On the Performance of Energy Criterion Method in Wi-Fi Transient Signal Detection

In the development of radiofrequency fingerprinting (RFF), one of the major challenges is to extract subtle and robust features from transmitted signals of wireless devices to be used in accurate identification of possible threats to the wireless network. To overcome this challenge, the use of the transient region of the transmitted signals could be one of the best options. For an efficient transient-based RFF, it is also necessary to accurately and precisely estimate the transient region of the signal. Here, the most important difficulty can be attributed to the detection of the transient starting point. Thus, several methods have been developed to detect transient start in the literature. Among them, the energy criterion method based on the instantaneous amplitude characteristics (EC-a) was shown to be superior in a recent study. The study reported the performance of the EC-a method for a set of Wi-Fi signals captured from a particular Wi-Fi device brand. However, since the transient pattern varies according to the type of wireless device, the device diversity needs to be increased to achieve more reliable results. Therefore, this study is aimed at assessing the efficiency of the EC-a method across a large set of Wi-Fi signals captured from various Wi-Fi devices for the first time. To this end, Wi-Fi signals are first captured from smartphones of five brands, for a wide range of signal-to-noise ratio (SNR) values defined as low (−3 to 5 dB), medium (5 to 15 dB), and high (15 to 30 dB). Then, the performance of the EC-a method and well-known methods was comparatively assessed, and the efficiency of the EC-a method was verified in terms of detection accuracy.

Microstructure and Microhardness of Powder Boronized Vanadis 6 Steel

A Cr-V ledeburitic steel Vanadis 6 was powder boronized for different durations, austenitized, quenched and tempered. All the boronized layers are two-phased, i.e. they are formed by MeB and Me2B compounds. The thickness of boronized compound layers increased moderately with boronizing time. The thickness of MeB individual layer increases more rapidly, and it makes up to 50% of total layer thickness when boronized for 150 min. Boronized layers contain enhanced amount of chromium but they are almost free of other alloying elements. The MeB compound has a microhardness of around 1860 HV 0.1 after short – time boronizing but its microhardness exceeded 2100 HV 0.1 after long – time processing. The microhardness of Me2B was correspondingly lower, its values were around 1760 – 1850 HV 0.1. Transient region manifested enhanced amount of carbides, resulting from carbon transport from growing boronized layers towards the substrate. This phenomenon was reflected in elevated hardness compared to the substrate.

Friction Force Analysis on Diaomond Lapping of Sapphire Wafers

This paper is to design and developing a friction sensor system (FSS) for prediction of endpoint detection (EPD) on diamond lapping of sapphire or mono-crystalline aluminum oxide wafers. The endpoint detection usually includes start region, lapping region, transient region and endpoint region to control the planarization procedure by diamond lapping with variant plate of copper, resin copper, or tin materials. Experiments have been performed with 9 tests composed by three kinds of viscosity of slurry lapping with three kinds of lap plates. The coefficient of friction (CoF) has been obtained by the designed FSS and then compared with different test parameters. The as-lapped sapphire wafers have also measured by coherence surface interferometer, CCI-Lite (Taylor Hobson, UK). Experimental results show that the hardness of plate and viscosity of slurry are critical factors for as-lapped wafer quality. The EPD of diamond lapping with resin copper plate can be determined by the CoF data and that can be used for justifying the appropriate lapping time of sapphire wafers. Future study can focus on the relationship of sub-surface crack caused by the diamond lapping process.

Creep Life Prediction of Gr.91 Using Creep Parameters in Transient Region

The creep deformation behavior and its effect on creep life have been investigated for Gr.91 by analyzing creep strain data in the NIMS Creep Data Sheet. The creep life tr is mainly determined by the minimum creep rate ε̇min, indicating tr ∝ (ε̇min)−1. The ε̇min is mainly determined by the time to minimum creep rate tm, indicating ε̇min ∝ (tm)−1. Then the creep life is correlated with the tm as tr=3.7tm, where the constant 3.7 is as an average value for a wide range of temperature (450–725 °C), stress (40–450 MPa) and test duration (11–68,755 h). Using this equation, we can predict the creep life by carrying out a short-term creep test for up to the end of transient region, corresponding to about 30% of creep life. The (tm/tr), the ratio of duration of transient region to the creep life, slightly decreases with decreasing stress and is evaluated to be 0.22 at 100 MPa and above 550 °C, which gives us tr= 4.5 tm at 100 MPa. Taking the stress dependence of the (tm/tr) into account, the accuracy of creep life prediction is further improved.

Role of the Rossby Waves in the Broadening of an Eastward Jet

To investigate the effect of the Rossby waves on an eastward jet such as the Kuroshio or Gulf Stream Extensions, a series of numerical experiments is conducted using a primitive equation model. In these experiments, an inflow and an outflow imposed on the western and eastern boundaries drive an unstable narrow jet and a broad interior flow in the western and eastern regions of the model domain, respectively. The barotropic Rossby waves are radiated from the transient region between the two regions. The eddy potential vorticity flux by the waves tends to compensate for the difference in the mean potential vorticity along mean streamlines between both sides of the transient region. Instability of the jet is insufficient for this compensation and weakens the mean potential vorticity gradient too much. Moreover, as the potential vorticity of the outflow is increased, the Rossby waves are intensified in order to compensate for the increase in the difference in the mean potential vorticity. These features strongly suggest that the Rossby waves are substantial in matching a jet with an interior flow. The speed of the waves and properties of eddies in recirculations of the jet are consistent with a two-layer analytic model, which indicates that the Rossby waves are radiated from eddies in recirculations. These eddies as well as the Rossby waves increase in amplitude with the transport of the recirculation near the surface presumably because of mean advection. Therefore, the mean potential vorticity of the interior flow, the intensity of the Rossby waves, and the transport of the recirculation change consistently with one another.