Pulse Time Research Articles

In search of the biggest bangs since the big bang

Many galaxies contain SuperMassive Black Holes (SMBHs), whose formation and history raise many puzzles. Pulsar timing arrays have recently discovered a low-frequency cosmological “hum” of gravitational waves that may be emitted by SMBH binary systems, and the JWST and other telescopes have discovered an unexpectedly large population of high-redshift SMBHs. We argue that these two discoveries may be linked, and that they may enhance the prospects for measuring gravitational waves emitted during the mergers of massive black holes, thereby opening the way towards resolving many puzzles about SMBHs as well as providing new opportunities to probe general relativity.

Cramér-Rao lower bounds on parameter estimation for a circular binary of supermassive black holes in gravitational wave observations using pulsar timing array

Abstract Pulsar timing arrays (PTAs) are effective in detecting low-frequency gravitational waves (GWs), especially in circular binary systems of supermassive black holes. To evaluate the effectiveness and accuracy of PTAs in searching for GW parameter estimation, we use the Cramer-Rao lower bound to estimate the parameters of the Virgo source under various search conditions, including both evolving and non-evolving scenarios, as well as Earth and pulsar term searches, and only Earth term searches. The results show that the estimation accuracy of the inclination angle and GW strain is lower in the evolving condition than in the non-evolving condition because the two parameters participate in the evolving process. In addition, we find that the parameters estimable relates to signal-to-noise ratio, which is beneficial for reducing the dimensionality in the search process. In summary, our method serves as a reference for exploring lower parameter limits under different conditions and assists in assessing the optimization of parameter estimation in GW detection algorithms. This helps lay the theoretical foundation for advances in the field of GWs and the optimization of PTAs.

Noise analysis of six pulsars and a limit on the gravitational wave background

The direct detection of ultra-low frequency gravitational waves (GWs, 10−9 − 10−6 Hz) using pulsar timing arrays (PTAs) is a significant application of millisecond pulsars. The initial detection of GWs in the nano-Hertz range will probably be an isotropic stochastic GW background (GWB) emitted by the combination of merging super-massive black hole binaries (SMBHBs). In this study, we utilize data from six pulsars collected with four European PTA (EPTA) telescopes to place an upper limit on the GWB amplitude A=2.34−1.32+0.75×10−15 (95%) as a function of the spectral slope α = − 2/3, corresponding to a GWB generated by inspiraling SMBHBs. The posterior for the amplitude that we obtained from the six brightest EPTA pulsars is strongly consistent with previously published upper limits set by the three PTAs. We also compare the sensitivity of our reprocessed pulsar pulse times of arrival (ToAs) determined by the superior ToA creation method, which utilizes a combination of the best template generation algorithm and template-matching algorithm, with the ToAs determined by the EPTA groups. Our analysis shows that the reprocessed ToAs obtained with the superior ToA creation method yield narrower posteriors, indicating an overall increased sensitivity to GW.

Memristor based on carbon nanotube gelatin composite film as artificial optoelectronic synapse for image processing

Photoelectric artificial synapses based on memristors is an effective method to realize neuromorphic computation. This study presents an optoelectronic responsive artificial synapse made of a composite material consisting of gelatin and carbon nanotubes. The memristor demonstrates characteristics of analog resistive switching, the ability to store multiple memory states, and impressive retention properties. It has the capability to induce an excitatory post-synaptic current by means of electrical pulses or pulsed light exposure. The excitatory post-synaptic current can be modulated by the number, amplitude and interval of electrical pulses, as well as the action time, interval and light intensity of optical pulses. The artificial synapse showcases the emulation of fundamental Hebbian learning protocols, including spike timing dependent plasticity and spike amplitude dependent plasticity. In addition, the charge transfer in the carbon nanotube gelatin composite optoelectronic memristor is investigated through first-principles calculations, shedding light on its operational mechanism. Experimental results show that these devices have the potential to be utilized for processing image information, resulting in a significant reduction of input data and training expenses when recognizing handwritten numbers. Overall, the optoelectronic synapse exhibits promising image processing prospects in the field of neuromorphic computing.

