Changes In Frequency Research Articles

Magnetization dynamics in single and trilayer nanowires.

We have studied the magnetization dynamics of single Py(t) (t = 20 nm, 50 nm) and trilayer [Py(50)/Pd(tPd)/Py(20)] nanowire arrays fabricated over large areas using deep ultraviolet lithography technique. The dynamic properties are sensitive to the field orientation and magnetic film thicknesses. A single resonant mode corresponding to the excitations at the bulk part of the wire is detected in all the single-layer nanowire arrays. Furthermore, the spacer layer thickness influenced the dynamic properties in trilayer samples due to the different coupling mechanisms. A single resonant mode is observed in tPd = 2 nm trilayer nanowires with a sharp frequency jump from 13 GHz to 15 GHz across the reversal regime. This indicates the exchange coupling and the coherence in magnetization precession in the top and bottom layers. On the other hand, tPd = 10 nm wires display two well-resolved modes separated by ~3GHz with a gradual change in frequency across the reversal regime from -26 mT to -46 mT, indicating the presence of long-range dipolar interactions instead of exchange coupling. The spacer layer of the proposed spin-valve-type structure can be tailored for desired microwave splitters or combiners.&#xD.

Canine hyper-sociability structural variants associated with altered three-dimensional chromatin state

Strong selection on complex traits can lead to skewed trait means and reduced trait variability in populations. An example of this phenomenon can be evidenced in allele frequency changes and skewed trait distributions driven by persistent human-directed selective pressures in domesticated species. Dog domestication is linked to several genomic variants; however, the functional impacts of these variants may not always be straightforward when found in non-coding regions of the genome. Four polymorphic transposable elements (TE) found within non-coding sites along a 5 Mb region on canine CFA6 have evolved due to directional selection associated with heightened human-directed hyper-sociability in domesticated dogs. We found that the polymorphic TE in intron 17 of the canine GTF2I gene, which was previously reported to be negatively correlated with canid human-directed hyper-sociability, is associated with altered chromatin looping and hence distinct cis-regulatory landscapes. We reported supporting evidence of an E2F1-DNA binding peak concordant with the altered loop and higher expression of GTF2I exon 18, indicative of alternative splicing. Globally, we discovered differences in pathways regulating the extra-cellular matrix with respect to TE copy number. Overall, we reported evidence suggesting an intriguing molecular convergence between the emergence of hypersocial behaviors in dogs and the same genes that, when hemizygous, produce human Williams Beuren Syndrome characterized by cranio-facial defects and heightened social behaviors. Our results additionally emphasize the often-overlooked potential role of chromatin architecture in social evolution.

An enhanced mathematical model for evaluating grid-to-rod fretting wear under complex boundary

Grid-to-rod fretting wear is a significant cause of fuel failure in pressurized water reactors and poses a challenge in fuel performance evaluation. As burnup increases, neutron irradiation can lead to complex changes in the grid-to-rod system, affecting its dynamic behavior. This paper presents an enhanced mathematical model that can simulate the coupled axial-lateral motion and complex boundary conditions, including relaxation support, friction, and gap constraint. Through multiple parametric studies, the model has revealed valuable results. Notably, grid relaxation of 10%–30% significantly impacts wear. Multiple critical excitation frequencies can cause drastic changes in vibration and wear. The increase in holding force due to rod swelling and the early opening of the gap due to creep down require careful attention. Moreover, the effect of axial force on changes in natural frequency and increased wear should be considered.

Revisiting Dominance in Population Genetics.

