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：Dislocations would be induced after plastic deformation, which might change the mechanical properties of solids. FeCrNi austenitic model alloy and its Mo-diluted alloy were cold rolled with different degree of thickness reduction. Positrons are sensitive to point defects, which are easily trapped and annihilated around the trapping sites. The mean positron lifetimes have been used to estimate the average dislocation concentration in solids. Meanwhile, the trapping efficiency μ was calculated from the lifetime results. The trapping efficiency value is estimated about 3.31×10-7 cm3s-1 for FeCrNi alloy and 3.31×10-7 cm3s-1 for Mo-diluted alloy, respectively. The increment of the hardness value during plastic deformation is related to the increase of the dislocation density and dislocation pile up in solids.
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： Solution annealed type 316L austenitic stainless steels were irradiated using 2 MeV Fe ions at room temperature. The implanted fluences were 2012 ions/cm2 and 1013 ions/cm2, respectively. Variable mono-energetic positron beam was performed to characterize the evolution of microstructure and irradiation induced defects. Results show that large amount of vacancy defects formed after heavy ion irradiation. In which, some of mono-vacancies might migrate to form small-sized clusters at room temperature. After irradiation, implanted Fe atoms mainly be interstitials atoms, but some Fe atoms might recombine with vacancies due to their high mobility, which could decrease the defect concentration, effectively.
分类： 物理学 >> 核物理学 提交时间： 2016-09-19
摘要：In this paper, we extend the Fritzsch ansatz of quark mass matrices while retaining their hierarchical structures and show that the main features of the Cabibbo-Kobayashi-Maskawa (CKM) matrix V, including |Vus|≃|Vcd|, |Vcb|≃|Vts| and |Vub|/|Vcb|<|Vtd|/|Vts|, can be well understood. This agreement is observed especially when the mass matrices have non-vanishing (1,3) and (3,1) off-diagonal elements. The phenomenological consequences of these for the allowed texture content and gross structural features of `hierarchical' quark mass matrices are addressed from a model independent prospective under the assumption of factorizable phases in these. The approximate and analytical expressions of the CKM matrix elements are derived, and a detailed analysis reveals that such structures are in good agreement with the observed quark flavor mixing angles and the CP-violating phase at the 1σ level and call upon a further investigation of the realization of these structures from a top-down prospective.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要：We infer the emission positions of twin kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low mass X-ray binaries (NS-LMXBs) based on the Alfven wave oscillation model (AWOM). For most sources, the emission radii of kHz QPOs cluster around a region of 16-19 km with the assumed NS radii of 15 km. Cir X-1 has the larger emission radii of 23-38 km than those of the other sources, which may be ascribed to its large magnetosphere-disk radius or strong NS surface magnetic field. SAX J1808.4-3658 is also a particular source with the relative large emission radii of kHz QPOs of 20 - 23 km, which may be due to its large inferred NS radius of 18 - 19 km. The emission radii of kHz QPOs for all the sources are larger than the NS radii, and the possible explanations of which are presented. The similarity of the emission radii of kHz QPOs (16-19 km) for both the low/high luminosity Atoll/Z sources is found, which indicates that both sources share the similar magnetosphere- disk radii.
分类： 物理学 >> 核物理学 提交时间： 2016-09-05
摘要：We study the purely leptonic decays of W±→e±e±μ∓ν and μ±μ±e∓ν produced at the LHC, induced by sterile neutrinos with mass mN below MW in the intermediate state. Since the final state neutrino escapes detection, one cannot tell whether this process violates lepton number, what would indicate a Majorana character for the intermediate sterile neutrino. Our study shows that when the sterile neutrino mixings with electrons and muons are different enough, one can still discriminate between the Dirac and Majorana character of this intermediate neutrino by simply counting and comparing the above decay rates. After performing collider simulations and statistical analysis, we find that at the 14 TeV LHC with an integrated luminosity of 3000 fb−1, for two benchmark scenarios mN = 20 GeV and 50 GeV, at least a 3σ level of exclusion on the Dirac case can be achieved for disparities as mild as e.g. |UNe|2<0.7 |UNμ|2 or |UNμ|2<0.7 |UNe|2, provided that |UNe|2, |UNμ|2 are both above ∼2×10−6.
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