Binary Dissociation Research Articles

Binary asteroid dissociation and accretion around white dwarfs

About 25–50% of white dwarfs (WDs) show metal lines in their spectra. Among the widely accepted explanations for this effect is that these WDs are accreting asteroids that are perhaps flung onto the WDs by a planet via resonance, for instance. A number of theoretical works have looked into the accretion of asteroids onto WDs and obtained a fair agreement with the observed accretion rate. However, it is solely a very recent study (referenced in this work) that has taken asteroid binarity into consideration, examining the scattering between an asteroid binary and planets and showing that a dissociation and ejection of the former might result and the effect on WD metal accretion is likely to be weak. Here, we investigate the close encounter between an asteroid binary and the central WD and consider how the binary’s dissociation may affect the WD’s accretion. We find that depending on the orbital and physical properties, the components may acquire orbits that are significantly different (even on the order of unity) from that of the parent binary. We assumed all the inner main belt asteroids are binaries and we studied their accretion onto the solar WD under the perturbation of the giant planets. We find that compared to the case without binaries, the components’ accretion may be postponed (or put forward) by millions of years or more, as the objects may be taken out of (or driven deeper into) the resonance due to the sudden orbital change upon dissociation. However, the overall influence of binary dissociation on the accretion rate is not very significant.

Close encounters of tight binary stars with stellar-mass black holes

ABSTRACT Strong dynamical interactions among stars and compact objects are expected in a variety of astrophysical settings, such as star clusters and the disks of active galactic nuclei. Via a suite of three-dimensional hydrodynamics simulations using the moving-mesh code arepo, we investigate the formation of transient phenomena and their properties in close encounters between an $2\, {\rm M}_{\odot }$ or $20\, {\rm M}_{\odot }$ equal-mass circular binary star and single $20\, {\rm M}_{\odot }$ black hole (BH). Stars can be disrupted by the BH during dynamical interactions, naturally producing electromagnetic transient phenomena. Encounters with impact parameters smaller than the semimajor axis of the initial binary frequently lead to a variety of transients whose electromagnetic signatures are qualitatively different from those of ordinary disruption events involving just two bodies. These include the simultaneous or successive disruptions of both stars and one full disruption of one star accompanied by successive partial disruptions of the other star. On the contrary, when the impact parameter is larger than the semimajor axis of the initial binary, the binary is either simply tidally perturbed or dissociated into bound and unbound single stars (‘micro-Hills’ mechanism). The dissociation of $20\, {\rm M}_{\odot }$ binaries can produce a runaway star and an active BH moving away from one another. Also, the binary dissociation can either produce an interacting binary with the BH, or a non-interacting, hard binary; both could be candidates of BH high- and low-mass X-ray binaries. Hence, our simulations especially confirm that strong encounters can lead to the formation of the (generally difficult to form) BH low-mass X-ray binaries.

Dynamic Dissociation Behaviors of sII Hydrates in Liquid Water by Heating: A Molecular Dynamics Simulation Approach.

An understanding of the dynamic behavior of subtle hydrate dissociation in the liquid water phase is fundamental for gas production from marine hydrate reservoirs. Molecular dynamics simulations are performed in this study to investigate the dissociation kinetics of pure propane and binary propane + methane sII hydrates in a liquid water environment. The results show that faster hydrate dissociation rates are observed at higher initial temperatures. The hydrate phase dissociates from the cluster surface to the inside in a layer-by-layer manner under the simulation temperature conditions, which is similar to the behavior of sI hydrates and is independent of the hydrate crystal type. Compared to the binary sII hydrate, the pure sII hydrate dissociates more easily under the same initial temperature conditions, which can be attributed to the stabilizing effect of guest molecules in the hydrate cages. The empty cages collapse in one step, in contrast to the two-step pathway induced by the guest-host interaction. In addition, a hydrocarbon phase forms in the binary hydrate dissociation system instead of nanobubbles. These results can provide molecular-level insights into the dynamic mechanism of hydrate dissociation and theoretical guidance for gas recovery by thermal injection from marine hydrate reservoirs.

