Amplitude Period Research Articles

Optimization of a wavy-channel compact solar receiver with supercritical carbon dioxide

The compact solar receiver stands out as a promising solar absorber for the direct supercritical carbon dioxide cycle, and the wavy channel exhibits notable comprehensive performance owing to its excellent heat transfer capabilities and relatively low flow resistance. However, there exists considerable room for improvement in performance through the optimization of geometric parameters in wavy channels. In this paper, the amplitude and the period of the wavy channel are optimized by a coupled response surface method with multi-objective genetic algorithm, with objectives of maximizing the heat transfer coefficient and minimizing the friction factor. Results indicated that smaller period or larger amplitude enhances heat transfer but also increases flow resistance. Through the non-dominated sorting genetic algorithm and k-means clustering method, five representative optimal solutions were identified. The optimal result, characterized by a period of 15.07 mm and an amplitude of 1.73 mm, was selected based on the highest comprehensive heat transfer factor under identical pump power, reaching 1.213. This solution demonstrated high comprehensive performance across a wide range of working conditions. The optimization results are not only valuable for the design of compact solar receivers but also hold significant potential for application in other compact heat exchangers, such as printed circuit heat exchangers.

Ion current oscillation of polyelectrolyte modified micropipettes.

Here, we report for the first time that ion current oscillation (ICO) with periodic amplitude and frequency can autonomously occur at polyimidazole brush (PvimB) modified pipettes in an asymmetric solution with a pH gradient (e.g. pH 6.0/pH 8.0). Experimental results demonstrated that under a strong bias voltage, the proton responsive PvimB-modified pipettes exhibited significant current switching behavior under negative bias voltages, which contributed to the periodic oscillating ion current under constant biases. Based on this dynamic, the frequency and amplitude of the ICO phenomenon were regulated by adjusting the pH gradient in the asymmetric solution. ICOs under different bias voltages were further explored to show the voltage-dependent nature of this phenomenon. This observation of ICO phenomena offers a new strategy for designing iontronic devices with dynamic conductivity changes induced by surface chemical interactions within spatial confinements.

Study of subharmonic oscillation processes in ferroresonance circuits

The article presents a general theory of the analysis of subharmonic oscillations at a frequency of 25 Hz in three-phase Ferro resonance circuits with common magnetic conductors. The abbreviated equations are obtained by averaging with the corresponding phases. From the condition of the existence of a periodic solution, the phase and amplitude ratios of the excited oscillations are determined, which differ from threephase circuits with a separate ferromagnetic element. In steady-state mode, the excitation conditions and the area of existence are determined depending on the parameters of the circuit, the bias current and the applied action. The stability of the solution of the initial system of nonlinear second-order differential equations is also studied by analysing the roots of the characteristic equation using a qualitative method. In the theory of nonlinear electrical circuits, the analysis of the physical processes occurring in threephase Ferro resonance circuits during the excitation of second-order subharmonic oscillations is of particular importance in the design and creation of various converter devices.

Investigation of Periodic Modulation Behaviors from Pulsar J2022+5154

We have carried out a detailed study of individual pulse emission from the pulsar J2022+5154 (B2021+51), observed at 2250 MHz using the Jiamusi 66 m radio telescope. We have investigated the modulations in single-pulse behavior using fluctuation spectral analysis, which shows the presence of two prominent periodicities, around 5 and 40 rotation periods, respectively. The shorter periodicity is associated with the phenomenon of subpulse drifting. In the absence of aliasing, the emission pattern is demonstrated to consist of eight subbeams, which rotate around the magnetic axis in about 45 periods. In addition to subpulse drifting, the pulsar also shows the presence of periodic amplitude modulation with a longer periodicity in the single-pulse sequence. The pulsar joins a select group that shows the presence of periodic phase-modulated drifting as well as amplitude-modulated drifting. This provides further evidence for the two phenomena being distinct from each other with different physical origins.

Regulated Behavior in Living Cells with Highly Aligned Configurations on Nanowrinkled Graphene Oxide Substrates: Deep Learning Based on Interplay of Cellular Contact Guidance.

