ABSTRACT
PSR J0636+5128 is a 2.87 ms binary millisecond pulsar (MSP) discovered by the Green Bank Northern Celestial Cap Pulsar Survey, and possesses the third shortest orbital period ( P = 1.6 h) ...among confirmed binary pulsars. Recent observations reported that this source is experiencing a rapid orbital expansion at a rate of $\dot{P}=(1.89\pm 0.05)\times 10^{-12}\,\rm s\, s^{-1}$. The evaporation winds of the companion induced by the spin-down luminosity of the MSP may be responsible for such a positive orbital period derivative. However, our calculations show that the winds ejecting from the vicinity of the companion or the inner Lagrangian point cannot account for the observation due to an implausible evaporation efficiency. Assuming that the evaporation winds eject from the vicinity of the MSP in the form of asymmetric disc winds or outflows, the evaporation efficiency can be constrained to be ∼0.1. Therefore, the rapid orbital expansion detected in PSR J0636+5128 provides evidence of outflows and accretion disc around the MSP.
The improvement of liquid dispersion by rotating wire mesh is one of the major causes for the mass transfer and micromixing intensification in rotating packed beds (RPBs). In particular, the initial ...dispersion region has been proved to have the greatest mass transfer and micromixing efficiency. However, the dispersion mechanism has not been revealed. This study investigated the dynamics of liquid dispersion in an RPB with single‐layer wire mesh. The liquid dispersion behaviors were obtained by high‐speed photography and numerical simulation. The liquid was found to stretch into ligaments and break into the main droplet and several satellite droplets. A new theoretical model was established to reveal the dispersion mechanism of these two stages. The stretching stage depends on the liquid initial momentum and acquired impulse, while the breakup stage was determined by the competition of ligaments recoil and pinch‐off behaviors. The model was validated in good agreement with the experimental and simulation results of the dispersion characteristics.
Abstract Both the anomalous magnetic braking of Ap/Bp stars and the surrounding circumbinary disk models can account for the formation of black hole (BH) low-mass X-ray binaries (LMXBs), while the ...simulated effective temperatures of the donor stars are significantly higher than the observed values. Therefore, the formation of BH LMXBs is still not completely understood. In this work, we diagnose whether the dynamical friction between dark matter and the companion stars can drive BH binaries to evolve toward the observed BH LMXBs and alleviate the effective temperature problem. Assuming that there exists a density spike of dark matter around BH, the dynamical friction can produce an efficient angular momentum loss, driving BH binaries with an intermediate-mass companion star to evolve into BH LMXBs for a spike index higher than γ = 1.58. Our detailed stellar evolution models show that the calculated effective temperatures can match the observed value of most BH LMXBs for a spike index range of γ = 1.7–2.1. However, the simulated mass-transfer rates when γ = 2.0 and 2.1 are too high to be consistent with the observed properties showing that BH LMXBs appear as soft X-ray transients. Therefore, the dynamical friction of dark matter can only alleviate the effective temperature problem of those BH LMXBs with a relatively short orbital period.
ABSTRACT It is generally believed that ultracompact X-ray binaries (UCXBs) evolved from binaries consisting of a neutron star accreting from a low-mass white dwarf (WD) or helium star where mass ...transfer is driven by gravitational radiation. However, the standard WD evolutionary channel cannot produce the relatively long-period (40-60 minutes) UCXBs with a high time-averaged mass-transfer rate. In this work, we explore an alternative evolutionary route toward UCXBs, where the companions evolve from intermediate-mass Ap/Bp stars with an anomalously strong magnetic field (100-10,000 G). Including the magnetic braking caused by the coupling between the magnetic field and an irradiation-driven wind induced by the X-ray flux from the accreting component, we show that intermediate-mass X-ray binaries (IMXBs) can evolve into UCXBs. Using the MESA code, we have calculated evolutionary sequences for a large number of IMXBs. The simulated results indicate that, for a small wind-driving efficiency f = 10−5, the anomalous magnetic braking can drive IMXBs to an ultra-short period of 11 minutes. Comparing our simulated results with the observed parameters of 15 identified UCXBs, the anomalous magnetic braking evolutionary channel can account for the formation of seven and eight sources with f = 10−3, and 10−5, respectively. In particular, a relatively large value of f can fit three of the long-period, persistent sources with a high mass-transfer rate. Though the proportion of Ap/Bp stars in intermediate-mass stars is only 5%, the lifetime of the UCXB phase is 2 Gyr, producing a relatively high number of observable systems, making this an alternative evolutionary channel for the formation of UCXBs.
