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Search Results: 1 - 10 of 33568 matches for " HE Gang "
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Magnetoacoustic Imaging of Electrical Conductivity of Biological Tissues at a Spatial Resolution Better than 2 mm
Gang Hu, Bin He
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0023421
Abstract: Magnetoacoustic tomography with magnetic induction (MAT-MI) is an emerging approach for noninvasively imaging electrical impedance properties of biological tissues. The MAT-MI imaging system measures ultrasound waves generated by the Lorentz force, having been induced by magnetic stimulation, which is related to the electrical conductivity distribution in tissue samples. MAT-MI promises to provide fine spatial resolution for biological tissue imaging as compared to ultrasound resolution. In the present study, we first estimated the imaging spatial resolution by calculating the full width at half maximum (FWHM) of the system point spread function (PSF). The actual spatial resolution of our MAT-MI system was experimentally determined to be 1.51 mm by a parallel-line-source phantom with Rayleigh criterion. Reconstructed images made from tissue-mimicking gel phantoms, as well as animal tissue samples, were consistent with the morphological structures of the samples. The electrical conductivity value of the samples was determined directly by a calibrated four-electrode system. It has been demonstrated that MAT-MI is able to image the electrical impedance properties of biological tissues with better than 2 mm spatial resolution. These results suggest the potential of MAT-MI for application to early detection of small-size diseased tissues (e.g. small breast cancer).
A Brief Review on Dark Matter Annihilation Explanation for $e^\pm$ Excesses in Cosmic Ray
Xiao-Gang He
Physics , 2009, DOI: 10.1142/S0217732309031740
Abstract: Recently data from PAMELA, ATIC, FERMI-LAT and HESS show that there are $e^{\pm}$ excesses in the cosmic ray energy spectrum. PAMELA observed excesses only in $e^+$, but not in anti-proton spectrum. ATIC, FERMI-LAT and HESS observed excesses in $e^++e^-$ spectrum, but the detailed shapes are different which requires future experimental observations to pin down the correct data set. Nevertheless a lot of efforts have been made to explain the observed $e^\pm$ excesses, and also why PAMELA only observed excesses in $e^+$ but not in anti-proton. In this brief review we discuss one of the most popular mechanisms to explain the data, the dark matter annihilation. It has long been known that about 23% of our universe is made of relic dark matter. If the relic dark matter was thermally produced, the annihilation rate is constrained resulting in the need of a large boost factor to explain the data. We will discuss in detail how a large boost factor can be obtained by the Sommerfeld and Briet-Wigner enhancement mechanisms. Some implications for particle physics model buildings will also be discussed.
B decays and models for CP violation
Xiao-Gang He
Physics , 1996, DOI: 10.1103/PhysRevD.53.6326
Abstract: The decay modes $B$ to $\pi\pi$, $\psi K_S$, $K^- D$, $\pi K$ and $\eta K$ are promising channels to study the unitarity triangle of the CP violating CKM matrix. In this paper I study the consequences of these measurements in the Weinberg model. I show that using the same set of measurements, the following different mechanisms for CP violation can be distinguished: 1) CP is violated in the CKM sector only; 2) CP is violated spontaneously in the Higgs sector only; And 3) CP is violated in both the CKM and Higgs sectors.
A Light $Z'$ Boson
Xiao-Gang He
Physics , 1994,
Abstract: A model of a light $Z'$ boson based on gauged $L_\mu - L_\tau$ $U(1)$ symmetry is constructed. The $Z'$ boson mass is constrained to be in the range of 0.8 to 1 GeV from Z and $Z'$ mass relation, g-2 of muon, and tau decays. The two body decay $\tau \rightarrow \mu Z'$ is possible. This will provide a striking signature to test the model. Talk presented at the Eighth Meeting of the American Physical Society, Division of Particles and Fields (DPF'94), Albuqurque, New Mexico, August 2-6, 1994.
A Possible Way of Connecting the Grassmann Variables and the Number of Generation
Xiao-Gang He
Physics , 1993, DOI: 10.1103/PhysRevD.49.567
Abstract: We construct a Left-Right symmetric model in which the number of generation is related to Grassmann variables. We introduce two sets of complex Grassmann variables ($\theta^1_q$,$\theta^2_q$), ($\theta^1_l$, $\theta ^2_l$) and associate each variable with left- and right-handed quark and lepton fields, respectively. Expanding quark and lepton fields in powers of the Grassmann variables, we find that there are exactly three generations of quarks and leptons. Integrating out the Grassmann variables, we obtain phenomenologically acceptable fermion mass matrices.
Anomalous $WWZ$ couplings and $K_L\rightarrow μ^+ μ^-$
Xiao-Gang He
Physics , 1993, DOI: 10.1016/0370-2693(93)90821-X
Abstract: We study contributions to $K_L \rightarrow \mu^+\mu^-$ from anomalous $WWZ$ interactions. There are, in general, seven anomalous couplings. Among the seven anomalous couplings, only two of them contribute significantly. The others are suppressed by factors like $m_s^2/M_W^2$, $m_d^2$, or $m_K^2/M_W^2$. Using the experimental data on $K_L\rightarrow \mu^+\mu^-$, we obtain strong bounds on the two anomalous couplings.
Xiao-Gang He
Physics , 1995,
Abstract: In this talk I discuss CP violation in hyperon decays in Left-Right symmetric models. I show that the asymmetry in polarization in $\Lambda \to p\pi^-$ can be as large as $6\times 10^{-4}$ in these models, which is an order of magnitude larger than the Standard Model prediction.
SU(3) Analysis of Annihilation Contributions and CP Violating Relations in $B \to PP$ Decays
Xiao-Gang He
Physics , 1998, DOI: 10.1007/s100529900064
Abstract: Several methods proposed to measure the angle $\gamma$ in the KM unitarity triangle assumed that the tree contribution to $B^-\to \pi^-\bar K^0 $ is purely due to annihilation contributions and is negligibly small. This assumption has to be tested in order to have a correct interpretation of the experimental data. In this paper we show that using SU(3) symmetry, the smallness of the tree contribution can be tested in a dynamic model independent way. We also derive several relations between CP violating rate differences for $B\to P P$ decays without assuming the smallness of the annihilation contributions. These relations provide important tests for the Standard Model of CP violation.
CP Violation in the SM and Beyond in Hadronic B Decays
Xiao-Gang He
Physics , 2000,
Abstract: Three different methods, using $B_d\to J/\psi K_S$, $J/\psi K_S \pi^0$, $B_d\to K^-\pi^+, \pi^+\pi^-$ and $B_u\to K^- \pi^0, \bar K^0 \pi^-, \pi^-\pi^0$, to extract hadronic model independent information about new physics are discussed in this talk.
CP Violation
Xiao-Gang He
Physics , 1997,
Abstract: In this lecture I review the present status of CP violation in the Standard Model and some of its extensions and discuss ways to distinguish different models. Contents 1. Introduction 2. CP violation in the Standard Model 3. Test the Standard Model in B decays 4. Models for CP violation 5. The KM unitarity triangle and new physics 6. Direct CP violation in neutral Kaon system 7. The electric dipole moment 8. Partial rate asymmetry 9. Test of CP violation involving polarization measurement 10. Baryon number asymmetry 11. Conclusion
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