Pulse Period Variations Research Articles

Retinal vascular tortuosity in schizophrenia and bipolar disorder

The micro-vasculature of retina and brain share common morphological, physiological, and pathological properties. Retina being easily accessible, retinal vascular examination provides an indirect assessment of cerebral vasculature. Considering the high prevalence of vascular morbidity in SCZ and BD a few studies have examined retinal vascular caliber and have reported increased retinal venular caliber in schizophrenia (SCZ). Retinal vascular tortuosity could serve as a better structural measure than caliber as it is static and less susceptible to pulse period variations. However, to date, no study has examined retinal vascular tortuosity in SCZ and bipolar disorder (BD). Hence, we examined retinal vascular tortuosity in comparison with healthy volunteers (HV). We included 255 subjects (78 HV, 79 SCZ, and 86 BD) in the age range of 18 to 50 years. Trained personnel acquired images using a non-mydriatic fundus camera. To measure the average retinal arteriolar tortuosity index (RATI) and retinal venular tortuosity index (RVTI), we used a previously validated, semi-automatic algorithm. The results showed significant differences across the three groups in RATI but not in RVTI; both BD and SCZ had significantly increased RATI compared to HV. There was also a significant difference between SCZ and BD, with BD having higher RATI. If shown to be of predictive utility in future longitudinal studies, it has the potential to identify patients at risk of development of adverse vascular events. As retinal vascular imaging is non-invasive and inexpensive, it could serve as a proxy marker and window to cerebral vasculature.

Discovery of a 3 s Spinning Neutron Star in a 4.15 hr Orbit in the Brightest Hard X-Ray Source in M31

Abstract We report the discovery with XMM-Newton of 3 s X-ray pulsations from 3XMM J004232.1+411314, a dipping source that dominates the hard X-ray emission of M31. This finding unambiguously assesses the neutron star (NS) nature of the compact object. We also measured an orbital period of 4.15 hr and a projected semi-axis at aX sin i = 0.6 lt-s, which implies a low-mass companion of about 0.2–0.3 M ⊙ assuming an NS of 1.5 M ⊙ and an orbital inclination i = 60°–80°. The barycentric orbit-corrected pulse period decreased by ∼28 ms in about 16 year, corresponding to an average spin-up rate of s s−1; pulse period variations, probably caused by X-ray luminosity changes, were observed on shorter timescales. We identify two possible extreme scenarios for the source: a mildly magnetic NS with B p ≃ few × 1010 G if the pulsar is far from its equilibrium period P eq and the disk is truncated at the value of the Alfvén radius corresponding to the observed luminosity, and a relatively young, highly magnetic NS with B eq ≃ 2 × 1013 G if spinning close to P eq and the disk is truncated close to the co-rotation surface.

A Comprehensive Library of X-Ray Pulsars in the Small Magellanic Cloud: Time Evolution of Their Luminosities and Spin Periods

AbstractWe have collected and analyzed the complete archive ofXMM-Newton(116),Chandra(151), andRXTE(952) observations of the Small Magellanic Cloud (SMC), spanning 1997–2014. The resulting observational library provides a comprehensive view of the physical, temporal, and statistical properties of the SMC pulsar population across the luminosity range oferg s−1. From a sample of 65 pulsars we report ∼1654 individual pulsar detections, yielding ∼1260 pulse-period measurements. Our pipeline generates a suite of products for each pulsar detection: spin period, flux, event list, high time-resolution light curve, pulse profile, periodogram, and spectrum. Combining all three satellites, we generated complete histories of the spin periods, pulse amplitudes, pulsed fractions, and X-ray luminosities. Some pulsars show variations in pulse period due to the combination of orbital motion and accretion torques. Long-term spin-up/spin-down trends are seen in 12/11 pulsars, respectively, pointing to sustained transfer of mass and angular momentum to the neutron star on decadal timescales. Of the sample, 30 pulsars have a relatively very small spin period derivative and may be close to equilibrium spin. The distributions of pulse detection and flux as functions of spin period provide interesting findings: mapping boundaries of accretion-driven X-ray luminosity and showing that fast pulsars (P < 10 s) are rarely detected, which as of yet are more prone to giant outbursts. Accompanying this paper is an initial public release of the library so that it can be used by other researchers. We intend the library to be useful in driving improved models of neutron star magnetospheres and accretion physics.

