Non-Markovian rotational relaxation matrix for fast collisions between two linear molecules in high-pressure gaseous media. I. General formalism and preliminary testing

2018 ◽  
Vol 149 (4) ◽  
pp. 044305 ◽  
Author(s):  
Alexander P. Kouzov ◽  
Jeanna V. Buldyreva ◽  
Andrei V. Sokolov
Keyword(s):  
High Pressure ◽  
Rotational Relaxation ◽  
Preliminary Testing ◽  
Relaxation Matrix ◽  
Gaseous Media ◽  
Linear Molecules

scholarly journals Спектральные моменты характеристик бинарных взаимодействий между линейными молекулами

2021 ◽  
Vol 129 (3) ◽  
pp. 253
Author(s):  
А.В. Соколов ◽  
А.П. Коузов ◽  
Ж.В. Булдырева ◽  
Н.И. Егорова
Keyword(s):  
Interaction Potential ◽  
Spectral Moments ◽  
New Approach ◽  
Relaxation Matrix ◽  
Arbitrary Rank ◽  
Molecular Pair ◽  
Linear Molecules ◽  
Computer Codes ◽  
Spectral Distributions ◽  
The Way

A new approach to derive symmetrized expressions of leading classical moments of spectral distributions characterizing different anisotropic terms of the interaction potential for the case of two liear molecules is presented. The results allow to calculate diffuse shapes formed by transitions between continuous eigenstates of a molecular pair and open the way to account for the nonMarkov effects (due to finite collision durations) in the rotatonal relaxation matrix of an arbitrary rank. The approach is also applied to the spectral moments of vector and tensor characteristics determining the band intensities in the collision-induced spectra of linear molecules. Generally, the use of symmetrized expressions lead to considerably faster computer codes.

scholarly journals Pressure-induced transformation of CH3NH3PbI3: the role of the noble-gas pressure transmitting media

2019 ◽  
Vol 75 (3) ◽  
pp. 361-370 ◽  
Author(s):  
Alla Arakcheeva ◽  
Volodymyr Svitlyk ◽  
Eleonora Polini ◽  
Laura Henry ◽  
Dmitry Chernyshov ◽  
...  
Keyword(s):  
High Pressure ◽  
Energy Conversion ◽  
Structural Changes ◽  
Chemical Reactivity ◽  
Noble Gas ◽  
Threshold Level ◽  
Energy Conversion Efficiency ◽  
Ambient Conditions ◽  
Gaseous Media ◽  
Composition Structure

The photovoltaic perovskite, methylammonium lead triiodide [CH3NH3PbI3 (MAPbI3)], is one of the most efficient materials for solar energy conversion. Various kinds of chemical and physical modifications have been applied to MAPbI3 towards better understanding of the relation between composition, structure, electronic properties and energy conversion efficiency of this material. Pressure is a particularly useful tool, as it can substantially reduce the interatomic spacing in this relatively soft material and cause significant modifications to the electronic structure. Application of high pressure induces changes in the crystal symmetry up to a threshold level above which it leads to amorphization. Here, a detailed structural study of MAPbI3 at high hydrostatic pressures using Ne and Ar as pressure transmitting media is reported. Single-crystal X-ray diffraction experiments with synchrotron radiation at room temperature in the 0–20 GPa pressure range show that atoms of both gaseous media, Ne and Ar, are gradually incorporated into MAPbI3, thus leading to marked structural changes of the material. Specifically, Ne stabilizes the high-pressure phase of Ne x MAPbI3 and prevents amorphization up to 20 GPa. After releasing the pressure, the crystal has the composition of Ne0.97MAPbI3, which remains stable under ambient conditions. In contrast, above 2.4 GPa, Ar accelerates an irreversible amorphization. The distinct impacts of Ne and Ar are attributed to differences in their chemical reactivity under pressure inside the restricted space between the PbI6 octahedra.

scholarly journals Media-assisted machining processes

Mechanik ◽  
2018 ◽  
Vol 91 (12) ◽  
pp. 1050-1056
Author(s):  
Wit Grzesik
Keyword(s):  
High Pressure ◽  
Material Removal ◽  
Tribological Behavior ◽  
Removal Rate ◽  
Subsurface Layer ◽  
Optimization Procedure ◽  
Special Group ◽  
Machining Processes ◽  
Gaseous Media ◽  
Cutting Zone

A special group of hybrid assisted processes termed media-assisted processes which various liquid and gaseous media supplied to the cutting zone is highlighted. Special attention is paid on such cooling techniques as high-pressure machining (HPC), high-pressure jet assisted machining (HPJAM), minimum quantity cooling/lubrication (MQC/MQL) and a group of cryogenically cooled machining including such cryogenic media as CO2 snow and liquid nitrogen (LN2). Some important effects resulting from the various cooling strategies are outlined and compared. In particular, quantitative effects concerning chip breaking, thermal and tribological behavior of the cutting process as well as burr reduction, surface quality and subsurface layer are presented. The optimization procedure concerning both energy consumption and machining costs in terms of material removal rate (MRR) is presented.

The Master Equation for the Dissociation of a Dilute Diatomic Gas IX. Rotation–Vibration Relaxation Times

1973 ◽  
Vol 51 (12) ◽  
pp. 1923-1932 ◽  
Author(s):  
E. Kamaratos ◽  
H. O. Pritchard
Keyword(s):  
Shock Wave ◽  
Relaxation Time ◽  
Vibrational Relaxation ◽  
Transition Probabilities ◽  
Transition Probability ◽  
Relaxation Times ◽  
Rotational Relaxation ◽  
Relaxation Matrix ◽  
Coupling Case ◽  
Increasing Temperature

The relationships between individual rotational or vibrational transition probabilities and the eigenvalues of the 172nd order relaxation matrix describing the rotation–vibration–dissociation coupling of ortho-hydrogen are explored numerically. The simple proportionality between certain transition probabilities and certain eigenvalues, which was found previously in the vibration–dissociation coupling case, breaks down. However, it is shown that at 2000°K the second smallest eigenvalue of the relaxation matrix (dn−2), hitherto regarded as determining the "vibrational" relaxation time, is related more to the transition probability assigned to the largest rotational gap which lies in the first (ν = 0 ↔ ν = 1) vibrational gap, i.e. to the transition ν = 0, J = 5 ↔ ν = 0, J = 7, than to anything else; this clearly supports an earlier suggestion that the transient which immediately precedes dissociation in a shock wave has to be regarded as a rotation–vibration relaxation time rather than a vibrational relaxation time. It is suggested that the Lambert–Salter relationships can be rationalized on this assumption.An analysis is then made of the energy uptake associated with each eigenvalue at three temperatures. At 500°K, the greatest energy increment is associated with two eigenvalues (dn−13 and dn−24) and can be characterized as essentially a rotational relaxation: the calculations confirm that the observed rotational relaxation time should first decrease and then increase with increasing temperature, as was recently found to be the case experimentally. At 2000°K, large energy increments are associated with several eigenvalues between dn−2 and dn−14, and at 5000°K, with most of the eigenvalues dn−2 to dn−23; thus, the higher the temperature, the more complex is the (T–VR) rotation–vibration relaxation. Further, relaxation times for the same temperature measured by ultrasonic and shock-wave techniques need not agree.

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