The Error of Approximate Calculations of the Weak Binary Electrolyte Dissociation Degree

The Error of Approximate Calculations of the Weak Binary Electrolyte Dissociation Degree

Experimental validation of a test gas substitution for simulating non-equilibrium giant planet entry conditions in impulse facilities

Scaled giant planet entry testing is beyond the simulation capability of most impulse facilities, which limits the ground testing data available for computational model validation. Substituting the He in their predominately H/He atmospheres with Ne has been used in the previous experiments. This enables higher-temperature shock layers to be recreated using the same facility performance. For binary hydrogen dissociation and ionization reactions, the substitution gives similarity with non-equilibrium processes, but has never been experimentally validated by direct comparison with H/He relaxation data in a region where the facility simulation capabilities in using H/He and H/Ne overlap. This work demonstrates and validates a scaling method based on the substitution in terms of flow relaxation. A H/Ne condition was designed to recreate the post-shock relaxation of a H/He condition in our X2 expansion tube. The two conditions were experimentally tested with cylindrical test models, and shock layer radiation from the Balmer series was measured. The spectroscopic data using the H/Ne condition show a successful recreation of the non-equilibrium processes of the target H/He condition, experimentally validating the scaling method. High-speed images demonstrate that the associated radiation field is also correctly reproduced. With the use of this substitution, the facility can now be used to simulate high-speed giant planet entries with confidence, and the available ground testing envelope is extended to much higher speeds.

Dancing with Venus in the shadow of the Earth: a pair of genetically related near-Earth asteroids trapped in a mean-motion resonance

ABSTRACT YORP-induced fission events may form dynamically coherent pairs or even families of asteroids. The outcome of this process is well documented among members of the main asteroid belt, but not in the case of the near-Earth asteroid (NEA) population because their paths randomize very efficiently in a short time-scale. Mean-motion resonances (MMRs) may stabilize the orbits of small bodies by making them avoid close encounters with planets. In theory, YORP-induced fission of asteroids trapped in MMRs can preserve evidence of this process even in near-Earth space. Here, we show that two NEAs, 2017 SN16 and 2018 RY7, are currently following an orbital evolution in which their relative mean longitude does not exhibit any secular increase due to the stabilizing action of the 3:5 MMR with Venus. The mechanism that makes this configuration possible may be at work both in the Solar system and elsewhere. Our analysis suggests that the pair 2017 SN16–2018 RY7 may have had its origin in one out of two mechanisms: YORP-induced splitting or binary dissociation.

Математическое моделирование влияния основных температурных эффектов на стационарный перенос ионов соли в диффузионном слое

This article is devoted to the construction of a new mathematical model, using a mathematical model of the system of Nernst-Planck-Poisson equations for electrodiffusion of four varieties of ions simultaneously (two salt ions, and H+, OH- ions) in the diffusion layer in electromembrane systems with a perfectly selective membrane and the heat equation, taking into account the Joule heating of the solution, endo- and exothermic nature of the reactions of dissociation of water molecules and recombination of ions. In addition, the model takes into account the dependence of the coefficient of equilibrium of the dissociation/recombination reaction on temperature. The mathematical model is a boundary value problem for the system of ordinary differential equations, the study of which allows determining the basic patterns of transport of ions of binary salt and water dissociation products taking into account the space charge, reactions dissociation/recombination of water and the corresponding temperature effects. The paper presents the conclusion of the formula for the amount of heat absorbed/emitted at each point $x$, during the course of the dissociation/recombination reaction of water. A boundary condition is derived at a point $x=\delta $ with allowance for the balance of heat fluxes at this point. The study determines the structure of the diffusion layer from the receiving side of the membrane, and, accordingly, the asymptotic solutions in each of the regions of the diffusion layer, to conduct their splicing. The conditions under which the practically irreversible dissociation of water with the maximum possible constant rate in the expanded space charge region are determined. In addition, the study shows that in the region of electroneutrality a narrow band (the recombination region) arises, where the recombination of water molecules prevails over their dissociation, and that the centers of the recombination and dissociation region, within the diffusion layer, are spaced from each other at a considerable distance.

