Theoretical Time Evolution of Numerical Errors When Using Floating Point Numbers in Shallow-Water Models

We carried out a theoretical investigation of the impact of the numerical errors caused by using floating point numbers (FPNs) in simulations, such as rounding errors. Under the presupposition that model variables can be written as the linear sum of the true value and the numerical error, equations governing the time evolution of numerical errors due to FPNs (FPN errors) are obtained by considering the total errors of the results of simulations of shallow-water models and estimating the errors incurred by using FPNs with varying precision. We can use the time evolution equations to estimate the behavior of the FPN errors, then confirm these estimations by carrying out numerical simulations. In a geostrophic wind balance state, the FPN error oscillates and gradually increases in proportion to the square root of the number of time steps, like a random walk. We found that the error introduced by using FPNs can be considered as stochastic forcing. In a state of barotropic instability, the FPN error initially evolves as stochastic forcing, as in the case of the geostrophic wind balance state. However, it then begins to increase exponentially, like a barotropic instability wave. These numerical results are obtained by using a staggered-grid arrangement and stable time-integration method to retain near-neutral numerical stability in the simulations. The FPN error tends to behave as theoretically predicted if the numerical stability is close to neutral

Adaptive hierarchical modulation and power allocation for superposition-coded relaying

We propose a relaying scheme based on superposition coding (SC) with discrete adaptive modulation and coding (AMC) for a three-node wireless relay system, based on half duplex transmission, where each node decodes messages by successive interference cancelation (SIC). Unlike the previous works where the transmission rate of each link is assumed to achieve Gaussian channel capacity, we design a practical superposition-coded relaying scheme with discrete AMC while taking into account the effect of decoding errors at each stage of the SIC process at each node. In our scheme, hierarchical modulation (HM) is used to create an SC message composed of one basic and one superposed message with optimized power allocation. We firstly introduce the proposed scheme without forward error correction (FEC) for high signal-to-noise ratio (SNR) region and provide the optimal power allocation between the superimposed messages. Next, we extend the uncoded scheme to incorporate FEC to overcome bad channel conditions. The power allocation in this case is based on an approximated expression of the bit error rate (BER). Numerical results show the performance gains of the proposed SC relaying scheme with HM compared to conventional schemes, over a large range of SNRs

An analytical investigation of body parts more susceptible to aging and composition changes using statistical hypothesis testing

In recent years, age-related changes in body composition in the elderly are attracting attention. This is associated with a decline in physical functions and an increased risk of disease development. In general, age-related changes in body composition can be minimized with appropriate exercise. However, there are no studies that investigate body parts susceptibility to aging and changes in body composition of those parts. Therefore, devising exercise programs and advising daily life while taking these into account becomes difficult. This study aims to identify body parts that are more susceptible to aging and their body composition changes. The body composition was obtained with a Direct Segmental Multi-frequency Bioelectrical Impedance Analysis using InBody770 in 8 male elderly patients who had been shortly hospitalized. Statistical hypothesis testing was used to determine whether site-specific body composition changed significantly between hospital discharge and 1 year, 1 year and 2 years, and hospital discharge and 2 years. The results showed that Lean body mass, Total Body Water, Intracellular Water, Extracellular Water in the right arm; Lean body mass and Total Body Water in the left arm and trunk are more sensitive to aging

Filament discharge enhances field emission properties by making twisted carbon nanofibres stand up

Twisted carbon nanofibers, named carbon nanotwists (CNTws), in a flocculated form were pasted, printed on the conductive silicon substrate, and then treated by dielectric barrier discharge using He and N2 gases. Vertically upright nanofibers were clearly obtained by "filament discharge mode" in N2 gas. As the treating time increased up to ~60 s, the height of the nanofiber tips became uniform. Consequently, the field emission property was greatly enhanced and showed a threshold electric field of 4.6 V/μm and maximum current of 0.433 mA/cm2 at 8 V/μm