分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Fast radio bursts (FRBs) are cosmic sources emitting millisecond-duration radio bursts. Although several hundreds FRBs have been discovered, their physical nature and central engine remain unclear. The variations of Faraday rotation measure and dispersion measure, due to local environment, are crucial clues to understanding their physical nature. The recent observations on the rotation measure of FRB 20201124A show a significant variation on a day time scale. Intriguingly, the oscillation of rotation measure supports that the local contribution can change sign, which indicates the magnetic field reversal along the line of sight. Here we present a physical model that explains observed characteristics of FRB 20201124A and proposes that repeating signal comes from a binary system containing a magnetar and a Be star with a decretion disk. When the magnetar approaches the periastron, the propagation of radio waves through the disk of the Be star naturally leads to the observed varying rotation measure, depolarization, large scattering timescale, and Faraday conversion. This study will prompt to search for FRB signals from Be/X-ray binaries.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Recent observations discovered that some repeating fast radio bursts (FRBs) show complicated variations and reversals of Faraday rotation measures (RMs), indicating that the sources of these FRBs are embedded in a dynamically magnetized environment. One possible scenario is that repeating FRBs are generated by pulsars in binary systems, especially containing a high-mass companion with strong stellar outflows. Here, we study the RM variations caused by stellar winds, and a possible stellar disc. If the magnetic field is radial in the stellar wind, RM will not reverse except if the magnetic axis inclination angle is close to $90 ^\circ$. For the toroidal magnetic field in the wind, RM will reverse at the super conjunction. For the case of the toroidal field in the disc, the RM variations may have a multimodal and multiple reversal profile because the radio signals travel through different components of the disc during periastron passage. We also apply this model to FRB 20180916B. By assuming its 16.35-day period is from a slowly rotating or freely precessing magnetar, we find that the secular RM variation can be explained by the periastron passage of a magnetar in a massive binary system. In addition, the clumps in the stellar wind and disc can cause short time-scale ($< 1$ day) variations or reversals of RM. Therefore, long-term monitoring of RM variations can reveal the environments of repeating FRBs.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-26
摘要: The effect of Cu content on the evolution of defects in Fe-x%Cu alloys (x= 0.15, 0.3, and 0.6) were investigated using Positron Annihilation Lifetime Spectroscopy. The vacancy-type and Cu-vacancy complexes defects were respectively produced by quenching from 1173 K and cold-rolled deformation followed by isochronal annealing. The isochronal annealing results obtained by PALS showed that Cu-vacancy complexes delayed the complete recovery of vacancy-type defects and the complete recovery temperature increased with the content of Cu in 30% deformed Fe-Cu alloys. The increment of Cu content also restrained the migration of vacancies in as-quenched Fe-Cu alloys.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-26
摘要: The microstructural features and the effect of Mo addition during incubation period in FeCrNi austenitic alloy were investigated using positron annihilation technique and micro-Vickers Hardness. The electron irradiation, which could induce vacancy defects in material, was performed at room temperature up to the dose of 1.70-4 and 50-4 dpa, respectively. The defect concentration was estimated about 10-4-10-7 though standard trapping model. The added Mo could trap vacancies to form Mo-vacancy complexes, which may suppress the migration and growth of vacancy defects during electron irradiation. In addition, the microstructural evolution during electron radiation resulted in hardening, while the added Mo might to improve the hardening property of the alloy.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-26
摘要: Abstract. The microstructural features and the effect of Mo addition in FeCrNi austenitic alloy during incubation period were investigated using positron annihilation technique and micro-Vickers Hardness. The electron irradiation, which could induce vacancy defects in material, was performed at room temperature up to the dose of 1.70-4 and 50-4 dpa, respectively. The defect concentration was estimated about 10-4-10-7 though the standard trapping model. The added Mo atoms could trap vacancies to form Mo-vacancy complexes, which may restrain the migration and growth of vacancy defects during electron irradiation. In addition, the microstructural evolution during electron radiation resulted in hardening, while the added Mo might improve the hardening property of the alloy.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-26
