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Probing shock geometry via the charge to mass ratio dependence of heavy ion spectra from multiple spacecraft observations of the 2013 November 4 event

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Research in Astronomy and Astrophysics 2016年第12期16卷 101-106页

作者： Lulu Zhao Gang Li Glenn M. Mason Christina Cohen Richard Mewaldt Mihir Desai Rob Ebert maher al-dayeh Department of Physics and Space Sciences Florida Institute of Technology FL 32901 USA Department of Space Science and CSPAR University of Alabama in Hun-tsville Huntsville Alabama 35801 USA Applied Physics Laboratory Johns Hopkins University Laurel MD 20723 USA California Institute of Technology Pasadena CA 91125 USA Southwest Research Institute San Antonio TX 78228 USA University of Texas at San Antonio San Antonio TX 78249 USA

In large Solar Energetic Particle （SEP） events, ions can be accelerated at coronal mass ejection （CME）-driven shocks to very high energies. The spectra of heavy ions in many large SEP events show features such as roll-overs or spectral breaks. In some events when the spectra are plotted in terms of energy/nucleon, they can be shifted relative to each other to make the spectral breaks align. The amount of shift is charge to mass ratio （Q/A） dependent and varies from event to event. This can be understood if the spectra of heavy ions are organized by the diffusion coefficients （Cohen et al. 2005）. In the work of Li et al. （2009）, the Q/A dependence of the scaling is related to shock geometry when the CME-driven shock is close to the Sun. For events where multiple in-situ spacecraft observations exist, one may expect that different spacecraft are connected to different portions of the CME-driven shock that have different shock geometries, therefore yielding different Q/A dependence. In this work, we examine one SEP event which occurred on 2013 November 4. We study the Q/A dependence of the energy scaling for heavy ion spectra using helium, oxygen and iron ions. Observations from STEREO-A, STEREO-B and ACE are examined. We find that the scalings are different for different spacecraft. We suggest that this is because ACE, STEREO- A and STEREO-B are connected to different parts of the shock that have different shock geometries. Our analysis indicates that studying the Q/A scaling of in-situ particle spectra can serve as a powerful tool to remotely examine the shock geometry for large SEP events.

关键词： Sun: particle emission -- acceleration of particles

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Experimental Analysis of Interacting HT22 Plasma Membrane Cholesterol and β-Amyloid

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Advances in alzheimer's Disease 2017年第4期6卷 75-96页

作者： George Livadiotis Leila Assas maher A. dayeh Saber Elaydi Chloe Phea James L. Roberts Yara Samman Rachel Tchen Southwest Research Institute San Antonio USA Department of Mathematics King Abdul Aziz University Jeddah Saudi Arabia Trinity University San Antonio USA

The peptide β-Amyloid (β-A) is known to be one of the primary factors causing neurodegeneration in the alzheimer disease. Hence, one would like to know the factors that would increase or decrease the toxicity of β-Amyloid in the brain. One of the factors that are debated in the literature is cholesterol, where it is not clear if modulating the levels of cholesterol would affect the degree of toxicity of β-Amyloid on neuron cells in the brain. In order to investigate this problem, data were collected and analyzed for three types of experiments: 1) Correspondence between cholesterol and methyl-β-cyclodextrin (MβCD) measurements;2) measurements of the relative fluorescence unit (RFU) with respect to MβCD concentration (with/without β-A);and 3) RFU measurements with respect to β-A concentration (with/without MβCD). HT22 hippocampal neurons immortalized with the simian virus SV-40 large T-antigen plasmid vector were used to conduct the experiments. Mito-ID Membrane potential cytotoxicity was used as a measure of mitochondrial potential change. The statistical analysis of the presented experimental results indicates that cholesterol has no statistically significant effect on the degree of toxicity of β-Amyloid.

关键词： alzheimer Disease β-Amyloid Cholesterol

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