Micro-/nanotopographical cues have emerged as a practical and promising strategy for controlling cell fate and reprogramming, which play a key role as biophysical regulators in diverse cellular processes and behaviors. Extracellular biophysical factors can trigger intracellular physiological signaling via mechanotransduction and promote cellular responses such as cell adhesion, migration, proliferation, gene/protein expression, and differentiation. Here, we engineered a highly ordered nanowrinkled graphene oxide (GO) surface via the mechanical deformation of an ultrathin GO film on an elastomeric substrate to observe specific cellular responses based on surface-mediated topographical cues. The ultrathin GO film on the uniaxially prestrained elastomeric substrate through self-assembly and subsequent compressive force produced GO nanowrinkles with periodic amplitude. To examine the acute cellular behaviors on the GO-based cell interface with nanostructured arrays of wrinkles, we cultured L929 fibroblasts and HT22 hippocampal neuronal cells. As a result, our developed cell-culture substrate obviously provided a directional guidance effect. In addition, based on the observed results, we adapted a deep learning (DL)-based data processing technique to precisely interpret the cell behaviors on the nanowrinkled GO surfaces. According to the learning/transfer learning protocol of the DL network, we detected cell boundaries, elongation, and orientation and quantitatively evaluated cell velocity, traveling distance, displacement, and orientation. The presented experimental results have intriguing implications such that the nanotopographical microenvironment could engineer the living cells' morphological polarization to assemble them into useful tissue chips consisting of multiple cell types.

Investigation of Emission States of PSR J1722–3207

We have conducted a detailed study of single-pulse emission from PSR J1722−3207, which was observed at 1369 MHz using the Parkes 64 m radio telescope. PSR J1722−3207 has an asymmetric two-component mean pulse profile. We find that the brighter leading component exhibits a periodic phase-stationary nondrift amplitude modulation while the trailing component remains unchanged. As a result of this, this pulsar switches between a strong state and a weak emission state periodically. Spectral analysis of the fluctuations showed that the modulation period is very short (∼2.0 s or 20P), where P is the rotation period of the pulsar. The polarization properties of the strong and weak states were investigated. The swings in the position angle of the two states are similar, suggesting that their basic emission geometry is the same. At present, it is difficult to explain the periodic mode-changing phenomenon observed in this pulsar with existing subpulse drifting models.

Mode Changing in PSR B0844-35 and PSR B1758-29 with Enhanced Emission at the Profile Centers

We have studied the single pulse emission from two pulsars, PSR B0844-35 and PSR B1758-29, over a wide frequency range of 300–750 MHz using the upgraded Giant Metrewave Radio Telescope. The two pulsars have relatively wide profiles with multiple components, which are a result of the line of sight traversing near the center of the emission beam. In both pulsars, the single pulse sequences show the presence of two distinct emission states, where the profiles become much brighter at the center, with prominent core components during one of the modes, while in the other mode the single pulses show odd–even subpulse drifting with a periodicity of around 2P, P being the rotation period of the pulsar. The centrally bright mode was seen for 10% of the observing duration in PSR B0844-35, which usually lasted for short durations of around 10 pulses, but had two longer sequences of around 100 pulses. On the contrary, the centrally bright mode was dominant in PSR B1758-29 and was seen for around 60% of the observing duration. PSR B1758-29 also showed period amplitude modulations of 60P–70P in both modes. The mode changing in these two pulsars facilitates investigation of the sparking process in the inner acceleration region, dominated by nondipolar magnetic fields. The change in the surface magnetic field configurations likely results in the emission mode change.

Pulsational Velocity Variations of the Radial Mode sdBV Star BPM 36430

Hot subdwarf B stars are core-helium burning objects that were once red giants stripped of their outer H envelopes due to binary interactions. Many exhibit pulsations that can be used to determine fundamental stellar parameters like mass and radius. High-cadence TESS photometry of the sdB star BPM 36430 revealed it to be a hybrid-mode pulsator showing several g-mode pulsations and a single strong p-mode oscillation. The latter is likely a radial mode oscillation, given its period (342 s) and high photometric amplitude (2%). Using time-series spectroscopy from the Goodman spectrograph on the 4.1 m SOAR telescope, we detect a sinusoidal radial velocity variation with a semi-amplitude of 4.4 ± 0.4 km s−1 and period consistent with photometry of the p-mode oscillation. This detection provides further evidence the 342 s mode is radial in nature, and that the Baade–Wesselink method can be used with additional observations to constrain the stellar mass and radius.

