A new Ignition-Growth reaction rate model for shock initiation

Accurately predicting reactive flow is a challenge when characterizing an explosive under external shock stimuli as the shock initiation time is on the order of a microsecond.The present study constructs a new Ignition-Growth reaction rate model,which can describe the shock initiation processes of explosives with different initial densities,particle sizes and loading pressures by only one set of model parameters.Compared with the Lee-Tarver reaction rate model,the new Ignition-Growth reaction rate model describes better the shock initiation process of explosives and requires fewer model parameters.Moreover,the shock initiation of a 2,4-Dinitroanisole(DNAN)-based melt-cast explosive RDA-2(DNAN/HMX(octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazoncine)/aluminum)are investigated both experimentally and numerically.A series of shock initiation experiments is performed with manganin piezoresistive pressure gauges and corresponding numerical simulations are carried out with the new Ignition-Growth reaction rate model.The RDA-2 explosive is found to have higher critical initiation pressure and lower shock sensitivity than traditional explosives(such as the Comp.B explosive).The calibrated reaction rate model parameters of RDA-2 could provide numerical basis for its further application.

Energy diffusion controlled reaction rate in dissipative Hamiltonian systems

In this paper the energy diffusion controlled reaction rate in dissipative Hamiltonian systems is investigated by using the stochastic averaging method for quasi Hamiltonian systems. The boundary value problem of mean first- passage time （MFPT） of averaged system is formulated and the energy diffusion controlled reaction rate is obtained as the inverse of MFPT. The energy diffusion controlled reaction rate in the classical Kramers bistable potential and in a two-dimensional bistable potential with a heat bath are obtained by using the proposed approach respectively. The obtained results are then compared with those from Monte Carlo simulation of original systems and from the classical Kraraers theory. It is shown that the reaction rate obtained by using the proposed approach agrees well with that from Monte Carlo simulation and is more accurate than the classical Kramers rate.

Key Role of Some Specific Occupied Molecular Orbitals of Short Chain n-Alkanes in Their Surface Tension and Reaction Rate Constants with Hydroxyl Radicals: DFT Study

Basing on the DFT calculations we propose the new theoretical model which describes both the surface tension σ of the short chain n-alkanes at their normal boiling points and their reaction rate constants with hydroxyl radicals OH• (at 297 ± 2 K) on the basis of their molecular orbital electronic characteristics. It has been shown that intermolecular dispersion attraction within the surface liquid monolayer of these compounds, as well as their reaction rate constants k with OH• radicals are determined by the energies Eorb of the specific occupied molecular orbitals which are the same in the determination of both the above physico-chemical characteristics of the studied n-alkanes. The received regression equations confirm the theoretically found dependences between the quantities of σ and k and the module |Eorb|. For the compounds under study this fact indicates the key role of their electronic structure particularities in determination of both the physical (surface tension) and the chemical (reaction rate constants) properties.

Determination of the stellar reaction rate for ^(12)C(α, γ)^(16)O: using a new expression with the reaction mechanism

The astrophysical reaction rate of 12C（α,γ）16O plays a key role in massive star evolution. However, this reaction rate and its uncertainties have not been well determined yet, especially at T9=0.2. The existing results even disagree with each other to a certain extent. In this paper, the El, E2 and total （E1＋E2） 12C（α,γ）16O reaction rates are calculated in the temperature range from T9=0.3 to 2 according to all the available cross section data. A new analytic expression of the 12C（α,γ）16O reaction rate is brought forward based on the reaction mechanism. In this expression, each part embodies the underlying physics of the reaction. Unlike previous works, some physical parameters are chosen from experimental results directly, instead of all the parameters obtained from fitting. These parameters in the new expression, with their 3σ fit errors, are obtained from fit to our calculated reaction rate from T9=0.3 to 2. Using the fit results, the analytic expression of 12C（α,γ）16Oreaction rate is extrapolated down to T9=0.05 based on the underlying physics. The 12C（α,γ）16O reaction rate at T9=0.2 is （8.78 ± 1.52） × 10^15 cm3s^-1mol^-1. Some comparisons and discussions about our new 12C（α,γ）16Oreaction rate are presented, and the contributions of the reaction rate correspond to the different part of reaction mechanism are given. The agreements of the reaction rate below T9=2 between our results and previous works indicate that our results are reliable, and they could be included in the astrophysical reaction rate network. Furthermore, we believe our method to investigate the 12C（α,γ）16O reaction rate is reasonable, and this method can also be employed to study the reaction rate of other astrophysical reactions. Finally, a new constraint of the supernovae production factor of some isotopes are illustrated according to our 12C（α,γ）16O reaction rates.