Binary stripping as a plausible origin of correlated pairs of extreme trans-Neptunian objects

Asteroids that follow similar orbits may have a dynamical connection as their current paths could be the result of a past interaction with a massive perturber. The pair of extreme trans-Neptunian objects or ETNOs (474640) 2004 VN112-2013 RF98 exhibits peculiar relative orbital properties, including a difference in longitude of the ascending node of just 1.61 degrees and 3.99 degrees in inclination. In addition, their reflectance spectra are similar in the visible portion of the spectrum. The origin of these similarities remains unclear. Neglecting observational bias, viable scenarios that could explain this level of coincidence include fragmentation and binary dissociation. Here, we present results of extensive direct N-body simulations of close encounters between wide binary ETNOs and one trans-Plutonian planet. We find that wide binary ETNOs can dissociate during such interactions and the relative orbital properties of the resulting unbound couples match reasonably well those of several pairs of known ETNOs, including 474640-2013 RF98. The possible presence of former binaries among the known ETNOs has strong implications for the interpretation of the observed anisotropies in the distributions of the directions of their orbital poles and perihelia.

Reformation of hydrogen sulfide to hydrogen in the presence of xylene

Hydrogen sulfide is a hazardous gas from environmental, human health and equipment prospective. Hydrogen sulfide occurs naturally from crude oil and natural gas wells along with some other hydrocarbon impurities. Reformation of hydrogen sulfide without or with the presence of xylene (a common impurity present in hydrogen sulfide) has been investigated. Production of hydrogen concurrent with destruction of hydrogen sulfide provides a good alternative method to treat hydrogen sulfide. The role of xylene addition on the reformation of hydrogen sulfide was experimentally investigated. A laboratory-scale reactor was used to examine the effect of reactor temperature in the range of 1273–1573K and various inlet stream composition on the production of hydrogen and destruction of both hydrogen sulfide and xylene. Results showed enhanced hydrogen production and higher hydrogen sulfide destruction at temperatures above 1273K. Xylene was destructed completely at a relatively low temperature of 1373K. Carbon disulfide formation increased with increase in temperature for all the inlet compositions of hydrogen sulfide and xylene examined. Reducing the formation of CS2 and also mitigation of carbon deposition by reducing the amounts of carbon introduced to the reactor were investigated and quantified experimentally. The most favorable operational conditions for reaction between hydrogen sulfide and xylene were established. The results showed new potential of this binary mixture dissociation as an alluring treatment method of hydrogen sulfide.

Disordered proteins make a dynamic switch.

Cellular Responses The proteins that regulate cellular responses to hypoxia form a sensitive on-off switch. Cells survive hypoxia by activating the transcription factor HIF-1α (hypoxia-inducible factor 1α). HIF-1α is active when it is associated with the transcriptional coactivator CBP. The protein CITED2 opposes such activation. CITED2 and HIF-1α bind overlapping regions of CBP with similar affinity. But CITED2 can much more effectively displace HIF-1α from CBP and inhibit transcription. The flexibility of intrinsically disordered regions of CITED2 apparently allows it to slip in and cause an allosteric change in CBP that hinders interaction with HIF-1α. Other such switches may exist, and in such cases, modeling on the basis of binary dissociation constants would be very misleading. Nature 10.1038/nature21705 (2017).

Visible spectra of (474640) 2004 VN112–2013 RF98 with OSIRIS at the 10.4 m GTC: evidence for binary dissociation near aphelion among the extreme trans-Neptunian objects

Abstract The existence of significant anisotropies in the distributions of the directions of perihelia and orbital poles of the known extreme trans-Neptunian objects (ETNOs) has been used to claim that trans-Plutonian planets may exist. Among the known ETNOs, the pair (474640) 2004 VN112–2013 RF98 stands out. Their orbital poles and the directions of their perihelia and their velocities at perihelion/aphelion are separated by a few degrees, but orbital similarity does not necessarily imply common physical origin. In an attempt to unravel their physical nature, visible spectroscopy of both targets was obtained using the OSIRIS camera-spectrograph at the 10.4 m Gran Telescopio Canarias (GTC). From the spectral analysis, we find that 474640–2013 RF98 have similar spectral slopes (12 versus 15 per cent/0.1 μm), very different from Sedna's but compatible with those of (148209) 2000 CR105 and 2012 VP113. These five ETNOs belong to the group of seven linked to the Planet Nine hypothesis. A dynamical pathway consistent with these findings is dissociation of a binary asteroid during a close encounter with a planet and we confirm its plausibility using N-body simulations. We thus conclude that both the dynamical and spectroscopic properties of 474640–2013 RF98 favour a genetic link and their current orbits suggest that the pair was kicked by a perturber near aphelion.

