Robustness and static-positional accuracy of the SteamVR 1.0 virtual reality tracking system

The use of low-cost immersive virtual reality systems is rapidly expanding. Several studies started to analyse the accuracy of virtual reality tracking systems, but they did not consider in depth the effects of external interferences in the working area. In line with that, this study aimed at exploring the static-positional accuracy and the robustness to occlusions inside the capture volume of the SteamVR (1.0) tracking system. To do so, we ran 3 different tests in which we acquired the position of HTC Vive PRO Trackers (2018 version) on specific points of a grid drawn on the floor, in regular tracking conditions and with partial and total occlusions. The tracking system showed a high inter- and intra-rater reliability and detected a tilted surface with respect to the floor plane. Every acquisition was characterised by an initial random offset. We estimated an average accuracy of 0.5 ± 0.2 cm across the entire grid (XY-plane), noticing that the central points were more accurate (0.4 ± 0.1 cm) than the outer ones (0.6 ± 0.1 cm). For the Z-axis, the measurements showed greater variability and the accuracy was equal to 1.7 ± 1.2 cm. Occlusion response was tested using nonparametric Bland–Altman statistics, which highlighted the robustness of the tracking system. In conclusion, our results promote the SteamVR system for static measures in the clinical field. The computed error can be considered clinically irrelevant for exercises aimed at the rehabilitation of functional movements, whose several motor outcomes are generally measured on the scale of metres.

Drop race: How electrostatic forces influence drop motion

Water drops sliding down inclined planes are an everyday phenomenon and are important in many technical applications. Previous understanding is that the motion is mainly dictated by viscous and capillary forces. Here we demonstrate that, in addition to these forces, drops on hydrophobic surfaces are affected by self-generated electrostatic forces. In a novel approach to determine forces on moving drops we imaged their trajectory when sliding down a tilted surface and apply the equation of motion. We found that drop motion on low-permittivity substrates is significantly influenced by electrostatic forces. Sliding drops deposit a negative charge on the surface, which interact with the positively charged drops. We derive an analytical model to describe the force and validate it by numerical computations. The results indicate how to describe and facilitate drop motion in applications, such as in microfluidics, water management on car surfaces, and the creation of sliding drop electrical generators.

Research and development of a PV converter-based stand-alone power supply system for technical security equipment power supply

The purpose of the work is to develop a methodology for designing a stand-alone power supply system based on photovoltaic (PV) converters for technical security equipment power supply. The object of the study is a PV converter - based stand-alone power supply system. Energy storage units, which are widely used in the designing of power supply systems for power supply of technical security equipment are presented. A methodology for designing a power supply system is used, which takes into account the integral effect of solar insolation, ambient temperature in the range from - 40°C to +50°C, temperature of a PV module and a storage battery; PV module capacity; requirements for independent operation of technical security equipment; electrical characteristics of the solar charge controller (rated open-circuit voltage and rated charge current). To calculate the total solar insolation arriving at the surface of a photovoltaic module, the Kastrov model is used for calculating direct solar radiation; the Berlage model is used for calculating the scattered solar energy and the Berland model is used for calculating insolation in cloudy conditions. The studies of lithium-titanate storage batteries have been carried out in the climate chamber and a corresponding mathematical model has been developed for the temperature-dependent capacity of the battery. To determine solar insolation falling on the tilted surface of the PV module the software has been developed in the C# programming language. The designed PV module-based power supply system provides an independent uninterrupted continuous power supply of equipment under constant consumption of no more than 115.2 Wh per day by technical security equipment. The results of the work can be used in the development of a stand-alone power supply system for power supply of technical security equipment, security and control.

Modeling and Optimization of Evacuated Tubular Solar Thermal Collector

Modeling and optimization of evacuated tubular solar thermal collector (ETSTC) is discussed using a modified simple additive weighting (M-SAW) method. To improve the system efficiency (η) and end day temperature (Tsfd), ETSTC parameter (i.e., start day temperature [Tsid], ambient temperature [Tad], global solar radiation on tilted surface [GT], and wind speed [Ws]) are optimized. The applied method is significantly improved the efficiency (η) and determined the best setting for ETSCT. Test no.10 is the optimal experimental trail run and corresponding collector efficiency is obtained as 43%. Further, experimental data are statistically tested via parametric, ANOVA analysis, and found satisfactory and acceptable. Last, confirmatory tests results show comparable and acceptable w.r.t. experimental results for the optimal setting obtained through proposed method. The proposed MCDM method can be recognized as potential use for modeling and optimization of other thermal systems.

Femtosecond Laser-Induced Periodic Surface Structures on Different Tilted Metal Surfaces

Laser-induced periodic surface structures (LIPSS) are used for the precision surface treatment of 3D components. However, with LIPSS, the non-normal incident angle between the irradiated laser beam and the specimen surface occurs. This study investigated LIPSS on four different metals (SUS 304, Ti, Al, and Cu), processed on a tilted surface by an s-polarized femtosecond fiber laser. A rotated low spatial frequency LIPSS (LSFL) was obtained on SUS 304 and Ti materials by the line scanning process. However, LSFL on Cu and Al materials was still perpendicular to the laser polarization. The reason for the rotated and un-rotated LSFL on tilted metal surfaces was presented. The electron-phonon coupling factor and thermal conductivity properties might induce rotational LSFL on tilted SUS 304 and Ti surfaces. When fabricating LSFL on an inclined plane, a calibration model between the LSFL orientation and inclined plane angle must be established. Hence, the laser polarization direction must be controlled to obtain suitable LSFL characteristics on a 3D surface.

Estimation of Solar Radiation on Tilted Surface by Using Regression Analysis at Different Locations in India

This study is to find the regression model for estimation of monthly mean hourly global solar radiation on tilted surface at different locations of India. This study is quite precious due to lack of solar radiation data availability on the tilted surface. Firstly, we have selected some locations having different climatic conditions such as New Delhi, Mumbai, Kolkata, Lucknow and Jaipur to find the solar radiation on tilted surface using Liu and Jordan model, HDKR model and Perez model. The mean values of these models are plotted along with the daytime. Based on regression techniques, four empirical models are developed which are tested to compute the solar radiation on tilted surface for three new stations Ahmadabad, Bangalore and Chennai. The estimated solar radiation by these four developed models are compared with the estimated values using existing models Lie & Jordan, HDKR and Perez based on mean bias error (MBE) and root mean square error (RMSE). It has been found that developed Model-3 has minimum error and the values estimated this model is comparable to existing models. The maximum values of RMSE in Model-3 in tested stations are 2.01% with Liu and Jordan, 2.63% with HDKR and 2.10% with Perez. Similarly, maximum values of MBE are −1.79% with Liu and Jordan, −2.27% with HDKR and −1.89% with Perez. Now the Model-3 finally selected to determine the solar radiation on Bhopal, Bhubneshwar, Dehradun, Guwahati and Trivendrum (Thiruvananthapuram).