Free Collisions Research Articles

Intelligent near-infrared light-activatable DNA machine with DNA wire nano-scaffold-integrated fast domino-like driving amplification for high-performance imaging in live biological samples

While there is significant potential for DNA machine-built enzyme-free fluorescence biosensors in the imaging analysis of live biological samples, they persist certain shortcomings. These encompass a deficiency of signal enrichment within a singular interface, uncontrolled premature activation during bio-delivery, and a slow reaction rate due to free nucleic acid collisions. In this contribution, we are committed to resolving the above challenges. Firstly, a single-interface-integrated domino-like driving amplification is constructed. In this conception, a specific target acts as the domino promotor (namely the energy source), initiating a cascading chain reaction that grafts onto a singular interface. Next, an 808 nm near-infrared (NIR) light-excited up-converting luminescence-induced light-activatable biosensing technique is introduced. By locking the target-specific identification segment with a photo-cleavage connector, the up-converted ultraviolet emission can activate target binding in a completely controlled manner. Moreover, a fast reaction rate is achieved by confining nucleic acid collisions within the surface of a DNA wire nano-scaffold, leading to a substantial enhancement in local contact concentration (30.8-fold increase, alongside a 15 times elevation in rate). When a non-coding microRNA (miRNA-221) is positioned as the model low-abundance target for proof-of-concept validation, our intelligent DNA machine demonstrates ultra-high sensitivity (with a limit of detection down to 62.65 fM) and good specificity for this hepatic malignant tumor-associated biomarker in solution detection. Going further, it is worth highlighting that the biosensing system can be employed to carry out high-performance imaging analysis in live bio-samples (ranging from the cellular level to the nude mouse body), thereby propelling the field of DNA machines in disease diagnosis.

Three-dimensional measurement method of binary particle collisions under dry and wet conditions

The description, calculation and design of solids processes, such as fluidization, pneumatic conveying or mixing, require knowledge of collision dynamics between particles and apparatus walls or interparticle collisions without, but often also with the presence of an additional liquid. For the study of such dry and wet interparticle collisions, an experimental setup is presented that allows the performance of dry or wet free binary collisions of spherical particles down to a minimum diameter of 1 mm. The recording of the particle motions in all three spatial directions is provided by two synchronized highspeed cameras. Methods and algorithms are presented for analyzing the translational and rotational motion in three-dimensional space, as well as for measuring the amount of liquid on the particles in the case of wet collisions. Motion data from dry collisions between equal sized and unequal sized spherical particles are compared with a three-parameter collision model. In addition, a first series of measurements of wetted collisions is used to compare the collision dynamics with dry collisions.

A NOVEL EXPERIMENTAL APPROACH TO STUDY DROP-PARTICLE COLLISIONS

Free drop-particle collisions occurring in air are experimentally produced by combining a stream of drops and a stream of particles, which results from the selective and ultra-fast hardening of another regular drop stream. The set-up offers the possibility to vary accurately the drop and particle diameter, the collision eccentricity, and the relative drop-particle velocity. First observations obtained with drop Weber numbers ranging from 30 to 300, drop Reynolds number between 390 and 4600, and with typical equilibrium contact angle of 70° evidence the existence of full deposition, separation, indicating possible bouncing events. For off-center separation, a liquid ligament forms between the particle and the outlying drop cap that fragments due to excessive stretching, a phenomenon similar to drop-drop collisions. In contrast, for head-on collisions and intermediate inertia, a lamella first forms, whose constrained recoil leads to liquid protuberance(s) that eventually pinch(es)-off. These outcomes can be distinguished using a bi-dimensional regime map built on the impact parameter and the drop Weber number. Despite remarkable similarities with binary drop collisions, important differences are observed especially for low and moderate eccentricities.