A statistical model for predicting thermal chemical reaction rate

A simple model based on the statistics of individual atoms [Europhys. Lett. 94 40002 （2011）] or molecules [Chin. Phys. Lett. 29 080504 （2012）] was used to predict chemical reaction rates without empirical parameters, and its physical basis was further investigated both theoretically and via MD simulations. The model was successfully applied to some reactions of extensive experimental data, showing that the model is significantly better than the conventional transition state theory. It is worth noting that the prediction of the model on ab initio level is much easier than the transition state theory or unimolecular RRKM theory.

A melt-cast Duan-Zhang-Kim mesoscopic reaction rate model and experiment for shock initiation of melt-cast explosives

A melt-cast Duan-Zhang-Kim(DZK)mesoscopic reaction rate model is developed for the shock initiation of melt-cast explosives based on the pore collapse hot-spot ignition mechanism.A series of shock initiation experiments was performed for the Comp B melt-cast explosive to estimate effects of the loading pressure and the particle size of granular explosive component,and the mesoscopic model is validated against the experimental data.Further numerical simulations indicate that the initial density and formula proportion greatly affect the hot-spot ignition of melt-cast explosives.

Measurement of niobium reaction rate for material surveillance tests in fast reactors

A highly accurate and precise technique for measurement of the 93 Nb(n,n’)93m Nb reaction rate was established for the material surveillance tests,etc.in fast reactors.The self-absorption effect on the measurement of the characteristic X-rays emitted by 93m Nb was decreased by the dissolution and evaporation to dryness of niobium dosimeter.A highly precise count of the number of 93 Nb atoms was obtained by measuring the niobium solution concentration using inductively coupled plasma mass spectrometry.X-rays of 93m Nb were measured accurately by means of comparing the X-ray intensity of irradiated niobium solution with that of the solution in which stable 93 Nb was added.The difference between both intensities indicates the effect of 182 Ta,which is generated from an impurity tantalum,and the intensity of X-rays from 93m Nb was evaluated.Measurement error of the 93 Nb(n,n’)93m Nb reaction rate was reduced to be less than 4%,which was equivalent to the other reaction rate errors of dosimeters used for Joyo dosimetry.In addition,an advanced technique using Resonance Ionization Mass Spectrometry was proposed for the precise measurement of 93m Nb yield,and 93m Nb will be resonance-ionized selectively by discriminating the hyperfine splitting of the atomic energy levels between 93 Nb and 93m Nb at high resolution.

A QUANTITATIVE STUDY ON ENHANCEMENT OF TYPE Ⅱ PHOTOSENSITIZED OXIDATION REACTION RATE BY HEAVY WATER

A method for quantitative evaluating the enhancement of the rate of Type Ⅱ photosensitized oxidation by D_2O was suggested. The effect of substrate concentration on this process was also discussed.

Fusion Reaction Rate Coefficient for Different Beam and Target Scenarios

Fusion power output is proportional not only to the fuel particle number densities participating in reaction but also to the fusion reaction rate coefficient （or reactivity）, which is dependent on reactant velocity distribution functions. They are usuMly assumed to be dual Maxwellian distribution functions with the same temperature for thermal nuclear fusion circumstances. However, if high power neutral beam injection and minority ion species ICRF plasma heating, or multi-pinched plasma beam head-on collision, in a converging region are required and investigated in future large scale fusion reactors, then the fractions of the injected energetic fast ion tail resulting from ionization or charge exchange will be large enough and their contribution to the non-Maxwellian distribution functions is not negligible, hence to the fusion reaction rate coefficient or calculation of fusion power. In such cases, beam-target, and beam-beam reaction enhancement effect contributions should play very important roles. In this paper, several useful formulae to calculate the fusion reaction rate coefticient for different beam and target combination scenarios are derived in detail

Molecular Orbital Nature of Solubility of Shot Chain n-Alkanes in Water and Their Reaction Rate Constants with Nitronium Cations: A DFT Study

The new theoretical models describe both the solubility S of the shot chain n-alkanes in water at 298.15 K, and their reaction rate constants k with nitronium cation NO2+ at 293.15 K on the basis of their molecular orbital characteristics. It is shown that both the quantities S and k are determined by the energies Eorb of the specific virtual (for S) and occupied (for k) molecular orbitals of these n-alkanes. The obtained regression equations confirm the theoretically found dependences of S and k on the absolute value of Eorb. This fact demonstrates that the electronic structure particularities of the studied n-alkanes play a crucial role in both their above-mentioned physicochemical properties.