摘要: By fitting the R values between 3.7 and 5.0 GeV measured by the BES Collaboration, the upper limit of the electron width of the newly discovered resonance Y(4260) is determined to be 240 eV at 90% C.L. Together with the BaBar measurement on Γee• B(Y(4260) → π+π- J/ψ), this implies a large decay width of Y (4260) → π+π- J/ψ final states.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Solar flare is one of the severest solar activities on the sun, and it has many important impacts on the near-earth space. It has been found that flight arrival delays will increase during solar flare. However, the detailed intrinsic mechanism of how solar flares influence the delays is still unknown. Based on 5-years huge amount of flight data, here we comprehensively analyze the flight departure delays during 57 solar flares. It is found that the averaged flight departure delay time during solar flares increased by 20.68% (7.67 min) compared to those during quiet periods. It is also shown that solar flare related flight delays reveal apparent time and latitude dependencies. Flight delays during dayside solar flares are more serious than those during nightside flares, and the longer (shorter) delays tend to occur in the lower (higher) latitude airport. Further analyses suggest that flight delay time and delay rate would be directly modulated by the solar intensity (soft X-ray flux) and the Solar Zenith Angle. For the first time, these results indicate that the communication interferences caused by solar flares will directly affect flight departure delay time and delay rate. This work also expands our conventional understandings to the impacts of solar flares on human society, and it could also provide us with brand new views to help prevent or cope with flight delays.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-23
摘要: The effect of isochronal annealing on vacancy-type defects in quenched FeCrNi alloys and SUS316 has been investigated by positron annihilation techniques. Vacancy-type defects gather and grow with the annealing temperature increasing to 523 K, and the vacancy-type defects annihilated gradually in FeCrNi alloys at the annealing temperature increasing. The results indicate that the addition of Mo and nonmetal elements is not the key reasons that determined the annihilated temperature of vacancy-type defects. It’s worth noting that the vacancy-type defects annihilated and dislocation-type defects formed in all sample alloys after 673 K annealing treatment. In addition, the density of defects in Mo diluted FeCrNi model alloy is lower than that in FeCrNi model alloy due to the Mo-vacancy complexes formed in Mo diluted FeCrNi model alloy. The long lifetime of vacancy-type defects in commercial stainless steel SUS316 is smaller than that in FeCrNi model alloys because the mobility of vacancy-type defects changed by nonmetal elements. In addition, vacancy-type and dislocation defects detected contribute to the S and W parameters of positron annihilation in the whole annealing treatment.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-26
摘要: Effects of deformed dislocation on helium retention in pure iron, including the helium atoms diffusion along the dislocation line and desorption from dislocation trapping sites, were investigated. The dislocation defect was introduced in specimens by cold-rolling, and then 5 keV helium ions were implanted into the deformed specimens. Slow positron beam technology and thermal desorption spectroscopy were used to investigate the evolution of dislocation defects and the desorption behavior of helium atoms under influence of dislocation. The behaviors of S-E, W-E and S-W plots indicate clearly that lots of helium atoms remain in the deformed specimen and helium atoms combining with dislocation change the distribution of electron density. The helium desorption plot indicates that dislocation accelerates helium desorption at 293 K-600 K and facilitates helium dissociation from HenVm (n/m=1.8) cluster.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-26
摘要: Cu precipitates played a key factor in irradiation induced hardening and embrittlement of reactor pressure vessel (RPV).In this work, two kinds of Fe-Cu model alloys with different Cu contents irradiated by Fe ion at 573 K were investigated using positron annihilation techniques and SEM. Doppler Broadening Spectroscopy(DBS) results indicated that with the irradiation dose increased from 0.1 dpa to 1.2 dpa, more vacancy-type defects were induced during Fe ion irradiation, and with different Cu contents, defects condition had few changes. Coincident Doppler Broadening (CDB) results indicated Cu precipitates were formed during the irradiation, which could be verified through the SEM results. The CDB results also showed that the Cu precipitates were the same at 0.1 dpa between the samples with different Cu contents. In Fe0.6Cu samples, more Cu precipitates were formed than that of Fe0.3Cu sample at 1.2 dpa.