Dominance refers to the effect of a heterozygous genotype relative to that of the two homozygous genotypes. The degree of dominance of mutations for fitness can have a profound impact on how deleterious and beneficial mutations change in frequency over time as well as on the patterns of linked neutral genetic variation surrounding such selected alleles. Since dominance is such a fundamental concept, it has received immense attention throughout the history of population genetics. Early work from Fisher, Wright, and Haldane focused on understanding the conceptual basis for why dominance exists. More recent work has attempted to test these theories and conceptual models by estimating dominance effects of mutations. However, estimating dominance coefficients has been notoriously challenging and has only been done in a few species in a limited number of studies. In this review, we first describe some of the early theoretical and conceptual models for understanding the mechanisms for the existence of dominance. Second, we discuss several approaches used to estimate dominance coefficients and summarize estimates of dominance coefficients. We note trends that have been observed across species, types of mutations, and functional categories of genes. By comparing estimates of dominance coefficients for different types of genes, we test several hypotheses for the existence of dominance. Lastly, we discuss how dominance influences the dynamics of beneficial and deleterious mutations in populations and how the degree of dominance of deleterious mutations influences the impact of inbreeding on fitness.

AcousTac: Tactile Sensing with Acoustic Resonance for Electronics-Free Soft Skin.

Sound is a rich information medium that transmits through air; people communicate through speech and can even discern material through tapping and listening. To capture frequencies in the human hearing range, commercial microphones typically have a sampling rate of over 40 kHz. These accessible acoustic technologies are not yet widely adopted for the explicit purpose of giving robots a sense of touch. Some researchers have used sound to sense tactile information, both monitoring ambient soundscape and with embedded speakers and microphones to measure sounds within structures. However, these options commonly do not provide a direct measure of steady state force or require electronics integrated somewhere near the contact location. In this work, we present AcousTac, an acoustic tactile sensor for electronics-free, force-sensitive soft skin. Compliant silicone caps and plastic tubes compose the resonant chambers that emit pneumatic-driven sound measurable with a conventional off-board microphone. The resulting frequency changes depend on the external loads on the compliant endcaps. The compliant cap vibrates with the resonant pressure waves and is a nonidealized boundary condition, initially producing a nonmonotonic force response. We characterize two solutions-adding a distal hole and mass to the cap-resulting in monotonic and nonhysteretic force readings with this technology. We can tune each AcousTac taxel to specific force and frequency ranges, based on geometric parameters including tube length, and thus uniquely sense each taxel simultaneously in an array. We demonstrate AcousTac's functionality on two robotic systems: a 4-taxel array and a 3-taxel astrictive gripper. Simple to implement with off-the-shelf parts, AcousTac is a promising concept for force sensing on soft robotic surfaces, especially in situations where electronics near the contact are not suitable. Equipping robots with tactile sensing and soft skin provides them with a sense of touch and the ability to safely interact with their surroundings.

Which droughts are becoming more frequent? A copula entropy analysis on the return period of droughts in Europe

AbstractClimate change and global warming have increased the frequency of extreme events, particularly over the past decades. Changes in drought frequency are not yet understood, especially regarding which drought features are becoming more frequent (e.g., are longer or high-magnitude droughts becoming more frequent, or both?). In this study, we present a novel methodology to accurately and consistently estimate changes in return periods of different types of droughts. For this purpose, we implemented copula-entropy theory to assess drought frequencies and their changes. As an example of the application of the proposed method, we used data from the European Climate Assessment and Dataset (ECA&D), from which we selected 26 stations in Central Europe with over 100 years of data and low incidence of missing days ($$\le$$ ≤ 0.3%). The results of the new analysis indicate that there was a high variability in the frequency change patterns across Central Europe over the last century; however, most regions have experienced an increase in the frequency of medium-to-high intensity droughts. The use of the copula-entropy theory to assess drought frequency is a reliable method that allows systematic monitoring and easy updating of current knowledge, and is computationally efficient and statistically robust.