The relevance of temporal cues in a fish sound: a first experimental investigation using modified signals in cichlids

Playback experiments have been a useful tool for studying the function of sounds and the relevance of different sound characteristics in signal recognition in many different species of vertebrates. However, successful playback experiments in sound-producing fish remain rare, and few studies have investigated the role of particular sound features in the encoding of information. In this study, we set-up an apparatus in order to test the relevance of acoustic signals in males of the cichlid Metriaclima zebra. We found that territorial males responded more to playbacks by increasing their territorial activity and approaching the loudspeaker during and after playbacks. If sounds are used to indicate the presence of a competitor, we modified two sound characteristics, that is, the pulse period and the number of pulses, in order to investigate whether the observed behavioural response was modulated by the temporal structure of sounds recorded during aggressive interactions. Modified sounds yielded little or no effect on the behavioural response they elicited in territorial males, suggesting a high tolerance for variations in pulse period and number of pulses. The biological function of sounds in M. zebra and the lack of responsiveness to our temporal modifications are discussed.

The effect of near‐fault directivity on building seismic collapse risk

SUMMARYForward directivity may cause large velocity pulses in ground motion time histories that are damaging to buildings at sites close to faults, potentially increasing seismic collapse risk. This study quantifies the effects of forward directivity on collapse risk through incremental dynamic analysis of building simulation models that are capable of capturing the key aspects of strength and stiffness degradation associated with structural collapse. The paper also describes a method for incorporating the effects of near‐fault directivity in probabilistic assessment of seismic collapse risk. The analysis is based on a suite of RC frame models that represent both past and present building code provisions, subjected to a database of near‐fault, pulse‐like ground motions with varying pulse periods. Results show that the predicted collapse capacity is strongly influenced by variations in pulse period and building ductility; pulse periods that are longer than the first‐mode elastic building period tend to be the most damaging. A detailed assessment of seismic collapse risk shows that the predicted probability of collapse in 50 years for modern concrete buildings at a representative near‐fault site is approximately 6%, which is significantly higher than the 1% probability in the far‐field region targeted by current seismic design maps in the US. Copyright © 2012 John Wiley & Sons, Ltd.

JD3 – Neutron Stars: Timing in Extreme Environments

AbstractThe space-time around Neutron Stars is indeed an extreme environment. Whether they are in accreting binary systems, isolated or in non-accreting binaries (perhaps with another Neutron Star), Neutron Stars provide a window onto physical processes not accessible by other means. In particular, the study of their time variability: pulsations, quasi-periodic oscillations, thermonuclear X-ray bursts, flares and giant-flares, pulsar glitches and pulse period variations, constitutes a valuable instrument to unveil those very same physical processes. Here we briefly summarize the most important results presented at Joint Discussion 3 of the XXVII IAU General Assembly.

Continuous monitoring of pulse period variations in Hercules X-1 usingSwift/BAT

Context: Monitoring of pulse period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accretion disk. While the X-ray flux of the brightest X-ray pulsars have been successfully monitored over many years (e.g. with RXTE/ASM, CGRO/BATSE, Swift/BAT), the possibility to monitor their pulse timing properties continuously has so far been very limited. Aims: In our work we show that the Swift/BAT observations can be used to monitor coherent pulsations of bright X-ray sources and use the Swift archival data to study one of the most enigmatic X-ray pulsars, Hercules X-1. A quasi-continuous monitoring of the pulse period and the pulse period derivative of an X-ray pulsar, here Her X-1, is achieved over a long time (<~ 4 yrs). We compare our observational results with predictions of accretion theory and use them to test different aspects of the physical model of the system. Methods: In our analysis we use the data accumulated with Swift/BAT starting from the beginning of 2005 (shortly after launch) until the present time. To search for pulsations and for their subsequent analysis we used the count rate measured by the BAT detector in the entire field of view. Results: The slope of the correlation between the locally determined spin-up rate and the X-ray luminosity is measured for Her X-1 and found to be in agreement with predictions of basic accretion torque theory. The observed behaviour of the pulse period together with the previously measured secular decrease of the system's orbital period is discussed in the frame of a model assuming ejection of matter close to the inner boundary of the accretion disk.

