Impulsive Pulse Research Articles

A competition model with impulsive interventions and environmental perturbations in moving environments

In order to understand how impulsive interventions and environmental perturbations affect dynamics of competitors, we focus on a diffusive competition model with free boundaries and periodic pulses in a temporally heterogeneous environment with upward or downward advection. The dependence of the principal eigenvalue of corresponding periodic impulsive eigenvalue problem on advection rates, habitat sizes and pulses is investigated, which gives precise conditions that classify the dynamics into four types of competition outcomes including coexistence, co-extinction, two different competition exclusions for small or negative advection rates. Some sufficient conditions on pulses or initial habitats for species spreading or vanishing, and spreading speeds are then established. Our results not only extend the existing ones to the case with pulses, but also reveal the effects of human and natural factors, that is, impulsive interventions factors including positive or negative impulsive effect, pulse intensity and timing can significantly affect and alter the competition outcomes. The different performances of the superior and inferior affected by environmental perturbations are also reflected in the simulations.

Global Distribution of Key Features of Streamer Corona Discharges in Thunderclouds.

We present nighttime worldwide distributions of key features of Blue LUminous Events (BLUEs) detected by the Modular Multispectral Imaging Array of the Atmosphere-Space Interaction Monitor. Around 10% of all detected BLUEs exhibit an impulsive single pulse shape. The rest of BLUEs are unclear (impulsive or not) single, multiple or with ambiguous pulse shapes. BLUEs exhibit two distinct populations with peak power density <25µWm-2 (common) and ≥25µWm-2 (rare) with different rise times and durations. The altitude (and depth below cloud tops) zonal distribution of impulsive single pulse BLUEs indicate that they are commonly present between cloud tops and a depth of ≤4km in the tropics and ≤1km in mid and higher latitudes. Impulsive single pulse BLUEs in the tropics are the longest (up to ∼4km height) and have the largest number of streamers (up to ∼3×109). Additionally, the analysis of BLUEs has turned out to be particularly complex due to the abundance of radiation belt particles (at high latitudes and in the South Atlantic Anomaly [SAA]) and cosmic rays all over the planet. True BLUEs can not be fully distinguished from radiation belt particles and cosmic rays unless other ground-based measurements associated with the optically detected BLUEs are available. Thus, the search algorithm of BLUEs presented in Soler etal. (2021), https://doi.org/10.1029/2021gl094657 is now completed with a new additional step that, if used, can considerably smooth the SAA shadow but can also underestimate the number of BLUEs worldwide.

Multi-channel analyzer based on a novel pulse fitting analysis method

A novel pulse fitting analysis (PFA) method is presented for the acquisition of nuclear spectra. The charging process of the feedback capacitor in the resistive feedback charge-sensitive preamplifier is equivalent to the impulsive pulse, and its impulse response function (IRF) can be obtained by non-linear fitting of the falling edge of the nuclear pulse. The integral of the IRF excluding the baseline represents the energy deposition of the particles in the detector. In addition, since the non-linear fitting process in PFA method is difficult to achieve in the conventional architecture of spectroscopy system, a new multi-channel analyzer (MCA) based on Zynq SoC is proposed, which transmits all the data of nuclear pulses from the programmable logic (PL) to the processing system (PS) by high-speed AXI-Stream in order to implement PFA method with precision. The linearity of new MCA has been tested. The spectrum of 137Cs was obtained using LaBr3(Ce) scintillator detector, and was compared with commercial MCA by ORTEC. The results of tests indicate that the MCA based on PFA method has the same performance as the commercial MCA based on pulse height analysis (PHA) method and excellent linearity for γ-rays with different energies, which infers that PFA method is an effective and promising method for the acquisition of spectra. Furthermore, it provides a new solution for nuclear pulse processing algorithms involving regression and iterative processes.

Dynamics of a lake-eutrophication model with nontransient/transient impulsive dredging and pulse inputting

In this work, we present a lake-eutrophication model with nontransient/transient impulsive dredging and pulse inputting. We obtain globally asymptotically stable conditions for the phytoplankton-extinction periodic solution of system (2.1). Furthermore, we gain the permanent conditions for system (2.1). Finally, we employ computer simulations to illustrate the results. Our results indicate the effective controlling strategy for water resource management.