MCSCF STUDIES ON THE IRC AND REACTION RATE CONSTANTS FOR THE DEHYDROGENATION REACTION OF VINYL RADICAL

The transition state(TS) and Intrinsic Reaction Coordinate (IRC) for the titled reaction were traced by means of MCSCF/6-31G (210 configurations). The reaction activation energy of this reaction is 140.2KJ/mol. The reaction rate constants of five temperetures were calculated by CVT involving the tunneling effects.

Reaction rates in blanket assemblies of a fusion-fission hybrid reactor

To validate neutronics calculation for the blanket design of fusion-fission hybrid reactor,experiments for measuring reaction rates inside two simulating assemblies are performed.Two benchmark assemblies were developed for the neutronics experiments.A D-T fusion neutron source is placed at the center of the setup.One of them consists of three layers of depleted uranium shells and two layers of polyethylene shells,and these shells are arranged alternatively.The ^(238)U capture reaction rates are measured using depleted uranium foils and an HPGe gamma spectrometer.The fission reaction rates are measured using a fission chamber coated with depleted uranium.The other assembly consists of depleted uranium and LiH shells.The tritium production rates are measured using the lithium glass scintillation detector which is placed in the LiH region of the assembly.The measured reaction rates are compared with the calculated ones predicted using MCNP code,and C/E values are obtained.

Measurement of absolute reaction rates in Be, Pb and Fe spherical systems

The absolute reaction rates in Be,Pb and Fe have been measured by using the activation foil technique with different reaction energy thresholds.Thicknesses of Be,Pb and Fe spheres were 5.3,19.1 and 31.9cm.respectively,Eight kinds of activation folis were used for Fe,and four kinds each for Be and Pb,The total experimental er5ror was about 5-7%.The measured results were compared to the values calculated with the 1-D ANISN code and the ENDF/B-VI library data.The average ratio of the experimental to the calculational is less than 7% for Be and Pb,about 5-30% for Fe.

Dependence of Reaction Rate Constants on Density in Supercritical Fluids

A new method,which correlates rate constants of chemical reactions and density or pressure in supercritical fluids,was developed.Based on the transition state theory and thermodynamic principles, the rate constant can be reasonably correlated with the density of the supercritical fluid,and a correlation equation was obtained. Coupled with the equation of state (EOS) of a supercritical solvent,the effect of pressure on reaction rate constant could be represented.Two typical systems were used to test this method.The result indicates that this method is suitable for dilute supercritical fluid solutions.

Stellar reaction rate of 55Ni（p,γ）56Cu in Type I X-ray bursts

^56Cu is close to the waiting-point nucleus ^56Ni and lies on the rapid proton capture (rp) process path in Type I X-ray bursts (XRBs). In this work, we obtained a revised thermonuclear reaction rate of ^55Niep;cT56Cu in the temperature region relevant to XRBs. This rate was recalculated based on the recent experimental level structure in ^56Cu, the recently measured proton separation energy of Sp = 579.8(7.1) keV, together with shell-model calculation, and the mirror nuclear structure in ^56Co. The associated uncertainties in the rates were estimated by a Monte Carlo method. Our revised rate is significantly different from the recent results, which were partially based on experimental results;in addition, we found that a result in a previous work was incorrect. We recommend our revised rate to be incorporated in the future astrophysical network calculations.

Efficient Solvent- and Catalyst-Free Syntheses of Imine Derivatives Applying the Pressure Reduction Technique: Remarkable Change of the Reaction Rate with the Phase Transition

Because imines could be used as convenient starting materials in various fields, the development of an easy synthetic method of imine was strongly desired. In response to this demand, we thought that it would be an effective synthesis method if an aldehyde and an amine could be reacted to give an imine in good yield under solvent- and catalyst-free conditions. In fact, we tried the reaction of benzaldehyde with various amines under solvent- and catalyst-free conditions followed by removal of water that was produced in the reaction system by a vacuum pump, and desired imines could be obtained in good yields. Observation of this reaction using a nuclear magnetic resonance spectrometer revealed that the reaction rate was extremely fast at the initial stage but slowed over time. However, the reaction of benzaldehyde with aniline differed greatly, and the reaction rate dramatically improved in 47 - 48 minutes after the start of the reaction. At this time, we found that the reaction system underwent a phase transition from the liquid phase to the solid phase.

