Nonparabolicity effects and the spin-split electron dwell time in symmetric III-V double-barrier structures

We start from the fourth order nonparabolic and anisotropic conduction band bulk dispersion relation to obtain an one-band effective Hamiltonian which we apply to an AlGaSb symmetric double-barrier structure with resonant energies significantly (more than 200meV) above the well bottom. The spin-splitting is described by the k3 Dresselhaus spin-orbit coupling term modifying only the effective mass of the spin eigenstates in the investigated structure. Apart from the bulk-like resonant energy shift due to the band nonparabolicity, we obtain a substantial shift depending on the choice of boundary conditions for the envelope functions at interfaces between different materials. The shift of resonant energy levels leads to the change of spin-splitting and the magnitude of the dwell times. We attempt to explain the influence of both the nonparabolicity and boundary conditions choice by introducing various effective masses

Vibration Quantity Share of Multiple Faults with Similar Frequency Spectrum Characteristics in Rotational Machinery

Characteristics of the vibrations of rotational systems with misalignment and rotating looseness are well known and they are used for fault detection in the rotating machinery. For the better understanding and easier decision make in the fault removing process it is necessary to know how severe each fault is. Lack of procedures for quantification of this faults in rotational machinery is evident. In this paper is investigated the possibility for use of multiple regression analysis for determination of quantity of faults in vibration velocity signal. An experimental motor – coupling – rotor system is created and produced. These systems have capability of changing the values of misalignment and rotational looseness. Measurement of vibrational quantities were conducted on these systems by using piezoelectrical accelerometers for different combinations of fault values. All measurements were stored and processed digitally. All measurements have shown the presence of the main characteristics of introduced faults. It is confirmed that it is not possible to use RMS (root mean square) of vibration velocity, since there is a lot of other factors which has significant impact on the vibration quantity

A one-dimensional model for flow and sediment interaction in a looped network ofnatural watercourses

U radu su prikazani razvoj, testiranje, kalibracija i verifikacija linijskog modela neustaljenog tečenja vode i transporta nanosa u mreži prirodnih vodotoka. Hidraulički model se zasniva na St. Venant -ovim jednačinama koje su diskretizovane primenom Preissmann-ove šeme. Za modelisanje transporta nanosa i deformacije korita je usvojen koncept koji daje mogućnost da se obuhvate oba vida kretanja nanosa (suspendovanog i vučenog). Primenom pristupa aktivnog sloja su definisani procesi razmene materijala između nanosa u suspenziji i nanosa u aktivnom sloju. Osnovne jednačine transporta nanosa i deformacije korita su rečene primenom metode etapnog rešavanja čija primena rezultuje u dva uzastopna koraka, advektivnom i difuzionom koraku. Jednaˇcine advektivnog koraka su ređavane metodom karakteristika, dok se za jednačine difuzionog koraka primenila CrankNicholson-ova šema metode konaˇcnih razlika. Dobijene jednačine su dopunjene sa dodatnim jednačinama kako bi se omogućilo modelisanje opisanih procesa u granatoj mrezi otvorenih tokova. Izvedene jednacine su primenjene za formiranje numerickog modela koji jeđvalitativno testiran na šematskim primerima, a kvantitativni testovi su urađeni na realnom primeru. Za realan primer je izabrana deonica Dunava u Srbiji sa glavnim pritokama Savom i Tisom. Kako bi se definisala oblast koja će se koristiti za verifikaciju modela napravljen je detaljan pregled i sistematizacija postojećih merenja morfologije korita, nivoa, proticaja i koncentracija suspendovanog nanosa. Na osnovu ovog pregleda je definisana morfologija modelisane mreže tokova. Pri kalibraciji hidrauličkog modela su razmotrena dva pristupa, kalibracija putem Manning-ovog koeficijenta zadatog kao funkcije od proticaja, i kalibracija zadavanjem apsolutne hrapavosti, dok je verifikacija modela urađena puštanjem simulacije od godinu dana i poređenjem rezultata proračuna sa merenjima. Kalibracija modela transporta je sprovedena za duži vremenski period kako bi se što bolje opisale godišnje varijacije koncentracije suspendovanog nanosa, a za verifikaciju modela je odabran petogodiˇsnji period tokom kojeg su upoređeni rezultati proracuna sa merenjima, čime je pokazano da razvijen model moze pouzdano da simulira procese strujanja vode i transprta nanosa u mreži otvorenih tokova.  This work presents the development, evaluation, calibration and verification of a one dimensional unsteady flow, sediment transport and bed evolution looped river network model. The hydraulic model is based on the St. Venant’s equations discretized using the Preissmann’s scheme. The sediment transport and bed evolution model implements a concept that differentiates sediment particles moving in the form of suspended sediment, and near bed and bed sediment. Applying the active layer concept the developed model includes definitions of the exchange mechanisms between the suspended sediment and active layer material. The governing transport equations were solved using the split operator approach that resulted in two successive steps, the advection and diffusion step. The advection step equations were solved using the characteristics method, whereas the diffusion step equations are discretized using the Crank-Nicholson’s scheme. The obtained system of the developed equations was complemented with additional equations in order to allow sediment transport and bed evolution simulation in a looped river network. The derived equations were applied to develop an open channel flow, sediment transport and bed evolution numerical model that was subjected to a series of schematic tests and a real life situation simulation. The model’s evaluation was conducted by comparison of the simulation results with the available measurements. The presented work was complemented with an comprehensive overview of the existing bathymetry, water level, discharge and suspended sediment concentration measurements in order to define the model’s domain, initial and boundary conditions. The calibration of the hydraulic model was done by assigning the Manning’s coefficient as a function of the discharge. As a result of the exhausting requirements of this approach, a second approach was considered, where the calibration is conducted by changing the absolute roughness. The verification of the hydraulic model was done by comparing the computed results of a one year flow simulation with the available measurements. Since the agrement between the two was satisfying, the sediment transport and bed evolution model was calibrated using a longer time interval in order to better capture the annual variations of the suspended sediment. The calibrated model was employed for a long term sediment transport and bed evolution simulation. The simulation results were compared with the existing measurements confirming the developed model’s reliability