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Analyzing the effects of space weather on aviation is a new and developing topic. It has been commonly accepted that the flight time of the polar flights may increase during solar proton events because the flights have to change their route to avoid the high-energy particles. However, apart from such phenomenon, researches related to the flight time during space weather events is very rare. Based on the analyses of 39 representative international air routes around westerlies, it is found that 97.44% (94.87%) of the commercial airplanes on the westbound (eastbound) air routes reveal shorter (longer) flight time during solar proton events compared to those during quiet periods, and the averaged magnitude of change in flight time is ~10 min or 0.21%-4.17% of the total flight durations. Comparative investigations reassure the certainty of such phenomenon that the directional differences in flight time are still incontrovertible regardless of over-land routes (China-Europe) or over-sea routes (China-Western America). Further analyses suggest that the solar proton events associated atmospheric heating will change the flight durations by weakening certain atmospheric circulations, such as the polar jet stream. While the polar jet stream will not be obviously altered during solar flares so that the directional differences in flight time are not found. Besides the conventional space weather effects already known, this paper is the first report that indicates a distinct new scenario of how the solar proton events affect flight time. These analyses are also important for aviation since our discoveries could help the airways optimize the air routes to save passenger time costs, reduce fuel costs and even contribute to the global warming issues.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-24
摘要: In order to study the fundamental processes of helium retention and thermal desorption from the structural material of future fusion reactors, thermal desorption measurements were performed to investigate helium trapping from defects in binary Fe9Cr model alloys irradiated by 3 keV and 0.2 keV He ions. Interstitial type dislocation loops, vacancies and vacancy clusters were produced by irradiation with 3 keV helium ions, which acted as the sink trapped the helium atoms. Helium thermal desorption peaks from dislocations, helium-vacancies were obtained by thermal desorption spectroscopy at ~ 540 篊, in the range from 205 篊 to 478 篊, respectively. Simple first order dissociation kinetics are used to estimate the activation energies associated with the desorption groups. A sharp desorption peak was observed at ~ 865 篊 due to the BCC-FCC phase transformation for specimens under all examined implantation conditions.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-26
摘要: Our results suggest that SE and PAS are effective techniques to study the optical and defect properties of HfO2 and the results provide insights for the fabrication of high-quality HfO2 thin films for optical application.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2017-03-23
摘要: The dependences of bending plasticity on compositional adjustment and structural relaxation in Zr-Cu-Ag-Al-Be bulk metallic glasses (BMGs) were systematically studied. We reveal that with the increase in the Zr content, the plasticity is enhanced at the expense of glass forming ability and the shear transformation zone (STZ) volume becomes larger, while structural relaxation results in the embrittlement accompanied with the further enlarged STZ volume. Average positron lifetime, representing average free volume, drops with the increase in the Zr content and structural relaxation. The results indicate that neither STZ volume nor average positron lifetime can solely describe the plastic deformability of BMGs. Analyzing positron annihilation lifetime spectra, a bimodal distribution of open volume size is observed. The smaller open volume shrinks with increased concentration and the larger open volume expands with decreased concentration due to the increase in the Zr content, while structural elaxation only reduces the size of smaller open volume. The effects of open volume size distribution on the STZ activation and shear band propagation have been discussed. It has been demonstrated that combining the STZ volume with open volume size distribution can explain the plasticity evolution with the composition and structural relaxation, which sheds light on understanding the deformation mechanism of BMGs.