Experiences of antenatal care practices to reduce stillbirth: surveys of women and healthcare professionals pre-post implementation of the Safer Baby Bundle

BackgroundThe Safer Baby Bundle (SBB) aimed to reduce stillbirth rates in Australia through improving pregnancy care across five elements; smoking cessation, fetal growth restriction (FGR), decreased fetal movements (DFM), side sleeping in late pregnancy and decision making around timing of birth. We assessed experiences of women and healthcare professionals (HCPs) with antenatal care practices around the five elements.MethodsA pre-post study design using online surveys was employed to assess change in HCPs awareness, knowledge, and frequency of performing recommended practices (22 in total) and women’s experiences of care received related to reducing their chance of stillbirth. Women who had received antenatal care and HCPs (midwives and doctors) at services participating in the SBB implementation program in two Australian states were invited to participate. Surveys were distributed over January to July 2020 (pre) and August to December 2022 (post). Comparison of pre-post responses was undertaken using Fisher’s exact, Pearson’s chi-squared or Wilcoxon rank-sum tests.Results1,225 women (pre-1096/post-129) and 1,415 HCPs (pre-1148/post-267, ≥ 83% midwives) completed the surveys. The frequency of HCPs performing best practice ‘all the time’ significantly improved post-SBB implementation across all elements including providing advice to women on side sleeping (20.4–79.4%, p < 0.001) and benefits of smoking cessation (54.5–74.5%, p < 0.001), provision of DFM brochure (43.2–85.1%, p < 0.001), risk assessments for FGR (59.2–84.1%, p < 0.001) and stillbirth (44.5–73.2%, p < 0.001). Practices around smoking cessation in general showed less improvement e.g. using the ‘Ask, Advise and Help’ brief advice model at each visit (15.6–20.3%, p = 0.088). Post-implementation more women recalled conversations about stillbirth and risk reduction (32.2–50.4%, p < 0.001) and most HCPs reported including these conversations in their routine care (35.1–83.0%, p < 0.001). Most HCPs agreed that the SBB had become part of their routine practice (85.0%).ConclusionsImplementation of the SBB was associated with improvements in practice across all targeted elements of care in stillbirth prevention including conversations with women around stillbirth risk reduction. Further consideration is needed around strategies to increase uptake of practices that were more resistant to change such as smoking cessation support.Trial registrationThe Safer Baby Bundle Study was retrospectively registered on the Australian New Zealand Clinical Trials Registry database, ACTRN12619001777189, date assigned 16/12/2019.

Death Feigning in Larvae of Scorpionflies (Mecoptera: Panorpidae): Frequency and Postural Changes Based on Larval Instars

Death Feigning in Larvae of Scorpionflies (Mecoptera: Panorpidae): Frequency and Postural Changes Based on Larval Instars

RB1 circulating-tumor DNA in the blood of Retinoblastoma patients increases in untreated patients.

Circulating tumor DNA (ctDNA) in plasma has been identified in many cancers, including retinoblastoma at diagnosis. We have previously shown that with treatment (enucleation or ophthalmic artery chemosurgery (OAC)) all ctDNA disappears; and if there is persistent plasma ctDNA after treatment metastases develop. The purpose of this study was to determine how the ctDNA RB1 variant allele frequency (VAF) changes in patients with retinoblastoma who have delayed treatment. Circulating tumor DNA RB1 was detected and VAF was measured at diagnosis and again prior to any intervention at some time later ranging from 2 to 28 days. Four patients with five ctDNA RB1 mutations were detected at diagnosis and VAF was increased on re-evaluation of the same RB1 mutations in ctDNA. In this small cohort, every patient (4) and every RB1 mutation (5) plasma level VAF% increased when measured at two time periods before treatment was instituted suggesting that growing tumors demonstrate increasing plasma ctDNA.

Asymmetry in the Perception of Electrical Chirps Presented to Cochlear Implant Listeners.

