PAMELA results on the cosmic-ray antiproton flux from 60 MeV to 180 GeV in kinetic energy

The satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray antiproton flux and the antiproton-to-proton flux ratio which extends previously published measurements down to 60 MeV and up to 180 GeV in kinetic energy. During 850 days of data acquisition approximately 1500 antiprotons were observed. The measurements are consistent with purely secondary production of antiprotons in the galaxy. More precise secondary production models are required for a complete interpretation of the results.Comment: 11 pages, 3 figures, 1 table. Accepted for publication in Physical Review Letter

Effective-Range Expansion of the Neutron-Deuteron Scattering Studied by a Quark-Model Nonlocal Gaussian Potential

The S-wave effective range parameters of the neutron-deuteron (nd) scattering are derived in the Faddeev formalism, using a nonlocal Gaussian potential based on the quark-model baryon-baryon interaction fss2. The spin-doublet low-energy eigenphase shift is sufficiently attractive to reproduce predictions by the AV18 plus Urbana three-nucleon force, yielding the observed value of the doublet scattering length and the correct differential cross sections below the deuteron breakup threshold. This conclusion is consistent with the previous result for the triton binding energy, which is nearly reproduced by fss2 without reinforcing it with the three-nucleon force.Comment: 21 pages, 6 figures and 6 tables, submitted to Prog. Theor. Phy

Detection of drug-induced conformational change of a transmembrane protein in lipid bilayers using site-directed spin labeling

As a target of antiviral drugs, the influenza A M2 protein has been the focus of numerous structural studies and has been extensively explored as a model ion channel. In this study, we capitalize on the expanding body of high-resolution structural data available for the M2 protein to design and interpret site-directed spin-labeling electron paramagnetic resonance spectroscopy experiments on drug-induced conformational changes of the M2 protein embedded in lipid bilayers. We obtained data in the presence of adamantane drugs for two different M2 constructs (M2TM 22–46 and M2TMC 23–60). M2TM peptides were spin labeled at the N-terminal end of the transmembrane domain. M2TMC peptides were spin labeled site specifically at cysteine residues substituted for amino acids within the transmembrane domain (L36, I39, I42, and L43) and the C-terminal amphipathic helix (L46, F47, F48, C50, I51, Y52, R53, F54, F55, and E56). Addition of adamantane drugs brought about significant changes in measured electron paramagnetic resonance spectroscopy environmental parameters consistent with narrowing of the transmembrane channel pore and closer packing of the C-terminal amphipathic helices

Time Dependence of the electron and positron components of the cosmic radiation measured by the PAMELA experiment between July 2006 and December 2015

Cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our Galaxy. Recent measurements of these particles are challenging our basic understanding of the mechanisms of production, acceleration, and propagation of cosmic rays. Particularly striking are the differences between the low energy results collected by the space-borne PAMELA and AMS-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. The PAMELA experiment has been measuring the time variation of the positron and electron intensity at Earth from July 2006 to December 2015 covering the period for the minimum of solar cycle 23 (2006-2009) until the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. The positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. These results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field