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Dennis Guster

Publications and source records attributed to Dennis Guster.

16 recordsLinked to original sources

Effect of strong $\bar{\rm p}$-p nuclear forces on the rate of the low-energy three-body protonium formation reaction: $\bar{p} + H_μ(1s) \rightarrow (\bar{p} p)_α + μ^-$

The effect of the strong $\bar{\rm p}$-p nuclear interaction in a three-charge-particle system with arbitrary masses is investigated. Specifically, the ($\bar{\rm p},\ μ^-$,\ p) system is considered, where $\bar{p}$ is an antiproton, $μ^-$ is a muon and p is a proton. A numerical computation in the framework of a detailed few-body approach is carried out for the following protonium (antiprotonic hydrogen) formation three-body reaction: $\bar{p} + H_μ(1s) \rightarrow (\bar{p} p)_α + μ^-$. Here, $H_μ(1s)$ is a ground state muonic hydrogen, i.e. a bound state of p and $μ^-$. A bound state of $p$ and its counterpart $\bar{p}$ is a protonium atom in a quantum atomic state $α$, i.e. $Pn = (\bar{p}p)_α$. The low-energy cross sections and rates of the $Pn$ formation reaction are computed in the framework of a Faddeev-like equation. The strong $\bar{\rm p}$-p interaction is included in these calculations within a first order approximation. It was found, that even in the framework of this approximation the inclusion of the strong interaction results in a quite significant correction to the rate of the three-body reaction. Therefore, the title three-body antiprotonic process with participation of muons should be useful, especially at low-energy collisions, in studying the $\bar{\rm p}$-p nuclear forces and the annihilation channels in $Pn$.

physics.atom-ph

Quantum-mechanical treatment of $^{1}$H$^{+}$ / $^{2}$H$^{+}$ / $^{3}$H$^{+}$ ion dynamics in carbon nanotubes

An investigation of quantum dynamical properties was conducted for $^{1}$H$^{+}$ / $^{2}$H$^{+}$ / $^{3}$H$^{+}$ ions as they traverse through a Carbon nanotube (CNT). The investigation is focused on a Fortran based program simulating a hydrogen ion passing through a CNT. Our work included testing convergence of the simulations, understanding dynamical behavior of hydrogen isotopes, and investigating the applied H$^{+}$ + CNT potential energy curve.

cond-mat.mes-hall

Low temperature HD + $ortho$-/$para$-H$_2$ inelastic scattering of astrophysical interest

State-selected total cross sections and thermal rate coefficients are computed for the HD + $ortho$-/$para$-H$_2$ rotational energy transfer collision at low temperatures: 2 K $\lesssim$ T $\lesssim$ 300 K. A modified H$_2$-H$_2$ potential energy surface (PES) devised by Hinde is used for this pure quantum-mechanical dynamical computation. A comparison of the new results for the HD + $ortho$-/$para$-H$_2$ scattering problem and previous calculations computed with the use of other older PESs is presented and discussed.

physics.chem-ph

On parallel implementation of a discrete optimization random search algorithm

A random search algorithm intended to solve discrete optimization problems is considered. We outline the main components of the algorithm, and then describe it in more detail. We show how the algorithm can be implemented on parallel computer systems. A performance analysis of both serial and parallel versions of the algorithm is given, and related results of solving test problems are discussed.

cs.DC

CN molecule collisions with H+ at a wide range of astrophysical energies

We analyze the quantum-mechanical rotational excitation/de-excitation spectrum and cross sections of CN molecules during low and high-energy collisions with protons, H+. The problem is of significant importance in astrophysics of the early Universe, specifically connected with the problems of cosmic microwave background (CMB) radiation. A quantum-mechanical close-coupling method is applied in this work. The cyanide molecule (CN) is treated as a rigid rotor, i.e. the distance between the carbon and nitrogen atoms is fixed at an average equilibrium value. The new results of the excitation/de-excitation cross-sections and corresponding thermal rate coefficients are compared with the results of few previous calculations performed on the basis of few approximate semiclassical frameworks. The interaction potential between CN and H+ is taken in the following form: proton induced polarization potential + proton-dipole potential + proton-quadrupole potential.

astro-ph.SR

Ultracold collisions between two light indistinguishable diatomic molecules: elastic and rotational energy transfer in HD+HD