Although a broadband acoustic click is physically the shortest duration sound we can hear, its peripheral neural representation is not as short because of cochlear filtering. The traveling wave imposes frequency-dependent delays to the sound waveform so that in response to a click, apical nerve fibers, coding for low frequencies, are excited several milliseconds after basal fibers, coding for high frequencies. Nevertheless, a click sounds like a click and these across-fiber delays are not perceived. This suggests that they may be compensated by the central auditory system, rendering our perception consistent with the external world. This explanation is difficult to evaluate in normal-hearing listeners because the contributions of peripheral and central auditory processing cannot easily be disentangled. Here, we test this hypothesis in cochlear implant listeners for whom cochlear mechanics is bypassed. Eight cochlear implant users ranked in perceived duration12 electrical chirpsof various physical durations and spanning the cochlea in the apex-to-base or base-to-apex direction (Exp. 1). Late-latency cortical potentials were also recorded in response toa subset of these chirps (Exp. 2). We show that an electrical chirp spanning the cochlea from base-to-apex is perceived as shorter than the same chirp spanning the cochlea in the opposite direction despite having the same physical duration. Cortical potentials also provide neural correlates of this asymmetry in perception. These results demonstrate that the central auditory system processes frequency sweeps differently depending on the direction of the frequency change and that this processing difference is not simply the result of peripheral filtering.

Evaluating changes in flood frequency due to climate change in the Western Cape, South Africa

AbstractThis study assesses the impact of climate change on flood frequency across seven sites in the Western Cape province of South Africa. The calibrated Water Resources Simulation Model (WRSM)/Pitman hydrological model was run using precipitation inputs from two representative concentration pathways (RCP) scenarios (RCP 4.5 and 8.5) using a combination of eight global circulatory models (GCM) for the two periods (2030–2060 and 2070–2100). GCMs were statistically downscaled using the delta change (DC), linear scaling (LS) and quantile delta mapping (QDM) approaches. Average daily discharge was estimated from each downscaled daily precipitation dataset using the Pitman/WRSM model with the Fuller and Sangal estimation methods used to calculate daily instantaneous peak flows. Flood frequency curves (FFC) were generated using the annual maximum series (AMS) for the GCM ensemble mean and individual GCMs for the return periods between 2 and 100 years. FFCs generated based on LS and QDM downscaling methods were aligned for the GCM ensemble mean in terms of the direction of FFCs. Further analysis was conducted using outputs based on the QDM approach, given its suitability in projecting peak flows. Under this method, both Fuller and Sangal FFCs exhibited a decreasing trend across the Jonkershoek and Little Berg River sites; however, estimated quantiles for low-probability events were higher under the Fuller method. This study noted the variation in FFCs from individual GCMs compared to the FFC representing the GCM ensemble mean. Further research on climate change flood frequency analysis (FFA) in South Africa should incorporate other advanced downscaling and instantaneous peak flow estimation (IPF) methods.

Flexible modeling of headache frequency fluctuations in migraine with hidden Markov models.

To explore hidden Markov models (HMMs) as an approach for defining clinically meaningful headache-frequency-based groups in migraine. Monthly headache frequency in patients with migraine is known to vary over time. This variation has not been completely characterized and is not well accounted for in the classification of individuals as having chronic or episodic migraine, a diagnosis with potentially significant impacts on the individual. This study investigated variation in reported headache frequency in a migraine population and proposed a model for classifying individuals by frequency while accounting for natural variation. The American Registry for Migraine Research (ARMR) was a longitudinal multisite study of United States adults with migraine. Study participants completed quarterly questionnaires and daily headache diaries. A series of HMMs were fit to monthly headache frequency data calculated from the diary data of ARMR. Changes in monthly headache frequency tended to be small, with 47% of transitions resulting in a change of 0 or 1 day. A substantial portion (24%) of months reflected daily headache with individuals ever reporting daily headache likely to consistently report daily headache. An HMM with four states with mean monthly headache frequency emissions of 3.52 (95% Prediction Interval [PI] 0-8), 10.10 (95% PI 4-17), 20.29 (95% PI 12-28), and constant 28 days/month had the best fit of the models tested. Of sequential month-to-month headache frequency transitions, 12% were across the 15-headache days chronic migraine cutoff. Under the HMM, 38.7% of those transitions involved a change in the HMM state, and the remaining 61.3% of the time, a change in chronic migraine classification was not accompanied by a change in the HMM state. A divide between the second and third states of this model aligns most strongly with the current episodic/chronic distinction, although there is a meaningful overlap between the states that supports the need for flexibility. An HMM has appealing properties for classifying individuals according to their headache frequency while accounting for natural variation in frequency. This empirically derived model may provide an informative classification approach that is more stable than the use of a single cutoff value.