Axion-gauge dynamics during inflation as the origin of pulsar timing array signals and primordial black holes

We demonstrate that the recently announced signal for a stochastic gravitational wave background (SGWB) from pulsar timing array (PTA) observations, if attributed to new physics, is compatible with primordial GW production due to axion-gauge dynamics during inflation. More specifically we find that axion-U(1) models may lead to sufficient particle production to explain the signal while simultaneously source some fraction of sub-solar mass primordial black holes (PBHs) as a signature. Moreover there is a parity violation in GW sector, hence the model suggests chiral GW search as a concrete target for future. We further analyze the axion-SU(2) coupling signatures and find that in the low/mild backreaction regime, it is incapable of producing PTA evidence and the tensor-to-scalar ratio is low at the peak, hence it overproduces scalar perturbations and PBHs.

Gravitational Wave Symphony from Oscillating Spectator Scalar Fields.

We investigate a generic source of stochastic gravitational wave background due to the parametric resonance of oscillating scalar fields in the early Universe. By systematically analyzing benchmark models through lattice simulations and considering a wide range of parameters, we demonstrate that such a scenario can lead to detectable signals in gravitational wave detectors over a broad frequency range and potentially address the recent findings by pulsar timing array experiments. Furthermore, these models naturally yield ultralight dark matter candidates or dark radiation detectable by cosmic microwave background observatories.

Phyllanthuse emblica polyphenols: Optimization of high-voltage pulsed electric field assisted extraction, an antioxidant and anti-inflammatory effects in vitro

BackgroundThe polyphenols extraction of Phyllanthus emblica is primarily carried out using organic solvents, and assisted by physical fields such as ultrasound and microwave for extraction. High voltage pulsed electric field technology (PEF) is a non-thermal processing technology that has high efficiency and minimal damage to thermosensitive substances. PEF has been applied to plant extraction in many studies, however, the extraction of polyphenols from Phyllanthus emblica using the PEF has still not been reported; ObjectiveThis study explores the optimal extraction process of polyphenols from Phyllanthus emblica using the PEF, and investigates its relaxation and anti-wrinkle based on anti-oxidation and anti-inflammatory experiment, in order to develop a Phyllanthus emblica extract with substantial efficacy; Materials and MethodsThe method of Phyllanthus emblica extract using PEF is established, and compared with a traditional extraction method. The experimental conditions, such as electric field intensity (0.5–6.0 kV/cm), pulse times (20−120), extraction time (0–60 min) and material concentration (0.5 %∼3 %), are investigated and optimized using orthogonal experiments; Resultsthe polyphenols in the Phyllanthus emblica extract were highest at the electric field intensity of 5 kV / cm, 120 pulses, extraction time of 30 min, and 2 % material concentration. The PEFcontained more polyphenols than the conventional water extraction and ultrasound-assisted extraction. The Phyllanthus emblica extract had substantial antioxidant and anti-inflammatory effects, with a good clearance effect on DPPH ( IC50 of 1.82 %) and ABTS ( IC50 of 1.80 %) radicals. At the Phyllanthus emblica extract concentration of 1.25 %, inflammatory factors (TNF-α) were reduced by 47.08 %; and ConclusionThe PEF is a leading-edge and promising method for preparing Phyllanthus emblica extracts.

Self-Interacting Dark Matter Solves the Final Parsec Problem of Supermassive Black Hole Mergers.