Dynamics of a stochastic eutrophication-chemostat model with impulsive dredging and pulse inputting on environmental toxicant

In this paper, we present a stochastic eutrophication-chemostat model with impulsive dredging and pulse inputting on environmental toxicant. The sufficient condition for the extinction of microorganisms is obtained. The sufficient condition for the investigated system with unique ergodic stationary distribution is also obtained. The results show that the stochastic noise, impulsive dredging, and pulse input on the environmental toxicant play important roles in the extinction of microorganisms. The results also indicate the effective and reliable controlling strategy for water resource management. Finally, numerical simulations are employed to illustrate our results.

Susceptibility of two-dimensional resonance Raman spectroscopies to cascades involving solute and solvent molecules.

Two-dimensional resonance Raman (2DRR) spectroscopies have been used to investigate the structural heterogeneity of ensembles and chemical reaction mechanisms in recent years. Our previous work suggests that the intensities of artifacts may be comparable to the desired 2DRR response for some chemical systems and experimental approaches. In a type of artifact known as a "cascade," the four-wave mixing signal field radiated by one molecule induces a four-wave mixing process in a second molecule. We consider the susceptibility of 2DRR spectroscopy to various types of signal cascades in the present work. Calculations are conducted using empirical parameters obtained for a molecule with an intramolecular charge-transfer transition in acetonitrile. For a fully impulsive pulse sequence, it is shown that "parallel" cascades involving two solute molecules are generally more intense than that of the desired 2DRR response when the solute's mode displacements are 1.0 or less. In addition, we find that the magnitudes of parallel cascades involving both solute and solvent molecules (i.e., a solute-solvent cascade) may exceed that of the 2DRR response when the solute possesses small mode displacements. It is tempting to assume that solute-solvent cascades possess negligible intensities because the off-resonant Raman cross sections of solvents are usually 4-6 orders of magnitude smaller than that of the electronically resonant solute; however, the present calculations show that the difference in solute and solvent concentrations can fully compensate for the difference in Raman cross sections under common experimental conditions. Implications for control experiments and alternate approaches for 2DRR spectroscopy are discussed.

Single-beam phase-modulated stimulated Raman scattering microscopy with spectrally focused detection

We present a single-beam coherent Raman microscopy method based on pump–probe, time-resolved stimulated Raman scattering (SRS) measurements with shaped probe pulses. In the single-beam method, we divide a broadband laser spectrum into three frequency bands for the pump, phase-modulated (PM) probe, and local oscillator (LO) probe pulses. Multiple low-wavenumber Raman modes are efficiently excited by an impulsive pump pulse, and a specific Raman mode can be selectively probed using temporal beam coupling between the PM and LO probe pulses via the Raman-induced refractive index modulation. To achieve both high sensitivity and a high spectral resolution, we allocate a large spectral bandwidth (164 cm−1) to two probe bands and use a new selective detection scheme based on the spectral focusing technique. By giving a strong group delay dispersion to the probes (45000 fs2), we can obtain an improved spectral resolution of down to 25 cm−1. In a proof-of-concept experiment, the intrinsic molecular-vibration contrast of sevoflurane, an inhaled anesthetic drug, is successfully visualized. This result suggests that single-beam SRS imaging with pulse shaping is a potentially powerful tool for detecting the Raman signals of small-molecule drugs in living cells and tissues.

Characterization of initial current pulses in negative rocket‐triggered lightning with sensitive magnetic sensor

AbstractWe report the new measurement of initial current pulses in rocket‐triggered lightning with a broadband magnetic sensor at 78 m distance. The high sensitivity of our sensor makes it possible to detect weak ripple deflections (as low as 0.4 A) that are not readily resolved in the typical measurements of channel‐base current in rocket‐triggered lightning experiments. The discernible magnetic pulses within 1 ms after the inception of a sustained upward positive leader from the triggering wire can be classified into impulsive pulses and ripple pulses according to the discernibility of separation between individual pulses. The time scale (usually &gt;20 µs) of ripple pulses is substantially longer than the leading impulsive pulses (with time scales typically &lt;10 µs), and the amplitude is significantly reduced, whereas there is no considerable difference in the interpulse pulse. Along with our previous finding on the burst of magnetic pulses during the initial continuous current in rocket‐triggered lightning, the new measurements suggest that the stepwise propagation might be a persistent feature for the upward positive leader in rocket‐triggered lightning, and the stepping of positive leader early in triggered lightning could be characterized with the observation of ripple pulses. The precedence of impulsive magnetic pulse measured at 78 m range relative to the arrival of corresponding current pulse at the channel base indicates that the ionization wave launched by individual stepping of positive leader propagates downward along the triggering wire at a mean velocity of 1.23 × 108 m/s to 2.25 × 108 m/s.

