THROUGHPUT INCREASE IN THE OFFICE LI-FI SYSTEM

Background. Wi-Fi has many disadvantages, such as how the maximum bandwidth is limited by the frequency of the range. The work uses Li-Fi technology, which uses visible light for data transmission. The frequency range of Li-Fi is 1000 times greater than the entire radio range. Feedback is used to increase the throughput. But the feedback decreases the bandwidth of the downstream signal. Objective. The purpose of the paper is to analyse what parameters are advisable to change to increase the throughput of the Li-Fi system. Methods. Study of the simulated dependence of the optimal interval change for using the feedback, and using this interval plot the dependence of the throughput on the change in the parameters of the Li-Fi system with a mobile user. Results. With an increase in the area of the photodiode and its refractive index, the throughput increases. As the receiver speed increases, the throughput decreases slightly <0.1%. Reducing the angle of the photodiode field of view and the half-angle of radiation significantly increases the throughput (by 50%) only when decreasing to small angles (<10 °). Conclusions. It is advisable to make photodiode from a material with a high refractive index, with a big area. Since mobile devices are often used in the office Li-Fi network, it is not advisable to reduce the receiver's viewing angle, as well as to reduce the half-angle of radiation. It may also be beneficial to give mobile users more download throughput than upload throughput.

The Design and Implementation of a High-Precision Positioner Fixture

In this paper, a novel positioner fixture with a high repeated positioning accuracy and a high stiffness is proposed and investigated. A high-precision end-toothed disc is used to achieve the high repeated positioning accuracy of the designed positioner fixture. The mathematical models of the cumulative error of the tooth pitch, the tooth alignment error and the error of the tooth profile half-angle of the end-toothed disc are analyzed. The allowable tolerance values of the cumulative error of the tooth pitch, the tooth alignment error and the error of the tooth profile half-angle of the end-toothed disc are given. According to the theoretical calculation results, a prototype positioner fixture is fabricated and its repeated positioning accuracy and stiffness are tested. The test results indicate that the stiffness of the proposed positioner fixture is 1050.5 N/μm, which is larger than the previous positioner fixtures of the same type. The repeated positioning accuracy of the proposed positioner fixture in the x, y and z directions are ± 0.48 μm, ± 0.45 μm and ± 0.49 μm, respectively, which is significantly higher than the previous positioner fixtures.

Aerodynamic Characteristics of Re-Entry Capsules with Hyperbolic Contours

For most re-entry capsules, the shape of the forebody of the capsule is designed based on the blunted nose cone. A similar shape can be created using a hyperboloid of revolution that can control the nose bluntness and the half angle of the cone easily. In this study, the hypersonic aerodynamic characteristics of re-entry capsules designed with hyperbolic contours were investigated using the CFD code, FaSTAR, developed by Japan Aerospace Exploration Agency (JAXA). The CFD results showed that, using the hyperbolic contours, the drag and lift coefficients can be increased compared to those for the Hayabusa re-entry capsule without changing the shape of the capsule drastically. This suggests that shape design based on the hyperbolic contours can improve the aerodynamic characteristics of re-entry capsules.

Evaluation of separation point in a divergent channel in the presence of non-uniform magnetic field

Due to the pressure gradient increasing downstream, the boundary layer separation phenomena may occur on the divergent channel flow wall. Still, several methods have been applied to control or postponed the separation. Exerting a magnetic field on the fluid flow is one solution. In the present research, we aim to investigate the impact of magnetic fields on the separation location in a divergent channel numerically. Hence, the finite volume method using the OpenFOAM CFD toolbox is employed, and a code for 2-D divergent channel flow under a non-uniform magnetic field is developed. The obtained results have been validated in comparison with previous studies. The results are presented for a test case of the channel with divergence half-angle equals 2.5°, 30 cm length, and 2 cm inlet height. It is demonstrated when Ha increases from 0 to 2, the separation points for liquid lithium fluid flow with Re = 208.33 are postponed from 12.93 cm to 23.18 cm. Moreover, it is shown that the separation phenomena disappear entirely for the Ha value of more than 3.

A New Approach for Design Optimization and Parametric Analysis of Symmetric Compound Parabolic Concentrator for Photovoltaic Applications

A compound parabolic concentrator (CPC) is a non-imaging device generally used in PV, thermal, or PV/thermal hybrid systems for the concentration of solar radiation on the target surface. This paper presents the geometric design, statistical modeling, parametric analysis, and geometric optimization of a two-dimensional low concentration symmetric compound parabolic concentrator for potential use in building-integrated and rooftop photovoltaic applications. The CPC was initially designed for a concentration ratio of “2×” and an acceptance half-angle of 30°. A MATLAB code was developed in house to provoke the CPC reflector’s profile. The height, aperture width, and concentration ratios were computed for different acceptance half-angles and receiver widths. The interdependence of optical concentration ratio and acceptance half-angle was demonstrated for a wide span of acceptance half-angles. The impact of the truncation ratio on the geometric parameters was investigated to identify the optimum truncation position. The profile of truncated CPC for different truncation positions was compared with full CPC. A detailed statistical analysis was performed to analyze the synergistic effects of independent design parameters on the responses using the response surface modeling approach. A set of optimized design parameters was obtained by establishing specified optimization criteria. A 50% truncated CPC with an acceptance half-angle of 21.58° and receiver width of 193.98 mm resulted in optimum geometric dimensions.

