PP equation indicates anomalous diffusion of the probe particles and yields a quasi-exponential stationary distribution obtained also from the nonadditive statistics proposed by C. Tsallis. We estimate energy loss in a nonadditive quark-gluon medium, and calculate the jet quenching parameter (qˆ) for the PP dynamics. With the help of the estimate of qˆ, we calculate the nuclear suppression factor (RAA) of the heavy-quarks passing through a nonadditive quark-gluon plasma using the model proposed by Dokshitzer and Kharzeev. In many a case, the parameters in the analysis are fixed from the experimental results to minimize arbitrariness. There is a good agreement between the theoretical calculation and experimental RAA data, indicating that fast heavy-quarks may be subjected to anomalous diffusion inside the QGP.