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 present observations of three-dimensional magnetic power spectra in wavevector space to investigate the anisotropy and scalings of sub-Alfvénic solar wind turbulence at ...magnetohydrodynamic (MHD) scale using the Magnetospheric Multiscale spacecraft. The magnetic power distributions are organized in a new coordinate determined by wavevectors (
κ
ˆ
) and background magnetic field (
b
^
0
) in Fourier space. This study utilizes two approaches to determine wavevectors: the singular value decomposition method and multispacecraft timing analysis. The combination of the two methods allows an examination of the properties of magnetic field fluctuations in terms of mode compositions without any spatiotemporal hypothesis. Observations show that fluctuations (
δ
B
⊥1
) in the direction perpendicular to
κ
ˆ
and
b
^
0
prominently cascade perpendicular to
b
^
0
, and such anisotropy increases with wavenumbers. The reduced power spectra of
δ
B
⊥1
follow Goldreich–Sridhar scalings:
P
ˆ
(
k
⊥
)
∝
k
⊥
−
5
/
3
and
P
ˆ
(
k
∥
)
∝
k
∥
−
2
. In contrast, fluctuations within the
k
ˆ
b
ˆ
0
plane show isotropic behaviors: perpendicular power distributions are approximately the same as parallel distributions. The reduced power spectra of fluctuations within the
k
ˆ
b
ˆ
0
plane follow the scalings
P
ˆ
(
k
⊥
)
∝
k
⊥
−
3
/
2
and
P
ˆ
(
k
∥
)
∝
k
∥
−
3
/
2
. Comparing frequency–wavevector spectra with theoretical dispersion relations of MHD modes, we find that
δ
B
⊥1
are probably associated with Alfvén modes. On the other hand, magnetic field fluctuations within the
k
ˆ
b
ˆ
0
plane more likely originate from fast modes based on their isotropic behaviors. The observations of anisotropy and scalings of different magnetic field components are consistent with the predictions of current compressible MHD theory. Moreover, for the Alfvénic component, the ratio of cascading time to the wave period is found to be a factor of a few, consistent with critical balance in the strong turbulence regime. These results are valuable for further studies of energy compositions of plasma turbulence and their effects on energetic particle transport.
Strongly textured Mg–3Al–1Zn (wt%) alloy samples with a high density of twins cut from three directions were used to investigate the effect of crystallographic orientation on dynamic ...recrystallization (DRX). The samples were deformed under a high strain rate at 300°C. The high strain rate allows rapid dislocation accumulation, making DRX possible at relatively low strain values. We demonstrate that crystallographic orientation and the initial twins have significant effects on DRX because of the different activities of dislocations and their interactions with twin boundaries. This research provides a potential pathway for improving the formability of Mg alloys.
We have recently reported that a high strain-rate rolling process is effective for producing strong and ductile Mg alloy sheets. Here we elucidate the fundamental mechanisms that are responsible for ...plastic deformation in this process via systematic physical thermomechanical plane-strain rolling simulations on a Mg–Zn–Zr alloy. The strain-rate sensitivities of the alloy’s microstructure and flow curves were closely correlated to the onset of deformation twinning and dynamic recrystallization (DRX). Unlike deformation at low strain rates, deformation at the high strain rates applied here induced a high number density of twins, including a predominance of {101¯1}–{101¯2} double twins in coarse grains, and a predominance of {101¯2} twins in fine DRX grains. We also report a new observation of {101¯2} nanotwins in ultrafine grains with high density in bulk Mg alloy when processed at high strain rates. We propose that the high propensity for twinning at high strain rates provides nucleation sites for DRX, resulting in a uniform, ultrafine-grained microstructure that exhibits a weakened basal texture and thus excellent mechanical properties.
Abstract
We report analysis of sub-Alfvénic magnetohydrodynamic (MHD) perturbations in the low-
β
radial-field solar wind employing the Parker Solar Probe spacecraft data from 2018 October 31 to ...November 12. We calculate wavevectors using the singular value decomposition method and separate MHD perturbations into three eigenmodes (Alfvén, fast, and slow modes) to explore the properties of sub-Alfvénic perturbations and the role of compressible perturbations in solar wind heating. The MHD perturbations show a high degree of Alfvénicity in the radial-field solar wind, with the energy fraction of Alfvén modes dominating (∼45%–83%) over those of fast modes (∼16%–43%) and slow modes (∼1%–19%). We present a detailed analysis of a representative event on 2018 November 10. Observations show that fast modes dominate magnetic compressibility, whereas slow modes dominate density compressibility. The energy damping rate of compressible modes is comparable to the heating rate, suggesting the collisionless damping of compressible modes could be significant for solar wind heating. These results are valuable for further studies of the imbalanced turbulence near the Sun and possible heating effects of compressible modes at MHD scales in low-
β
plasma.
