30 research outputs found
Stress-strain analysis of pipelines laid in permafrost
Increasing reliability of pipelines becomes a real challenge at all stages: design, construction and operation of pipeline systems. It is very important to determine the behaviour of the constructed pipeline under the operational and environmental loads using the design model in accordance with that one adopted in the rules and regulations. This article presents the simulation of pipeline in permafrost. The evaluation of the stress-strain state is given herein and the areas of the stress concentration are detected with the account for different loads occurred during the pipeline operation. Information obtained from the assessment of the stress-strain state of the pipeline allows determining sections in pre-emergency state (even before damages) and take all the necessary measures for eliminating them, thus increasing the pipeline system reliability. It is shown that the most critical pipeline cross-section is observed at the point of transition from one environment to another. The maximum strains decrease the level of the pipeline reliability. The finite element model is presented to determine the pipeline sections in pre-emergency state
Non-thermal transport of energy driven by photoexcited carriers in switchable solid states of GeTe
Phase change alloys have seen widespread use from rewritable optical discs to
the present day interest in their use in emerging neuromorphic computing
architectures. In spite of this enormous commercial interest, the physics of
carriers in these materials is still not fully understood. Here, we describe
the time and space dependence of the coupling between photoexcited carriers and
the lattice in both the amorphous and crystalline states of one phase change
material, GeTe. We study this using a time-resolved optical technique called
picosecond acoustic method to investigate the \textit{in situ} thermally
assisted amorphous to crystalline phase transformation in GeTe. Our work
reveals a clear evolution of the electron-phonon coupling during the phase
transformation as the spectra of photoexcited acoustic phonons in the amorphous
(-GeTe) and crystalline (-GeTe) phases are different. In particular
and surprisingly, our analysis of the photoinduced acoustic pulse duration in
crystalline GeTe suggests that a part of the energy deposited during the
photoexcitation process takes place over a distance that clearly exceeds that
defined by the pump light skin depth. In the opposite, the lattice
photoexcitation process remains localized within that skin depth in the
amorphous state. We then demonstrate that this is due to supersonic diffusion
of photoexcited electron-hole plasma in the crystalline state. Consequently
these findings prove the existence of a non-thermal transport of energy which
is much faster than lattice heat diffusion
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
A microscopic theory for the generation and propagation of coherent LA
phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum
well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is
driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump
laser and is treated theoretically using the density matrix formalism. We use
realistic wurzite bandstructures taking valence-band mixing and strain-induced
piezo- electric fields into account. In addition, the many-body Coulomb
ineraction is treated in the screened time-dependent Hartree-Fock
approximation. We find that under typical experimental conditions, our
microscopic theory can be simplified and mapped onto a loaded string problem
which can be easily solved.Comment: 20 pages, 17 figure
Ceramic materials based on silicon-containing mineral raw material
The possibility of using silicon-containing mineral raw material (quartz sand and sandy opoka) mined in the Belgorod region for manufacturing ceramic materials with a combination of high thermostability and satisfac-tory mechanical compressive strength was demonstratedyesBelgorod State Universit
Ceramic materials based on silicon-containing mineral raw material
yesThe possibility of using silicon-containing mineral raw material (quartz sand and sandy opoka) mined in the Belgorod region for manufacturing ceramic materials with a combination of high thermostability and satisfac-tory mechanical compressive strength was demonstratedBelgorod State Universit