The molecular dynamics simulation of lignite combustion process in O2/CO2 atmosphere with ReaxFF force field

Pressurized oxy-fuel combustion is a complex process consisting of free radical collisions and reactions. ReaxFF reactive Molecular Dynamics (MD) simulation method is a useful tool to investigate the chemical events in coal combustion at atomistic level. In this work, the impact of operating conditions on the distribution of main fragments and the reaction mechanisms were examined using a lignite coal model with ReaxFF force field to simulate the process of oxy-fuel combustion under pressures. The ReaxFF MD simulations found that the decomposition of coal molecular structure would be enhanced by increasing the pressure/density, oxygen concentration and temperature. The variety of initial reactions increased with temperature. Increasing pressure promoted the effective collision of molecules and the coal structure was more likely to be attacked by oxidants, so the chemical bonds in coal molecule broke earlier and the consumption of O2 increased at higher pressure. The dehydrogenation reaction on the macromolecular structure of coal and small fragments was also promoted after increasing pressure/density. However, the number of fragments decreased as the pressure/density continued to grow, because large fragments further decomposed or some small molecular benzene ring structures with less than 6C atoms were re-polymerized. The dehydrogenation reaction of coal molecule and small fragments was promoted after increasing the pressure. O2 attacked the benzene ring structure, the C atom on the outer side of the coal, and the carbon-containing fragments in the system, indicating that the increase of O2 concentration promoted the ring opening and oxidation reactions, thereby promoting the decomposition and combustion of coal. The work in this paper has confirmed the findings obtained by other oxy-fuel experimental work from the microscopic point of view.

Evaluating the Performance of a Hockey Helmet in Mitigating Concussion Risk Using Measures of Acceleration and Energy During Simulated Free Fall

Hockey helmets represent the best form of head protection available to reduce the occurrence of skull fracture and concussion. Currently, helmet testing protocols focus on the reduction of peak linear acceleration measures. Gaps exist in analyzing how certain impact factors such as angle, neck stiffness, and location influence the energy loaded to the helmet and the risk of injury during head collisions. This study examined the effect of helmet impact angle, neck stiffness-torque levels, and helmet impact locations on energy reduction and risk of head injury grounded on acceleration measures using simulated free fall head collisions. The researchers conducted 540 impacts to collect the data. The results revealed statistical interaction effects between the angle of impact and location on measures of energy and risk of head injury. This study builds on existing literature by introducing an energy measurement technique to assess helmet performance. The outcome also provides an avenue for helmet manufacturers to evaluate the performance of the helmet in reducing concussion risk.

Exclusion of quadruple collisions in minimizers of the planar equal-mass N-body problem

It has been shown by Chen that if all masses are in the same proper vector subspace of Rd(d≥2) on one of the free boundaries, local minimizers connecting the two free boundaries have no collision on that boundary. However, not much is known for other types of boundary configurations.In this paper, we consider minimizers connecting two free boundaries and study possible quadruple collisions under the following four symmetric configurations: isosceles trapezoid configuration, rectangular configuration, double isosceles configuration and diamond configuration. Whenever the boundary configuration of four bodies coincides with one of the four symmetric configurations, we show that these four bodies are free of quadruple collision on that boundary set. New ideas and detailed analysis are introduced in order to construct deformed paths in some of the cases and estimate their action values. As its applications, we show the existence of several sets of periodic orbits in the planar four-body and five-body problems.

A Smoking Gun for Planetesimal Formation: Charge-driven Growth into a New Size Range

Abstract Collisions electrically charge grains, which promotes growth by coagulation. We present aggregation experiments with three large ensembles of basalt beads (150–180 μm), two of which are charged, while one remains almost neutral as a control system. In microgravity experiments, free collisions within these samples are induced with moderate collision velocities (0–0.2 m s−1). In the control system, coagulation stops at (sub-)mm size while the charged grains continue to grow. A maximum agglomerate size of 5 cm is reached, limited only by bead depletion in the free volume. For the first time, charge-driven growth well into the centimeter range is directly proven by experiments. In protoplanetary disks, this agglomerate size is well beyond the critical size needed for hydrodynamic particle concentration as, e.g., by the streaming instabilities.