A complete look at the multi-channel dissociation of propenal photoexcited at 193 nm: branching ratios and distributions of kinetic energy

We observed fifteen photofragments upon photolysis of propenal (acrolein, CH(2)CHCHO) at 193 nm using photofragment translational spectroscopy and selective vacuum-ultraviolet (VUV) photoionization. All the photoproducts arise from nine primary and two secondary dissociation pathways. We measured distributions of kinetic energy of products and determined branching ratios of dissociation channels. Dissociation to CH(2)CHCO + H and CH(2)CH + HCO are two major primary channels with equivalent branching ratios of 33%. The CH(2)CHCO fragment spontaneously decomposes to CH(2)CH + CO. A proportion of primary products CH(2)CH from the fission of bond C-C of propenal further decompose to CHCH + H but secondary dissociation HCO → H + CO is negligibly small. Binary dissociation to CH(2)CH(2) (or CH(3)CH) + CO and concerted three-body dissociation to C(2)H(2) + CO + H(2) have equivalent branching ratios of 14%-15%. The other channels have individual branching ratios of ∼1%. The production of HCCO + CH(3) indicates the formation of intermediate methyl ketene (CH(3)CHCO) and the production of CH(2)CCH + OH and CH(2)CC + H(2)O indicate the formation of intermediate hydroxyl propadiene (CH(2)CCHOH) from isomerization of propenal. Distributions of kinetic energy release and dissociation mechanisms are discussed. This work provides a complete look and profound insight into the multi-channel dissociation mechanisms of propenal. The combination of a molecular beam apparatus and synchrotron VUV ionization allowed us to untangle the complex mechanisms of nine primary and two secondary dissociation channels.

Phase Equilibrium Data of Binary Hydrate in the System Hydrogen plus Acetone plus Water

In this work, we reported experimental equilibrium data for binary acetone-hydrogen clathratc hydrates with different initial molar concentrations of acetone [(0.030, 0.0556, and 0.0937) mol fraction]. Measurements were made using the isochoric pressure-search method. The hydrate dissociation data for the methane + acetone + water system at 0.0519 mol fraction or acetone were obtained in advance and compared with experimental data reported in the literature, and the acceptable agreements demonstrate the reliability of the experimental method and apparatus employed in this work. Hydrate equilibrium pressures in the ternary system hydrogen + acetone + water were investigated in the temperature range of (265.6 to 269.9) K and in the pressure range of (10.84 to 28.90) MPa, respectively. At 0.0556 mol fraction of acetone. the hydrate has the lowest phase equilibrium pressure. With the addition of acetone, a hydrogen molecule can be incorporated into hydrate cages more easily as the binary hydrate dissociation points shifted to a lower pressure and higher temperature region.

Phase Equilibrium Data of Binary Hydrate in the System Hydrogen + Acetone + Water

In this work, we reported experimental equilibrium data for binary acetone-hydrogen clathrate hydrates with different initial molar concentrations of acetone [(0.030, 0.0556, and 0.0937) mol fraction]. Measurements were made using the isochoric pressure-search method. The hydrate dissociation data for the methane + acetone + water system at 0.0519 mol fraction of acetone were obtained in advance and compared with experimental data reported in the literature, and the acceptable agreements demonstrate the reliability of the experimental method and apparatus employed in this work. Hydrate equilibrium pressures in the ternary system hydrogen + acetone + water were investigated in the temperature range of (265.6 to 269.9) K and in the pressure range of (10.84 to 28.90) MPa, respectively. At 0.0556 mol fraction of acetone, the hydrate has the lowest phase equilibrium pressure. With the addition of acetone, a hydrogen molecule can be incorporated into hydrate cages more easily as the binary hydrate dissociation points shifted to a lower pressure and higher temperature region.

