Effects of the Predominant Pulse on the Inelastic Displacement Ratios of Pulse-Like Ground Motions Based on Wavelet Analysis

Having a predominant pulse is the main feature for pulse-like ground motions differing from others. To investigate the influence of the predominant pulse on the inelastic displacement ratios of pulse-like ground motions, the wavelet analysis method is used to extract the predominant pulse. The results indicate that the inelastic displacement ratios of the pulse-removed parts obtained by subtracting the extracted pulse from the original pulse-like ground motions are close to the results of non-pulse-like ground motions. The ratio of the energy of the extracted pulse to the energy of the original ground motion is used to represent the pulse intensity. The results indicate that the pulse period determines the locations in which the inelastic displacement ratios would have noticeable increments, and the pulse intensity determines the degree of the increments. Besides, the effects of five commonly used parameters (PGV, PGD, PGV/PGA, Arias intensity Ia, and soil condition) on the inelastic displacement ratios of pulse-like ground motions and their relations to the pulse period and the pulse intensity are studied. Finally, a new model, in which the influence of pulse intensity is considered, to predict the inelastic displacement ratios of pulse-like ground motions is proposed.

Constant Resting Frequency and Auditory Midbrain Neuronal Frequency Analysis of Hipposideros pratti in Background White Noise

Acoustic communication signals are inevitably challenged by ambient noise. In response to noise, many animals adjust their calls to maintain signal detectability. However, the mechanisms by which the auditory system adapts to the adjusted pulses are unclear. Our previous study revealed that the echolocating bat, Hipposideros pratti, increased its pulse intensity in the presence of background white noise. In vivo single-neuron recording demonstrated that the auditory midbrain neurons tuned to the second harmonic (H2 neurons) increased their minimal threshold (MT) to a similar degree as the increment of pulse intensity in the presence of the background noise. Furthermore, the H2 neurons exhibited consistent spike rates at their best amplitudes and sharper intensity tuning with background white noise compared with silent conditions. The previous data indicated that sound intensity analysis by auditory midbrain neurons was adapted to the increased pulse intensity in the same noise condition. This study further examined the echolocation pulse frequency and frequency analysis of auditory midbrain neurons with noise conditions. The data revealed that H. pratti did not shift the resting frequency in the presence of background noise. The auditory midbrain neuronal frequency analysis highly linked to processing the resting frequency with the presence of noise by presenting the constant best frequency (BF), frequency sensitivity, and frequency selectivity. Thus, our results suggested that auditory midbrain neuronal responses in background white noise are adapted to process echolocation pulses in the noise conditions.

Improving laser standards for three-photon microscopy

SignificanceThree-photon excitation microscopy has double-to-triple the penetration depth in biological tissue over two-photon imaging and thus has the potential to revolutionize the visualization of biological processes in vivo. However, unlike the ‘plug-and-play’ operation and performance of lasers used in two-photon imaging, three-photon microscopy presents new technological challenges that require a closer look at the fidelity of laser pulses.AimWe implemented state-of-the-art pulse measurements and developed new techniques for examining the performance of lasers used in three-photon microscopy. We then demonstrated how these techniques can be used to provide precise measurements of pulse shape, pulse energy and pulse-to-pulse intensity variability, all of which ultimately impact imaging.ApproachWe built inexpensive tools, e.g., a second harmonic generation frequency resolved optical gating (SHG-FROG) device, and a deep-memory diode imaging (DMDI) apparatus, to examine laser pulse fidelity.ResultsFirst, SHG-FROG revealed very large third order dispersion (TOD). This extent of phase distortion prevents the efficient temporal compression of laser pulses to their theoretical limit. Furthermore, TOD cannot be quantified when using a conventional method of obtaining the laser pulse duration, e.g., when using an autocorrelator. Finally, DMDI showed the effectiveness of detecting pulse-to-pulse intensity fluctuations on timescales relevant to three-photon imaging, which were otherwise not captured using conventional instruments and statistics.ConclusionsThe distortion of individual laser pulses caused by TOD poses significant challenges to three-photon imaging by preventing effective compression of laser pulses and decreasing the efficiency of nonlinear excitation. Moreover, an acceptably low pulse-to-pulse amplitude variability should not be assumed. Particularly for low repetition rate laser sources used in three-photon microscopy, pulse-to-pulse variability also degrades image quality. If three-photon imaging is to become mainstream, our diagnostics may be used by laser manufacturers to improve system design and by end-users to validate the performance of their current and future imaging systems.