Effect of the Ions on the Electron Collision Operator through Electronic Trajectory Modification

We investigate the ion effect on the broadening of the spectral line profile by the free electrons collisions with the emitters in plasmas. We only considered the weak collisions’ contribution. This effect has a consequence on the trajectories of the free electrons through the electric microfield created by the ions of the plasma. Thanks to the Meijer’s functions, the calculation of the electronic Stark broadening is precisely established.

High potential, near free molecular regime Coulombic collisions in aerosols and dusty plasmas

AbstractDetermination of the particle charge in aerosols and dusty plasmas requires an accurate calculation of the particle-ion collision kernel taking into account the particle-ion Coulombic coupling and ion-neutral gas molecule collisions. While the effect of Coulombic interactions of any strength is described accurately in the continuum limit and free molecular limit, an accurate physical description at intermediate collisional regimes remains elusive. Specifically, the Coulomb influenced collisions between oppositely charged particles and ions have evaded accurate theoretical description in the past. We use Langevin dynamics (LD) calculations to infer the non-dimensional collision kernel H as a function of the electrostatic potential energy to thermal energy ratio ΨE and the diffusive Knudsen number KnD, the index of ion-neutral collisionality in a finite pressure system. The LD approach yields a simple, approximate treatment of particle charging in the entire ion-neutral collision regime under the as...

Effects of shadowing in Pb + Pb collisions at energies available at the CERN Large Hadron Collider within the HIJING code

The charged particle central rapidity density per participant nucleon pair ( $(\mathrm{d} N_{ch}/\mathrm{d} \eta)/(0.5\langle N_{part} \rangle)$ ) as a function of the average number of participants ( $ N_{part}$ ) for $ \mathrm{Au}+\mathrm{Au}$ ( $ \mathrm{Cu}+\mathrm{Cu}$ ) collisions at $ \sqrt{s_{\mathrm{NN}}}=62.4$ and 200 GeV, and $ \mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ and 5.02 TeV is investigated within an improved HIJING (ImHIJING/Cas) model. Compared to the standard HIJING version, it incorporates: i) more consistent parton densities, ii) a QCD running coupling, defined by the exact solution of the renormalization group equation, and iii) a spatial dependent nucleon shadowing, triggered by collective nucleon interactions with an incoming nucleon, and simulated by the collective cascade recipe. Predictions are compared using four different settings of nuclear shadowing of partons, based on the standard HIJING1.0(2.0) parameterizations. It is shown that ImHIJING/Cas/Set2 (that with both quark and soft gluon shadowing of strength $ s_{q(g)}$ can nicely reproduce the measured centrality dependence of $ (\mathrm{d} N_{ch}/\mathrm{d} \eta)/(0.5\langle N_{part} \rangle)$ at RHIC energy. As for LHC, a reduction of $ s_{g}$ by $ \sim 40$ % at very peripheral (90-100%) $ \mathrm{Pb}+\mathrm{Pb}$ collisions, as compared to free nucleon-nucleon collisions, is found to reproduce the measured data. The values of $s_{q(g)}$ used in ImHIJING/Cas/Set2 calculations for most central 0-3(5)% $ \mathrm{Au}+\mathrm{Au} (\mathrm{Pb}+\mathrm{Pb})$ collisions at RHIC(LHC) energy, are found to be consistent with those employed in Set2 that reproduce the measured structure function ratios ( $ 12F^{Pb}_{2}/207F^{C}_{2}$ ) as a function of x.