A close coupling quantum-mechanical calculation is performed for rotational energy transfer in a HD+HD collision at very low energy, down to the ultracold temperatures: $T \sim 10^{-8}$ K. A global six-dimensional H$_2$-H$_2$ potential energy surface is adopted from a previous work [Boothroyd {\it et al.}, J. Chem. Phys., {\bf 116}, 666 (2002).] State-resolved integral cross sections $σ_{ij\rightarrow i'j'}(\varepsilon_{kin})$ of different quantum-mechanical rotational transitions $ij\rightarrow i'j'$ in the HD molecules and corresponding state-resolved thermal rate coefficients $k_{ij\rightarrow i'j'}(T)$ have been computed. Additionally, for comparison, H$_2$+H$_2$ calculations for a few selected rotational transitions have also been performed. The hydrogen and deuterated hydrogen molecules are treated as rigid rotors in this work. A pronounced isotope effect is identified in the cross sections of these collisions at low and ultracold temperatures.

physics.chem-ph

A comparative study of the low energy HD+o-/p-H2 rotational excitation/de-excitation collisions and elastic scattering

The Diep and Johnson (DJ) H$_2$-H$_2$ potential energy surface (PES) obtained from the first principles [P. Diep, K. Johnson, J. Chem. Phys. 113, 3480 (2000); 114, 222 (2000)], has been adjusted through appropriate rotation of the three-dimensional coordinate system and applied to low-temperature ($T<300$ K) HD+$o$-/$p$-H$_2$ collisions of astrophysical interest. A non-reactive quantum mechanical close-coupling method is used to carry out the computation for the total rotational state-to-state cross sections $σ_{j_1j_2\rightarrow j'_1j'_2}(ε)$ and corresponding thermal rate coefficients $k_{j_1j_2\rightarrow j'_1j'_2}(T)$. A rather satisfactory agreement has been obtained between our results computed with the modified DJ PES and with the newer H$_4$ PES [A.I. Boothroyd, P.G. Martin, W.J. Keogh, M.J. Peterson, J. Chem. Phys. 116, 666 (2002)], which is also applied in this work. A comparative study with previous results is presented and discussed. Significant differences have been obtained for few specific rotational transitions in the H$_2$/HD molecules between our results and previous calculations. The low temperature data for $k_{j_1j_2\rightarrow j'_1j'_2}(T)$ calculated in this work can be used in a future application such as a new computation of the HD cooling function of primordial gas, which is important in the astrophysics of the early Universe.

physics.chem-ph

Weakly bound states of neutrons in gravitational fields

In this paper a quantum-mechanical behaviour of neutrons in gravitational fields is considered. A first estimation is made using the semiclassical approximation, neglecting General Relativity, magnetic and rotation effects, for neutrons in weakly bound states in the weak gravitational field of the Earth. This result was generalized for a case, in which the Randall - Sundrum correction to Newton's gravitational law on the small scales was applied. Application of the results to Neutron Star physics is considered and further possible perspectives are discussed.

physics.atom-ph

Quenching of $para$-H$_2$ with an ultra-cold anti-hydrogen atom $\bar{H}_{1s}$

In this work we report the results concerning calculations for quantum-mechanical rotational transitions in molecular hydrogen, H$_2$, induced by an ultra-cold ground state anti-hydrogen atom $\bar{H}_{1s}$. The calculations are accomplished using a non-reactive close-coupling quantum-mechanical approach. The H$_2$ molecule is treated as a rigid rotor. The total elastic scattering cross section $σ_{el}(ε)$ at energy $ε$, state-resolved rotational transition cross sections $σ_{jj'}(ε)$ between states $j$ and $j'$ and corresponding thermal rate coefficients $k_{jj'}(T)$ are computed in the temperature range 0.004 K $ \lesssim T \lesssim$ 4 K. Satisfactory agreement with other calculations (variational) has been obtained for $σ_{el}(ε)$.

physics.atom-ph

State-resolved rotational cross sections and thermal rate coefficients for ortho-/para-H2+HD at low temperatures and HD+HD elastic scattering

Results for quantum mechanical calculations of the integral cross sections and corresponding thermal rate coefficients for para-/ortho-H2+HD collisions are presented. Because of significant astrophysical interest in regard to the cooling of primodial gas the low temperature limit of para-/ortho-H2+HD is investigated. Sharp resonances in the rotational state-resolved cross sections have been calculated at low energies. These resonances are important and significantly contribute to the corresponding rotational state-resolved thermal rate coefficients, particularly at low temperatures, that is less than $T \sim 100$K. Additionally in this work, the cross sections for the elastic HD+HD collision have also been calculated. We obtained quite satisfactory agreement with the results of other theoretical works and experiments.

physics.chem-ph

Computer Simulations of Pulsatile Human Blood Flow Through 3D-Models of the Human Aortic Arch, Vessels of Simple Geometry and a Bifurcated Artery: Investigation of Blood Viscosity and Turbulent Effects