Nonlinear fractional stimulated Raman exact passage in three-level systems

We adapt nonlinear stimulated Raman exact passage (NL-STIREP) technique first proposed by Dorier etal. [Phys. Rev. Lett. 119, 243902 (2017)] to fractional population transfer in configurations and extend itto nonlinear N-pod systems. We use NLF-STIRAP technique in a system and indicate that, NLF-STIREPtechnique can guide the dynamics of the system as efficiently as a NLF-STIRAP but with considerably smallerRabi frequency amplitudes. We implement NLF-STIREP technique in fractional creation of ground molecularBose-Einstein condensates (BECs) from atomic BECs and show that, this technique is robust with respect tochanges in the time delay between the pulses and pulse intensity.

Predicting earthquake-induced sliding displacements using effective incremental ground velocity

This article evaluates a pulse intensity measure, the effective incremental ground velocity ( EIGV), for predicting sliding displacements induced by real ground motions. EIGV is based on computing the additional incremental velocity of a pulse after a system begins to slide. Predictions of peak sliding displacements are made using multiple ground motion and pulse intensity measures, and it is found that at high friction levels, defined here as friction coefficient above 0.15, EIGV is a very effective parameter with a lognormal standard deviation of predicted displacements around 0.5, despite including only the properties of the largest pulse in a record. For high-friction systems, very few pulses usually cause the peak sliding displacement during the response history, hence the potential for an effective pulse intensity measure. EIGV improves sliding displacement predictions compared to existing intensity measures, which are geared toward conventional hysteretic systems. Prediction equations are developed for peak relative sliding displacement as a function of EIGV, the sliding interface coefficient of friction, and the radius of curvature for concave sliding surfaces.

Generation of intense spectral continuum and isolated attosecond pulse by selecting single harmonic emission peak

Generally, due to the interference of different harmonic emission peaks (HEPs), the intensity of high-order harmonic spectrum cannot keep enhancing as the pulse intensity increases. Thus, in this paper, a potential method to obtain an intense spectral continuum and isolated attosecond pulse (IAP) by selecting single HEP has been theoretically investigated. First, we choose the harmonic cutoff and the harmonic intensity from the optimal single-color laser intensity as the referenced values. Next, by properly choosing a lower-intensity negative chirped pulse, we see that the harmonic cutoff from this field is similar as that from the referenced field. Moreover, the spectral continuum is contributed by single HEP. However, the intensity of the spectral continuum from the negative chirped pulse is lower than that from the referenced field. As the pulse duration of the chirped pulse increases, the similar harmonic cutoff can also be found by using a much lower-intensity negative chirped pulse. However, the intensity of the spectral continuum is decreased compared with that from the shorter chirped pulse duration. Further, with the introduction of an IR or UV controlling pulse, the intensity of the spectral continuum can be enhanced up to the referenced value. Moreover, the longer the pulse duration of the controlling pulse is used, the lower the controlling pulse intensity is needed. Also, due to the UV resonance ionization, much lower UV intensity is needed to enhance the harmonic yield compared with that for adding IR controlling pulse case. All in all, the total laser intensity of the combined field (the fundamental pulse + the controlling pulse) is lower than that of the referenced field. Most importantly, the signal of the spectral continuum is only coming from single HEP, which can support the generations of intense IAPs with the durations of 30 as.