A unified gas-kinetic scheme for axisymmetric flow in all Knudsen number regimes

Based on kinetic model equation, a unified gas-kinetic scheme for axisymmetric flow (UGKS-AS) is proposed in the whole flow regimes. The flux transport of UGKS-AS is based on a reduced gas distribution function of a time integral solution of the full 3D BGK model. In the cylindrical coordinate system, the local time evolution of convection and source terms for the macroscopic and microscopic flow variables is fully coupled with particle free transport and collisions. As a result, a multiple scale UGKS-AS is developed and used for the flow simulation from the free molecular transport to the Navier–Stokes solutions. In comparison with the full 3D UGKS method for axisymmetric flow, the present scheme is much more efficient and gives accurate solution in all flow regimes. Different from operator splitting methods with decoupled treatment of particle transport and collision, for the Navier–Stokes solution in the continuum regime the UGKS-AS doesn't have the constraint on the time step being less than the particle collision time. To further improve the efficiency of the scheme for steady state solution, an implicit UGKS-AS method is also developed. A large number of numerical tests for axisymmetric flow are conducted by the proposed explicit and implicit UGKS-AS, which include inner and outer, steady and unsteady, low and high speed flows. Some tests are very challenging due to the delicate capturing of very small flow variations. The good agreement among the solutions from the present scheme and other analytical, numerical, and experimental studies, validates the high accuracy and efficiency of the UGKS-AS for non-equilibrium flow simulation in all regimes.

Effect of stable and metastable dimers on collision-induced rototranslational spectra: Carbon dioxide – rare gas mixtures

The role of stable and metastable dimers as well as of free collisions in the collision-induced rototranslational absorption by the compressed CO2–Ar and CO2–Xe gas mixtures is elucidated using the classical three-dimensional trajectories method. The contribution from the stable dimers is obtained via Fourier transform of the dipole correlation function. The spectral bandshape due to the unbound trajectories (metastable dimers and free collisions) is calculated as an averaged Fourier spectrum of the collision-induced dipole moment. The mean lifetimes of metastable dimers have been estimated as 3.8 ps for CO2–Ar and 5.9 ps for CO2–Xe pairs. Trajectory computations are complemented by calculations of zero spectral moments using pair distribution functions. The stable and metastable dimer contribution to the zero spectral moment is shown to be comparable with that from free collisions.

Engineering bright matter-wave solitons of dipolar condensates

We present a comprehensive analysis of the form and interaction of dipolar bright solitons across the full parameter space afforded by dipolar Bose–Einstein condensates, revealing the rich behavior introduced by the non-local nonlinearity. Working within an effective one-dimensional description, we map out the existence of the soliton solutions and show three collisional regimes: free collisions, bound state formation and soliton fusion. Finally, we examine the solitons in their full three-dimensional form through a variational approach; along with regimes of instability to collapse and runaway expansion, we identify regimes of stability which are accessible to current experiments.

Collisions of solid ice in planetesimal formation

We present collision experiments of centimetre projectiles on to decimetre targets, both made up of solid ice, at velocities of $15\,\mathrm{m\,s^{-1}}$ to $45\,\mathrm{m\,s^{-1}}$ at an average temperature of $\mathrm{T_{avg}}=255.8\pm0.7\,\mathrm{K}$. In these collisions the centimetre body gets disrupted and part of it sticks to the target. This behaviour can be observed up to an upper threshold, that depends on the projectile size, beyond which there is no mass transfer. In collisions of small particles, as produced by the disruption of the centimetre projectiles, we also find mass transfer to the target. In this way the larger body can gain mass, although the efficiency of the initial mass transfer is rather low. These collision results can be applied to planetesimal formation near the snowline, where evaporation and condensation is expected to produce solid ice. In free fall collisions at velocities up to about $7\,\mathrm{m\,s^{-1}}$, we investigated the threshold to fragmentation and coefficient of restitution of centimetre ice spheres.