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Among the heavy metal ions, copper(II) can cause eye and liver damage at high uptake. The existence of copper ions (Cu2+) even with an ultralow concentration of less than 0.1 μg g−1 can be toxic to living organisms. Thus, it is highly desirable to develop efficient adsorbents to remove Cu2+ from aqueous solu- tions. In this work, without any surface functionalization or pretreatment, a water-stable zeolitic imidazo- late framework (ZIF-8) synthesized at room temperature is directly used as a highly efficient adsorbent for removal of copper ions from aqueous solutions. To experimentally unveil the adsorption mechanism of Cu2+ by using ZIF-8, we explore various effects from a series of important factors, such as pH value, contact time, temperature and initial Cu2+ concentration. As a result, ZIF-8 nanocrystals demonstrate an unexpected high adsorption capacity of Cu2+ and high removal efficiency for both high and low concen- trations of Cu2+ from water. Moreover, ZIF-8 nanocrystals possess fast kinetics for removing Cu2+ with the adsorption time of less than 30 min. In addition, the pH of the solution ranging from 3 to 6 shows little effect on the adsorption of Cu2+ by ZIF-8. The adsorption mechanism is proposed for the first time and systematically verified by various characterization techniques, such as TEM, FTIR, XPS, XRD and SEM.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Surface plasmons in graphene provide a compelling strategy for advanced photonic technologies thanks to their tight confinement, fast response and tunability. Recent advances in the field of all optical generation of graphene plasmons in planar waveguides offer a promising method for high speed signal processing in nanoscale integrated optoelectronic devices. Here, we use two counter propagating frequency combs with temporally synchronized pulses to demonstrate deterministic all optical generation and electrical control of multiple plasmon polaritons, excited via difference frequency generation (DFG). Electrical tuning of a hybrid graphene fibre device offers a precise control over the DFG phase matching, leading to tunable responses of the graphene plasmons at different frequencies across a broadband (0 - 50 THz) and provides a powerful tool for high speed logic operations. Our results offer insights for plasmonics on hybrid photonic devices based on layered materials and pave the way to high speed integrated optoelectronic computing circuits.
分类: 物理学 >> 核物理学 提交时间: 2016-09-14
摘要: The Baryon Acoustic Oscillation (BAO) feature in the power spectrum of galaxies provides a standard ruler to measure the accelerated expansion of the Universe. To extract all available information about dark energy, it is necessary to measure a standard ruler in the local, z<0.2, universe where dark energy dominates most the energy density of the Universe. Though the volume available in the local universe is limited, it is just big enough to measure accurately the long 100 Mpc/h wave-mode of the BAO. Using cosmological N-body simulations and approximate methods based on Lagrangian perturbation theory, we construct a suite of a thousand light-cones to evaluate the precision at which one can measure the BAO standard ruler in the local universe. We find that using the most massive galaxies on the full sky (34,000 sq. deg.), i.e. a K(2MASS)<14 magnitude-limited sample, one can measure the BAO scale up to a precision of 4\% and 1.2\% using reconstruction). We also find that such a survey would help to detect the dynamics of dark energy.Therefore, we propose a 3-year long observational project, named the Low Redshift survey at Calar Alto (LoRCA), to observe spectroscopically about 200,000 galaxies in the northern sky to contribute to the construction of aforementioned galaxy sample. The suite of light-cones is made available to the public.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Poly(vinylidene fluoride) (PVDF) membranes have been widely applied to treat wastewater, however, the removal of toxic aromatic phenolic compounds remains a technical challenge due to the serious adsorption fouling and difficult degradation. Herein, we aimed to design a superhydrophilic PVDF membrane decorated with Au nanoparticles, which enhanced the rapid degradation of p-nitrophenol (4-NP). The superhydrophilic PVDF membrane with a micro/nano structured surface was decorated with Au nanoparticles via poly(dopamine) (PDA) as a spacer. The influences of membrane affinity (e.g. Hydrophilic Membrane (HM), micro/nano structured superhydrophilic membrane (MSiM), and micro/ nano structured superhydrophobic membrane (MSoM)) on PDA deposition and the subsequent Au decoration were comprehensively investigated. The synthesized Au nanoparticles were characterized using transmission electron microscopy (TEM) and UV-vis absorption spectra. The morphology and composition was evaluated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Static catalytic experiments demonstrated that MSiM degraded over 90% of 4-NP in 5 minutes with a kinetic reaction rate constant of 47.84 10 2 min 1 and high stability over 6 cycles. A membrane catalytic reactor (MCR) was designed to realize the continuous catalytic degradation of 4-NP with a kinetic reaction rate constant of 7 10 2 min 1.
