上海光源X射线成像实验站相位衬度CT初步结果

X射线相位衬度CT能获得样品内部结构的边缘增强图像,可观察到传统X射线吸收CT无法观察到的生物软组织内部微细结构,具有巨大发展潜力。经初步调试,上海光源X射线成像实验站的8-72.5keV单色X射线输出已能用于实验研究。本文在X射线成像实验站上开展生物样品(蝗虫)同轴X射线相位衬度CT研究,获得蝗虫样品的切片重构图像和三维重建图像。结果图像中,蝗虫样品的翅膀、表面纹理和内部组织分布情况清晰可见。

Competition between fusion-evaporation and multifragmentation in central collisions in ^(58)Ni+^(48)Ca at 25A MeV

The experimental data concerning the58Ni+48Ca reaction at Elab(Ni)=25A MeV,collected by using the CHIMERA 4π device,have been analyzed in order to investigate the competition among different reaction mechanisms for central collisions in the Fermi energy domain.As a main criterion for centrality selection we have chosen the flow angle(flow) method,making an event-by-event analysis that considers the shape of events,as it is determined by the eigenvectors of the experimental kinetic-energy tensor.For the selected central events(flow >60°) some global variables,good to characterize the pattern of central collisions have been constructed.The main features of the reaction products were explored by using different constraints on some of the relevant observables,like mass and velocity distributions and their correlations.Much emphasis was devoted,for central collisions,to the competition between fusion-evaporation processes with subsequent identification of a heavy residue and a possible multifragmentation mechanism of a well defined(if any) transient nuclear system.Dynamical evolution of the system and pre-equilibrium emission were taken into account by simulating the reactions in the framework of transport theories.Different approaches have been envisaged(dynamical stochastic BNV calculations + sequential SIMON code,QMD,CoMD,etc.).Preliminary comparison of the experimental data with BNV calculations shows reasonable agreement with the assumption of sequential multifragmentation emission in the mass region of IMFs close to the heavy residues.Possible deviations from sequential processes were found for those IMFs in the region of masses intermediate between the mass of heavy residues and the mass of light IMFs.Further simulations are in progress.The experimental analysis will be enriched also by information obtained inspecting the IMF-IMF correlation function,in order to elucidated the nature of space-time decay property of the emitting source associated with events having the largest IMF multiplicity.

Combined Environmental and Magnetic Effects on Elementary Matter: A Quantum Field Theory Description of Fermion Epigenetics

We compute in a theoretical quantum field theory framework the effects that a classic environment will have on an elementary one-fermion state, assumed for simplicity to be that of one electron, in the presence of a magnetic field. We consider its total energy and its spin angular momentum as relevant observables of the state. We show that the changes of these quantities produced by the combined environmental and magnetic effects can be expressed in a simple and compact form. We obtain expressions that only depend on the values of the external environment and magnetic fields, and on the special spin features of the free fermion state. We call these effects “fermion epigenetics” and try to motivate this definition discussing possible relevant analogies with the corresponding medical treatment of epigenetics in organic cells.

Angular Momentum Minimal Magnetization of an Elementary Quantum Fermion System

I consider, in a Quantum Field Theory theoretical approach, the effects of an electromagnetic field on the components of the total angular momentum of an elementary fermion system, assuming the “minimal” form of the relative interaction. When the electromagnetic field can be treated as a classical one, these effects are particularly simple to be computed and exhibit a number of very general characteristic features in the case of a constant magnetic field. A qualitative possible analogy with similar features of an elementary organic system is finally proposed.

基于玻恩近似相位恢复的X射线显微CT实验研究

结合同轴X射线相位衬度成像(XPCI)中的Born近似相位恢复法和CT技术,实现了基于单一物像距同轴X射线相位衬度CT(IL-XPCT)投影图像的相位恢复切片重构方法。利用上海光源X射线成像及生物医学应用光束线站的单色光开展模型和生物样品(蝗虫)IL-XPCT研究。对比显示,进行相位恢复后,能获得更好的IL-XPCT重构切片和三维重建图像。实验结果表明,本方法具有用于生物活体样品三维无损成像研究的潜力。

Phase Contrast Micro-Computed Tomography of Biological Sample at SSRF

In line X-ray phase contrast micro-computed tomography （IL-XPCT）, which can be implemented at third generation synchrotron radiation sources or by using a micro-focus X-ray tube, is a powerful technique for non-destructive, high-resolution investigations of a broad variety of materials. At the Shanghai Synchrotron Radiation Facility （SSRF）, the X-ray Imaging and Biomedical Applications Beamline was built and started regular user operation in May 2009. Both qualitative （without phase retrieval） and quantitative （with phase retrieval） three-dimensional IL-XPCT experimental techniques have been established at the beamline IL-XPCT experiments of a test sample （plastic pipes） used to evaluate the technique, and of a biological sample （locust） at the beamline are reported. Two series of images, qualitative and quantitative, including tomographic slices and three-dimensional rendering images were obtained. In qualitative images, there is a strong edge-enhancement which leads to very clear sample contours, while in quantitative images, the edge-enhancement fades but quantitative measurement of sample＇s phase information could be achieved. The experiments demonstrate that the combination of qualitative and quantitative images is useful for biological sample studies.

Exploring fermionic multiplet dark matter through precision measurements at the CEPC

New physics could be explored through loop effects using the precision measurements at the Circular Electron Positron Collider(CEPC)owing to its clean collision environment and high luminosity.In this paper,we focus on two dark matter models that involve additional electroweak fermionic multiplets.We calculate their one-loop corrections in five processes,i.e.,e^(+)e^(-)→μ^(+)μ^(-),Zh,W^(+)W^(-),ZZ,and,Zγ,and investigate the corresponding signatures at the CEPC with the projected sensitivity.We observe that the detectable parameter regions of these processes are complementary.The combined analysis shows that the mass of dark matter m_(χ^(0)_(1))in these two models can be probed up to-150GeV and-450GeV,respectively,at a 95%confidence level.

Measurement of the integrated luminosity of the Phase 2 data of the Belle Ⅱ experiment

From April to July 2018,a data sample at the peak energy of the T(4 S) resonance was collected with the Belle Ⅱ detector at the SuperKEKB electron-positron collider.This is the first data sample of the Belle Ⅱ experiment.Using Bhabha and digamma events,we measure the integrated luminosity of the data sample to be(496.3±0.3±3.0) pb-1,where the first uncertainty is statistical and the second is systematic.This work provides a basis for future luminosity measurements at Belle Ⅱ.

Measurement of Ξcc++ production in pp collisions at s1/2=13 TeV

The production of ■baryons in proton-proton collisions at a centre-of-mass energy of √s = 13 TeV is measured in the transverse-momentum range 4<pT<15GeV/c and the rapidity range2.0<y<4.5.The data used in this measurement correspond to an integrated luminosity of 1.7fb^-1,recorded by the LHCb experiment during 2016.The ratio of the ■ production cross-section times the branching fraction of the■→∧^+cK^-π^+ π^+decay relative to the prompt ∧^+c production cross-section is found to be(2.22±0.27±0.29)×10^-4,assuming the central value of the measured lifetime,where the first uncertainty is statistical and the second systematic.