Free collisions in a microgravity many-particle experiment. IV. – Three-dimensional analysis of collision properties

The bouncing barrier, a parameter combination at which dust particles in the protoplanetary disk always rebound in mutual collisions, is one of the crucial steps of planet formation. In the past years, several experiments have been performed to determine the mass and velocity regimes at which perfect bouncing does occur and those where there is a chance of the aggregates sticking together. We conducted a microgravity experiment, which allows us to investigate free collisions of millimeter-sized SiO2 dust aggregates at the relevant velocities. We analyzed 52 collisions in detail with velocities of 3.4×10-3ms-1 to 6.2×10-2ms-1 and found four of them leading to sticking, while the other aggregates rebounded. Three out of the four sticking collisions occurred at velocities where previously only bouncing had been predicted. Although the probability for sticking is low, this opens a new possibility for growth beyond millimeter sizes. Our setup allowed us to obtain the complete three-dimensional collision information. Since most previous experiments were interpreted based on two-dimensional information, we compare our three-dimensional values with those obtained if only one projection had been available. We find that the error of a two-dimensional analysis of the collision velocity is very small. The distribution of the coefficient of restitution in the two-dimensional view is representative of the real case, but for any given collision its value can be far off. Impact parameters always have to be analyzed three-dimensionally, because the two-dimensional values are not meaningful in any way.

Energy transfer models in nitrogen plasmas: analysis of N₂(X¹Σg⁺)-N(⁴S(u))-e⁻ interaction.

The relaxation of N₂(X¹Σg⁺) molecules in a background gas composed of N((4)S(u)) atoms and free electrons is studied by using an ideal isochoric and isothermic chemical reactor. A rovibrational state-to-state model is developed to study energy transfer process induced by free electron and atomic collisions. The required cross sections and the corresponding rate coefficients are taken from two well-known kinetic databases: NASA Ames kinetic mechanism for the description of the N₂(X¹Σg⁺)-N((4)S(u)) processes and the Phys4Entry database for the electron driven processes, N₂(X¹Σg⁺)-e(-). The evolution of the population densities of each individual rovibrational level is explicitly determined via the numerical solution of the master equation for temperatures ranging from 10000 to 30,000 K. It was found that the distribution of the rovibrational energy levels of N₂(X¹Σg⁺) is strongly influenced by the electron driven collisional processes, which promote the excitation of the low lying vibrational levels. The macroscopic vibrational energy relaxation is governed by the molecule-atom collisions, when free electrons, initially cold are relaxing to the final heat-bath temperature. Thus, the main role of the free electrons is to ensure the equilibration of vibrational and free electron excitation, thus validating the existence of the local equilibrium T(V)-T(e). However, if electrons and heavy particles are assumed to be in equilibrium at the heat bath temperature, electron driven processes dominate the vibrational relaxation. Finally, we have assessed the validity of the Landau-Teller model for the description of the inelastic energy transfer between molecules and free electrons. In the case of free-electron temperatures lower than 10,000 K, Landau-Teller relaxation model gives an accurate description of the vibrational relaxation, while at higher temperatures the error in the predictions can be significant and the model should not be used.

Collision dynamics of particle clusters in a two-dimensional granular gas

In a granular gas, inelastic collisions produce an instability in which the constituent particles cluster heterogeneously. These clusters then interact with each other, further decreasing their kinetic energy. We report experiments of the free collisions of dense clusters of particles in a two-dimensional geometry. The particles are composed of solid CO(2), which float nearly frictionlessly on a hot surface due to sublimated vapor. After two dense clusters of ≈100 particles collide, there are two distinct stages of evolution. First, the translational kinetic energy rapidly decreases by over 90% as a "jamming front" sweeps across each cluster. Subsequently, the kinetic energy decreases more slowly as the particles approach the container boundaries. In this regime, the measured velocity distributions are non-Gaussian with long tails. Finally, we compare our experiments to computer simulations of colliding, two-dimensional, granular clusters composed of circular, viscoelastic particles with friction.

