Abstract
The frequency evolution behavior of radio pulse profiles is an important clue for the radiation mechanism of a pulsar. Combined with the latest results of the European Pulsar Network and the ...Australia Telescope National Facility data, we systematically study the evolution of
W
50
(the full width of the pulse profile at 50% of the pulsar amplitude) for 74 pulsars with frequencies from tens to thousands of megahertz. We find that 71 pulsars show “absorption” features, which indicates that the absorption is an universal phenomenon in the pulsar population and independent of the type of pulsar profile. It is found that for most pulsars, the absorption features appear in the frequency range of 100–800 MHz, and the evolution trend of
W
50
at frequencies less than ∼100 MHz and larger than ∼800 MHz can be described as a power-law function.We quantify the absorption intensity and analyze the correlation between the absorption intensity and the pulsar parameters (such as the spin period, magnetic field, and age of the pulsar). It is found that there is no direct correlation between them. Our results will provide good samples and clues for the study of the physical mechanism of the absorption phenomenon.
ABSTRACT
The study of polarization and micro-structure is very important for understanding the radiation mechanism of Rotating Radio Transients (RRATs). Due to the limitations of telescope ...sensitivity and time resolution, studies of the polarization and micro-structure of RRATs have been rare in the past. In this work, we report on a high-time resolution and full polarization observation of RRAT J0139+3336 with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). A total of 96 burst pulses were detected in the 3-h observation. The degrees of linear and circular polarization and the shape of the polarization position angle (PPA) of the single pulses vary significantly. The average profile displays a small degree of linear and circular polarization, and the PPA exhibits a remarkably smooth and steep S-shaped curve, which are also characteristics of pulsars. The circular polarization in some single pulses demonstrates a clear sign change. We discuss the geometric structure of the emission beam based on the results from fitting the RVM model to the changes in the PPA. Using an autocorrelation analysis, the quasi-periodic micro-structure in the single pulse emission is detected with a median period of about 0.91 ms. We show that the position of RRAT J0139+3336 on the P–Pμ diagram falls in the normal pulsar (NP) region . The radio emission of RRAT J0139+3336 shows unique properties, such as the sign change in the circular polarization and quasi-periodicity in the micro-structure, which will provide important clues to the emission mechanism of RRATs.
ABSTRACT
We present the first measurement of pulse scattering close to the eclipse region of PSR B1957+20, which is in a compact binary system with a low-mass star. We measured pulse scattering ...time-scales up to 0.2 ms close to the eclipse and showed that it scales with the dispersion measure (DM) excess roughly as τ ∝ ΔDM2. Our observations provide the first evidence of strong scattering due to multipath propagation effects in the eclipsing material. We show that Kolmogorov turbulence in the eclipsing material with an inner scale of ∼100 m and an outer scale of the size of the eclipse region can naturally explain the observation. Our results show that the eclipsing material in such systems can be highly turbulent and suggest that scattering is one of the main eclipsing mechanisms at around 1.4 GHz.
Abstract
MAX-phase Cr
2
AlC containing thin films were synthesized by magnetron sputtering in an industrial system. Nanometre-scale 3D defects are observed near the boundary between regions of Cr
2
...AlC and of the disordered solid solution (CrAl)
x
C
y
. Shrinkage of the Cr-Cr interplanar distance and elongation of the Cr-Al distance in the vicinity of the defects are detected using transmission electron microscopy. The here observed deformation surrounding the defects was described using density functional theory by comparing the DOS of bulk Cr
2
AlC with the DOS of a strained and unstrained Cr
2
AlC(0001) surface. From the partial density of states analysis, it can be learned that Cr-C bonds are stronger than Cr-Al bonds in bulk Cr
2
AlC. Upon Cr
2
AlC(0001) surface formation, both bonds are weakened. While the Cr-C bonds recover their bulk strength as Cr
2
AlC(0001) is strained, the Cr-Al bonds experience only a partial recovery, still being weaker than their bulk counterparts. Hence, the strain induced bond strengthening in Cr
2
AlC(0001) is larger for Cr d – C p bonds than for Cr d – Al p bonds. The here observed changes in bonding due to the formation of a strained surface are consistent with the experimentally observed elongation of the Cr-Al distance in the vicinity of nm-scale 3D defects in Cr
2
AlC thin films.