Magnetic skin effect in Pb(Fe _{1/2}$ Nb _{1/2}$ )O3

Relaxor-ferroelectrics display exceptional dielectric properties resulting from the underlying random dipolar fields induced by strong chemical inhomogeneity. An unusual structural aspect of relaxors is a skin-effect where the near-surface region in single crystals exhibit structures and critical phenomena that differ from the bulk. Relaxors are unique in that this skin effect extends over a macroscopic lengthscale of ∼100 μm whereas usual surface layers only extend over a few unit cells (or ∼nm). We present a muon spectroscopy study of Pb(Fe _{1/2} Nb _{1/2} )O3 (PFN) which displays ferroelectric order, including many relaxor-like dielectric properties such as a frequency broadened dielectric response, and antiferromagnetism with spatially short-range polar correlations and hence can be termed a multiferroic. In terms of the magnetic behavior determined by the Fe3+ ( S=5/2 , L ≈ 0) ions, PFN has been characterized as a unique example of a ‘cluster spin-glass’. We use variable momentum muon spectroscopy to study the depth dependence of the slow magnetic relaxations in a large 1 cm3 crystal of PFN. Zero-field positive muon spin relaxation is parameterized using a stretched exponential, indicative of a distribution of relaxation rates of the Fe3+ spins. This bandwidth of frequencies changes as a function of muon momentum, indicative of a change in the Fe3+ relaxation rates as a function of muon implantation depth in our single crystal. Using negative muon elemental analysis, we find small-to-no measurable change in the Fe3+/Nb5+ concentration with depth implying that chemical concentration alone cannot account for the change in the relaxational dynamics. PFN displays an analogous magnetic skin effect reported to exist in the structural properties of relaxor-ferroelectrics.

Effect of Bias Frequency on Bottom-Up SiO2 Gap-Filling Using Plasma-Enhanced Atomic Layer Deposition.

High-aspect-ratio patterns are required for next-generation three-dimensional (3D) semiconductor devices. However, it is challenging to eliminate voids and seams during gap-filling of these high-aspect-ratio patterns, such as deep trenches, especially for nanoscale high-aspect-ratio patterns. In this study, a SiO2 plasma-enhanced atomic layer deposition process incorporated with ion collision using bias power to the substrate was used for bottom-up trench gap-filling. The effect of bias power frequency on SiO2 trench gap-filling was then investigated. Results showed that changes in bias power frequency did not significantly change the process rate, such as SiO2 growth per cycle. At relatively low bias power frequencies, high-energy ions formed an overhang at the entrance of the high-aspect-ratio trench pattern through sputter etching and redeposition, blocking the pattern entrance. However, at relatively high-frequency bias power, overhang formation due to sputtering did not occur. In the trench interior, due to a scattering effect of ions, deposition was thicker at the bottom of the trench than that at the top, achieving bottom-up gap-filling and void-free gap-filling.

A molecular synergy of non-covalent interactions facilitated via theobromine modifying the self-assembly process of type I collagen