Tethered-Hopping Model for Protein-DNA Binding and Unbinding Based on Sox2-Oct1-Hoxb1 Ternary Complex Simulations

The sliding and hopping models encapsulate the essential protein-DNA binding process for binary complex formation and dissociation. However, the effects of a cofactor protein on the protein-DNA binding process that leads to the formation of a ternary complex remain largely unknown. Here we investigate the effect of the cofactor Sox2 on the binding and unbinding of Oct1 with the Hoxb1 control element. We simulate the association of Oct1 with Sox2-Hoxb1 using molecular dynamics simulations, and the dissociation of Oct1 from Sox2-Hoxb1 using steered molecular dynamics simulations, in analogy to a hopping event of Oct1. We compare the kinetic and thermodynamic properties of three model complexes (the wild-type and two mutants) in which the Oct1-DNA base-specific interactions or the Sox2-Oct1 protein-protein interactions are largely abolished. We find that Oct1-DNA base-specific interactions contribute significantly to the total interaction energy of the ternary complex, and that nonspecific Oct1-DNA interactions are sufficient for driving the formation of the protein-DNA interface. The Sox2-Oct1 protein-protein binding interface is largely hydrophobic, with remarkable shape complementarity. This interface promotes the formation of the ternary complex and slows the dissociation of Oct1 from its DNA-binding site. We propose a simple two-step reaction model of protein-DNA binding, called the tethered-hopping model, that explains the importance of the cofactor Sox2 and may apply to similar ternary protein-DNA complexes.

Automated mass action model space generation and analysis methods for two-reactant combinatorially complex equilibriums: an analysis of ATP-induced ribonucleotide reductase R1 hexamerization data.

BackgroundRibonucleotide reductase is the main control point of dNTP production. It has two subunits, R1, and R2 or p53R2. R1 has 5 possible catalytic site states (empty or filled with 1 of 4 NDPs), 5 possible s-site states (empty or filled with ATP, dATP, dTTP or dGTP), 3 possible a-site states (empty or filled with ATP or dATP), perhaps two possible h-site states (empty or filled with ATP), and all of this is folded into an R1 monomer-dimer-tetramer-hexamer equilibrium where R1 j-mers can be bound by variable numbers of R2 or p53R2 dimers. Trillions of RNR complexes are possible as a result. The problem is to determine which are needed in models to explain available data. This problem is intractable for 10 reactants, but it can be solved for 2 and is here for R1 and ATP.ResultsThousands of ATP-induced R1 hexamerization models with up to three (s, a and h) ATP binding sites per R1 subunit were automatically generated via hypotheses that complete dissociation constants are infinite and/or that binary dissociation constants are equal. To limit the model space size, it was assumed that s-sites are always filled in oligomers and never filled in monomers, and to interpret model terms it was assumed that a-sites fill before h-sites. The models were fitted to published dynamic light scattering data. As the lowest Akaike Information Criterion (AIC) of the 3-parameter models was greater than the lowest of the 2-parameter models, only models with up to 3 parameters were fitted. Models with sums of squared errors less than twice the minimum were then partitioned into two groups: those that contained no occupied h-site terms (508 models) and those that contained at least one (1580 models). Normalized AIC densities of these two groups of models differed significantly in favor of models that did not include an h-site term (Kolmogorov-Smirnov p < 1 × 10-15); consistent with this, 28 of the top 30 models (ranked by AICs) did not include an h-site term and 28/30 > 508/2088 with p < 2 × 10-15. Finally, 99 of the 2088 models did not have any terms with ATP/R1 ratios >1.5, but of the top 30, there were 14 such models (14/30 > 99/2088 with p < 3 × 10-16), i.e. the existence of R1 hexamers with >3 a-sites occupied by ATP is also not supported by this dataset.ConclusionThe analysis presented suggests that three a-sites may not be occupied by ATP in R1 hexamers under the conditions of the data analyzed. If a-sites fill before h-sites, this implies that the dataset analyzed can be explained without the existence of an h-site.ReviewersThis article was reviewed by Ossama Kashlan (nominated by Philip Hahnfeldt), Bin Hu (nominated by William Hlavacek) and Rainer Sachs.