AIMTo develop a split glomerular filtration rate (sGFR) prediction model based on unilateral renal volume parameters using three-dimensional (3D) computed tomography (CT) volumetry. MATERIALS AND ...METHODSClinical data (age, sex, height, weight, serum creatinine level sCr, and sGFR measured by 99mTc-diethylene triamine pentaacetic acid nuclear renal scintigraphy with the double plasma sample method) of 67 healthy renal donors and 111 patients with hydronephrosis admitted from April 2016 to September 2021 were analysed. The split renal parenchymal volume (sRPV) and split renal calyces and pelvis volume (sRCPV) of 67 unilateral donor left kidneys and 111 hydronephrotic kidneys were measured. Statistical analysis of these parameters was performed to develop and validate the sGFR prediction model. RESULTSsRPV (p<0.001), sRCPV (p=0.012), age (p=0.015), serum creatinine level (p=0.004), and weight (p=0.006) were significantly associated with the measured sGFR and were included in the sGFR prediction formula, which was constructed as: 68.710 + 0.093 × sRPV-0.041 × sRCPV-0.228 × W-0.219 × A-14.432 × sCr (r2 = 0.416; where A is age, W is weight). The paired difference of internal validation between the measured sGFR (42.34 ± 13.71 ml/min/1.73 m2) and the sGFR estimated by the prediction model (41.46 ± 8.99 ml/min/1.73 m2) was 0.879 ± 11.475 ml/min/1.73 m2 (p=0.492) with a 95% confidence interval of the mean difference of ±2.54 ml/min/1.73 m2. CONCLUSIONThe proposed model based on sRPV and sRCPV parameters could be used for estimating split renal function of healthy renal donors and patients with hydronephrosis to some extent. Further studies are required to evaluate and rectify the model.
This work demonstrates a direct density functional description of the finite-temperature thermodynamic properties of solids exhibiting phase transitions through positional and spin symmetry breaking ...degrees of freedom. A classic example addressed here is the rare-earth (R) nickelates RNiO3 where the ground state is characterized by crystallographic and magnetic (e.g., antiferromagnetic) long-range order (LRO), whereas the higher temperature paramagnetic phase manifests a range of local spin and positional symmetry breaking motifs with short-range order (SRO). Unlike time-dependent simulations of spin and positional degrees of freedom, in the present work, phases are described via a superposition of static configurations constructed by populating a periodic base lattice supercell allowing for the formation of energy lowing distribution of positional and spin local motifs. The thermal populations of the configurations in such a superposition phase are obtained from the energy-minimized Density Functional Theory (DFT)-calculated partition functions at different temperatures. This approach offers flexible inclusion of different physical contributions to the free energy, such as elastic, electronic and phonon free energies, all obtained from the same underlying DFT total energy calculations of periodic structures. The thermodynamic and magnetic properties of both LRO and SRO crystallographic and spin phases, including antiferromagnetic (AFM) to paramagnetic (PM) Néel phase transition in YNiO3 are studied. Including spin and phonon contributions, we find a DFT-calculated Néel temperature to be 144 K in satisfactory agreement with the experimental value of 145 K; whereas omitting the phonon contribution, one obtains a Néel temperature of 81 K. We present phonon contributions to the DFT-calculated temperature-dependent SRO, heat capacities, and the polymorphous distribution of nonzero local magnetic moments in the PM phase. This approach thus extends to finite temperatures the symmetry-broken DFT description of both the AFM and PM phases, demonstrating that a thermodynamic superposition approach based on symmetry broken configurations evaluated by a mean-field like DFT is sufficient to obtain a consistent description of the thermal physics of the AFM, PM phases and their interconversion in 3d oxides illustrated by YNiO3.
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The highlights and main advantages of the present superposition approach to spatially fluctuating phases are that:(i)The existence of spatially fluctuating components in a para phase (i.e., paramagnetic or paraelectric phase) is explicitly included as a superposition without using a time domain as in dynamic simulations.(ii)The energetics is obtained from first-principles DFT without requiring the step of resolving DFT total energies into elementary interactions (such as effective cluster interactions) then truncating, as in the cluster expansion method or the Heisenberg Hamiltonian.(iii)One can readily include the interaction between the various microscopic degrees of freedom such as electronic structure physics included in DFT, along with phonon physics, calculated from the same supercell in DFT, allowing electron-phonon coupling.(iv)Once one computes the probability or thermal populations of the different configurations, it is possible to use them for describing other physical observables of superposition phases.
