Pulse Pattern Research Articles

Impact of Pulsed Laser Parameters and Scanning Pattern on the Properties of Thin-Walled Parts Manufactured Using Laser Metal Deposition

The quality of parts manufactured using laser metal deposition (LMD), similar to other additive manufacturing methods, is influenced by processing parameters. Such parameters determine geometric stability, favorable microstructures, and good mechanical properties. This study aimed to investigate the effects of pulsed laser parameters (duty cycle and pulse frequency) and scanning patterns (unidirectional and bidirectional patterns) on the properties of parts fabricated using LMD. Results show that the properties of the LMD-fabricated parts are obviously influenced by pulsed laser parameters and scanning patterns. Using the unidirectional scanning pattern in both pulsed laser parameters enhances the properties of the thin-walled parts prepared using LMD. An increase in duty cycle can improve geometric stability, increase grain size, and reduce microhardness. Furthermore, the geometric stability does not vary considerably with the use of different frequencies, but the microstructure of fabricated parts shows various grain sizes with different pulse frequencies. In addition, the microhardness increases as the frequency increases from 13.33 to 50 Hz. In general, the influence of the duty cycle on geometric properties is greater than that of frequency. Meanwhile, the impact of frequency on microhardness is greater than that of the duty cycle.

Zero-voltage and frequency pattern selection for DC-link loss minimization in PWM-VSI drives

The modulation of a voltage source inverter output causes losses and harmonic distortions on the load side and the DC-link capacitor due to the discrete switching of the semiconductors. High-frequent voltage pulses are digitally programmed to control the inverter output and determine the harmonic distortions. This paper presents an optimization in terms of pulse- and frequency-pattern selection for reducing load distortions while keeping DC-link losses minimal. In detail, the fact that pulse and frequency patterns are independent from each other is utilized and a modified three-zone hybrid space vector pulse-width modulation is proposed where optimal frequency patterns are selected for every carrier cycle. Simulations and experimental results validate the optimizations.

An auditory-responsive interneuron descending from the cricket brain: a new element in the auditory pathway.

Crickets receive auditory information from their environment via ears located on the front legs. Ascending interneurons forward auditory activity to the brain, which houses a pattern recognition network for phonotaxis to conspecific calling songs and which controls negative phonotaxis to high-frequency sound pulses. Descending brain neurons, however, which are clearly involved in controlling these behaviors, have not yet been identified. We describe a descending auditory-responsive brain neuron with an arborization pattern that coincides with the ring-like auditory neuropil in the brain formed by the axonal arborizations of ascending and local interneurons, indicating its close link to auditory processing. Spiking activity of this interneuron occurs with a short latency to calling song patterns and the neuron copies the sound pulse pattern. The neuron preferentially responds to short sound pulses, but its activity appears to be independent of the calling song pattern recognition process. It also receives a weaker synaptic input in response to high-frequency pulses, which may contribute to its short latency spiking responses. This interneuron could be a crucial part in the auditory-to-motor transformation of the nervous system and contribute to the motor control of cricket auditory behavior.

Changes in Radical Levels as a Cause for the FLASH effect: Impact of beam structure parameters at ultra-high dose rates on oxygen depletion in water.

The influence of different average and bunch dose rates in electron beams on the FLASH effect was investigated. The present study measures O2 content in water at different beam pulse patterns and finds strong correlation with biological data, strengthening the hypothesis of radical-related mechanisms as a reason for the FLASH effect.

Response properties of spiking and non-spiking brain neurons mirror pulse interval selectivity

In the bispotted field cricket auditory pulse pattern recognition of the species-specific calling song is based on a delay-line and coincidence detection network, established by the activity and synaptic connections of only 5 auditory neurons in the brain. To obtain a more detailed understanding of the network and the dynamic of the neural activity over time we analyzed the response properties of these neurons to test patterns, in which the pulse duration was kept constant while the duration of specific pulse intervals was systematically altered. We confirm that the ascending interneuron AN1 and the local interneuron LN2 copy the structure of the pulse pattern, however with limited resolution at short pulse intervals, further evident in downstream neural responses. In the non-spiking delay-line interneuron LN5 during long pulse intervals full-blown rebound potentials develop over a time course of 35–70 ms. LN5 also reveals an overall increase in its membrane potential tuned to chirps of the calling song pulse pattern. This may contribute to the pattern recognition process by driving the activity of the coincidence-detector LN3 and may indicate a further function of the delay-line neuron LN5. The activity of LN3 and of the feature detector LN4 match the tuning of the phonotactic behavior and demonstrate an increasingly sparse coding of the calling song pulse patterns as evident in the response of the feature detector LN4. The circuitry reveals a fundamental mechanism of auditory pattern recognition and demonstrates a principle of neuronal coding.