Evidence for a stochastic gravitational wave (GW) background, plausibly originating from the merger of supermassive black holes (SMBHs), is accumulating with observations from pulsar timing arrays. An outstanding question is how inspiraling SMBHs get past the "final parsec" of separation, where they have a tendency to stall before GW emission alone can make the binary coalesce. We argue that dynamical friction from the dark matter (DM) spike surrounding the black holes is sufficient to resolve this puzzle, if the DM has a self-interaction cross section of order cm^{2}/g. The same effect leads to a softening of the GW spectrum at low frequencies as suggested by the current data. For collisionless cold DM, the friction deposits so much energy that the spike is disrupted and cannot bridge the final parsec, while for self-interacting DM, the isothermal core of the halo can act as a reservoir for the energy liberated from the SMBH orbits. A realistic velocity dependence, such as generated by the exchange of a massive mediator like a dark photon, is favored to give a good fit to the GW spectrum while providing a large enough core. A similar velocity dependence has been advocated for solving the small-scale structure problems of cold DM.

Effects of pulse time offset between Cr and Zr dual cathodes in closed-magnetic-field unipolar high-power impulse magnetron sputtering

Two cathode (target) materials, Cr and Zr, were paired in a closed-field magnetron dual-cathode configuration and used in unipolar high-power impulse magnetron sputtering (HiPIMS). Two pulse widths (pulse-on durations) and various pulse-time offsets between the negative-voltage pulses of the Cr and Zr targets were investigated by setting the synchronization delay between the HiPIMS power supplies of the two targets at two different Ar pressures. Several trends were observed by analyzing the waveforms of the target discharge current, target discharge voltage, and substrate current. The closed-magnetic-field dual-cathode configuration significantly enhanced the HiPIMS discharge efficiency of the Zr target at all pressures; however, the enhancement for the Cr target was considerably lower. The ion fluxes toward the substrate were influenced by two competing mechanisms. The charged species generated from the previous pulse on one target could be attracted by the subsequent pulse of the adjacent target as a preionized medium to enhance the HiPIMS discharge. However, the fraction of the previously emitted ion flux toward the substrate could be reduced. When a shorter pulse width of 70 μs was applied, the ion flux that reached the substrate was mainly affected by the pulse power of the Zr target, and delaying the pulses of the Cr target with a relatively lower ion yield can achieve a higher ion flux toward the substrate. Increasing the pulse width significantly increased ion fluxes emitted from both the Cr and Zr targets, increasing the total ion flux toward the substrate. The study indicates that for the Cr and Zr dual cathode pair, a pulse time offset of one pulse width plus more than approximately 200 μs would be the most efficient way to obtain the highest ion fluxes toward the substrate and achieve a better film quality.

The effect of the Solar System Ephemeris on the search for the nano-Hz gravitational wave background

ABSTRACT The detection of the nano-Hz gravitational-wave background (GWB) is one of the main targets of Pulsar timing arrays (PTAs). The detection can be achieved via searching for a common signal with quadrapolar correlation between pulsar pairs. Errors in the Solar-System ephemeris (SSE) can induce dipolar correlations in PTA data, which may affect the results of GWB searches, especially when the data quality is not high enough to constrain the correlation pattern. We investigate the effect of unmodelled SSE errors on GWB searches with PTAs, using simulations with properties based on the European Pulsar Timing Array data set. When the GWB signal is strong, SSE errors have little effect on the GWB search results, including parameter inference and model selection. When the GWB signal is weak, SSE errors can lead to overestimation of the GWB amplitude. However, model comparison would show strong support for dipolar correction, which implies the source of the common signal to be SSE-related and helps avoid its misidentification as a GWB signal. This indicates that SSE error is unlikely to be the main source of the common signal detected recently with real PTA data. We also use simulations to test the ability of the SSE model LINIMOSS in absorbing SSE-error signals and leaving the GWB signal intact. We show that marginalizing LINIMOSS planetary parameters with infinite priors is good at absorbing SSE errors, but may also lead to improper absorption of a GWB signal. Caution is therefore required when setting appropriate limits on the priors of SSE parameters.

Dopamine Release Dynamics in the Nucleus Accumbens Are Modulated by the Timing of Electrical Stimulation Pulses When Applied to the Medial Forebrain Bundle and Medial Prefrontal Cortex.