分类: 生物学 >> 生态学 提交时间: 2017-11-17
摘要: Background: The adapter proteins Appl1 (adaptor protein containing pleckstrin homology domain, phosphotyrosine domain, and leucine zipper motif 1) and Appl2 are highly homologous and involved in several signaling pathways. While previous studies have shown that Appl1 plays a pivotal role in adiponectin signaling and insulin secretion, the physiological functions of Appl2 are largely unknown. Results: In the present study, the role of Appl2 in sepsis shock was investigated by using Appl2 knockout (KO) mice. When challenged with lipopolysaccharides (LPS), Appl2 KO mice exhibited more severe symptoms of endotoxin shock, accompanied by increased production of proinflammatory cytokines. In comparison with the wild-type control, deletion of Appl2 led to higher levels of TNF-alpha and IL-1 beta in primary macrophages. In addition, phosphorylation of Akt and its downstream effector NF-kappa B was significantly enhanced. By co-immunoprecipitation, we found that Appl2 and Appl1 interacted with each other and formed a complex with PI3K regulatory subunit p85 alpha, which is an upstream regulator of Akt. Consistent with these results, deletion of Appl1 in macrophages exhibited characteristics of reduced Akt activation and decreased the production of TNF alpha and IL-1 beta when challenged by LPS. Conclusions: Results of the present study demonstrated that Appl2 is a critical negative regulator of innate immune response via inhibition of PI3K/Akt/NF-kappa B signaling pathway by forming a complex with Appl1 and PI3K.Conclusions: Results of the present study demonstrated that Appl2 is a critical negative regulator of innate immune response via inhibition of PI3K/Akt/NF-kappa B signaling pathway by forming a complex with Appl1 and PI3K.
分类: 生物学 >> 生态学 提交时间: 2017-11-17
摘要: From the (a)CAS Key Laboratory of Regenerative Biology, Joint School of Life Sciences, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou 510530, China, and Guangzhou Medical University, Guangzhou 511436, China, (b)CAS Key Laboratory of Regenerative Biology and Guangdong Provincial Key Laboratory of Stem Cells and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou 510530, China, (c)Laboratory of RNA, Chromatin, and Human Disease, CAS Key Laboratory of Regenerative Biology and Guangdong Provincial Key Laboratory of Stem Cells and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou 510530, China, (d)Cardiology Division, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong SAR, China, (e)Hong Kong-Guangdong Stem Cell and Regenerative Medicine Research Centre, The University of Hong Kong and Guangzhou Institutes of Biomedicine and Health, Hong Kong SAR, China, (f)Department of Ophthalmology, The Third Affiliated Hospital of Sun Yat-sen University, Guangzhou 510630, China, (g)State Key Laboratory of Organ Failure Research, Guangdong Provincial Key Laboratory of Viral Hepatitis Research, Guangdong Provincial Research Center for Liver Fibrosis, Department of Infectious Diseases and Hepatology Unit, Nanfang Hospital and (h)Biomedical Research Center, Southern Medical University, Guangzhou 510515, China, (i)Institute of Immunology and Immunotherapy, College of Medical and Dental Sciences, (j)National Institute for Health Research (NIHR) Birmingham Liver Biomedical Research Unit and Centre for Liver Research, and (k)Institute of Cancer and Genomic Sciences, College of Medical and Dental Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom, (l)Cambridge Institute for Medical Research, Wellcome Trust/Medical Research Council (MRC) Building, Cambridge CB2 0XY, United Kingdom, mDepartment of Clinical Biochemistry Unit, Queen Mary Hospital, Hong Kong SAR, China, (n)Department of Medicine, University of Hong Kong-Shenzhen Hospital, Shenzhen 518053, Guangdong, China, and (o)Laboratory of Metabolism and Cell Fate, CAS Key Laboratory of Regenerative Biology and Guangdong Provincial Key Laboratory of Stem Cells and Regenerative Medicine, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou 510530, Guangdong, China