A modular switched-capacitor voltage multiplier-based multi-module high-voltage pulse generator for electrostatic precipitators applications

Due to the severe impacts of climatic change, many recent developments in air cleaning systems have received an increasing attention. The best solution for expelling pollutant particles, met in industrial and commercial applications, is the electrostatic precipitator (ESP). One of the key components in the ESP system is the high-voltage power supply. Many recent studies have proven that the sectionalization of industrial ESPs enhances their particle collection efficiency. Consequently, this paper proposes a new modular switched-capacitor voltage multiplier-based multi-module high-voltage pulse power supply. In the proposed configuration, the two different patterns of output pulse are adopted. The proposed scheme is characterized by its modular structure and its capability of providing two isolated high-voltage pulse generators for each two ESP bus sections from one low-voltage AC source with an adjustable repetition rate, a controllable pulse width, and the desired values of the base and pulse voltages. A detailed illustration and simulation results are presented for the proposed approach. A comparative study is presented to elucidate the advantages of the proposed topology in contrast with the existing topologies. Finally, a -1.2-kV, 0.36-kW experimental setup has been built to show the viability of the proposed concept.

River culture: How socio‐ecological linkages to the rhythm of the waters develop, how they are lost, and how they can be regained

AbstractThe hydrological patterns of all natural water bodies pulse in variable rhythms of high and low water. The biodiversity of these ecosystems is driven by the changing nature of the environment, allowing different life strategies to coexist, e.g., by the fast reuse of nutrients when aquatic biota flourish in the recently wetted zones and vice versa. Much of the human culture in hydroscapes has developed as an adaptation to this rhythm, e.g., by using the flood‐fertilised floodplains for agriculture or fisheries, or by seasonal migration into or out of the floodplain (transhumance). Technological advances have allowed humans to control, change, or even eliminate this natural water rhythm by building dams, dikes, and canals. Consequently, important ecosystem functions fail, often resulting in failure of human life‐support systems but also in the failure and decline of cultural activities. I argue that the loss of socio‐cultural connectivity to the rhythms of rivers and other hydrosystems occurs in four phases: (i) loss of direct relationships (e.g., uses of waterborne resources), (ii) loss of indirect relationships (cultural activities that are connected to theses uses), (iii) turning away from the river/hydrosystem (often caused by decreased water quality), and (iv) total oblivion (caused by removal or burial of the hydrosystem). Reintegrating more riverine rhythms into human life would not mean to step back in time but rather to find a combination of revised traditional ecological knowledge, learning from nature, changing values in the context of use of natural resources, and innovations. This paper draws on social‐environmental aspects of the River Culture Concept – which attempts to reintegrate respect for the pulsing nature of hydrosystems into modern, sustainable management – and on diverse case studies. Examples are presented on how River Culture Concept approaches may contribute to revitalising socio‐ecological linkages to the rhythm of the waters.

Optimizing supercontinuum spectro-temporal properties by leveraging machine learning towards multi-photon microscopy

Multi-photon microscopy has played a significant role in biological imaging since it allows to observe living tissues with improved penetration depth and excellent sectioning effect. Multi-photon microscopy relies on multi-photon absorption, enabling the use of different imaging modalities that strongly depends on the properties of the sample structure, the selected fluorophore and the excitation laser. However, versatile and tunable laser excitation for multi-photon absorption is still a challenge, limited by e.g. the narrow bandwidth of typical laser gain medium or by the tunability of wavelength conversion offered by optical parametric oscillators or amplifiers. As an alternative, supercontinuum generation can provide broadband excitations spanning from the ultra-violet to far infrared domains and integrating numerous fluorophore absorption peaks, in turn enabling different imaging modalities or potential multiplexed spectroscopy. Here, we report on the use of machine learning to optimize the spectro-temporal properties of supercontinuum generation in order to selectively enhance multi-photon excitation signals compatible with a variety of fluorophores (or modalities) for multi-photon microscopy. Specifically, we numerically explore how the use of reconfigurable (femtosecond) pulse patterns can be readily exploited to control the nonlinear propagation dynamics and associated spectral broadening occurring in a highly-nonlinear fiber. In this framework, we show that the use of multiple pulses to seed optical fiber propagation can trigger a variety of nonlinear interactions and complex propagation scenarios. This approach, exploiting the temporal dimension as an extended degree of freedom, is used to maximize typical multi-photon excitations at selected wavelengths, here obtained in a versatile and reconfigurable manner suitable for imaging applications. We expect these results to pave the way towards on-demand and real time supercontinuum shaping, with further multi-photon microscopy improvements in terms of spatial 3D resolution, optical toxicity, and wavelength selectivity.

