Capture Collisions Research Articles

Performance of Unslotted ALOHA With Capture and Multiple Collisions in LoRaWAN

This paper explores the capacity limits and the tradeoff between the antagonistic means of enabling reliable data delivery in a loaded LoRaWAN cell. In fact, channel attenuation and variability call for robust transmission settings but the associated load increase causes more collisions between frames. In addition to the physical layer parameters of the LoRa modulation, this paper considers the benefits and tuning of inter-packet Error Correction Codes (ECC), which also trades transmission redundancy for reliability. We thus start by proposing a refined Packet Delivery Ratio (PDR) model that improves the ones found in the literature in that, first, it takes into account the dependency between overcoming ambient noise and dominating colliding frames, and second, it considers the sum of interference powers when multiple colliding frames are present, even if the interference preexists. Moreover, the model extends to the case of a gateway with receiver diversity. In a second step, the model allows to set out the level of redundancy at which ECC is the most effective without hindering capacity: a coding rate of one third. When this is fixed, it allows to define the transmission parameters allocation within a cell and thus the size of the cell. We finally develop an ad-hoc Python discrete-event simulator, freely accessible, to complement the model for assessing the effect of inter-SF and near-far interference and to show the benefits of power control in this respect.

Design and optimisation of seed-metering plate of air-suction vegetable seed-metering device based on DEM-CFD

The common problem of missed seeding during high-frequency sowing with air-suction seed-metering devices was investigated. A device was optimised and fitted with an auxiliary seed-supporting mechanism using pelletised Chinese flowering cabbage seeds as a typical example. Seed-metering was examined at the micro scale and the critical points were drag force and seed velocity. Suction hole capture duration, migration resistance and collision limit speed were defined as performance evaluation indices for seed filling and seed cleaning, respectively. Modelling by coupled discrete element method and computational fluid dynamics was adopted to simulate the gas–solid two-phase working process of the air-suction seed-metering device. The relationship between seed velocity and drag force was analysed to determine the characteristics of seed flow as well as airflow. At the macro scale, the evaluation indexes of filling and cleaning performance were defined, and experiments designed using quadratic orthogonal rotation combination were performed with maximum single seed rate as the final optimisation goal. The optimal parameter combination for the seed-metering plate was a seed spoon thickness of 1.2 mm, a spoon arc length of 3.2 mm, and a seed cleaning knife inclination of 61.2°. Bench comparison tests were applied to compare optimised seed-metering plate with the original seed-metering plate and the other two control groups at different operating speeds. Results showed that the optimised seed-metering plate had a seedless rate of 1.24%, which was lower than 4.26% obtained by the non-optimised seed-metering plate, indicating that the optimise device had excellent performance.

Calculated rate coefficients between CI-MS reagent ions and organosulfur compounds causing food taints and off-flavours

Volatile sulfur compounds play a crucial role in the aroma profile of food and fermented beverages. We explore chemical-ionization mass spectrometry (CI-MS) ion-molecule reaction kinetics of commonly used reagent ions to a list of volatile organic sulfur compounds (VOSCs). We compute the rate coefficients of ion-molecule reactions, useful for the accurate identification and quantification of trace gases, using capture collision models based on the electric dipole moment and polarizability of the neutral VOSCs. To this aim, we evaluate molecular properties, such as the electric dipole moment, polarizability, proton affinity (PA), and ionization energy (IE) for each VOSC, by means of hybrid density functional theory (DFT) simulations. The PA and IE values are useful in the selection of appropriate reagent ions to be used in CI-MS. We thoroughly investigate collision rate coefficients at effective temperatures and internal energies, as relevant for highly energetic proton transfer reaction mass spectrometry (PTR-MS) drift tube conditions. The data provided will be valuable for the rapid quantification of VOSCs in food and fermented beverages.