Type I Collagen is a multifunctional fibrous protein present significantly in the connective tissues. Generally, fibril formation process of an interstitial collagen begins with a triple helix alignment to form a pentafibril, which sequentially self-assembles into a microfibril. Typically, this sequential formation can be achieved under an in vitro condition as well by maintaining certain specific physiological parameters to mimic the interstitial microenvironment of collagen. The necessity to study such a kinetically driven process is due to its implications in template fabrication particularly as a scaffold to enhance the growth of specific stem cells or accelerating nanoparticle synthesis. Drawing inspiration from this, theobromine, a methylxanthine that contributes towards the hydrogen bond network via dimerization and stacking interaction was used as a small molecule in modifying the molecular level interactions of a self-assembled collagen. Initially, rheological studies revealed certain variations in the viscous properties of collagen on addition of theobromine. Turbidity assay showed an increase in the rate of fibril formation and its topographical changes were observed through the high-resolution scanning electron microscope. The stability and probable physico-chemical interactions between collagen and theobromine were comprehended from the vibrational frequency changes recorded using (FT-IR) (ATR) and conformational changes using Circular Dichroism (CD) studies. Our results show possible multibinding sites on theobromine, which would compete to bind with the polar and non-polar residues exposed over the monomeric surfaces of triple helix causing a local conformational fluctuation modifying protein-protein interaction.

Worsening trends in the frequency of methamphetamine and other stimulant use between treatment admission and discharge

BackgroundTreatment for methamphetamine and other stimulants can be effective but dropout and relapse are very high. Abstinence is the conventional outcome used to evaluate treatment success, but sefining treatment success in this way misses opportunities to promote improved health even when abstinence is not achieved. Reducing methamphetamine and stimulant use without abstinence is associated with many positive outcomes. However, little is known about drug use patterns during treatment or trends in use over time. MethodsWe used the Treatment Episode Dataset-Discharges (TEDS-D) to identify treatment episodes that had a stimulant drug indicated as the primary substance of use (2017-2021; N=251,841; methamphetamine, cocaine, other amphetamines, or other stimulants). Our outcome was the change in the frequency of drug use between admission and discharge (decreased use with abstinence, decreased use without abstinence, increased use). We used multiple logistic regression to model a change in drug use frequency, predicted by year, stimulant type, and their interaction. ResultsNearly two-thirds of the sample (60%) had methamphetamine indicated as the primary stimulant of use. There was a decrease in the predicted rate of abstinence over time and worsening trends were strongest among those using methamphetamine. Daily and periodic drug use at both admission and discharge (no change in use) became worse over time, particularly for those using methamphetamine. ConclusionTreatment outcomes worsened over time and declined fastest among those reporting methamphetamine. Abstinence was rare and most treatment clients did not change their drug use behavior. We recommend a renewed focus on evidence-based harm reduction while the nation’s treatment systems continue grappling with the stimulant crises.

Long term safety, continuation rates and subjective and objective success of Posterior Tibial Nerve Stimulation for Overactive Bladder

Introduction:Posterior tibial nerve stimulation (PTNS) is currently offered to patients with refractory overactive bladder (OAB). We aim to evaluate the efficacy, safety and long-term continuation of PTNS over 11 years. Methods:We conducted a retrospective cohort study on all patients who underwent PTNS from 2012 to 2023. The primary outcomes were change in urinary frequency over 24 hours, maximum voided volume (MVV), number of episodes of urgency urinary incontinence (UUI) and patient perception of intensity of urgency scale (PPIUS). Results:We identified 81 patients. 83% of patients completed 12 treatments of PTNS, and 54% of those that did not complete their full course of treatment stated that this was due to inefficacy. 33% of patients underwent PTNS ‘top ups’ as needed. Only 1 patient reported an adverse effect of musculoskeletal leg pain.28% of patients reported a subjective improvement of their symptoms by 50% or more. There was an average reduction in daytime frequency by 0.6 episodes (p = 0.033), an increase in MVV by 13mls (p = 0.927), a reduction in UUI episodes each day by 0.7 (p = 0.008) and a reduction in average PPIUS by 0.4 (p = 0.024). Conclusion:PTNS remains a safe treatment option for patients with refractory OAB with evidence of both subjective and objective improvement to most symptoms. The majority of our patients completed a 12-week cycle but only 1 in 3 chose to have further PTNS ‘top ups’ and only 1 in 5 are continuing with PTNS for long term management of their OAB.

