Optimization of the Unambiguity of Cross-Correlated Ultrasonic Signals through Coded Excitation Sequences for Robust Time-of-Flight Measurements

The cross-correlation function (CCF) is an established technique to calculate time-of-flight for ultrasonic signals. However, the quality of the CCF depends on the shape of the input signals. In many use cases, the CCF can exhibit secondary maxima in the same order of magnitude as the main maximum, making its interpretation less robust against external disturbances. This paper describes an approach to optimize ultrasonic signals for time-of-flight measurements through coded excitation sequences. The main challenge for applying coded excitation sequences to ultrasonic signals is the influence of the piezoelectric transducer on the outgoing signal. Thus, a simulation model to describe the transfer function of an experimental setup was developed and validated with common code sequences such as pseudo noise sequences (PN), Barker codes and chirp signals. Based on this model an automated optimization of ultrasonic echoes was conducted with random generated sequences, resulting in a decrease in the secondary positive maximum of the CCF to 56.6%. Based on these results, further empiric optimization leveraging the nonlinear regime of the piezoelectric transducer resulted in an even lower secondary positive maximum of the CCF with a height of 25% of the first maximum. Experiments were conducted on different samples to show that the findings hold true for small variations in the experimental setup; however, further work is necessary to develop transfer functions and simulations able to include a wider parameter space, such as varying transducer types or part geometry.

The positive maximum principle on symmetric spaces

We investigate the Courrège theorem in the context of linear operators that satisfy the positive maximum principle on a space of continuous functions over a symmetric space. Applications are given to Feller–Markov processes. We also introduce Gangolli operators, which satisfy the positive maximum principle, and generalise the form associated with the generator of a Lévy process on a symmetric space. When the space is compact, we show that Gangolli operators are pseudo-differential operators having scalar symbols.

KORELASI RIBA,ZAKAT DAN SHODAQOH DALAM TEORI BATAS MUHAMMAD SYAHRUR

Thisarticlewants to expose the thinking of a controversial Syrian thinker,Prof.Ir. Muhammad Syahrur about the correlation of usury, zakah and shodaqoh. The correlation between these three things to explain one of the forms of boundary theory he found. According to Syahrur usury and zakat contained in the theory of the sixth limit is "the maximum limit (positive) should not be passed and the lower limit (negative) may be passed". This restriction applies to the transition of wealth between people. These two limits consist of the maximum limit that should not be violated, namely usury and the minimum limit of zakat that can be exceeded. This form exceeds the minimum limit of a variety of alms. These two boundaries are in two regions: positive and negative regions, and midpoints in neutral positions denoted by zero. In practice, the positive maximum limit of usury, the neutral limit of interest-free loans and the minimum limit of negatives in the form of zakat and alms. According to Syahrur usury is divided into two forms that are related to borrowing and borrowing and borrowing. Syahrur argues that usury is the same as bank interest and he justifies bank interest as the modern banking mechanism that has been run for this.After describing Syahrur's thoughts, this paper provides some notes on the important points that need to be discussed further. Keywords:usury,zakah,shodaqoh<br /><br />

Thermoelectric Power of Gd4(Co-A)3 Compounds (A = Cu, Pt)

We report on a comparative study of thermoelectric power measurements (S(T)) in ferrimagnetic Gd4(Co1-xAx)3 compounds with A = Cu, Pt, in the temperature range 8 K – 300 K. Whereas in Gd4Co3S(T) is always negative, for x > 0 the substitution of Co for Cu/Pt gives rise to the appearance of a low temperature positive maximum in S(T) at around 30 K. Based on our previous study of Gd4(Co1-xCux)3 compounds, we argue that this maximum in S(T) originates from electron-magnon scattering and is sensitive to electron band structure changes resulting from the substitution of Co for Cu/Pt and the accompanying reduction in the ratio between the electron-magnon and the electron-phonon scattering strengths. The decreasing role of Co 3d electrons with the progressive substitution of Co for Cu/Pt, evidenced by a strong reduction in the spin disorder resistivity and the Co magnetic moment, is seen to be crucial for the existence of such low temperature maximum in S(T) for x > 0. It is seen that the substitution of Co for Pt leads to higher values of the amplitude and temperature of the positive maximum in S(T) than the substitution of Co for Cu.

Dynamic Loads Due to Blowdown Through a Sparger

An experiment has been performed using a facility, which simulates the safety depressurization system (SDS) and in-containment refueling water storage tank (IRWST) of APR1400, an advanced PWR being developed in Korea, to investigate the dynamic load resulting from the blowdown of steam from a steam generator through a sparger. The influence of the key parameters, such as air mass, steam pressure, submergence, valve opening time, and pool temperature, on frequency and peak loads was investigated. The blowdown phenomenon was analyzed to find out the real cause of the initiation of bubble oscillation and discrepancy in frequencies between the experiment and calculation by conventional equation for bubble oscillation. The cause of significant damping was discussed and is presumed to be the highly tortuous flow path around bubble. The Rayleigh-Plesset equation modified by the introduction of method of image reasonably reproduce the bubble oscillation in a confined tank. Right after the completion of air discharge the steam discharge immediately follows and it condenses abruptly to provide low-pressure pocket. It may contribute to the negative maximum being greater than positive maximum. The subsequently discharging steam does not play as the driving force anymore. The effect of various parameters on the peak pressure and frequency was analyzed. The air mass, valve opening time, and submergence give significant effect on both of frequency and peak pressure while steam mass flux gives questionable effect and pool temperature gives almost none.

Coexistence of Periodic Roll Motion and Chaotic One in a Forced Flooded Ship

This letter describes the coexistence of periodic and chaotic roll motion of a flooded ship in waves. We found experimentally, both with a flooded ferry model and with a simplified box-shaped model, that the two types of roll motion can coexist under the same wave condition. A trajectory reconstructed in a delay-coordinate state space from the time series data of the measured roll angle looks like a low-dimensional strange attractor. Moreover, a mathematical model for the simplified box-shaped ship shows the coexistence of a periodic solution and a chaotic one with a positive maximum Liapunov exponent.