Prompt and delayed dissociation of N2O2+ induced by highly-charged-ion collisions

The prompt and delayed dissociations of ${\mathrm{N}}_{2}{\mathrm{O}}^{2+}\ensuremath{\rightarrow}{\mathrm{N}}^{+}+\mathrm{N}{\mathrm{O}}^{+}$ induced by electron capture collisions of 56-keV/u ${\mathrm{Ne}}^{4+}$ and ${\mathrm{Ne}}^{8+}$ ions are studied by measuring ion-pair fragments and charge-changed projectiles in triple coincidence. For the prompt dissociation, the kinetic energy release (KER) distributions are obtained and indicate this process is mainly attributed to the decay of the low-lying $1\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Sigma}}^{\ensuremath{-}}$ state ${\mathrm{N}}_{2}{\mathrm{O}}^{2+}$ into ${\mathrm{N}}^{+}(^{3}P)+{\mathrm{NO}}^{+}(^{1}\mathrm{\ensuremath{\Sigma}}^{+})$. For the delayed dissociation, since it is of difficulty to directly retrieve three-dimensional momentum vectors of ionic fragments for all the events from ${\mathrm{N}}_{2}{\mathrm{O}}^{2+}$ dissociation in flight, an alternative way is proposed to only catch and analyze the events from which the ${\mathrm{N}}_{2}{\mathrm{O}}^{2+}$ breakup direction is perpendicular to the time-of-flight axis. The KER distributions for these events are obtained and the metastable states of ${\mathrm{N}}_{2}{\mathrm{O}}^{2+}$ are confirmed to be $1\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Pi}}$ and $2\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Pi}}$. The survival time spectra for the metastable ${\mathrm{N}}_{2}{\mathrm{O}}^{2+}$ are also extracted and the mean lifetimes for the $1\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Pi}}$ and $2\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Pi}}$ conjoin, as well as the lifetimes for the identified individual metastable state, are deduced both in ${\mathrm{Ne}}^{8+}$ and ${\mathrm{Ne}}^{4+}$ collision experiments.

Kinetic energy deposited into a nanodroplet, cluster, or molecule in a sticking collision with background gas.

In processes when particles such as nanodroplets, clusters, or molecules move through a dilute background gas and undergo capture collisions, it is often important to know how much translational kinetic energy is deposited into the particles by these pick-up events. For sticking collisions with a Maxwell-Boltzmann gas, an exact expression is derived, which is valid for arbitrary relative magnitudes of the particle and thermal gas speeds.

Kinetic energy distributions of the fragment ions from multiply ionized C2H6 as functions of the charge state of the intermediate states

Here, we report the kinetic energy distributions (KEDs) of the fragment ions produced from multiply ionized ethane (C2H6) molecules in single electron capture collisions with 1.2 MeV C2+. To systematically investigate the fragmentation dynamics, the KEDs were obtained as functions of the charge state of the intermediate C2H6r+* ions r transiently generated prior to fragmentation. r was determined from coincidence measurement of the fragment ions and the number of emitted electrons. The KEDs are drastically different depending on the number of broken C–H bonds. The underlying causes are explained by the variation of the relative contributions of the multiply ionized states and preferential fragmentation pathways. For instance, CHn+ fragment ions with smaller n exhibit lower KEs because they are likely to be correlated with H+ emission, which carries away a large portion of the KE release. In addition, we report the KEDs of H3+ produced from doubly and triply charged states.

Correlated formation of the excited states of recoil and scattered ions in multiple electron capture collision of Ar8+ with CO2 and OCS

Multiple ionization events induced by low energy collisions between Ar8+ projectiles and linear triatomic molecular targets, CO2 and OCS, were studied in order to shed light on the correlation between the electronic states of the scattered ion and the ionic fragmentation processes. Position-sensitive time-of-flight measurements of all the recoil fragments, triggered by detection of a charge-selected scattered ion, allowed us to distinguish between ionic fragmentation processes in which different numbers of Auger electrons were emitted by the projectile, just after multiple electron capture. A strong correlation is found for triple capture collisions, between fragmentation with high kinetic energy and events when only single Auger electron emission takes place.