Considerable effects of lateralization and aging in intracortical excitation and inhibition.

Findings based on the use of transcranial magnetic stimulation and electromyography (TMS-EMG) to determine the effects of motor lateralization and aging on intracortical excitation and inhibition in the primary motor cortex (M1) are inconsistent in the literature. TMS and electroencephalography (TMS-EEG) measures the excitability of excitatory and inhibitory circuits in the brain cortex without contamination from the spine and muscles. This study aimed to investigate the effects of motor lateralization (dominant and non-dominant hemispheres) and aging (young and older) and their interaction effects on intracortical excitation and inhibition within the M1 in healthy adults, measured using TMS-EMG and TMS-EEG. This study included 21 young (mean age = 28.1 ± 3.2 years) and 21 older healthy adults (mean age = 62.8 ± 4.2 years). A battery of TMS-EMG measurements and single-pulse TMS-EEG were recorded for the bilateral M1. Two-way repeated-measures analysis of variance was used to investigate lateralization and aging and the lateralization-by-aging interaction effect on neurophysiological outcomes. The non-dominant M1 presented a longer cortical silent period and larger amplitudes of P60, N100, and P180. Corticospinal excitability in older participants was significantly reduced, as supported by a larger resting motor threshold and lower motor-evoked potential amplitudes. N100 amplitudes were significantly reduced in older participants, and the N100 and P180 latencies were significantly later than those in young participants. There was no significant lateralization-by-aging interaction effect in any outcome. Lateralization and aging have independent and significant effects on intracortical excitation and inhibition in healthy adults. The functional decline of excitatory and inhibitory circuits in the M1 is associated with aging.

The Far Side of the Galactic Bar/Bulge Revealed through Semi-regular Variables

The Galactic bulge is critical to our understanding of the Milky Way. However, due to the lack of reliable stellar distances, the structure and kinematics of the bulge/bar beyond the Galactic center have remained largely unexplored. Here, we present a method to measure distances of luminous red giants using a period–amplitude–luminosity relation anchored to the Large Magellanic Cloud, with random uncertainties of 10%–15% and systematic errors below 1%–2%. We apply this method to data from the Optical Gravitational Lensing Experiment to measure distances to 190,302 stars in the Galactic bulge and beyond out to 20 kpc. Using this sample, we measure a distance to the Galactic center of R 0 = 8108 ± 106stat ± 93sys pc, consistent with direct measurements of stars orbiting Sgr A*. We cross-match our distance catalog with Gaia DR3 and use the subset of 39,566 overlapping stars to provide the first constraints on the Milky Way’s velocity field (V R , V ϕ , V z ) beyond the Galactic center. We show that the V R quadrupole from the bar’s near side is reflected with respect to the Galactic center, indicating that the bar is bisymmetric and aligned with the inner disk. We also find that the vertical height V Z map has no major structure in the region of the Galactic bulge, which is inconsistent with a current episode of bar buckling. Finally, we demonstrate with N-body simulations that distance uncertainty plays a factor in the alignment of the major and kinematic axes of the bar, necessitating caution when interpreting results for distant stars.

Harmonic generation in Palu Bay, Indonesia

Harbor resonance, which occurs when an incoming wave’s period matches the natural period of the harbor, can be severely damaging to the surrounding areas. Using shallow water equations, we estimated the (natural) resonant period of a bay, particularly one with a hyperbolic-cosine squared bottom shape. There are two scenarios discussed: a constant-width harbor and a non-constant-width harbor. The resonant period is determined analytically by employing the separation of variables method. Further, using the staggered finite volume method, we constructed a computational scheme and performed numerous simulations to recreate and analyze wave resonance. Moreover, we investigated the parameter dependence of resonant wave features. In both constant-width and non-constant-width harbors, only the depth and length of the harbor affect the resonant period and wave amplitude. Meanwhile, changes in the harbor’s maximum width do not have any impact on either feature, despite the fact that changes in width do. The application of the model to the real bathymetry of Palu Bay in Central Sulawesi, Indonesia, proves that resonance occurrences could aggravate the potential danger of tsunami waves whose period coincides with the bay’s resonant period. We believe that by applying the model proposed in this study, we will be able to predict the potential occurrence of resonance in specific bays and therefore design an appropriate coastal defense system.