Coherence specific signal detection via chiral pump-probe spectroscopy.

We examine transient circular dichroism (TRCD) spectroscopy as a technique to investigate signatures of exciton coherence dynamics under the influence of structured vibrational environments. We consider a pump-probe configuration with a linearly polarized pump and a circularly polarized probe, with a variable angle θ between the two directions of propagation. In our theoretical formalism the signal is decomposed in chiral and achiral doorway and window functions. Using this formalism, we show that the chiral doorway component, which beats during the population time, can be isolated by comparing signals with different values of θ. As in the majority of time-resolved pump-probe spectroscopy, the overall TRCD response shows signatures of both excited and ground state dynamics. However, we demonstrate that the chiral doorway function has only a weak ground state contribution, which can generally be neglected if an impulsive pump pulse is used. These findings suggest that the pump-probe configuration of optical TRCD in the impulsive limit has the potential to unambiguously probe quantum coherence beating in the excited state. We present numerical results for theoretical signals in an example dimer system.

Selective excitation of spin resonance in orthoferrite PrFeO3 with impulsive polarized terahertz radiation

Single cycle terahertz (THz) pulses were employed to excite coherent spin waves in (110)-oriented PrFeO3 single crystal. The free induction decay radiations at frequency of 0.34 THz (quasi-ferromagnetic mode, FM mode) and 0.41 THz (quasi-antiferromagnetic mode, AFM mode) were observed arising from the coupling of magnetic moment with the impulsive magnetic field of polarized terahertz radiation. These two spin modes in PrFeO3 can be excited and modulated by the magnetic field of THz pulse with a specific polarization with respect to the crystal axis. The extracted complex dielectric permittivity and magnetic permeability dispersion in THz range suggest a higher efficiency of energy transfer from the impulsive THz pulse into the AFM than the FM spin system.

Two‐dimensional simulation of ionospheric variations in the vicinity of the epicenter of the Tohoku‐oki earthquake on 11 March 2011

Unusual ionospheric variations were observed in the M9.0 Tohoku‐oki earthquake on 11 March 2011. Among various kinds of features in the ionosphere, significant depletion of total electron content (TEC) near the epicenter was observed after the earthquake. Although previous studies have suggested that the coseismic ionospheric variations are associated with atmospheric perturbation caused by vertical displacement of the sea surface, the mechanism of the TEC depletion has not been fully understood. In this paper, a two‐dimensional nonlinear nonhydrostatic compressible atmosphere‐ionosphere model is employed to investigate the ionospheric variations in the vicinity of the epicenter. The simulation results reveal that an impulsive pressure pulse produced by a sudden uplift of the sea surface leads to local atmospheric expansion in the thermosphere and that the expansion of the thermosphere combined with the effect of inclined magnetic field lines in the ionosphere causes the sudden TEC depletion above the epicenter region.

Molecular alignment and orientation with a hybrid Raman scattering technique

We demonstrate a scheme for the preparation of molecular alignment and angular momentum orientation using a hybrid combination of two limits of Raman scattering. First a weak, impulsive pump pulse initializes the system via the nonresonant dynamic Stark effect. Then, having overcome the influence of the vacuum fluctuations, an amplification pulse selectively enhances the initial coherences by transient stimulated Raman scattering, generating alignment and angular momentum orientation of molecular hydrogen. The amplitude and phase of the resulting coherent dynamics are experimentally probed, indicating an amplification factor of $4.5$. An analytic theory is developed to model the dynamics.

Dynamical analysis of a five-dimensioned chemostat model with impulsive diffusion and pulse input environmental toxicant

In this paper, we consider a five-dimensioned chemostat model with impulsive diffusion and pulse input environmental toxicant. Using the discrete dynamical system determined by the stroboscopic map, we obtain a microorganism-extinction periodic solution. Further, it is globally asymptotically stable. The permanent condition of the investigated system is also analyzed by the theory on impulsive differential equation. Our results reveal that the chemostat environmental changes play an important role on the outcome of the chemostat.