Transcranial ultrasound neuromodulation induces neuronal correlation change in the rat somatosensory cortex

Objective. Transcranial focused ultrasound (tFUS) is a neuromodulation technique which has been the focus of increasing interest for noninvasive brain stimulation with high spatial specificity. Its ability to excite and inhibit neural circuits as well as to modulate perception and behavior has been demonstrated, however, we currently lack understanding of how tFUS modulates the ways neurons interact with each other. This understanding would help elucidate tFUS’s mechanism of systemic neuromodulation and allow future development of therapies for treating neurological disorders. Approach. In this study, we investigate how tFUS modulates neural interaction and response to peripheral electrical limb stimulation through intracranial multi-electrode recordings in the rat somatosensory cortex. We deliver ultrasound in a pulsed pattern to induce frequency dependent plasticity in a manner similar to what is found following electrical stimulation. Main Results. We show that neural firing in response to peripheral electrical stimulation is increased after ultrasound stimulation at all frequencies, showing tFUS induced changes in excitability of individual neurons in vivo. We demonstrate tFUS sonication repetition frequency dependent pairwise correlation changes between neurons, with both increases and decreases observed at different frequencies. Significance. These results extend previous research showing tFUS to be capable of inducing synaptic depression and demonstrate its ability to modulate network dynamics as a whole.

Towards a Counting Point Detector for Nanosecond Coherent X-ray Science

We present the technical realization of a high-speed hard X-ray single-photon counting-detection scheme based on a commercial avalanche silicon photodiode and high-speed oscilloscope. The development is motivated by the need to perform pulse-resolved photon-correlation and pump-probe studies at synchrotron sources with densely packed pulse patterns that result in high repetition rate pulses on the order of hundreds of MHz. Commissioning experiments are performed at the 1C PAL-KRISS beamline at PLS-II of South Korea operating at a burst mode maximum repetition rate of 500 MHz. In such a high count-rate measurement, detector dead-time can lead to a distortion of counting statistics. We are able to model the counting behavior of our detector under these conditions with a detector dead-time comparable to time between X-ray pulses, implying that nanosecond X-ray photon correlation spectroscopy should be possible at diffraction-limited light sources.

Generalized Model Predictive Pulse Pattern Control Based on Small-Signal Modeling—Part 1: Algorithm

A model predictive controller based on optimized pulse patterns is proposed that is suitable for higher-order linear systems, such as converters with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$LC$</tex-math></inline-formula> filters. The controller manipulates the switching times of an optimized pulse pattern. The switching time modifications are approximated by the strengths of impulses, which are based on a small-signal linearization around the nominal switching instants. With these, the evolution of the state variables over the prediction horizon can be described by a set of linear differential equations. An objective function penalizes the predicted tracking error of the controlled variables, such as the converter currents, filter capacitor voltages, and grid currents, over a prediction horizon. Thanks to the use of impulse strengths, the underlying optimization problem is a convex quadratic program, which can be solved in real time to determine the switching time modifications of the pulse pattern to be applied by the controller.

Generalized Model Predictive Pulse Pattern Control Based on Small-Signal Modeling—Part 2: Implementation and Analysis

A newly proposed model predictive pulse pattern controller, which is applicable to higher-order converter systems, is implemented on a low-cost field-programmable gate array. It is shown that how the computations of the underlying quadratic program of the control algorithm can be reduce, thus enabling a resource-efficient implementation. The implemented control algorithm is evaluated via hardware-in-the-loop simulations. The results show that the proposed controller achieves a short settling time during transients and the superior harmonic performance of optimized pulse patterns during steady-state operation.