Respiratory Diaphragm Motion-Based Asynchronization and Limitation Evaluation on Chronic Obstructive Pulmonary Disease.

Background: Chronic obstructive pulmonary disease (COPD) typically causes airflow blockage and breathing difficulties, which may result in the abnormal morphology and motion of the lungs or diaphragm. Purpose: This study aims to quantitatively evaluate respiratory diaphragm motion using a thoracic sagittal magnetic resonance imaging (MRI) series, including motion asynchronization and limitations. Method: First, the diaphragm profile is extracted using a deep-learning-based field segmentation approach. Next, by measuring the motion waveforms of each position in the extracted diaphragm profile, obvious differences in the independent respiration cycles, such as the period and peak amplitude, are verified. Finally, focusing on multiple breathing cycles, the similarity and amplitude of the motion waveforms are evaluated using the normalized correlation coefficient (NCC) and absolute amplitude. Results and Contributions: Compared with normal subjects, patients with severe COPD tend to have lower NCC and absolute amplitude values, suggesting motion asynchronization and limitation of their diaphragms. Our proposed diaphragmatic motion evaluation method may assist in the diagnosis and therapeutic planning of COPD.

Performance-scaled rotor design method for model testing of floating vertical axis wind turbines in wave basins

The wave basin model tests of floating wind turbines typically follow the Froude scaling law, where a geometric-scaled rotor cannot achieve the target thrust due to the Reynolds-number scaling effect. To tackle this issue, a performance-scaled rotor (PSR) has been successfully used in the wave basin model testing of floating horizontal axis wind turbines (HAWTs). Unlike HAWT, the thrust and side forces of a vertical axis wind turbine (VAWT) present periodic and large amplitude variations with the azimuth angle. In this study, a novel PSR design method is proposed for the model testing of floating VAWTs. An alternative airfoil with good aerodynamic performances at low-Reynolds-number is selected to replace the original one. The relationship between the thrust coefficient and the chord length is derived analytically, with accuracy-enhancing corrections. The chord length of the PSR is then determined. The method and procedure are demonstrated by designing and testing a PSR of a 5 MW floating VAWT with three straight blades and a scale ratio of 1:50. Thrust and lateral forces of the floating VAWT are compared and analyzed. Results indicate that the designed PSR can reproduce the thrust and side forces and is applicable for model testing of floating VAWTs.

Site response measurements and implications to soil liquefaction potential using microtremor H/V in Greater Metro Manila, Philippines

This research explores the use of microtremor horizontal-to-vertical spectral ratio (H/V) in obtaining site response characteristics and investigating its relationship with soil liquefaction potential in Greater Metro Manila. We performed single station microtremor measurements in 61 sites along with in situ geotechnical techniques to verify liquefaction potential. The resulting 238 spectral curves were classified according to dominant features and subsequently grouped with the calculated liquefaction potential index (LPI) of the soil. Based on a robust comparison of obtained primary parameters, it is revealed that the shape of the H/V curve, its predominant period and relative amplitude are fundamentally linked to the spatial variability and the shear strength of soils. Therefore, areas of high seismic demand can also have high liquefaction potential, and vice versa. We then correlated the predominant period with the LPI of the soil and extracted a boundary using simple statistical techniques to classify high and low potential for liquefaction subsequently validating its use as a complementary tool for rapid site-specific liquefaction assessment. Such findings are a novel contribution to liquefaction studies employing rapid techniques since the application of microtremors to liquefaction in the Philippines has not been practiced extensively.