A one-dimensional model for flow and sediment interaction in a looped network ofnatural watercourses

U radu su prikazani razvoj, testiranje, kalibracija i verifikacija linijskog modela neustaljenog tečenja vode i transporta nanosa u mreži prirodnih vodotoka. Hidraulički model se zasniva na St. Venant -ovim jednačinama koje su diskretizovane primenom Preissmann-ove šeme. Za modelisanje transporta nanosa i deformacije korita je usvojen koncept koji daje mogućnost da se obuhvate oba vida kretanja nanosa (suspendovanog i vučenog). Primenom pristupa aktivnog sloja su definisani procesi razmene materijala između nanosa u suspenziji i nanosa u aktivnom sloju. Osnovne jednačine transporta nanosa i deformacije korita su rečene primenom metode etapnog rešavanja čija primena rezultuje u dva uzastopna koraka, advektivnom i difuzionom koraku. Jednaˇcine advektivnog koraka su ređavane metodom karakteristika, dok se za jednačine difuzionog koraka primenila CrankNicholson-ova šema metode konaˇcnih razlika. Dobijene jednačine su dopunjene sa dodatnim jednačinama kako bi se omogućilo modelisanje opisanih procesa u granatoj mrezi otvorenih tokova. Izvedene jednacine su primenjene za formiranje numerickog modela koji jeđvalitativno testiran na šematskim primerima, a kvantitativni testovi su urađeni na realnom primeru. Za realan primer je izabrana deonica Dunava u Srbiji sa glavnim pritokama Savom i Tisom. Kako bi se definisala oblast koja će se koristiti za verifikaciju modela napravljen je detaljan pregled i sistematizacija postojećih merenja morfologije korita, nivoa, proticaja i koncentracija suspendovanog nanosa. Na osnovu ovog pregleda je definisana morfologija modelisane mreže tokova. Pri kalibraciji hidrauličkog modela su razmotrena dva pristupa, kalibracija putem Manning-ovog koeficijenta zadatog kao funkcije od proticaja, i kalibracija zadavanjem apsolutne hrapavosti, dok je verifikacija modela urađena puštanjem simulacije od godinu dana i poređenjem rezultata proračuna sa merenjima. Kalibracija modela transporta je sprovedena za duži vremenski period kako bi se što bolje opisale godišnje varijacije koncentracije suspendovanog nanosa, a za verifikaciju modela je odabran petogodiˇsnji period tokom kojeg su upoređeni rezultati proracuna sa merenjima, čime je pokazano da razvijen model moze pouzdano da simulira procese strujanja vode i transprta nanosa u mreži otvorenih tokova.  This work presents the development, evaluation, calibration and verification of a one dimensional unsteady flow, sediment transport and bed evolution looped river network model. The hydraulic model is based on the St. Venant’s equations discretized using the Preissmann’s scheme. The sediment transport and bed evolution model implements a concept that differentiates sediment particles moving in the form of suspended sediment, and near bed and bed sediment. Applying the active layer concept the developed model includes definitions of the exchange mechanisms between the suspended sediment and active layer material. The governing transport equations were solved using the split operator approach that resulted in two successive steps, the advection and diffusion step. The advection step equations were solved using the characteristics method, whereas the diffusion step equations are discretized using the Crank-Nicholson’s scheme. The obtained system of the developed equations was complemented with additional equations in order to allow sediment transport and bed evolution simulation in a looped river network. The derived equations were applied to develop an open channel flow, sediment transport and bed evolution numerical model that was subjected to a series of schematic tests and a real life situation simulation. The model’s evaluation was conducted by comparison of the simulation results with the available measurements. The presented work was complemented with an comprehensive overview of the existing bathymetry, water level, discharge and suspended sediment concentration measurements in order to define the model’s domain, initial and boundary conditions. The calibration of the hydraulic model was done by assigning the Manning’s coefficient as a function of the discharge. As a result of the exhausting requirements of this approach, a second approach was considered, where the calibration is conducted by changing the absolute roughness. The verification of the hydraulic model was done by comparing the computed results of a one year flow simulation with the available measurements. Since the agrement between the two was satisfying, the sediment transport and bed evolution model was calibrated using a longer time interval in order to better capture the annual variations of the suspended sediment. The calibrated model was employed for a long term sediment transport and bed evolution simulation. The simulation results were compared with the existing measurements confirming the developed model’s reliability

