Papers by Keyword: Mobility

Abstract: Several well-known Unmanned Aerial Vehicle (UAV) mobility models that make use of cellular networks will be compared in this study. The acquisition of services for ground-based User Equipment (UE) from Drone Base Stations (DBSs) is the primary focus of the examination. The four distinguishable mobility models— Random Waypoint (RWP), Straight Line (SL), Random Stop (RS), and Random Walk (RW)—are analysed and compared in this work. The UDM and UIM are two service models that are researched in this study. The primary contribution of this work is the development of a thorough method for investigating the point process of DBSs across different mobility and service models. The study compares the basic SL mobility model to more complex models that incorporate curved trajectories and finds performance disparities between the two. It also looks at the average session and received pricing of standard user equipment (UEs). The results of this study shed light on how well drone mobility models perform in cellular network settings, which can help with the development and refinement of drone-optimized cellular networks.

Abstract: To understand the kinetics of changes in the majority current carriers Hall mobility temperature-dependency (in the temperature range of 77–300 K) in n- and p-type silicon crystals irradiated with high doses of high-energy particles during isochronous annealing, there are investigated P-doped n-Si samples irradiated with 25 MeV protons with dose of 8.1·10¹² cm^–2 at flux density of 1.5∙10¹¹ cm^–2·s^–1 and B-doped p-Si samples irradiated with 8 MeV electrons with dose of 1.0·10¹⁵ cm^–2 at flux density of 5.0·10¹² cm^–2·s^–1 at room temperature. Their isochronous annealing is performed in the temperature range of 80–500°C. The oscillatory character of the change in the majority current carriers Hall mobility in process of isochronous annealing of irradiated silicon samples is explained by the formation of disordered regions and the changes in degree of screening of their electric field potential barriers depending on charge states of nonequilibrium vacancies induced by irradiation.

Abstract: Gated Hall measurements are conducted to calculate interface trap density of a nitric oxide (NO) annealed 4H silicon carbide (4H-SiC) MOSFET. The free carriers are measured using split CV method. Application of body bias confirms that the total trap quantity does not change at the interface when changing the electric field through body bias for a given device. The effect of positive gate stress on Hall mobility is also studied. A stress voltage of +36 V is applied for different stress times (0, 10, 30, 100, and 300 sec). With the increased stress time, the Hall mobility value drops at low gate voltages, while at higher gate voltages they merge. Higher stress creates more interface traps that in turn increase Coulomb scattering which lowers mobility at low gate voltages. The effect of gate stress on Hall mobility provides accurate insight of the channel behavior due to interface traps at 4H-SiC / SiO₂ interface.

Abstract: We present the improvement of SiO₂/4H-SiC interface quality and high field-effect (FE) mobility (µ_FE) in 4H-SiC MOSFETs. This is achieved by introducing a nitrous oxide (N₂O) plasma in-situ pre-treatment before gate stack formation using plasma enhanced chemical vapour deposition (PECVD) oxide followed by a post deposition anneal (PDA) in diluted N₂O for times ranging from 30 to 120 minutes thereby creating an ultra-thin thermally grown SiO₂ layer at the SiO₂/4H-SiC interface. MOS capacitors with SiO₂ deposited on in-situ pre-treated SiC surfaces had a lower density of interface traps (D_IT) for all PDA durations, compared with devices having untreated PECVD oxides or control devices with 30 nm thermally grown oxide. After PDA for 90 minutes, a minimum D_IT value of 1.2×10¹¹ cm^-2·eV^-1 was measured. A peak µ_FE value reaching 94 cm²/(V·s) was measured in n-channel planar MOSFETs fabricated with PECVD oxide on in-situ pre-treated devices, which significantly exceeds a maximum µ_FE of 6 cm²/(V·s) in control devices.

Abstract: Bulk mobility and dopant activation of implanted species into 4H-SiC plays a crucial role in the carrier conduction, blocking behavior, and channel properties of a 4H-SiC vertical power MOSFET. Nitrogen and phosphorus ion implantation became the norm as n-type dopants for 4H-SiC. Therefore, the doping and temperature behavior of both species in 4H-SiC needs to be well characterized. In this study, we report a comparison in electrical characteristics between nitrogen and phosphorus implanted 4H-SiC as a function of temperature for various doping levels. For this purpose, 4-point van der Pauw samples are prepared, resistivity and Hall measurements are conducted. We found that resistivities drop as temperature increases from 140 K with phosphorus having higher resistivities at all implanted doping concentrations. The carrier concentrations increase with increase of temperature, indicating incomplete ionization of dopants. Mobilities drop at low temperature due to increased impurity scattering, reaches a peak near 300 K and drops at higher temperature due to increased phonon scattering. From the obtained data, using a two-level charge neutrality equation, the activation percentage and ionization energies of dopants in hexagonal and cubic sites for both species are extracted and compared.