We report computational results of blood flow through a model of the human aortic arch and a vessel of actual diameter and length. On the top of the aortic arch the branching of the %%three arteries are included: the subclavian and jugular. A realistic pulsatile flow is used in all simulations. Calculations for bifurcation type vessels are also carried out and presented. Different mathematical methods for numerical solution of the fluid dynamics equations have been considered. The non-Newtonian behaviour of the human blood is investigated together with turbulence effects. A detailed time-dependent mathematical convergence test has been carried out. The results of computer simulations of the blood flow in vessels of three different geometries are presented: for pressure, strain rate and velocity component distributions we found significant disagreements between our results obtained with realistic non-Newtonian treatment of human blood and the widely used method in the literature: a simple Newtonian approximation. A significant increase of the strain rate and, as a result, a wall shear stress distribution, is found in the region of the aortic arch. Turbulent effects are found to be important, particularly in the case of bifurcation vessels.

physics.flu-dyn

3D Computer Simulations of Pulsatile Human Blood Flows in Vessels and in the Aortic Arch: Investigation of Non-Newtonian Characteristics of Human Blood

Methods of Computational Fluid Dynamics are applied to simulate pulsatile blood flow in human vessels and in the aortic arch. The non-Newtonian behaviour of the human blood is investigated in simple vessels of actual size. A detailed time-dependent mathematical convergence test has been carried out. The realistic pulsatile flow is used in all simulations. Results of computer simulations of the blood flow in vessels of two different geometries are presented. For pressure, strain rate and velocity component distributions we found significant disagreements between our results obtained with realistic non-Newtonian treatment of human blood and widely used method in literature: a simple Newtonian approximation. A significant increase of the strain rate and, as a result, wall sear stress distribution, is found in the region of the aortic arch. We consider this result as theoretical evidence that supports existing clinical observations and those models not using non-Newtonian treatment underestimate the risk of disruption to the human vascular system.

physics.comp-ph

Close-coupling calculations of rotational energy transfer in p-H2+HD

We report quantum-mechanical close-coupling calculations for rotational state resolved cross sections for p-H2+HD collisions. The low temperature limit of p-H2+HD is investigated, which is of significant astrophysical interest in regard to the cooling of primordial gas and the interstellar media. Sharp resonances have been reproduced in the cross sections of some transition states at very low kinetic energies, E< 0.00001 eV.

physics.chem-ph

Rotational Energy Transfer in H2+H2

Quantum-mechanical close-coupling calculations for state-to-state cross sections and thermal rates are reported for H2+H2 collisions. Two recently developed potential energy surfaces (PES) for the H2-H2 system are applied, namely, the global potential surface from the work of A.I. Boothroyd, P.G. Martin, W.J. Keogh, M.J. Peterson, J. Chem. Phys., 116 (2002) 666, and a restricted, model surface from the works of P. Diep, J.K. Johnson, J. Chem. Phys., 113 (2000) 3480; ibid. 112, 4465. The low temperature limit is investigated. We found significant differences in cross sections and corresponding thermal rates calculated with these two PESs.

physics.chem-ph

Parallel computing for 4-atomic molecular dynamics calculations

We report the results of intensive numerical calculations for four atomic H2+H2 energy transfer collision. A parallel computing technique based on LAM/MPI functions is used. In this algorithm, the data is distributed to the processors according to the value of the momentum quantum number J and its projection M. Most of the work is local to each processor. The topology of the data communication is a simple star. Timings are given and the scaling of the algorithm is discussed. Two different recently published potential energy surfaces for the H2-H2 system are applied. New results obtained for the state resolved excitation-deexcitation cross sections and rates valuable for astrophysical applications are presented. Finally, more sophisticated extensions of the parallel code are discussed.

physics.chem-ph

State resolved rotational excitation cross sections and rates in H2+H2 collisions

Rotational transitions in molecular hydrogen collisions are computed. The two most recently developed potential energy surfaces for the H2-H2 system are used from the following works: 1) A.I. Boothroyd, P.G. Martin, W.J. Keogh, M.J. Peterson, J. Chem. Phys., 116 (2002) 666, and 2) P. Diep, J.K. Johnson, J. Chem. Phys., 113 (2000) 3480; ibid. 112, 4465. Cross sections for rotational transitions 00->20, 22, 40, 42, 44 and corresponding rate coefficients are calculated using a quantum-mechanical approach. Results are compared for a wide range of kinetic temperatures 300 K < T < 3000 K.

physics.chem-ph