Experimental Force Coefficients of a Hydrostatic Thrust Bearing and Comparisons to Predictions

Abstract Reliable fluid film bearings for high-performance turbomachinery provide significantly extended operating life with controllable stiffness and damping force coefficients at low cost. Hydrostatic thrust bearings support thrust loads and control axial motions. This paper reports measurements and predictions of static and dynamic load characteristics of a hydrostatic thrust bearing fed with pressurized air. The current bearing model uses dynamic axial periodic motion amplitudes, that is, models as a function of the initial film thickness, to predict the dynamic force coefficients. Note that, presently, the recorded frequencies and their amplitudes of pneumatic hammer instability along the axial direction are implemented as an external excitation source. The measured and predicted static stiffnesses increase as the film thickness decrease and supply pressure into the bearing increase. The predicted dynamic force coefficients show a favorable agreement with the test data. Analysis reveals the negative damping coefficients and damping ratios as a distinctive onset condition of the present pneumatic hammer instability of the test bearing. A careful recess design and adequate operation conditions along with an accurate prediction can avoid or prevent undesirable pneumatic hammer instability in hydrostatic thrust bearings. This work extends the knowledge database of hydrostatic thrust bearings with pneumatic hammer instability and provides their design guideline for various operating conditions.

Systematic analysis of circadian disrupting substances with a high-throughput zebrafish circadian behavior screening approach

Circadian rhythm aligns numerous biological functions in majority of animals. Aside from well-known external factors such as the light-dark cycle and temperature, circadian rhythm can also be regulated by rarely explored factors such as synthetic substances. Here, we established a circadian behavior screening approach utilizing zebrafish larvae model, which integrated high-throughput capabilities with automated batch processing. With this approach, we systematically analyzed the circadian disruptive effects of >60 synthetic substances commonly detected in aquatic environment by assessing both the circadian period length and amplitude of circadian behavior, with an exposure concentration set at 100 μg/L. Among tested substances, a series of circadian disrupting compounds (circadian disruptors) were identified. Several categories of the hit compounds can be recognized, such as phthalate (diisopentyl phthalate (DIPP), with 10.1 % and 49.6 % increases for circadian period length and amplitude, respectively), neuroactive substance (mirtazapine, with 10.6 % and 63.1 % increases, respectively), and biocides (thiamethoxam, with 100.3 % increase for amplitude). Among these compounds, DIPP increased circadian period length and amplitude with a high degree. Aside from DIPP, we further examined eleven other phthalates and demonstrated that benzyl butyl phthalate, diisobutyl phthalate and diisohexyl phthalate could also significantly increase the zebrafish circadian period length by 7.9 %, 3.7 % and 8.5 %, respectively. Collectively, the present findings substantiated the feasibility of this high throughput screening strategy for circadian disruptor's discovery and provided novel insights into understanding of the potential risks of synthetic substances.

The Role of Entrainment and Aperiodicity in Vibrotactile Discrimination

The extent to which entrainment – the phenomenon in neuroscience where neurons synchronize their firing patterns to external stimuli with rhythmic or periodic features – occurs in response to aperiodic or irregular flutter stimuli remains debatable. It has been proposed by Mountcastle et al. that information is processed in a periodic manner; however, more recently, Romo et al. challenged Mountcastle’s theory and proposed that flutter stimulus was encoded based on the rapidly adapting fibers, not the periodicity.1-5 Therefore, if Mountcastle et al. is correct, the brain should be more adept at discriminating frequency between periodic stimuli than between aperiodic stimuli; conversely, if Romo et al. is correct, the brain should be equally good at discriminating frequencies between periodic and aperiodic stimuli. In this study, a two-point vibrotactile stimulation device (The Brain Gauge, Cortical Metrics, USA) was used to stimulate digits II and III of 43 participants’ preferred hand to determine their difference limen (DL) for both amplitude (AD) and frequency (FD) discrimination tests, given aperiodic or periodic stimuli. The tests were performed in the following order: periodic AD, aperiodic AD, periodic FD, and aperiodic FD. The results suggest that the periodicity of the stimuli affects frequency discrimination more than amplitude discrimination and the participants were significantly better at discriminating stimuli with periodic frequencies than aperiodic frequencies. A paired, one-tailed t-test indicated that the subject DLs resulting from periodic stimuli were significantly different (p<0.05) from that resulting from aperiodic stimuli for frequency discrimination, while it was not statistically significant for amplitude discrimination. The results were in favor of Mountcastle’s theory; however, more trials with a more controlled experimental environment may be needed to definitively conclude.

