Abstract The relationships between several parameters of an emission geometry and jitter noise in 17 millisecond pulsars (MSPs) are investigated. By assuming the jitter noise is due only to a pulse ...variation in phase, the former can be modeled as changes in the plasma flow rate leading to variation in the measured pulse arrival time relative to the predicted time. In the model for pulsar magnetospheres with multiple emission states, the plasma flow is associated with the emission states, and a change in the emission state corresponds to a change in the plasma flow causing variation in the pulse arrival time. These can be specified in an emission geometry defined by the obliquity and viewing angles, measured from the rotation axis to the magnetic axis and to the line of sight, respectively. We calculate the maximum change in the emission state based on the reported jitter noise for each of the MSPs. Using the results, we show that the MSPs possess relatively large obliquity angles, which is consistent with observation, and the jitter noise exhibits dependency on frequency. We find that the jitter noise in our sample displays an exponential decay as a function that combines the obliquity angle and the rotation period, revealing the correlation among the three parameters. This suggests that the magnitude of the jitter noise is likely specific to an MSP. We discuss how jitter noise may be related to the evolution of an MSP.
Abstract
We investigate the distributions of the obliquity angle and impact parameters of nulling pulsars of different duty cycles based on the simulation of more than 600,000 samples. We adopt a ...purely geometric approach for pulsar visibility, in which visible emission is emitted tangentially to the magnetic field line and parallel to the line-of-sight direction. The geometry is incorporated with the model for pulsar magnetospheres of multiple emission states, in which the plasma charge density is dependent on the emission state. We assume that an emission state can only exist between two limiting conditions described by the vacuum and corotation models, respectively. In this model, pulse nulling corresponds to emission switching to a state in which the plasma charge density is zero. The event is detectable only if the switching occurs at source points that lie on a trajectory, whose locus defines the locations of visible emission, within an open-field region. Our results show that detectable nulling is dependent on all three parameters, such that nulling pulsars prefer a small obliquity angle and duty cycle, and tend to have positive impact parameters. We find that the total population of nulling pulsars in our samples is around 23%, of which about 47% possess a duty cycle of 0.1 or smaller. The former implies that there are more nulling pulsars than currently known. Our model predicts that the number of nulling pulsars increases as the obliquity angle decreases, which also implies that the occurrence of nulling in a pulsar should evolve over time.
Aims. We aim to simulate the proportions of non-detectable emission, measured as radio-off fractions ( f off ), in rotating radio transients (RRATs). We also investigate the properties related to the ...underlying mechanism for such sporadic emission. Methods. From observations of intermittent pulsars, radio emission originates from two distinct emission states and it becomes non-detectable when the pulsar switches to an emission state characterized by magnetospheric plasma density of zero. We performed simulations of f off based on 10 000 samples, each with 10 000 rotations and using a model that tracks changes in the plasma density in a pulsar magnetosphere with multiple emission states. We assumed that (i) RRATs are radio pulsars, (ii) radio pulse intensity is correlated with the emitting plasma density as stated in the conventional models, and (iii) a pulse emission corresponds to a change in the plasma density under favorable conditions. Results. A best-fit distribution for f off is obtained when emission from RRATs is defaulted to radio-off. The resulting wait time distribution can be fitted by two functions of an exponential and a Gaussian, which is consistent with the observations. We demonstrate that the switch rate is low and that the burst rate is dependent on rotation period. In addition, the switch rate is related to the obliquity angle, which implies that the mechanism varies over time. Our results suggest that switching to radio-on is a random process, which implies that the burst rate is different for different RRATs. We show that RRAT emission and pulse nulling may share similar origins, but with different default emission. We discuss how the emission may change from that of RRAT to pulse nulling (or vice versa) as a pulsar evolves.
BACKGROUND
Inactivation of the maternally or paternally derived X chromosome (XCI) initially occurs in a random manner in early development; however as tissues form, a ‘patchiness’ will occur in ...terms of which X is inactivated if cells positioned near each other are clonally descended from a common precursor. Determining the relationship between skewed XCI in different tissues and in different samples from the same tissue provides a molecular assessment of the developmental history of a particular tissue that can then be used to understand how genetic and epigenetic variation arises in development.