Electrical brain stimulation has been used in vivo and in vitro to investigate neural circuitry. Historically, stimulation parameters such as amplitude, frequency, and pulse width were varied to investigate their effects on neurotransmitter release and behavior. These experiments have traditionally employed fixed-frequency stimulation patterns, but it has previously been found that neurons are more precisely tuned to variable input. Introducing variability into the interpulse interval of stimulation pulses will inform on how dopaminergic release can be modulated by variability in pulse timing. Here, dopaminergic release in rats is monitored in the nucleus accumbens (NAc), a key dopaminergic center which plays a role in learning and motivation, by fast-scan cyclic voltammetry. Dopaminergic release in the NAc could also be modulated by stimulation region due to differences in connectivity. We targeted two regions for stimulation─the medial forebrain bundle (MFB) and the medial prefrontal cortex (mPFC)─due to their involvement in reward processing and projections to the NAc. Our goal is to investigate how variable interpulse interval stimulation patterns delivered to these regions affect the time course of dopamine release in the NAc. We found that stimulating the MFB with these variable stimulation patterns saw a highly responsive, frequency-driven dopaminergic response. In contrast, variable stimulation patterns applied to the mPFC were not as sensitive to the variable frequency changes. This work will help inform on how stimulation patterns can be tuned specifically to the stimulation region to improve the efficiency of electrical stimulation and control dopamine release.

Detecting superfluid transition in the pulsar core

ABSTRACT It is believed that the core of a neutron star can be host to various novel phases of matter, from nucleon superfluid phase to exotic high baryon density quantum chromodynamics (QCD) phases. Different observational signals for such phase transitions have been discussed in the literature. Here, we point out a unique phenomenon associated with phase transition to a superfluid phase, which may be the nucleon superfluid phase or a phase like the colour-flavour locked phase, allowing for superfluid vortices. In any superfluid phase transition, a random network of vortices forms via the so-called Kibble–Zurek mechanism, which eventually mostly decays away, finally leaving primarily vortices arising from the initial angular momentum of the core. This transient, random vortex network can have a non-zero net angular momentum for the superfluid component, which will generally be oriented in an arbitrary direction. This is in contrast to the final vortices, which arise from initial rotation and hence have the initial angular momentum of the neutron star. The angular momentum of the random vortex network is balanced by an equal and opposite angular momentum in the normal fluid due to the conservation of angular momentum, thereby imparting an arbitrarily oriented angular momentum component to the outer shell of the neutron star. This will affect the pulse timing and pulse profile of a pulsar. These changes in the pulses will decay away in a characteristic manner that this as the random vortex network decays, obeying specific scaling laws leading to universal features for the detection of superfluid transitions occurring in a pulsar core.

Fast Parameter Inference on Pulsar Timing Arrays with Normalizing Flows.

Pulsar timing arrays perform Bayesian posterior inference with expensive Markov chain MonteCarlo (MCMC) methods. Given a dataset of ∼10-100 pulsars and O(10^{3}) timing residuals each, producing a posterior distribution for the stochastic gravitational wave background (SGWB) can take days to a week. The computational bottleneck arises because the likelihood evaluation required for MCMC is extremely costly when considering the dimensionality of the search space. Fortunately, generating simulated data is fast, so modern simulation-based inference techniques can be brought to bear on the problem. In this Letter, we demonstrate how conditional normalizing flows trained on simulated data can be used for extremely fast and accurate estimation of the SGWB posteriors, reducing the sampling time from weeks to a matter of seconds.