Mass action models versus the Hill model: An analysis of tetrameric human thymidine kinase 1 positive cooperativity

BackgroundThe Hill coefficient characterizes the extent to which an enzyme exhibits positive or negative cooperativity, but it provides no information regarding the mechanism of cooperativity. In contrast, models based on the equilibrium concept of mass action can suggest mechanisms of cooperativity, but there are often many such models and often many with too many parameters.ResultsMass action models of tetrameric human thymidine kinase 1 (TK1) activity data were formed as pairs of plausible hypotheses that per site activities and binary dissociation constants are equal within contiguous stretches of the number of substrates bound. Of these, six 3-parameter models were fitted to 5 different datasets. Akaike's Information Criterion was then used to form model probability weighted averages. The literature average of the 5 model averages was K = (0.85, 0.69, 0.65, 0.51) μM and k = (3.3, 3.9, 4.1, 4.1) sec-1 where K and k are per-site binary dissociation constants and activities indexed by the number of substrates bound to the tetrameric enzyme.ConclusionThe TK1 model presented supports both K and k positive cooperativity. Three-parameter mass action models can and should replace the 3-parameter Hill model.ReviewersThis article was reviewed by Philip Hahnfeldt, Fangping Mu (nominated by William Hlavacek) and Rainer Sachs.

IRREGULAR SATELLITE CAPTURE BY EXCHANGE REACTIONS

The study of the origin of irregular satellites remains important in planetary science because it provides constraints on the formation process of giant planets and probes the properties of a now-extinct planetesimal disk that existed at 5-30 AU early in solar system history. While several putative scenarios of irregular-satellite capture around giant planets have been developed, various uncertainties and the lack of an accurate model of the evolutionary history of the solar system usually prevent an assessment of their overall likelihood. Here we study a three-body interaction scenario in which irregular satellites are formed by dissociation of a planetesimal binary in the gravity field of a planet. Within the frame of the Nice model, we determine how many irregular satellites are expected to be formed about each of the giant planets. We pay special attention to a possible capture of Triton via this mechanism. We find that Triton could have been captured via a binary dissociation very soon after Neptune's formation when the planetesimal disk was still dynamically cold. Triton was most likely captured by a dissociation of a binary system where the more massive component was ~2-5 times heavier than Triton. Our results suggest that Neptune, the formation of Triton's binary, and the capture of Triton around Neptune all occurred within the first ~5-10 Myr of solar system formation when the gas disk was still present. This would rule out the late formation of ice giants. Our results also indicate that binary dissociation is a highly unlikely process for the origin of small irregular satellites for two reasons. First, the orbital distribution of the captured bodies is inconsistent with that of the observed irregular satellites. Second, the efficiency of the captures is too low to explain the numerous populations of small irregular satellites.

Photodissociation dynamics of propene at 157.6 nm: Kinetic energy distributions and branching ratios

Photodissociation dynamics of propene at 157.6 nm has been investigated in a molecular beam apparatus using the photofragment translational spectroscopic technique combined with the vacuum ultraviolet ionization method. Eleven photofragments have been successfully detected and ascribed to eight (five binary and three triple) dissociation channels: namely, C3H5+H, C3H4+H+H, C3H4+H2, C3H3+H2+H, C2H4+CH2, C2H3+CH3, C2H2+CH4, and C2H2+CH3+H. Their branching ratios have been determined to be 1%, 7%, &amp;lt;0.2%, 17%, 6%, 4%, 5%, and 60%, respectively. The complicated multichannel dissociation process has a propensity towards triple dissociations, notably the C2H2+CH3+H channel. In addition, the averaged kinetic energy releases and the fractions in translational energy have also been determined from the measured kinetic energy distributions. For the binary dissociation channels, the fractions in translational energy are less than 18% except the C3H5+H channel, whereas they are more than 42% for the triple dissociation channels. An intriguing finding indicates that the C2H4+CH2 channel has a nearly identical kinetic energy distribution and a similar branching ratio to the C2H3+CH3 channel, although the former undergoes a three-center elimination process different from the C–C bond rupture occurring in the latter.

Photodissociation dynamics of cyclopropane at 157 nm

Photodissociation dynamics of cyclopropane at 157 nm has been investigated using a new molecular beam apparatus based on vacuum ultraviolet ionization by synchrotron radiation. Four distinct dissociation pathways have been observed. The observed channels are the H formation process, the H2 formation process, the CH2+C2H4 formation process, and the CH3+C2H3 formation process. Experimental results indicate that the H atom products are possibly produced via a synchronous, concerted 2H elimination process, while other channels are all binary dissociation processes. Product kinetic energy distribution of each dissociation channel has been determined from simulating the experimental time of flight spectra. Relative branching ratios for all observed dissociation channels were also estimated based on all detected products.