Results 1 - 10 of 5819
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[en] The linearly polarized gravitational waveforms from a certain type of rotating, evaporating cosmic string-the Allen-Casper-Ottewill loop-are constructed and plotted over the lifetime of the loop. The formulae for the waveforms are simple and exact, and describe waves which attenuate self-similarly, with the amplitude and period of the waves falling off linearly with time.
[en] We investigate extremal statistical properties such as the maximal and the minimal heights of randomly generated binary trees. By analyzing the master evolution equations we show that the cumulative distribution of extremal heights approaches a traveling wave form. The wave front in the minimal case is governed by the small-extremal-height tail of the distribution, and conversely, the front in the maximal case is governed by the large-extremal-height tail of the distribution. We determine several statistical characteristics of the extremal height distribution analytically. In particular, the expected minimal and maximal heights grow logarithmically with the tree size, N, hmin∼vmin ln N, and hmax∼vmax ln N, with vmin=0.373365(hor ellipsis) and vmax=4.31107(hor ellipsis), respectively. Corrections to this asymptotic behavior are of order O(ln ln N)
[en] This paper proposes an indexing method of plasma waveforms for accelerating search and retrieval of their subsequences. The proposed method divides a waveform into fine-grained segments. The similar segments are grouped into a segment group. A multi-dimensional index is used for quick retrieval. Grouping segments could save the amount of the index. In the retrieval, a sequence of segments, which is called a section, is used as a unit in matching subsequences. Overlapping sections could overcome the shift errors of subsequences, and results in good retrieval correctness.
[en] Characteristics of tokamak current quenches are an important issue for the determination of electro-magnetic forces that act on the in-vessel components and vacuum vessel during major disruptions. The characteristics of current quenches in spontaneous disruptions in the J-TEXT tokamak have been investigated. It is shown that the waveforms for the fastest current quenches are more accurately fitted by linear current decays than exponential, although neither is a good fit in many slower cases. The minimum current quench time is about 2.4 ms for the J-TEXT tokamak. The maximum instantaneous current quench rate is more than seven times the average current quench rate in J-TEXT. (paper)
[en] The optimal driving waveform among a wide class of admissible functions for an overdamped, adiabatic rocking ratchet is shown to be dichotomous. 'Optimum' is defined as that which achieves the maximum (or minimum negative) average particle velocity. Implications for the design of ratchets, for example in nanotechnological transport, may follow. The main result is applicable to a general class of adiabatic responses. Much scope exists for further studies of ratchet waveform optimization in other regimes
[en] A classical way for the frequency domain identification of systems is applying a sine wave excitation with certain frequency to the input and measuring the output response to excitation using phase sensitive instruments based mostly on Fourier transform. Such a parameter as time is out of scope in this case. Mathematically saying, Fourier transform expects the time interval from minus to plus infinity. In practice, it means that we have to wait until the transient process will be fully over in the system after applying the excitation. Therefore, covering a wide frequency range takes a long time when using frequency stepping or a slow enough sweeping over the whole frequency range. To perform faster measurements, sine wave based chirp pulses with certain duration are proposed for excitation. In this case the sine wave does not has only one certain frequency any more, but its instantaneous angle frequency changes over the required frequency range during the pulse. When the frequency changing (acceleration) is constant, then we have a linear chirp. Linear chirp can cover several decades of frequency with a constant spectral density within the excitation bandwidth. But for shaping of the excitation spectrum, more complicated chirps are introduced. Chirp excitation can contain thousands of cycles, but can be even as short as one quarter of a single cycle. Therefore, we can say that the chirp excitation is scalable in time - we can choose the time interval independently on the frequency bandwidth. On the other hand, we can choose the frequency bandwidth independently on the excitation time. Such the freedom - double scalability in time and frequency - is especially important when time variant dynamic systems (electronic circuits with controllable parameters, beating heart, breathing lungs, working mechanism, ongoing electrochemical reaction) has to be identified. Every special case has its own optimal excitation waveform, which enables to derive the maximum amount of information about the time variant system under study.
[en] This extends a previous study (2012 J. Phys. A: Math. Theor. 45 302001) of two initial waveforms whose far-field radiation patterns possess sidelobes separated by the Riemann zeros. The analysis suffered from the disadvantage that the sidelobes were very weak, making it difficult to detect the zeros between them. To overcome this, new Fourier pairs are derived, whose sidelobes are not weak. These are transforms of the zeta function on the critical line, modulated by functions with no zeros on the line. (paper)