Changes in the Frequency of Actions Associated With Mental Health During Online Treatment: Analysis of Demographic and Clinical Factors.

Specific daily actions (eg, goal setting, meaningful activities) are associated with mental health. Performing specific daily actions at a higher frequency is associated with significantly lower baseline symptoms of depression and anxiety, as well as better psychological treatment outcomes for depression and anxiety. This study explored how the frequency of specific daily actions associated with mental health may differ prior to, during, and following treatment according to demographic and clinical characteristics. Using a sample of 448 patients from an Australian national digital psychology service, we examined baseline differences in daily action frequency and changes in daily action frequency during a digital psychological treatment according to demographic and clinical subgroups. A total of 5 specific types of daily actions were measured using the Things You Do Questionnaire: healthy thinking, meaningful activities, goals and plans, healthy habits, and social connections. The frequency of daily actions differed according to employment status (largest P=.005) and educational level (largest P=.004). Daily action frequency was lower in those participants with more severe or chronic depression or anxiety symptoms (largest P=.004). Participants reported larger increases in how often they did these daily actions from baseline to midtreatment compared to mid- to posttreatment. Depression duration (P=.01) and severity (P<.001) were associated with differences in how daily action frequency changed during treatment. The findings of this study support continued research exploring the relationship between daily actions and mental health, how this relationship might differ between individuals, and the clinical potential of supporting individuals to increase the frequency of daily actions to improve mental health.

Beat frequency induced transitions in synchronization dynamics

In neurosciences, the brain processes information via the firing patterns of connected neurons operating across a spectrum of frequencies. To better understand the effects of these frequencies in the neuron dynamics, we have simulated a neuronal network of Izhikevich neurons to examine the interaction between frequency allocation and intermittent phase synchronization dynamics. As the synchronized population of neurons passes through a bifurcation, an additional frequency mode emerges, enabling a match in the mean frequency while retaining distinct most probable frequencies among neurons. Subsequently, the network intermittently transits between two patterns, one partially synchronized and the other unsynchronized. Through our analysis, we demonstrate that the frequency changes on the network lead to characteristic transition times between synchronization states. Moreover, these transitions adhere to beat frequency statistics when the neurons’ frequencies differ by multiples of a frequency gap. Finally, our results can improve the performance in predicting transitions on problems where the beat frequency strongly influences the dynamics.

Hemodynamic effects of pulsatile frequency of right ventricular assist device (RVAD) on pulmonary perfusion: a simulation study.

Right ventricular assist devices (RVADs) have been extensively used to provide hemodynamic support for patients with end-stage right heart (RV) failure. However, conventional in-parallel RVADs can lead to an elevation of pulmonary artery (PA) pressure, consequently increasing the right ventricular (RV) afterload, which is unfavorable for the relaxation of cardiac muscles and reduction of valve complications. The aim of this study is to investigate the hemodynamic effects of the pulsatile frequency of the RVAD on pulmonary artery. Firstly, a mathematical model incorporating heart, systemic circulation, pulmonary circulation, and RVAD is developed to simulate the cardiovascular system. Subsequently, the frequency characteristics of the pulmonary circulation system are analyzed, and the calculated results demonstrate that the pulsatile frequency of the RVAD has a substantive impact on the pulmonary artery pressure. Finally, to verify the analysis results, the hemodynamic effects of the pulsatile frequency of the RVAD on pulmonary artery are compared under diffident support modes. It is found that the pulmonary artery pressure decreases by approximately 6% when the pulsatile frequency changes from 1 to 3Hz. The increased pulsatile frequency of RA-PA support mode may facilitate the opening of the pulmonary valve, while the RV-PA support mode can more effectively reduce the load of RV. This work provides a useful method to decrease the pulmonary artery pressure during the RVAD supports and may be beneficial for improving myocardial function in patients with end-stage right heart failure, especially those with pulmonary hypertension.