Line Ratios for Solar Wind Charge Exchange with Comets

Abstract Charge exchange (CX) has emerged in X-ray emission modeling as a significant process that must be considered in many astrophysical environments—particularly comets. Comets host an interaction between solar wind ions and cometary neutrals to promote solar wind charge exchange (SWCX). X-ray observatories provide astronomers and astrophysicists with data for many X-ray emitting comets that are impossible to accurately model without reliable CX data. Here, we utilize a streamlined set of computer programs that incorporate the multi-channel Landau–Zener theory and a cascade model for X-ray emission to generate cross sections and X-ray line ratios for a variety of bare and non-bare ion single electron capture (SEC) collisions. Namely, we consider collisions between the solar wind constituent bare and H-like ions of C, N, O, Ne, Na, Mg, Al, and Si and the cometary neutrals H2O, CO, CO2, OH, and O. To exemplify the application of this data, we model the X-ray emission of Comet C/2000 WM1 (linear) using the CX package in SPEX and find excellent agreement with observations made with the XMM-Newton RGS detector. Our analyses show that the X-ray intensity is dominated by SWCX with H, while H2O plays a secondary role. This is the first time, to our knowledge, that CX cross sections have been implemented into a X-ray spectral fitting package to determine the H to H2O ratio in cometary atmospheres. The CX data sets are incorporated into the modeling packages SPEX and Kronos.

Calculation of the sensitivity of proton-transfer-reaction mass spectrometry (PTR-MS) for organic trace gases using molecular properties

Proton-transfer-reaction mass spectrometry (PTR-MS) allows the detection of a large number of trace gases in air through proton-transfer reaction with H3O+ reagent ions and detection by a mass spectrometer. Measurement sensitivities can be experimentally determined using calibration gases or calculated using the rate constant for the proton-transfer reaction, but rate constants have only been measured for a subset of compounds. Numerous theoretical approaches that describe the ion-molecule collision processes have shown how to accurately calculate capture collision rate constants between an ion and neutral molecules using the polarizability and permanent dipole moment of the molecule. Here we show that polarizability, dipole moment, and resulting capture rate constants for proton-transfer reactions of H3O+ with various different volatile organic compounds (VOCs) can be obtained using the molecular mass, elemental composition, and functionality of VOCs. The polarizabilities of a class of VOCs possessing a specific number of electronegative atoms were linearly correlated with their molecular mass. The dipole moments in a series of VOCs, in which VOCs contain a specific functional group and arbitrary residual hydrocarbon parts, can be approximated as a constant value. The capture rate constants calculated using polarizability and dipole moment, as estimated from molecular mass, elemental composition, and functional group, agreed within 10% with measured values for most VOCs. Those capture rate constants were applied to the calculation of the sensitivities of VOCs detected by our PTR-MS, taking into account the ion transmission efficiency and the degree of fragmentation of protonated VOCs observed in that instrument as well as chemical properties of the VOCs. The resulting calculated sensitivities agreed within 20–50% of those measured by PTR-MS, but several notable exceptions exist. This result shows that the neutral concentration of a VOC detected as a protonated molecule in PTR-MS can be approximated using only molecular mass, elemental composition, and functionality of the VOC. The present study is useful for all PTR-MS instruments regardless of the type of mass analyzer; however, the identification of elemental composition by high mass resolution instrumentation is important.

Electron capture dissociation and collision induced dissociation behavior of peptides containing methionine, selenomethionine and oxidized methionine

The electron capture dissociation and collision induced dissociation of doubly and triply charged ions of peptides RPLGMSPFK, RPLGM(Se)SPFK and RPLGM(O)SPFK were determined by Fourier transform ion cyclotron resonance mass spectrometry. The results suggest that ECD of analyzed species strongly depends on the nature of a single element (i.e., sulfur and selenium atoms, sulfoxide group) and can provide both primary sequence information and structural information regarding the modification. The properties of sulfur and selenium atoms are negligible in the case of CID processes. The CID loss of CH3SOH, which is unique in peptides to the Met(O) side chain, does not depend on the peptide sequence.

Fragmentation of multiply ionized biomolecules induced by MeV heavy ions

SynopsisCollision-induced ionization and fragmentation of gas-phase adenine molecules (C5N5H5) have been investigated for single electron capture collisions of 1.2 MeV C2+ ions. Coincidence measurements between the number of ejected electrons and the time-of-flight of fragment ions allows us to determine charge states of intermediate parent ions r. Highly charged parent ions are observed up to r ∼ 6 and the production of lighter fragment ions becomes predominant with increasing r. We found that kinetic energies of H+ are significantly larger than those of other fragment ions and become nearly equivalent irrespective of r for r > 1.