Investigation of effect of polyurea on response of steel plates to impulsive loads in direct pressure-pulse experiments

We summarize the results of the response of monolithic steel plates and steel-polyurea bilayer plates to impulsive blast loads produced in direct pressure-pulse experiments, focusing on the deformation and failure modes of the plates. In these experiments, an impulsive pressure pulse is applied to a steel plate through water or soft polyurethane that simulates shock loading with a peak pressure of ∼80 MPa and duration of ∼50 μs, followed by a cavitation period and a post-cavitation peak pressure of ∼40 MPa and ∼400 μs duration. The pressure pulse is produced by a projectile that impacts either a confined water- or soft polyurethane-layer which in turn transmits the pulse and loads the sample supported by a hollow steel cylinder. Using high-speed photography, the deformation and fracturing of some of the plates are also captured. In addition, the total force acting on the steel plate is measured as a function of time in several selected cases. The experimental results suggest that the presence of polyurea on the back face (opposite to the load-receiving side) of the steel plates can enhance the energy absorption of the plates and help to mitigate their failure. On the other hand, when polyurea is placed on the front face (load-receiving side), it will magnify the initial shock effect and promote failure. These experimental results are paralleled by numerical simulations of the entire experiment, employing physics-based models for the DH-36 steel and polyurea ( Amini et al., 2010b.

Development of a Simultaneously Frequency- and Time-Resolved Raman-Induced Kerr Effect Probe

We detail the development of an optical probe technique based on time-resolved Raman-induced Kerr effect polarization spectroscopy (tr-RIKES). This technique, termed fs/ps RIKES, combines an ultrafast pump pulse with a narrowband probe that directly allows spectral resolution of low-frequency (0-600 cm(-1)) modes typically observable via RIKES. The narrowband probe pulse alleviates the need to scan the time delay between pump and probe pulses to observe molecular coherences, thus making this multiplexed technique a convenient probe for studying low-frequency molecular dynamics. An important distinguishing characteristic of this polarization-sensitive technique arises from the fact that the delay between the impulsive pump pulse and the picosecond-duration probe pulse is optimized to maximize suppression of nonresonant background signal. Model systems, including the rotational spectrum of gas-phase hydrogen and the low-frequency vibrational spectrum of neat bromoform, are used to compare fs/ps RIKES with the conventional time-resolved RIKES technique.

Investigation of the multiple‐component structure of the 20 January 2005 cosmic ray ground level enhancement

Worldwide observations of the cosmic ray ground level enhancement (GLE) of 20 January 2005 are used to investigate a commonly observed but poorly understood feature of this class of event. It is argued that the GLE comprised two distinctly different cosmic ray populations. The first resulted in an impulsive, highly anisotropic, field‐aligned pulse with a relatively hard rigidity spectrum and significant velocity dispersion. The characteristics of the anisotropy were almost identical to those for similar impulsive increases observed during GLEs in 1960, 1978, and 1989. The π0γ ray observations from the RHESSI and CORONAS‐F spacecraft and Type III radio emissions yield a path length of 1.76 ± 0.1 AU to Earth for the first pulse. After the highest energies in the initial anisotropic pulse had passed Earth, another field‐aligned but mildly anisotropic cosmic ray pulse developed slowly worldwide, exhibiting the characteristics of the conventional GLE. The risetime and anisotropy of this second population indicate substantial scattering, apparently at variance to the essentially scatter‐free nature of the initial pulse. We show that the coexisting scatter‐free initial impulsive increase and the diffusive character of the second pulse are consistent with the standard quasi‐linear theory of pitch angle diffusion. Throughout the GLE, the anisotropy remained field‐aligned, and a third maximum, seen by some stations, is shown to be due to changes in the direction of the heliospheric magnetic field (HMF). Examination of 22 large (&gt;20%) GLEs in the historical record shows that the impulsive pulse never occurs after the commencement of the P2 pulse, indicating that the impulsive‐gradual combination is not due to a chance sampling of differing scattering regions of the HMF. It is further shown that impulsive pulses, or their equivalents, have been observed in 13 out of the 15 GLEs associated with solar activity in the solar longitude range 24°–98°W, leading us to propose that the event of 20 January 2005 should be regarded as the defining example of the GLE. The observations lead us to propose two separate acceleration episodes in the typical GLE: (1) acceleration directly associated with the flare itself and located in the lower corona and (2) acceleration by a supercritical shock driven by the associated coronal mass ejection, located at ∼3–5 solar radii and farther in the upper corona. A one‐to‐one association with so‐called impulsive and gradual solar energetic particle events at lower energies is proposed. On the basis of these observations, a generic model for the GLE is proposed.