Lung‐ and liver‐dominant phenotypes of Korean eight constitution medicine have different profiles of genotype associated with each organ function

Eight Constitution Medicine (ECM), a ramification of traditional Korean medicine, has categorized people into eight constitutions. The main criteria of classification are inherited differences or predominance in the functions of organs, such as the liver or lung, diagnosed through ECM‐specific pulse patterns. This study investigated the association between single nucleotide polymorphism (SNP) genotypes and ECM phenotypes and explored candidate genetic makeups responsible for each constitution using a genome‐wide association study (GWAS). Sixty‐three healthy volunteers, who were either categorized as the Hepatonia (HEP, n = 32) or Pulmotonia (PUL, n = 31) constitution, were enrolled. HEP and PUL are two contrasting ECM types representing the dominant liver and lung phenotypes, respectively. SNPs were analyzed from the oral mucosa DNA using a commercially available microarray chip that can identify 820,000 SNPs. We conducted GWAS using logistic regression analysis and additive mode genotypes and constructed phylogenetic trees using the SNPhylo program with 8 SNPs specific for the liver phenotype and 15 SNPs for the lung phenotype. Although genome‐wide significant SNPs were not found, the phylogenetic tree showed a clear difference between the two constitutions. This is the first observation suggesting genetic involvement in the ECM and can be extended to all ECM constitutions.

Contemporary music genre rhythm generation with machine learning

In this article, we present research on customizing a variational autoencoder (VAE) neural network to learn models and play with musical rhythms encoded within a latent space. The system uses a data structure that is capable of encoding rhythms in simple and compound meter and can learn models from little training data. To facilitate the exploration of models, we implemented a visualizer that relies on the dynamic nature of the pulsing rhythmic patterns. To test our system in real-life musical practice, we collected small-scale datasets of contemporary music genre rhythms and trained models with them. We found that the non-linearities of the learned latent spaces coupled with tactile interfaces to interact with the models were very expressive and lead to unexpected places in composition and live performance musical settings. A music album was recorded and it was premiered at a major music festival using the VAE latent space on stage.

Improving the formation probability and stability of noise-like pulse by weakening the spectrum filtering effect.

Noise-like pulses (NLP) are extremely sought after in low-coherence tomography and supercontinuum, etc. Here, we propose an effective method to form the NLP in the all-normal-dispersion (ANDi) fiber laser by weakening the spectrum filtering for the first time. Numerical explorations are performed in detail and demonstrate that the NLP can be originated from the clustering behavior of amplified random sub-pulses led by the saturable absorber. By simulating the pulse-pattern distribution in the two-dimensional parameter space, it is further found that this kind of NLP pattern is widely distributed where are with a weak spectrum filtering. Since, the weaker the filtering, the harder the dissipative system to achieve balance, which helps to avoid the evolution from the pulse cluster to other coherent states and supports the NLP stability. To prove the feasibility experimentally, we built an ANDi fiber laser based on the nonlinear polarization rotating (NPR). The built laser can operate at the stable dissipative soliton (DS) state with a spectrum filter, which also with a 45 nm wavelength tuning performance. Replacing the filter, only NLP with a 40.2 ps pedestal and 237 fs spike can be attained. The experiments agree well with the numerical predictions. This exploration significantly broadens the design possibilities for ultrafast lasers, making them much more accessible to produce desired pulse patterns.

Optoacoustic tones generated by nanosecond laser pulses can cover the entire human hearing range.

The aim of this work is to generate defined tones that cover the human hearing range in aqueous media for a later application in middle or inner ear implants. In our experiments, we investigated the characteristics of single laser pulses and pulse trains with different laser repetition rates of nanosecond laser pulses that were focused into aqueous media in a small volume. The frequency of the generated tones was limited by the spectral properties of the single acoustic pulses, which depended on the medium. Tones with fundamental frequencies above 8kHz were generated using laser pulses focused into water. By replacing water with gel, tones between 500 Hz and 20 kHz could be produced. The generation of tones in the low-frequency range was only possible when laser pulse trains with pulse density modulated pulse patterns were applied in gel. This enabled the generation of tones between 20 Hz and 2kHz. Consequently, the combination of different pulse patterns for the different frequency ranges allows generating optoacoustic tones between 20 Hz and 20 kHz in gel. Thus, we can cover the complete range of human hearing through optoacoustically generated tones.