Timing irregularities and glitches from the pulsar monitoring campaign at IAR

Pulsars have a very stable rotation overall. However, sudden increases in their rotation frequency, known as glitches, perturb their evolution. While many observatories commonly detect large glitches, small glitches are harder to detect because of the lack of daily cadence observations over long periods of time (years). We aim to explore and characterise the timing behaviour of young pulsars on daily timescales, looking for small glitches and other irregularities, in order to further our comprehension of the real distribution of glitch sizes. Our findings have consequences for the theoretical modelling of the glitch mechanism. We observed six pulsars with up to daily cadence between December 2019 and January 2024 with the two antennas of the Argentine Institute of Radio Astronomy (IAR). We used standard pulsar timing tools to obtain the times of arrival of the pulses and to characterise the pulsar's rotation. We developed an algorithm to look for small timing events in the data and calculate the changes in the frequency (nu ) and its derivative ($ at those epochs. We find that the rotation of all pulsars in this dataset is affected by small step changes in nu and $ Among them, we find three new glitches that have not been reported before: two glitches in PSR J1048$-$5832 with relative sizes of $ $ and $ $, and one glitch in the Vela pulsar with a size of $ $. We also report new decay terms on the 2021 Vela giant glitch, and on the 2022 giant glitches in PSR J0742$-$2822 and PSR J1740$-$3015, respectively. In addition, we find that the red noise contribution significantly diminished in PSR J0742$-$2822 after its giant glitch in 2022. Our results highlight the importance of high-cadence monitoring with an exhaustive analysis of the residuals to better characterise the distribution of glitch sizes and to deepen our understanding of the mechanisms behind glitches, red noise, and timing irregularities.

Improving pulsar timing precision through superior time-of-arrival creation

Context. The measurement of pulsar pulse times-of-arrival (ToAs) is a crucial step in detecting low-frequency gravitational waves. To determine ToAs, we can use template-matching to compare each observed pulse profile with a standard template. However, using different combinations of templates and template-matching methods (TMMs) without careful consideration can lead to inconsistent results. Aims. In pulsar timing array (PTA) experiments, distinct ToAs from the same observations can be obtained due to the use of diverse templates and TMMs. In other words, employing diverse approaches can yield different timing results and would thus have a significant impact on subsequent gravitational wave searches. In this paper we examine several commonly used combinations to analyze their effect on pulse ToAs. Methods. We evaluated the potential impact of template and TMM selection on 13 typical millisecond pulsars within the European PTA. We employed pulsar timing methods, specifically the root mean square and reduced chi-square (χ2r) of the residuals of the best timing solution, to assess the outcomes. Additionally, we evaluated the system-limited noise floor (SLNF) for each pulsar at various telescopes operating around 1.4 GHz using frequency-resolved templates. Results. Our findings suggest that utilizing data-derived and smoothed templates in conjunction with the Fourier-domain with Markov chain Monte Carlo TMM is generally the most effective approach, though there may be exceptions that require further attention. Furthermore, we determine that pulse phase jitter noise does not significantly limit the current precision of the European PTA’s timing, as jitter levels derived from other studies are much lower than the SLNF.

Realisation of the ultra-slow roll phase in Galileon inflation andPBH overproduction

We demonstrate the explicit realisation of the ultra-slow roll phase in the framework of the effective field theory of single-field Galileon inflation. The pulsar timing array (PTA) collaboration hints at the scalar-induced gravity waves (SIGW) from the early universe as an explanation for the origin of the observed signal, which, however, leads to an enhancement in the amplitude of the scalar power spectrum giving rise to the overproduction of primordial black holes (PBHs). In the setup under consideration, we examine the generation of SIGW consistent with PTA (NANOGrav15 and EPTA) data, in addition to which we also consider the impact from QCD crossover at the nHz frequencies and address the PBH overproduction issue assuming linear approximations for the over-density without incorporating non-Gaussian effects from the comoving curvature perturbation. The framework is shown to give rise to SIGWs well consistent with the PTA signal with comfortable PBH abundance, 10-3 ≲ fPBH < 1, of near solar-mass black holes.