Unitary photoassociation: One-step production of ground-state bound molecules

Bound-state molecules can be photoassociated directly from ultracold free-atom pairs by excitation to a purely repulsive electronic state. The process is explained on the basis of quantum unitarity: the initially free-scattering state is transformed by an impulsive light pulse to a deformed superposition which contains bound-state components. For pulse durations which are short compared to the ultracold dynamics, the maximal rate of photoassociation was found to be determined by the initial stationary distribution of scattering states of the atom pairs. The process was simulated for an ultracold gas of $^{87}\text{R}\text{b}$ with a temperature of $T=44\text{ }\ensuremath{\mu}\text{K}$ and a density of $\ensuremath{\approx}{10}^{11}\text{ }{\text{cm}}^{\ensuremath{-}3}$. Transform-limited pulses maximize the photoassociation, yielding $\ensuremath{\sim}1$ bound molecule per pulse. Coherent control calculated by a local control scheme can increase the photoassociation yield by two orders of magnitude.

Development of a capacitive ultrasonic sensor having parylene diaphragm and characterization of receiving performance of arrayed device

The present paper reports the development of a capacitive ultrasonic sensor having Parylene diaphragm. Parylene diaphragm is flexible and non-brittle, allowing good sensitivity and durability. The resonant frequency under the tensile stress of Parylene and the influence of the number and the radius of acoustic holes on damping ratio are investigated by FEM (finite element method) simulation. Practical sensor devices are fabricated. They can receive an impulsive ultrasonic pulse transmitted by a spark discharge. The ranging system using this sensor can detect the distance up to 1m with the error less than 1mm. The developed sensor can be approximated to be non-directional. An arrayed sensor device comprising 5×5 developed sensors is fabricated, and its receiving performance is characterized. It is proven that the electric scanning of directivity based on delay-and-sum principle is possible.

Polarization dependence of vibrational coupling signals in femtosecond stimulated Raman spectroscopy

The polarization dependence of vibrational coupling signals seen in femtosecond stimulated Raman spectroscopy (FSRS) is investigated. Changing the polarization of a pulse used to impulsively excite coherent low frequency chlorine bending motion in CDCl(3) has a dramatic effect on the line shape of vibrational sidebands which arise from the anharmonic coupling of the pumped modes at 262 and 365 cm(-1) with the higher frequency symmetric stretching mode at 652 cm(-1). The asymmetric bend sideband (652+262 cm(-1)) changes sign and magnitude as the impulsive pulse polarization is rotated relative to the Raman pulses, while the symmetric bend sideband (652+365 cm(-1)) is relatively polarization independent. These experiments demonstrate the ability of FSRS to obtain time-resolved information on not only the vibrational coupling strength but also the symmetry of anharmonically coupled modes.

Development of Capacitive Ultrasonic Sensor with Parylene Diaphragm Using Micromachining Technique

In this paper, we reports the development of a miniaturized capacitive ultrasonic sensor with a Parylene diaphragm using a micromachining technique. Since the polymer diaphragm is flexible and nonbrittle, good sensitivity and durability are expected. Moreover, Parylene has good complementary metal oxide semiconductor (CMOS) compatibility, since it can be deposited at room temperature. Practical sensor devices were fabricated, and their performance was characterized. They can receive an impulsive ultrasonic pulse transmitted by a spark discharge with an open-circuit sensitivity of 0.3 mV/Pa. A well-damped waveform was obtained by setting appropriate acoustic holes. The ranging system using this sensor can detect distances up to 1 m with an error of less than 1 mm. The developed sensor can receive ultrasound from a wide area. The wide directivity could be effective for realizing the omni-directional characteristics of the future arrayed sensor, which contains many of the developed sensors.