DeepPAD: Detection of Peripheral Arterial Disease Using Deep Learning

Peripheral arterial disease (PAD) is a common circulatory disease caused by the deposition of fatty plaque on the arterial wall. Early detection and treatment of PAD are essential in preventing further cardiovascular and health complications. It was recently shown that PAD can be detected using an oscillometric device by characterizing the peripheral arterial system at different externally applied cuff pressures. However, the extraction of the complex relationship between the pattern of the oscillometric waveforms and the presence of PAD remained challenging. This study proposes a novel deep learning approach for the detection of PAD by capturing the peripheral arterial system behavior at different cuff pressures. The periodic pattern of the oscillometric pulses and their variations as a function of cuff pressure were modeled using a deep recurrent neural network based on the bidirectional long short-term memory and attention mechanism. The proposed model was evaluated by analyzing the raw oscillometric pulses as well as statistical features on data collected from 33 individuals (14 PAD and 19 normal). The results show a high accuracy of up to 94.8%, a sensitivity of up to 90.0%, and a specificity of up to 97.4% in detecting PAD. The proposed method provides new opportunities for noninvasive cardiovascular screening and early detection of PAD using the oscillometric principle.

Temporal Stimulus Patterns Drive Differentiation of a Synthetic Dipeptide-Based Coacervate.

The fate of living cells often depends on their processing of temporally modulated information, such as the frequency and duration of various signals. Synthetic stimulus-responsive systems have been intensely studied for >50 years, but it is still challenging for chemists to create artificial systems that can decode dynamically oscillating stimuli and alter the systems' properties/functions because of the lack of sophisticated reaction networks that are comparable with biological signal transduction. Here, we report morphological differentiation of synthetic dipeptide-based coacervates in response to temporally distinct patterns of the light pulse. We designed a simple cationic diphenylalanine peptide derivative to enable the formation of coacervates. The coacervates concentrated an anionic methacrylate monomer and a photoinitiator, which provided a unique reaction environment and facilitated light-triggered radical polymerization─even in air. Pulsed light irradiation at 9.0 Hz (but not at 0.5 Hz) afforded anionic polymers. This dependence on the light pulse patterns is attributable to the competition of reactive radical intermediates between the methacrylate monomer and molecular oxygen. The temporal pulse pattern-dependent polymer formation enabled the coacervates to differentiate in terms of morphology and internal viscosity, with an ultrasensitive switch-like mode. Our achievements will facilitate the rational design of smart supramolecular soft materials and are insightful regarding the synthesis of sophisticated chemical cells.

Power Quality Improvement Meeting Important Grid Codes Using Three-Phase Five-Level CHB Inverter With Improved Quarter and Half-Wave Symmetry Based Optimized SHM-PAM

Selective harmonic minimization-pulse amplitude modulation (SHM-PAM) scheme suppresses more number of selected voltage harmonic components of a predefined voltage waveform pattern for a wider range. This article presents formulations of some improved five-level pulse patterns based on both quarter-wave symmetry (QWS) and half-wave symmetry (HWS) with a low number of switching instants using the optimized SHM-PAM scheme to meet the CIGRE WG36-05/EN 50160 and IEC 61000-3-6 grid codes. The switching angles and normalized value of dc voltage sources are calculated by the recently reported dragonfly algorithm based optimization technique. The performance of the proposed schemes has been verified through simulation and experimentation on a three-phase five-level cascaded H-bridge (CHB) inverter. A comparison between the proposed two types of formulations has been carried out based on various aspects, such as waveform quality, dc power conversion capability, and power loss in the power semiconductor devices of the CHB inverter and efficiency. It is observed that QWS formulations exhibit better waveform quality than the HWS formulations sacrificing the efficiency of CHB inverter due to higher switching losses. Moreover, the effectiveness of the proposed schemes has been compared with some prior conventional modulation schemes.

The burst gap is a peripheral temporal code for pitch perception that is shared across audition and touch

When tactile afferents were manipulated to fire in periodic bursts of spikes, we discovered that the perceived pitch corresponded to the inter-burst interval (burst gap) in a spike train, rather than the spike rate or burst periodicity as previously thought. Given that tactile frequency mechanisms have many analogies to audition, and indications that temporal frequency channels are linked across the two modalities, we investigated whether there is burst gap temporal encoding in the auditory system. To link this putative neural code to perception, human subjects (n = 13, 6 females) assessed pitch elicited by trains of temporally-structured acoustic pulses in psychophysical experiments. Each pulse was designed to excite a fixed population of cochlear neurons, precluding place of excitation cues, and to elicit desired temporal spike trains in activated afferents. We tested periodicities up to 150 Hz using a variety of burst patterns and found striking deviations from periodicity-predicted pitch. Like the tactile system, the duration of the silent gap between successive bursts of neural activity best predicted perceived pitch, emphasising the role of peripheral temporal coding in shaping pitch. This suggests that temporal patterning of stimulus pulses in cochlear implant users might improve pitch perception.