Measurement of Reaction Rate of Gelled Acids and Calcite with the Rotating Disk Apparatus

An investigation has been made to study the reaction kinetics of gelled acids with calcite using a rotating disk apparatus. The rheological experiments revealed that all gelled acids behaved as non-Newtonian shear thinning fluids. With the rotating disk apparatus, the reaction kinetics parameters, activation energy, and effective diffusion coefficients were determined. It was found that the reaction of gelled acid with calcite was mass transfer limited at low polymer concentration and moving toward surface reaction limited at higher polymer concentration. And the diffusion rate marginally decreased, with increasing the polymer concentration.

Astrophysical S-factor and reaction rate for 15N(p,γ)16O within the modified potential cluster model

We study radiative p^(15)N capture on the ground state of ^(16)O at stellar energies within the framework of a modified potential cluster model(MPCM)with forbidden states,including low-lying resonances.The investigation of the ^(15)N(p,γ0)^(16)O reaction includes the consideration of ^(3)S_(1) resonances due to E1 transitions and the contribution of the ^(3)P_(1) scattering wave in the p+^(15)N channel due to the ^(3)P_(1)→^(3)P_(0)M1 transition.We calculated the astrophysical low-energy S-factor,and the extrapolated S(0)turned out to be within 34.7−40.4 keV·b.The important role of the asymptotic constant(AC)for the ^(15)N(p,γ0)16O process with interfering ^(3)S_(1)(312)and ^(3)S_(1)(962)resonances is elucidated.A comparison of our calculation for the S-factor with existing experimental and theoretical data is addressed,and a reasonable agreement is found.The reaction rate is calculated and compared with the existing rates.It has negligible dependence on the variation of AC but shows a strong impact of the interference of ^(3)S_(1)(312)and ^(3)S_(1)(962)resonances in reference to the CNO Gamow windows,especially at low temperatures.We estimate the contribution of cascade transitions to the reaction rate based on the exclusive experimental data from Phys.Rev.C.85,065810(2012).The reaction rate enhancement due to the cascade transitions is observed from T_(9)>0.3 and reaches the maximum factor~1.3 at T_(9)=1.3.We present the Gamow energy window and a comparison of rates for radiative proton capture reactions ^(12)N(p,γ)^(13)O,^(13)N(p,γ)^(14)O,^(14)N(p,γ)^(15)O,and ^(15)N(p,γ)^(16)O obtained in the framework of the MPCM and provide the temperature windows,prevalence,and significance of each process.

Study on the assimilation of the sulphate reaction rates based on WRF-Chem/DART

Sulphate(SO_(4)^(2-))is a main component of PM_(2.5)in China.The chemical formation mechanisms of sulphate are complex,and many air quality models have been used to analyse these mechanisms.To improve the accuracy of Weather Research Forecast-Chemistry(WRF-Chem)on sulphate,an alternative method is proposed in this paper.Moreover,data assimilation is performed to adjust the chemical reaction rates of sulphate.Based on the original reactions,a new sulphate parameterisation scheme,which includes two hypothetical reactions and six undetermined parameters,was added.Based on the WRF-Chem/DART(Data Assistance Research Testbed)system,the near-ground concentrations of SO_(4)^(2-),SO_(2),NO_(2),O_(3)and particulate matter are assimilated to adjust the six parameters.After adjusting the parameters,the new scheme can effectively solve the underestimation of SO_(4)^(2-)and overestimation of SO_(2).The simulation of SO_(4)^(2-)improved as the mean bias changed from-13.1μg m^(-3)to 3.5μg m^(-3)while SO_(2)improved from 17.0μg m^(-3)to 6.3μg m^(-3).The temporal and spatial variation characteristics predicted by the new scheme are consistent with the theoretical research results,indicating that the complex mechanism of sulphate formation could be replaced by the temporal and spatial variation characteristics predicted by the new scheme and that the parameters can be adjusted by data assimilation.Furthermore,the reaction rates of the SO_(4)^(2-)parameterisation scheme of the WRF-Chem model are improved in this study,and a new method for improving the accuracy of the air quality model is provided.