Abstract Cerebral hypoxia may be the main component of cell damage caused by ischemia. Previous studies demonstrated a neuroprotective effect of early hyperbaric oxygen (HBO) treatment in various ...animal models of focal cerebral ischemia. Neuropathologic study showed that exposure of HBO may prevent cell death in ischemic cortex. In the present study, we aimed to assess cellular function of ischemic rat brain after HBO treatment by means of a high-resolution positron emission tomography scanner (microPET) used specifically for small animal imaging. The male Sprague–Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO), with the regional cerebral blood flow monitored in vivo by laser Doppler flowmetry. One hour after ischemia, HBO therapy (3 atm absolute, 1 h) was initiated. Local cerebral glucose utilization in the ischemic area was measured before, 1 h and 3 h after ischemia, with 2-18 F-fluoro-2-deoxy-d-glucose (FDG) as a tracer. Neurological deficits and infarct volumes were assessed at 24 h after ischemia. Our study showed that early HBO therapy significantly reduced infarct volume of brain 24 h after ischemia. Moreover, glucose utilization in the ischemic area underwent a severe decrease during 1–3 h after MCAO, while the early HBO treatment significantly attenuated the decrease in cerebral metabolic rate of glucose in the ischemic core of the cortex compared with controls. We report for the first time the application of microPET to quantify the rates of glucose metabolism in the ischemic core of rats exposed to HBO. Our results suggest that the early exposure of HBO can partially reverse the downward trend for glucose utilization in the ischemic core, which might contribute to the reported beneficial effects of early HBO therapy on permanent cerebral ischemia.
Floating objects will drift due to the action of surface gravity waves. This drift will depart from that of a perfect Lagrangian tracer due to both viscous effects (non-potential flow) and wave–body ...interaction (potential flow). We examine the drift of freely floating objects in regular (non-breaking) deep-water wave fields for object sizes that are large enough to cause significant diffraction. Systematic numerical simulations are performed using a hybrid numerical solver, qaleFOAM, which deals with both viscosity and wave–body interaction. For very small objects, the model predicts a wave-induced drift equal to the Stokes drift. For larger objects, the drift is generally greater and increases with object size (we examine object sizes up to $10\,\%$ of the wavelength). The effects of different shapes, sizes and submergence depths and steepnesses are examined. Furthermore, we derive a ‘diffraction-modified Stokes drift’ akin to Stokes (Trans. Camb. Phil. Soc., vol. 8, 1847, pp. 411–455), but based on the combination of incident, diffracted and radiated wave fields, which are based on potential-flow theory and obtained using the boundary element method. This diffraction-modified Stokes drift explains both qualitatively and quantitatively the increase in drift. Generally, round objects do not diffract the wave field significantly and do not experience a significant drift enhancement as a result. For box-shape objects, drift enhancement is greater for larger objects with greater submergence depths (we report an increase of $92\,\%$ for simulations without viscosity and $113\,\%$ with viscosity for a round-cornered box whose size is $10\,\%$ of the wavelength). We identify the specific standing wave pattern that arises near the object because of diffraction as the main cause of the enhanced drift. Viscosity plays a small positive role in the enhanced drift behaviour of large objects, increasing the drift further by approximately $20\,\%$.
•Carry out a combined wind tunnel test and CFD study on the wind effects on an elliptical cylinder.•Investigate the surface roughness effects on the wind loading of an elliptical cylinder using ...DES.•DES and LES models and numerical treatments adopted in this study can provide reasonably good correspondence with wind tunnel tests.•DES model can reproduce the effects of surface roughness effects on the wind loading with the modified wall function.