Radiative lifetime of the1S0metastable state in doubly charged Kr ions

The radiative lifetime of the $4{s}^{2}4{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{1}{S}_{0}$ metastable state in $\mathrm{K}{\mathrm{r}}^{2+}$ ions has been experimentally determined using an electrostatic ion trap of the ion-beam storage type. The radiative lifetime was obtained by measuring the number of 350-nm photons emitted during the ${}^{1}{S}_{0}{\ensuremath{\rightarrow}}^{3}{P}_{1}$ magnetic dipole transition of $\mathrm{K}{\mathrm{r}}^{2+}$ as a function of the storage time. The storage lifetime of the $\mathrm{K}{\mathrm{r}}^{2+}$ beam in the trap, which is a correction term in the determination of the radiative lifetime, was measured by detecting Kr neutrals produced by electron capture collisions with residual gases in the trap. We have obtained a lifetime value of $17.4\ifmmode\pm\else\textpm\fi{}0.4\phantom{\rule{0.16em}{0ex}}\mathrm{ms}$, which is larger than the previous experimental results, but consistent with theoretical predictions.

Capture Collisions of Polyynide Anions with Hydrogen Atoms: Effect of the Ion Dipole, Quadrupole, and Anisotropic Polarizability

Classical capture rate constants are calculated for a molecular ion with a dipole moment, quadrupole moment, and anisotropic polarizability colliding with a neutral polarizable atom. The free-energy effective potential method is used to average the potential energy over the interaction angle. Numerical methods are used to calculate the effective potential from the full anisotropic induction potential energy function, to solve for the position of the centrifugal barrier, and to determine the thermal rate constants. The capture collision model is applied to the reactions of polyynide anions, HC4−, HC6−, and HC8−, with atomic hydrogen, which are of interest in astrophysical environments, using calculated multipole moments and anisotropic polarizabilities. The dipole moment, quadrupole moment, and polarizability of the ion each contribute significantly toward the total predicted classical capture collision rates for these systems.

Dynamics of Kepler problem with linear drag

We study the dynamics of Kepler problem with linear drag. We prove that motions with nonzero angular momentum have no collisions and travel from infinity to the singularity. In the process, the energy takes all real values and the angular velocity becomes unbounded. We also prove that there are two types of linear motions: capture–collision and ejection–collision. The behaviour of solutions at collisions is the same as in the conservative case. Proofs are obtained using the geometric theory of ordinary differential equations and two regularizations for the singularity of Kepler problem equation. The first, already considered in Diacu (Celest Mech Dyn Astron 75:1–15, 1999), is mainly used for the study of the linear motions. The second, the well known Levi-Civita transformation, allows to complete the study of the asymptotic values of the energy and to prove the existence of collision solutions with arbitrary energy.

Fragmentation of molecules under charge-changing collisions of a few MeV heavy ions

We investigated molecular fragmentation of CO and C2H2 molecules by impact of various fast heavy ions. Fragment ions produced in electron capture and loss collisions of projectile ions were measured in coincidence with final projectile charge states. Data acquisition using position sensitive detection system allows us to obtain 3D momentum imaging of fragment ions and kinetic energy release (KER) in various charge-changing collisions. It was found that the KER spectra show strong dependence on the type of charge-changing collisions. This may be caused by the difference of impact parameters associated with individual charge-changing collisions. Moreover we revealed the different fragmentation pathway between ion impacts and photoionization.

Single-electron capture collisions of ground and metastable Ne2+ ions with molecular gases

Using the translational energy-gain spectroscopy technique, we have measured the energy-gain spectra and absolute total cross sections for single-electron capture in collisions of Ne2+ with N2, CO2 and H2O at laboratory impact energies between 50 and 400 eV and 0° scattering angles. In all the collision systems studied here, reaction channels have been observed which indicate the presence of the long-lived metastable states of (2s2 2p4 1D and 1S) in the Ne2+ incident beam. These measurements also indicate that capture from the metastable states into excited states of the projectile product ions is the most important inelastic process. Contributions from capture accompanied by the excitation and ionization of the target product are also detected. In addition, the energy dependence of the total single-electron capture cross sections is studied and found to slowly increase with increasing impact energy. The present data are compared with the theoretical calculations of the classical over the barrier, extended classical over the barrier and Landau–Zener models.