Free collisions in a microgravity many-particle experiment. III. The collision behavior of sub-millimeter-sized dust aggregates

We conducted micro-gravity experiments to study the outcome of collisions between sub-mm-sized dust agglomerates consisting of μm-sized SiO2 monomer grains at velocities of several cms−1. Prior to the experiments, we used X-ray computer tomography (nano-CT) imaging to study the internal structure of these dust agglomerates and found no rim compaction so that their collision behavior is not governed by preparation-caused artefacts. We found that collisions between these dust aggregates can lead either to sticking or to bouncing, depending mostly on the impact velocity. While previous collision models derived the transition between both regimes from contact physics, we used the available empirical data from these and earlier experiments to derive a power law relation between dust-aggregate mass and impact velocity for the threshold between the two collision outcomes. In agreement with earlier experiments, we show that the transition between both regimes is not sharp, but follows a shallower power law than predicted by previous models (Güttler, C., Blum, J., Zsom, A., Ormel, C.W., Dullemond, C.P. [2010]. Astron. Astrophys. 513, A56). Furthermore, we find that sticking between dust aggregates can lead to the formation of larger structures. Collisions between aggregates-of-aggregates can lead to growth at higher velocities than homogeneous dust agglomerates.

Free collisions in a microgravity many-particle experiment – II: The collision dynamics of dust-coated chondrules

The formation of planetesimals in the early Solar System is hardly understood, and in particular the growth of dust aggregates above millimeter sizes has recently turned out to be a difficult task in our understanding (Zsom, A., Ormel, C.W., Güttler, C., Blum, J., Dullemond, C.P. [2010]. Astron. Astrophys., 513, A57). Laboratory experiments have shown that dust aggregates of these sizes stick to one another only at unreasonably low velocities. However, in the protoplanetary disk, millimeter-sized particles are known to have been ubiquitous. One can find relics of them in the form of solid chondrules as the main constituent of chondrites. Most of these chondrules were found to feature a fine-grained rim, which is hypothesized to have formed from accreting dust grains in the solar nebula. To study the influence of these dust-coated chondrules on the formation of chondrites and possibly planetesimals, we conducted collision experiments between millimeter-sized, dust-coated chondrule analogs at velocities of a few cms−1. For 2 and 3mm diameter chondrule analogs covered by dusty rims of a volume filling factor of 0.18 and 0.35–0.58, we found sticking velocities of a few cms−1. This velocity is higher than the sticking velocity of dust aggregates of the same size. We therefore conclude that chondrules may be an important step towards a deeper understanding of the collisional growth of larger bodies. Moreover, we analyzed the collision behavior in an ensemble of dust aggregates and non-coated chondrule analogs. While neither the dust aggregates nor the solid chondrule analogs show sticking in collisions among their species, we found an enhanced sicking efficiency in collisions between the two constituents, which leads us to the conjecture that chondrules might act as “catalyzers” for the growth of larger bodies in the young Solar System.

Free collisions in a microgravity many-particle experiment. I. Dust aggregate sticking at low velocities

Over the past years the processes involved in the growth of planetesimals have extensively been studied in the laboratory. Based on these experiments, a dust-aggregate collision model was developed upon which computer simulations were based to evaluate how big protoplanetary dust aggregates can grow and to analyze which kinds of collisions are relevant in the solar nebula and are worth further studies in the laboratory. The sticking threshold velocity of millimeter-sized dust aggregates is one such critical value that have so far only theoretically been derived, as the relevant velocities could not be reached in the laboratory. We developed a microgravity experiment that allows us for the first time to study free collisions of mm-sized dust aggregates down to velocities of ∼0.1cms−1 to assess this part of the protoplanetary dust evolution model. Here, we present the results of 125 free collisions between dust aggregates of 0.5–2mm diameter. Seven collisions with velocities between 0.2 and 3cms−1 led to sticking, suggesting a transition from perfect sticking to perfect bouncing with a certain sticking probability instead of a sharp velocity threshold. We developed a model to explain the physical processes involved in dust-aggregate sticking, derived dynamical material properties of the dust aggregates from the results of the collisions, and deduced the velocity below which dust aggregates always stick. For millimeter-sized porous dust aggregates this velocity is 8×10−5ms−1.