In this study, detached-eddy simulations (DES) and large-eddy simulations (LES) of wind effect on a high-rise structure with elliptical shape are performed. The aim of this study is to examine the accuracy of the numerical simulations for wind flow around a complex high-rise structure and investigate the effects of surface roughness on the wind loading. In order to reproduce appropriate inflow turbulence, the improved recycling method combined with the weighted amplitude wave superposition (WAWS) method is used to generate the inflow turbulence in the streamwise direction. Also, to study the surface roughness effects on the wind loading, the rough wall boundary conditions are adopted in the DES models. Typical results including the mean and fluctuating pressure coefficients, force spectra, Reynolds stresses and wind-induced top-floor response are obtained and compared with the corresponding wind tunnel experimental data. Through the cross-comparisons, the numerical results by the DES and LES models are found to be comparable with the experimental results. Additionally, the surface roughness effects on the wind loading is well reproduced with the DES models, such as the slow pressure recovery in the separation regions and the increased mean drag force coefficients. It is demonstrated through the validations that the DES and LES models and the numerical treatments adopted in this study can provide reasonably good results.
Objective
The purpose of this study was to investigate whether isolated maternal hypothyroxinaemia (IMH) is associated with risks of small/large‐for‐gestational‐age (SGA/LGA) infants.
Design
...Population‐based prospective cohort study.
Setting
Ma'anshan Maternal and Child Health (MCH) clinics, China.
Population
Pregnant women with singleton births (n = 3178).
Methods
Descriptive statistics were calculated for the demographic characteristics of the mothers and their newborns. Linear regression was applied to estimate the association between thyroid hormone levels and birthweight. Logistic regression was performed to calculate the association between IMH and SGA/LGA.
Main outcome measures
Outcomes included SGA/LGA.
Results
The prevalence of IMH, defined as a free thyroxine value (FT4) lower than the 2.5th percentile with normal thyroid stimulating hormone, was 2.5% (78/3080) and 2.5% (74/2999) in the first and second trimesters, respectively. Additionally, 306 (9.6%) and 524 (16.5%) infants were defined as SGA and LGA, respectively. No evidence supported the notion that IMH is associated with an increased risk for SGA in either the first odds ratio (OR): 1.762, 95% confidence interval (CI): 0.759–4.089 or the second (OR: 0.763, 95% CI: 0.231–2.516) trimester. However, an increased risk of LGA was observed among IMH women in the second trimester (OR: 2.088, 95% CI: 1.193–3.654). Maternal TPO‐Ab positivity in the second trimester increased the risk of SGA (OR: 2.094, 95% CI: 1.333–3.290).
Conclusion
This study provides evidence that IMH is associated with LGA.
Funding
This work was supported by the National Natural Science Foundation of China (No. 81330068).
Tweetable
Isolated maternal hypothyroxinaemia may increase the risk of large‐for‐gestational‐age infants.
Tweetable
Isolated maternal hypothyroxinaemia may increase the risk of large‐for‐gestational‐age infants.
Paroxysmal kinesigenic dyskinesias is a paroxysmal movement disorder characterized by recurrent, brief attacks of abnormal involuntary movements induced by sudden voluntary movements. Although ...several loci, including the pericentromeric region of chromosome 16, have been linked to paroxysmal kinesigenic dyskinesias, the causative gene has not yet been identified. Here, we identified proline-rich transmembrane protein 2 (PRRT2) as a causative gene of paroxysmal kinesigenic dyskinesias by using a combination of exome sequencing and linkage analysis. Genetic linkage mapping with 11 markers that encompassed the pericentromeric of chromosome 16 was performed in 27 members of two families with autosomal dominant paroxysmal kinesigenic dyskinesias. Then, the whole-exome sequencing was performed in three patients from these two families. By combining the defined linkage region (16p12.1-q12.1) and the results of exome sequencing, we identified an insertion mutation c.649_650InsC (p.P217fsX7) in one family and a nonsense mutation c.487C>T (p.Q163X) in another family. To confirm our findings, we sequenced the exons and flanking introns of PRRT2 in another three families with paroxysmal kinesigenic dyskinesias. The c.649_650InsC (p.P217fsX7) mutation was identified in two of these families, whereas a missense mutation, c.796C>T (R266W), was identified in another family with paroxysmal kinesigenic dyskinesias. All of these mutations completely co-segregated with the phenotype in each family. None of these mutations was identified in 500 normal unaffected individuals of matched geographical ancestry. Thus, we have identified PRRT2 as the first causative gene of paroxysmal kinesigenic dyskinesias, warranting further investigations to understand the pathogenesis of this disorder.
PDF