The objectives of the study were to characterize the selectivity of dantrolene to breast cancer resistance protein (Bcrp) and to evaluate whether cerebrospinal fluid (CSF) can be used as a surrogate ...to assess brain exposures of BCRP and P-glycoprotein (Pgp) substrates. The impact of Bcrp and Pgp on dantrolene exposures in brain and CSF was examined in Bcrp and Mdr1a/1b knockout mice and was further investigated in wild-type mice in the presence of the Bcrp inhibitor (3S,6S,12aS)-1,2,3,4,6,7,12,12a-octahydro-9-methoxy-6-(2-methylpropyl)-1,4-dioxopyrazino1',2':1,6pyrido3,4-bindole-3-propanoic acid 1,1-dimethylethyl ester (Ko143), the Pgp inhibitor 6-(2S,4R,6E)-4-methyl-2-(methylamino)-3-oxo-6-octenoic acid-7-l-valine-cyclosporine A (PSC833), and the dual inhibitor N-(4-2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918). The effect of Bcrp and Pgp on digoxin exposures in brain and CSF was investigated in wild-type mice in the presence of the inhibitors. In vivo studies showed dantrolene exposures in brain and CSF, but not the blood, increased in Bcrp(-/-) and Mdr1a/1b(-/-)/Bcrp(-/-) mice, or in the presence of the Bcrp inhibitors Ko143 or GF120918. Inhibition of Pgp by GF120918 and PSC833 significantly increased digoxin exposures in brain, CSF, and blood to a lesser extent. Results from the present study demonstrated that inhibition of Bcrp and Pgp increased not only the exposures of dantrolene and digoxin in brain, but also the exposures in CSF. In addition, the change of exposures in CSF reflected the changes in brain. The present study strongly suggests that the dantrolene and digoxin exposures in CSF are primarily determined by the rapid transport from brain to CSF, and inhibition of Bcrp and Pgp exhibits little impact on using CSF as surrogates to assess brain exposures of Bcrp and Pgp substrates.
In this study, the adhesion strength of thermal barrier coatings 8YSZ (ZrO
2
+
8
wt.% Y
2O
3) deposited on NiCrAlY bond coats by atmospheric plasma spraying is investigated experimentally. A modified ...four-point bending specimen that can generate a single interface crack to facilitate the control of crack growth was adopted for testing. The fracture surfaces were examined using a scanning electron microscope. Images show that cracks are initiated along YSZ/NiCrAlY interfaces, then kink and grow uniformly within the YSZ layer. The load–displacement curves obtained indicate three distinct stages in crack initiation and stable crack growth. Based on a microstructural model, finite element analyses were performed to extract the bonding strength of the thermal barrier coatings. The fracture toughness of the plasma-sprayed 8YSZ coatings, in terms of critical strain energy release rate
G
c, can be reliably obtained from an analytical solution or from a numerical simulation of the cracking process using compliance methods.
Atomic structure, diffusivity and viscosity of Al1-xMgx (x=0, 0.0039, 0.1172, 0.9180, 0.9961, 1)melts at 875, 1000, 1125, and 1250K were investigated by the ab initio molecular dynamics (AIMD) ...simulations. The simulated results are compared with available experimental and calculated data in the literature with reasonable agreements. Considering the results of pair correlation function g(r), it can be observed that Mg atoms in Al0.8828Mg0.1172 melt aggregate more obviously at 1000 and 1250K. For Al0.0820Mg0.9180, Al atom segregation is more obvious at 875 and 1000K. The tracer diffusion coefficients of Al or Mg in Al1-xMgx (x=0.1172, 0.9180) melts, and interdiffusion coefficients of Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts are all close to the self-diffusion coefficients of Al or Mg. With the increasing temperature, the diffusivity increases linearly. In dilute melts, the tracer diffusion coefficients of solute atom and the interdiffusion coefficients increase nonlinearly with the increasing temperature. For Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts, the viscosities ? are comparatively higher than pure melts. The viscosities of all melts decrease with the increasing temperature, then increase at 1250K. The results obtained in the present work provide an insight into the design of Al and Mg alloys.
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