The substantial heterogeneity and hierarchical organization in liver cancer support the theory of liver cancer stem cells (LCSCs). However, the relationship between chronic hepatic inflammation and ...LCSC generation remains obscure. Here, we observed a close correlation between aggravated inflammation and liver progenitor cell (LPC) propagation in the cirrhotic liver of rats exposed to diethylnitrosamine. LPCs isolated from the rat cirrhotic liver initiated subcutaneous liver cancers in nonobese diabetic/severe combined immunodeficient mice, suggesting the malignant transformation of LPCs toward LCSCs. Interestingly, depletion of Kupffer cells in vivo attenuated the LCSC properties of transformed LPCs and suppressed cytokeratin 19/Oval cell 6–positive tumor occurrence. Conversely, LPCs cocultured with macrophages exhibited enhanced LCSC properties. We further demonstrated that macrophage‐secreted tumor necrosis factor‐α triggered chromosomal instability in LPCs through the deregulation of ubiquitin D and checkpoint kinase 2 and enhanced the self‐renewal of LPCs through the tumor necrosis factor receptor 1/Src/signal transducer and activator of transcription 3 pathway, which synergistically contributed to the conversion of LPCs to LCSCs. Clinical investigation revealed that cytokeratin 19/Oval cell 6–positive liver cancer patients displayed a worse prognosis and exhibited superior response to sorafenib treatment. Conclusion: Our results not only clarify the cellular and molecular mechanisms underlying the inflammation‐mediated LCSC generation but also provide a molecular classification for the individualized treatment of liver cancer. (Hepatology 2017;66:1934–1951)
Abstract PSR J1012+5307 is a millisecond pulsar with an extremely low-mass white dwarf (WD) companion in an orbit of 14.5 hr. Magnetic braking (MB) plays an important role in influencing the orbital ...evolution of binary systems with a low-mass (≲1–2 M ⊙ ) donor star. At present, there exist several different MB descriptions. In this paper, we investigate the formation of PSR J1012+5307 as a probe to test plausible MB models. Employing a detailed stellar evolution model with the MESA code, we find that the convection- and rotation-boosted MB and “Intermediate” MB models can reproduce the WD mass, WD radius, WD surface gravity, neutron star mass, and orbital period observed in PSR J1012+5307. However, our simulated WD has a higher effective temperature than the observations. Three other MB mechanisms, including the standard MB model, are too weak to account for the observed orbital period in the Hubble time. A long cooling timescale caused by H-shell flashes of the WD may alleviate the discrepancy between the simulated effective temperature and the observed value.
Source 2A 1822-371 is an eclipsing low-mass X-ray binary (LMXB) consisting of a neutron star (NS) and a ∼0.5
M
⊙
donor star in an orbit of 5.57 h. Based on the timing of the eclipse arrival times, ...this source was found to experience a rapid orbital expansion with an orbital period derivative as
Ṗ
orb
= (1.51 ± 0.05) × 10
−10
s s
−1
, implying that the mass-transfer rate is probably higher than at least three times the Eddington accretion rate. The standard magnetic braking (MB) model cannot produce a mass-transfer rate this high. The modified MB model can produce a high mass-transfer rate, resulting in a high
Ṗ
orb
. We propose an alternative model to account for the anomalously high mass-transfer rate and
Ṗ
orb
of 2A 1822-371. During the mass transfer, a tiny fraction of the transferred material is thought to form a circumbinary (CB) disk around the LMXB, which can efficiently extract orbital angular momentum from the system by the interaction between the CB disk and the binary. We used the MESA code to model the formation and evolution of 2A 1822-371 for different CB-disk masses. When the CB-disk mass is 2.3 × 10
−8
M
⊙
, the simulation can reproduce the observed donor-star mass, orbital period, and orbital period derivative. This CB disk can accelerate the evolution of the binary and produce a high mass-transfer rate of 1.9 × 10
−7
M
⊙
yr
−1
, driving the binary to evolve toward a wide-orbit system. Therefore, we propose that CB disks may cause the rapid orbital changes observed in some LMXBs.
Highly efficient kinetic resolution of P-chiral phosphindole oxides via rhodium-catalyzed asymmetric arylation under mild conditions is described. Selectivity factors of up to 569 were achieved by ...employing chiral diene* as a ligand. The transformation of the enantiopure benzophosphole derivative into a useful P-chiral bisphosphine ligand is also demonstrated.
With the huge amount of uncharacterized protein sequences generated in the post-genomic age, it is highly desirable to develop effective computational methods for quickly and accurately predicting ...their functions. The information thus obtained would be very useful for both basic research and drug development in a timely manner.
Although many efforts have been made in this regard, most of them were based on either sequence similarity or protein-protein interaction (PPI) information. However, the former often fails to work if a query protein has no or very little sequence similarity to any function-known proteins, while the latter had similar problem if the relevant PPI information is not available. In view of this, a new approach is proposed by hybridizing the PPI information and the biochemical/physicochemical features of protein sequences. The overall first-order success rates by the new predictor for the functions of mouse proteins on training set and test set were 69.1% and 70.2%, respectively, and the success rate covered by the results of the top-4 order from a total of 24 orders was 65.2%.
The results indicate that the new approach is quite promising that may open a new avenue or direction for addressing the difficult and complicated problem.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
The space gravitational wave (GW) detector Laser Interferometer Space Antenna (LISA) that is planned to be launched in the early 2030s will detect the low-frequency GW signals in the Galaxy. ...AM CVn stars were generally thought to be important low-frequency GW sources. Employing the MESA code, in this work we calculate the evolution of a great number of binary systems consisting of a white dwarf (WD) and a main sequence (MS) star, and diagnose whether their descendant-AM CVn stars will be visible with LISA. The simulated results show that the progenitors of these LISA sources, within a distance of 1 kpc, are WD–MS binaries with a donor star of 1.0–1.4
M
⊙
(for initial WD mass of 0.5
M
⊙
) or 1.0–2.0
M
⊙
(for initial WD mass of 0.7
M
⊙
), and an initial orbital period slightly smaller than the bifurcation period. Our simulations also indicate that 10 verification AM CVn sources can be reproduced by the standard magnetic braking model, and are potential LISA sources. Based on the birth rate of AM CVn stars simulated by the population synthesis, the birth rate of AM CVn-LISA sources evolving from the evolved donor star channel within a distance of 1 kpc can be estimated to be (0.6–1.4) × 10
−6
yr
−1
, and the predicted number of AM CVn-LISA sources is about 340–810. Therefore, the evolved donor star channel plays an important role in forming AM CVn-LISA sources in the Galaxy.
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