Now you see it, now you don't – the circumstellar disc in the GRO J1008−57 system

Multiwavelength observations are reported here of the Be/X-ray binary pulsar system GRO J1008−57. Over ten years worth of data are gathered together to show that the periodic X-ray outbursts are dependant on both the binary motion and the size of the circumstellar disc. In the first instance an accurate orbital solution is determined from pulse periods, and in the second case the strength and shape of the Hα emission line is shown to be a valuable indicator of disc size and its behaviour. Furthermore, the shape of the emission line permits a direct determination of the disc size which is in good agreement with theoretical estimates. A detailed study of the pulse period variations during outbursts determined the binary period to be 247.8 ± 0.4 d, in good agreement with the period determined from the recurrence of the outbursts.

EXOSAT observations of the iron line in CEN X-3

Properties of the iron line in Cen X-3 have been studied, using the gas scintillation proportional counter onboard EXOSAT. The iron line energy is seen to be constant (kT = 6.59 ± 0.06 keV) over orbital and pulse periods. On the other hand the iron line intensity is seen to vary with both periods. The pulse period variations are sinusoidal, but the orbital period variations are more complex. These variations can be explained assuming that the iron line emission comes from, at least, two different emitting regions; the Alfven sphere and the primary's atmosphere. The pulse period variations are produced at the Alfven sphere and the orbital period variations at the primary's atmosphere.

The transient 42 second X-ray pulsar EXO 2030+375. I - The discovery and the luminosity dependence of the pulse period variations

The discovery of a new transient X-ray pulsar, EXO 2030+375, that is associated with a Be star companion, is reported. The results of a series of EXOSAT observations, where the evolution of the pulsar's properties over two orders of magnitude in luminosity was monitored. The dependence of the change in pulsar period on luminosity is measured and compared with that predicted by accretion torque theory. The pulsar properties are also compared with those of other transient X-ray pulsars. 58 refs.

The X-ray pulsar A0535 + 26 - Pulse profile and its time variability in hard X-rays

view Abstract Citations (37) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The X-ray pulsar A 0535+26 : pulse profile and its time variability inhard X-rays. Frontera, F. ; dal Fiume, D. ; Morelli, E. ; Spada, G. Abstract A hard X-ray observation 8400 s long of the recurrent transient X-ray pulsar A0535 + 26 has been performed. The data were obtained with a balloon-borne experiment in the energy range 27-190 keV when the source was near the maximum of the 1980 October transient outburst. Results from the pulse shape analysis show that the time-averaged pulse profile in the hard X-ray range is quite different from that measured by other observers at different epochs. It exhibits a double-peaked structure fairly stable with energy, with the greatest variation seen in the intensity ratio between the two peaks. In addition, the pulsed fraction shows a clear increase at higher energies, which converges to 100 percent at about 100 keV. A timing analysis has shown significant pulse period variations (up to an absolute value of Delta P/P of about 0.007) on time scales of thousands of seconds. Finally, a high variability in pulse shape and intensity was discovered on time scales varying from the order of seconds to few tens of minutes. The short time scale variability was studied using Power Spectral Density estimates and direct inspection of the data. This variability appears to be chaotic, and shot-like events with typical duration of 10 s and mean frequency of one every 25 s have been observed. Publication: The Astrophysical Journal Pub Date: November 1985 DOI: 10.1086/163643 Bibcode: 1985ApJ...298..585F Keywords: Neutron Stars; Pulsars; Stellar Oscillations; X Ray Binaries; Light Curve; Luminosity; Magnetic Fields; Periodicals; Astrophysics full text sources ADS | data products SIMBAD (1)