Traversing a kinetic pole during inflation: primordial black holes and gravitational waves

We consider an inflationary kinetic function with an integrable polethat is traversed during inflation.This scenario leads to enhanced spectra of primordial scalar inhomogeneities with detectable signals:formation of primordial black holes(that could explain Dark Matter) andscalar-induced gravitational waves (that couldreproduce the recent Pulsar Timing Array observation, or predict signals in future detectors such as LISA or ET).Spectral signatures depend on whether the inflaton mass dimensionat the pole is above or below 2.Values mildly below 2 allow a big power spectrum enhancement with a mild tuning.Finally, we discuss the possibility that a kinetic pole can arise as anomalousdimension of the inflaton due to quantum effects of Planckian particles that becomelight at some specific inflaton field value.

Enhanced curvature perturbation and primordial black hole formation in two-stage inflation with a break

We investigate a model of R2-gravity with a non-minimally coupled scalar field that gives rise to two-stage inflation with a break, that is, with an intermediate stage where inflation momentarily halts. We find that the power spectrum of the primordial curvature perturbation is significantly enhanced at the break scale, which can account for the primordial black hole (PBH) formation, without affecting the CMB constraint on large scales. The behavior of the curvature perturbation is carefully analyzed and we find a few notable new features in the spectrum. In particular, we find that the k3 growth of the spectrum of toward the end of the first stage of inflation. We argue that this is a universal feature common to all two-stage models where the field dominating the second stage is heavy during the first stage. By appropriately tuning the model parameters, we find that our model can realize the scenario of PBHs as the cold dark matter of the Universe. We also find that we can choose the parameters so that the spectrum of the induced gravitational waves from the enhanced curvature perturbation fits the NANOGrav-15yr data of pulsar timing array observation.

Cobalt-vanadium coating deposition via programmed electrolysis mode

In the current work, the co-deposition of cobalt with vanadium from a complex citrate electrolyte via stationary and pulse electrolysis modes was investigated. The process was carried out at a current density of 1–15 Adm–2 in stationary electrolysis mode and 2–10 Adm–2 in pulse electrolysis mode, with variable ratio of pulse time to pause time at a temperature range of 35–400С and pH 3.0–3.5. According to the results of X-ray fluorescence spectrometry, the maximum content of vanadium in the coating obtained via the programmed electrolysis mode is 1.20–1.45%, which is tens of times higher than in the coating deposited by the stationary electrolysis mode (vanadium content of 0.007–0.017%) under similar conditions. The obtained results may confirm the hypothesis of additional vanadium reduction from oxo-anions by adsorbed hydrogen atoms formed on the cathode surface during the pause period. Based on the results of the analysis of 3D graphs, the optimal parameters of the process for fabricating a cobalt-vanadium coating with the maximum vanadium content in the alloy and a coating current efficiency of 80% have been established.

The “Magnificent Seven” X-Ray Isolated Neutron Stars Revisited. I. Improved Timing Solutions and Pulse Profile Analysis

We present the first systematic X-ray pulse timing analysis of the six members of the so-called “Magnificent Seven” nearby thermally emitting isolated neutron stars (XINS) with detected pulsations. Using the extensive collection of archival XMM-Newton, Chandra, and NICER observations spanning over two decades, we obtain the first firm measurement of the spin-down rate for RX J2143.0+0654, while for the rest we improve upon previously published spin ephemerides and extend them by up to an additional decade. Five of the XINS follow steady spin-down with no indication of major anomalies in their long-term timing behavior; the notable exception is RX J0720.4−3125, for which, in addition to confirming the previously identified glitch, we detect a second spin derivative. The high-quality folded X-ray pulse profiles produced with the updated timing solutions exhibit diverse and complex morphologies, as well as striking energy dependence. These peculiarities cannot be readily explained by blackbody-like isotropic emission and simple hot-spot configurations, hinting at the presence of complex multitemperature surface heat distributions and highly anisotropic radiation patterns, such as may arise from a strongly magnetized atmospheric layer.