An Untargeted Survey of the Rotational Properties of Main-belt Asteroids using the Transiting Exoplanet Survey Satellite (TESS)

We present photometric data for minor planets observed by the Transiting Exoplanet Survey Satellite during its Cycle 1 operations. In total, we extracted usable detections for 37,965 objects. We present an examination of the reliability of the rotation period and light-curve amplitudes derived from each object based upon the number of detections and the normalized Lomb–Scargle power of our period fitting and compare and contrast our results with previous similar works. We show that for objects with 200 or more photometric detections and a derived normalized, generalized Lomb–Scargle power greater than 0.2, we have an 85% confidence in that period; this encompasses 3492 rotation periods we consider to be highly reliable. We independently examine a series of periods first reported by Pál et al.; periods derived in both works found to have similar results should be considered reliable. Additionally, we demonstrate the need to properly account for the true proportion of slow rotators (P > 100 hr) when inferring shape distributions from sparse photometry.

Prediction of pulsating turbulent pipe flow by deep learning with generalization capability

The spatiotemporal development of turbulent pipe flows with various conditions of pulsation is predicted by deep learning. In the present model, convolutional autoencoder (CAE) extracts the spatial features of the input as latent space vectors and long short-term memory (LSTM) evolves them in time. Time-delay neural network (TDNN) is accompanied by LSTMs to treat general unsteady variations of the spatial mean pressure gradient of the pulsatile flows. Temporal evolution is processed in a sequence-to-sequence manner. Note that the pulsating turbulent pipe flows are statistically unsteady flows for which the spatiotemporal development has been seldom predicted by the deep learning technique. The flow field obtained by direct numerical simulation (DNS) was used to train the model. When the pulsating parameters for the training and prediction are the same, several model parameters are validated. To examine further generalization capability, the present model was trained by data from four pulsation conditions. The model was tested afterward by test data from twenty different pulsation conditions of which the range of parameters is either within or out of the range covered by the training data. The model successfully predicts the various pulsating flow fields with reasonable accuracy. The change in the period yields a larger influence on prediction accuracy than the change in the amplitude. The degradation of the prediction accuracy of the bulk velocity for the case with a long period and large amplitude is not caused by the latent space vectors themselves, but by the decoder which reconstructs the flow field from the latent space vectors.

Development and application of a semantic differential for perception-based optimization of wind turbine and other broadband sounds

Growing numbers of the population are exposed to wind turbine (WT) and other broadband sound sources from the environment. Acoustically optimizing emissions of environmental noise sources to minimize negative effects on the population therefore becomes increasingly important. The objective of this study was to develop and apply a semantic differential (SD) for multidimensional perception-based assessment of WT and other broadband sounds, to be potentially applied for acoustic optimization. An SD was developed specifically for broadband sounds and applied in a laboratory listening experiment, using outdoor WT and other broadband sounds covering a wide spectral range, at 40 dBA playback level. Fifty-two participants rated the sounds using the SD. Relevant perceptual dimensions were extracted, and a prediction model for noise annoyance was established on this basis. The experiment revealed that participants could well describe and discriminate the sound characteristics using the affective-evaluative everyday language of the SD. Four perceptual dimensions (or factors) were identified: Evaluation, Timbre, Activity and Randomness, with the latter three describing spectral shape, periodic amplitude modulation and random amplitude modulation, respectively. The factors were strongly linked with annoyance and well suited to establish an annoyance prediction model. The results can be applied in a perception-influenced design to identify how to optimize (perceived) acoustical characteristics and thus minimize annoyance effects on the population. Also, they might potentially be used in field surveys for a multidimensional assessment of broadband sounds to study the long-term annoyance potential of specific perceptual characteristics. This might eventually help to refine exposure–response relationships using predictors beyond basic noise metrics.