The Research and Simulation of a Prey Pursuit Algorithm

General prey pursuit problem used capture strategy between agents in limited grid space. In prey pursuit problem, there are a lot of problems such as occurrence of collision between agents, imperfection capture that can be produced from corner of restricted grid space. But, this causes actuality deficiency problem of experiment environment itself. In this paper, we propose an experiment environment that considers actuality and new capture strategy that using direction vector to solve prey pursuit problem that is typical experiment model of multi agent system. Therefore, we proposed continuous experiment space of grid space of circular type that is environment similar to the actuality world in this paper, and agents in proposed experiment space solved prey pursuit problem through direction vector that uses distance information and direction information between each others. The proposed method could capture prey effectively through using direction vector in new environment, and we solved imperfection capture and agent collision problem that happens in general research.

Electron Capture Dissociation and Collision Induced Dissociation of S-Dipalmitoylated Peptides

Here we investigate the effect of S-dipalmitoylation on the electron capture dissociation (ECD) behavior of peptides. The ECD and collision induced dissociation (CID) of peptides modified by covalent attachment of [(RS)-2,3-di(palmitoyloxy)-propyl] (PAM2) group to cysteine residues [C(PAM2)LEYDTGFK and RPPGC(PAM2)SPFK] were examined. The results suggest that ECD of S-dipalmitoylated peptides can provide both primary sequence information and structural information regarding the modification. The structural information provided by CID is complementary to that provided by ECD.

Absolute detection efficiencies for keV energy atoms incident on a microchannel plate detector

The absolute detection efficiencies of a microchannel plate detector (MCP) were determined experimentally for neutral hydrogen, carbon, and tungsten atoms with impact energies of 0.5–4.5keV. We measured detection efficiencies using our recently developed method, which uses coincidence counting between neutralized incident ions and ionized target atoms in single-electron capture collisions. The obtained detection efficiencies showed similar impact-energy and mass dependence to those of rare gas atoms (Ne, Ar, Kr, and Xe), measured previously using our method. The detection efficiencies increased with increasing impact energy and converged to the open area ratio (∼50%) of the MCP used. The efficiencies at fixed energies decreased as the mass of the incident atom increased. The absolute detection efficiencies obtained for H, C, W, Ne, Ar, Kr, and Xe atoms could be scaled according to the average electron emission yield estimated using the formulas for electronic and nuclear stopping powers.

HYPERACCRETING BLACK HOLE AS GAMMA-RAY BURST CENTRAL ENGINE. I. BARYON LOADING IN GAMMA-RAY BURST JETS

A hyper-accreting stellar-mass black hole has been long speculated as the best candidate of central engine of gamma-ray bursts (GRBs). Recent rich observations of GRBs by space missions such as Swift and Fermi pose new constraints on GRB central engine models. In this paper, we study the baryon loading processes of a GRB jet launched from a black hole central engine. We consider a relativistic jet powered by $\nu \bar\nu$-annihilation or by the Blandford-Znajek (BZ) mechanism. We consider baryon loading from a neutrino-driven wind from a neutrino-cooling-dominated accretion flow. For a magnetically dominated BZ jet, we consider neutron-drifting from the magnetic wall surrounding the jet and subsequent positron capture and proton-neutron inelastic collisions. The minumim baryon loads in both types of jet are calculated. We find that in both cases, a more luminous jet tends to be more baryon poor. A neutrino-driven "fireball" is typically "dirtier" than a magnetically dominated jet, while a magnetically dominated jet can be much cleaner. Both models have the right scaling to interpret the empirical $\Gamma-L_{\rm iso}$ relation discovered recently. Since some neutrino-driven jets have too much baryon loading as compared with the data, we suggest that at least a good fraction of GRBs should have a magnetically dominated central engine.