ANALYSIS ON THE EFFECT OF HALF ANGLE ON THE DISPLACEMENT OF PEDICLE SCREW DURING AXIAL PULL-OUT TEST IN CANCELLOUS BONE USING 2D AXISYMMETRIC FE MODEL

Pedicle screw fixations are commonly used in the treatment of spinal pathologies. For effective treatment, stable anchorage between the screw and bone is necessary. In this study, the influence of proximal and distal half angle of the screw, on the displacement of fixation and stress transfer are simulated using a 2D axisymmetric finite element model. A parametric study was performed by varying the proximal half-angle between 0° and 60° in steps of 10° and the distal half angles are considered as 30° and 40°. The material properties and boundary conditions are applied based on previous studies. Frictional contact is considered between the bone and screw. Results show that, displacement of fixation is observed to be minimum at a proximal half angle of 0° and maximum at an angle of 60°. High stress concentration is observed in first few threads with highest maximum von Mises stress at an angle of 60°. High stress transfer was obtained for proximal half-angles of 40° and 50°. It is observed that, this method might aid to develop better pedicle screws for treatment of Scoliosis.

Investigation of Regional Geomagnetic Field Modelling in Indonesia

<p>This thesis deals with the application of the Spherical Cap Harmonic Analysis (SCHA) modelling technique to obtain geomagnetic field models for Indonesia, which have better resolution and accuracy than the International Geomagnetic Reference Field (IGRF). B-splines basis function and autoregressive forecasting are applied to improve estimates of secular variation and its forecast over the Indonesian region. The modelling technique is applied to geomagnetic observation data compiled from 68 geomagnetic repeat stations in Indonesia covering the period 1985 - 2015 from BMKG (Badan Meteorologi Klimatologi dan Geofisika / Agency for Meteorology, Climatology, and Geophysics) Indonesia, definitive data from five BMKG geomagnetic observatories and 13 INTERMAGNET (The International Real-Time Magnetic Observatory Network) observatories. Synthetic cartesian X, Y, and Z components at sea level at 17 fixed locations, calculated from IGRF-13, are also used. The area covered by the models in this thesis is the Indonesian region with a spherical cap half-angle of 30° and with the coordinate of the spherical cap pole at 122°E and 3°S. From statistical analysis and comparison with the IGRF, the SCHA model with index k = 7 is considered as the best SCHA model, both in resolution and accuracy. Compared with the root mean square deviation (RMSD) of the IGRF model, the RMSD of the SCHA model with index k = 7 is lower by 28 nT, 11 nT, and 34 nT for X, Y, and Z components, respectively. A model from interpolation of the SCHA with index k = 7 using the B-splines basis function for the year 1985.5 – 2015.5 shows that the SCHA model gives better results than the IGRF. The forecasting calculation for the year 2015.5 – 2020.5 suggests that the autoregressive order 3 of the SCHA with index k = 7 gives better results than the forecasting of the IGRF model, especially in the X, Z, and F components. However, in the Y component, the IGRF is still better than the SCHA model. The RMSD of the forecasted SCHA model is 154.92 nT, 200.87 nT, 104.39 nT, and 135.81 nT for X, Y, Z, and F components, respectively, while the RMSD of the IGRF model is 172.62 nT, 95.52 nT, 117.55 nT, and 162.38 nT for X, Y, Z, and F components. Thus, the forecasted SCHA model is suitable for data reduction of geomagnetic surveys in the Indonesian region but not preferable for navigation.</p>

Investigation of Regional Geomagnetic Field Modelling in Indonesia

<p>This thesis deals with the application of the Spherical Cap Harmonic Analysis (SCHA) modelling technique to obtain geomagnetic field models for Indonesia, which have better resolution and accuracy than the International Geomagnetic Reference Field (IGRF). B-splines basis function and autoregressive forecasting are applied to improve estimates of secular variation and its forecast over the Indonesian region. The modelling technique is applied to geomagnetic observation data compiled from 68 geomagnetic repeat stations in Indonesia covering the period 1985 - 2015 from BMKG (Badan Meteorologi Klimatologi dan Geofisika / Agency for Meteorology, Climatology, and Geophysics) Indonesia, definitive data from five BMKG geomagnetic observatories and 13 INTERMAGNET (The International Real-Time Magnetic Observatory Network) observatories. Synthetic cartesian X, Y, and Z components at sea level at 17 fixed locations, calculated from IGRF-13, are also used. The area covered by the models in this thesis is the Indonesian region with a spherical cap half-angle of 30° and with the coordinate of the spherical cap pole at 122°E and 3°S. From statistical analysis and comparison with the IGRF, the SCHA model with index k = 7 is considered as the best SCHA model, both in resolution and accuracy. Compared with the root mean square deviation (RMSD) of the IGRF model, the RMSD of the SCHA model with index k = 7 is lower by 28 nT, 11 nT, and 34 nT for X, Y, and Z components, respectively. A model from interpolation of the SCHA with index k = 7 using the B-splines basis function for the year 1985.5 – 2015.5 shows that the SCHA model gives better results than the IGRF. The forecasting calculation for the year 2015.5 – 2020.5 suggests that the autoregressive order 3 of the SCHA with index k = 7 gives better results than the forecasting of the IGRF model, especially in the X, Z, and F components. However, in the Y component, the IGRF is still better than the SCHA model. The RMSD of the forecasted SCHA model is 154.92 nT, 200.87 nT, 104.39 nT, and 135.81 nT for X, Y, Z, and F components, respectively, while the RMSD of the IGRF model is 172.62 nT, 95.52 nT, 117.55 nT, and 162.38 nT for X, Y, Z, and F components. Thus, the forecasted SCHA model is suitable for data reduction of geomagnetic surveys in the Indonesian region but not preferable for navigation.</p>