Abstract: When an astronaut transitions out of the weightless environment of space (e.g., landing on Earth, Mars, or the Moon), they can experience balance and co-ordination issues due to sensorimotor dysfunction. This paper details the development of the base layer garment for a Sensorimotor Countermeasure Skinsuit (SMCS), and test ideas to improve comfort and mobility through considered patternmaking techniques. A Version 1 (V1) SMCS base layer was made-to-measure for one participant. The garment was assessed for comfort and mobility through a series of tests: sit and reach (S&R), active range-of-motion (ROM) joint angles, and timed up and go (TU&G), etc. The SMCS V1 caused a restriction to mobility, and scored high discomfort ratings, when compared to a baseline of loose gym clothing. A Version 2 (V2) SMCS base layer was developed with an objective of improving upon the discomfort and mobility ratings. The SMCS V2 base layer garment was assessed and was found to have improved discomfort ratings (= ‘Minor discomfort if worn all day’) when compared to the SMCS V1 (≥ ‘Too uncomfortable to wear all day’). The SMCS V2 base layer garment was found to have improved mobility during S&R tests and TU&G tests when compared to the results from SMCS V1. The SMCS V2 base layer garment was also found to have improved active ROM during shoulder extension, shoulder abduction, hip flexion, and knee flexion, when compared to the SMCS V1. However, active ROM decreased during hip-extension and hip-abduction.The results of this study can be used to advance the design of compression garments that are used within the sports and medical industries.

Abstract: High-quality, low resistivity n-type (nitrogen-doped) single crystal 4H-SiC wafers are needed to grow high-quality epitaxial SiC layers used for the active blocking layers of high-voltage power devices. The resistance of the substrate constitutes a portion of the device resistance for vertical devices, and therefore the SiC substrate properties must be fully characterized. In this study we report the 4H-SiC substrate electrical properties as a function of temperature measured using van der Pauw structures to measure resistivity from 4-point measurements, and carrier concentration and mobility from Hall effect measurements. We find that the SiC substrate resistivity has a minimum around 425K for typical substrate doping levels, due to a competition between the decreasing mobility and increasing carrier concentration with increasing temperature. The measured energy levels of the N donor (hexagonal / cubic sites) are extracted for a 5.8×10¹⁸ cm^-3 N-doped substrate, and found to be 15 meV and 105 meV, respectively.

Abstract: The paper is devoted to research of influence of “MC-Bauchemie” additions on the fine-grained concrete properties, namely compressive strength. The results of testing of fine-grained concrete made on the basis of two different natural sands are presented. Characteristics of the initial materials used in the work (Portland cement, sands and additions-plasticizers) are given. The basic methods of preparation of mixes and testing of hardened cement stone and concrete are described. The optimal quantity of the selected additions on the example of cement paste and stone are established. Mobility dependences of concrete mixes on a type and quantity of plasticizers are received. The dependence of the additions effectiveness on the mobility of the concrete mix on the quality of the fine aggregate is shown. It is established that the most effective additive is PowerFlow 3100, its optimal amount for obtaining fine-grained concrete on the basis of JSC “Kar’er Myisyi” sand is 0.2 %.

Abstract: In this work, the impact of channel implantations (IMP) on the electrical characteristics of SiC n-and p-MOSFETs and analog SiC-CMOS operational amplifiers (OpAmp) is investigated. For this purpose, MOSFETs and Miller OpAmps with and without IMP were fabricated and electrically characterized from room temperature up to 350°C. For devices with IMP the absolute values of the threshold voltages of n-and p-MOSFETs were reduced by 1.5 V and the mobility of the n-MOSFET was increased from 13 to 23 cm2/Vs whereas the mobility of the p-MOSFET remained constant at 6 cm2/Vs. For the resulting OpAmp with IMP, the common-mode input voltage range as well as the open loop gain was increased by 1.5 V and 4 dB compared to non-implanted devices. This improvement was observed across the entire analyzed temperature range from room temperature up to 350°C.

Abstract: This paper is devoted to research of directional regulation possibility of the properties of a composite based on the Portland cement by using limestone waste. It is shown that the introduction of limestone waste contributes to changing the nature of crystallization and structure formation of cement stone. With the introduction of limestone waste, in the amount of 15 % by weight of cement, it is possible to obtain the compositions of the class not less than B25-B35.