Time delay in thin slabs with self-focusing Kerr-type nonlinearity

Time delays for an intense transverse electric (TE) wave propagating through a Kerr-type nonlinear slab are investigated. The relation between the bidirectional group delay and the dwell time is derived and it is shown that the difference between them can be separated into three terms. The first one is the familiar self interference time, due to the dispersion of the medium surrounding the slab. The other two terms are caused by the nonlinearity and oblique incidence of the TE wave. It is shown that the electric field distribution along the slab may be expressed in terms of Jacobi elliptic functions while the phase difference introduced by the slab is given in terms of incomplete elliptic integrals. The expressions for the field intensity dependent complex reflection and transmission coefficients are derived and the multivalued oscillatory behavior of the delay times for the case of a thin slab is demonstrated

VIBRATION ANALYSIS AND REPAIR PROCESS FOR THE VENTILATION SYSTEM FOR SMOKE DRAIN IN THE THERMAL POWER PLANT

Vibrations are common phenomenon in the rotating machinery, which could carry important information about condition of the rotating machinery. All specific failures in rotating machinery have their own characteristics of the vibrations. By measuring and analysis of vibrations cause of increased vibrations could be determined. Since misalignment and rotating looseness have similar frequency spectrum characteristics, it is difficult to determine which one of the failures is present. When cause of increased vibrations is determined, it is possible to plan the future steps for the repairing and neutralising present cause of the possible failure. Process of vibration analysis followed by present cause of increased vibration in rotating machinery repairing is presented in this paper through example on the ventilation system for smoke drain in the thermal power plant

Magnetotunnelling in resonant tunnelling structures with spin-orbit interaction

Magnetotunnelling spectroscopy of resonant tunnelling structures provides information on the nature of the two-dimensional electron gas in the well. We describe a model based on nonequilibrium Green's functions that allows for a comprehensive study of the density of states, tunnelling currents and current spin polarization. The investigated effects include the electron-phonon interaction, interface roughness scattering, Zeeman effect and the Rashba spin-orbit interaction. A qualitative agreement with experimental data is found regarding the satellite peaks. The spin polarization is predicted to be larger than ten percent for magnetic fields above 2 Tesla and having a structure even at the satellite peaks. The Rashba effect is confirmed to be observable as a beating pattern in the density of states but found to be too small to affect the tunnelling current.Comment: 31 pages, 11 figure

Coordinate transformation based design of confined metamaterial structures

The coordinate transformation method is applied to bounded domains to design metamaterial devices for steering spatially confined electromagnetic fields. Both waveguide and free-space beam applications are considered as these are analogous within the present approach. In particular, we describe devices that bend the propagation direction and squeeze confined electromagnetic fields. Two approaches in non-magnetic realization of these structures are examined. The first is based on using a reduced set of material parameters, and the second on finding non-magnetic transformation media. It is shown that transverse-magnetic fields can be bent or squeezed to an arbitrary extent and without reflection using only dielectric structures.Comment: The previous version has been revised and considerably expande

Tamm plasmon modes on semi-infinite metallodielectric superlattices

We analyze the fundamental properties of optical waves referred to as Tamm plasmon modes (TPMs) which are tied to the interface of a semi-infinite two-phase metallodielectric superlattice with an arbitrary homogeneous capping medium. Such modes offer new ways of achieving high electromagnetic field localization and spontaneous emission enhancement in the vicinity of the interface in conjunction with absorption loss management, which is crucial for future applications. The homointerface, formed when the capping medium has the same permittivity as one of the superlattice constituents, is found to support a TPM whose dispersion overlaps the single-interface surface plasmon polariton (SPP) dispersion but which has a cut off at the topological transition point. In contrast, a heterointerface formed for an arbitrary capping medium, is found to support multiple TPMs whose origin can be traced by considering the interaction between a single-interface SPP and the homointerface TPM burried under the top layer of the superlattice. By carrying out a systematic comparison between TPMs and single-interface SPPs, we find that the deviations are most pronounced in the vicinity of the transition frequency for superlattices in which dielectric layers are thicker than metallic ones.Publisher correction: A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper