The spectra of the Dirac quasi-electrons transmission through the Fibonacci quasi-periodical superlattice (SL) are calculated and analyzed in the continuum model with the help of the transfer matrix method. The one-dimensional SL based on a monolayer graphene modulated by the Fermi velocity barriers is studied. A new quasi-periodical factor is proposed to be considered. We show that the Fibonacci quasi-periodic modulation in graphene superlattices with the velocity barriers can be effectively realized by virtue of a difference in the velocity barrier values (no additional factor is needed and we keep in mind that not each factor can provide the quasi-periodicity). This fact is true for a case of normal incidence of quasi-electrons on a lattice. In contrast to the case of other types of the graphene SL spectra studied reveal the remarkable property, namely the periodic character over all the energy scale and the transmission coefficient doesn't tend asymptotically to unity at rather large energies. Both the conductance (using the known Landauer - Buttiker formula) and the Fano factor for the structure considered are also calculated and analyzed. The dependence of spectra on the Fermi velocity magnitude and on the external electrostatic potential as well as on the SL geometrical parameters (width of barriers and quantum wells) is analyzed. Using the quasi-periodical SL one can control the transport properties of the graphene structures in a wide range. The obtained results can be used for applications in the graphene-based electronics.

Індекс рубрикатора НБУВ: В371.213 + В377.15

Рубрики:

Тубулярні і цибулинні графени

Електричні явища при контакті твердих тіл

Шифр НБУВ: Ж69879 Пошук видання у каталогах НБУВ 

Індекс рубрикатора НБУВ: В379.371

Рубрики:

Електричні властивості діелектриків

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

Індекс рубрикатора НБУВ: В379.371

Рубрики:

Електричні властивості діелектриків

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

Індекс рубрикатора НБУВ: В383.32

Рубрики:

Альфа - розпад. Альфа - випромінювання.

Шифр НБУВ: Ж69879 Пошук видання у каталогах НБУВ 

Індекс рубрикатора НБУВ: В379.271.25

Рубрики:

Тунельний ефект

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

The aim of this research is to study the stability of haulage drifts and the manifestations of rock pressure in them lengthwise the working area when protecting them with coal pillars. To assess the stability of workings, field experiments were conducted to study the manifestations of rock pressure in the haulage drifts of a steep coal seam. It has been registered that as the breakage face progresses, the displacement of roof rocks on the contour of the drift linearly increases with an increase in the length of the working area. The deformation properties of coal pillars were studied taking into consideration the extent of the convergence of the roof and soil. This paper reports a theoretical model that describes the destruction of the above-drift coal pillars when unloading the coal-bearing massif that hosts the workings. It has been determined that the equilibrium state of coal pillars is ensured when the specific deformation and stress potentials are equal before the occurrence of main cracks of destruction. As the relative deformation of coal pillars increases at compression, when this equality is broken, the specific energy intensity of destruction increases. It is noted that at a distance exceeding l >> 10 m behind the breakage face, the occurrence of the main cracks of destruction is followed by a stability loss in the coal pillars. As a result of external forces, the change in the volume and shape of the coal pillars causes the intensification of the process of convergence of lateral rocks on the contour of haulage drifts lengthwise the working area and leads, with a certain degree of probability, to a deterioration in the stability of workings. The results of this study could be used to justify the choice of technique to protect haulage drifts. This would allow the timely development of minefield reserves thereby improving the safety of operations. It is recommended that the technique of protecting haulage drifts by coal pillars should be abandoned.

Індекс рубрикатора НБУВ: В368.3 + В312.232

Рубрики:

Фізика низьких температур

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