METHODS
XCI skewing was evaluated in and compared between amnion, chorion, trophoblast and mesenchyme using multiple sampling sites from 14 term placentae. XCI was also evaluated in chorionic villus samples obtained at multiple sites and depths from four additional term placentae. The pattern of variation was then compared with methylation variation associated with the H19/IGF2 imprinting control region (ICR); promoter regions of KISS1, PTPN6, CASP8 and APC; and LINE-1 elements.
RESULTS
Mean placental level of skewing for amnion and chorion are correlated, consistent with a common developmental origin of at least a component of these membranes from inner cell mass derivatives subsequent to XCI, while trophoblast appears to be derived independently, consistent with its origin from the trophectoderm. Villus samples taken from different depths spanning the fetal to maternal side of the placenta were highly clonally related. Comparing patterns of clonal growth identified through XCI to the distribution of epigenetic variation in other genomic regions suggests that some variation arises early in development (e.g. LINE-1 methylation), whereas other variation arises predominantly after villus tree formation (e.g. methylation at H19/IGF2 ICR).
CONCLUSIONS
The patterns of XCI skewing are consistent with a model whereby each biopsied site of chorionic villi represents one or a few individual villus trees, each of which is clonally derived from only one or a few precursor cells. Sampling of placentae to evaluate changes associated with clinical pathology should be done with consideration of the tree-to-tree differences. A limitation of this study is the small number of placentas used and therefore placental-specific differences in variation could not be assessed.
The inherently poor flame retardancy and comparatively low tensile strength of poly(lactic acid) (PLA) have limited its wide adoption as alternative 'green' engineering plastic in many fields. This ...manuscript reports the synthesis of a new phosphorus flame retardant - phenylphosphonic 3(2-aminobenzothiazole) (P-TAB) and its combination with recycled short wool fibers (WF) for improving the flame retardancy and the mechanical properties of PLA. Fourier transform infrared (FTIR),1H, and13C nuclear magnetic resonance (NMR) spectra proved that P-TAB was effectively synthesized. Considerable reductions in heat release rate, total heat released, CO and CO2 produced were attained with 3 wt% P-TAB and various WF loadings. The fire performance index (FPI), and fire growth index (FGI) improved by 38.2 and 48.1% respectively. The composite achieved a V-0 rating at 20 wt% WF loading and an LOI value of 28.5%. TG-IR results showed substantial reductions in evolved gaseous products. The tensile strength and Young's modulus improved significantly with the increasing content of WF in the composite.
Abstract We report two phenomena detected in PSR J0344−0901 from two observations conducted at frequencies centered at 1.25 GHz using the Five-hundred-meter Aperture Spherical Radio Telescope. The ...first phenomenon manifests as the pulse emission shifting to later longitudinal phases and then gradually returning to its original location. The event lasts for about 216 pulse periods, with an average shift of about 0.°7 measured at the peak of the integrated profile. Changes in the polarization position angle (PPA) are detected around the trailing edge of the profile, together with an increase in the profile width. The second phenomenon is characterized by the apparent movement of subpulses, which results in different subpulse track patterns across the profile window. For the first time in this pulsar, we identify four emission modes, each with unique subpulse movement, and determine the pattern periods for three of them. Pulse nulling was not detected. Modeling of the changes in the PPA using the rotating vector model gives an inclination angle of 75.°12 ± 3.°80 and an impact parameter of −3.°17 ± 5.°32 for this pulsar. We speculate that the subpulse movement may be related to the shifting of the pulse emission.
Abstract
We have carried out a detailed study of polarimetric individual pulse emission from the pulsar J1701−3726 (B1658−37), observed at 1369 MHz using the Parkes 64 m radio telescope. The ...single-pulse sequences reveal the presence of the three major emission phenomena of pulse nulling, mode changing, and subpulse drifting. Trimodal distribution of the pulse energy is present, implying one population of nulls and two others of emission in the phase window. The mean flux density of the normal mode is almost two times that of the abnormal mode. Our data show that, for PSR J1701−3726, 64% of the time was spent in the normal mode and 12% was in the abnormal mode. The single pulses show the presence of two distinct periodic modulations using a fluctuation spectral analysis. About 24% of the nulls are found to create alternating bunches of nulls and bursts in a quasiperiodic manner with a longer periodicity of 48 ± 4 rotational periods. Additionally, the pulsar presents a steady even–odd modulated feature with a stationary longitude within the pulse window. The ramifications for constraining the viewing geometry and understanding the radio emission mechanisms are discussed.
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