New effects in low energy scattering of pµ atoms

Strong solid state effects in low energy scattering of pμ atoms in solid hydrogen are reported and analyzed. Such effects have been observed in TRIUMF experiment E742 where muons are stopped in thin frozen (3 K) layers of hydrogen. Emission of low energy pμ atoms from the hydrogen layer into adjacent vacuum was much higher than expected, based on calculations which ignored the solid nature of hydrogen. Monte Carlo simulations, performed using the scattering cross-sections with solid state effects taken into account, show the important role of the coherent elastic Bragg scattering in the diffusion of pμ atoms. For pμ energies lower than the Bragg cut-off limit (∼2 meV) the total scattering cross-section falls by several orders of magnitude, the hydrogen target becomes transparent and the emission of cold pμ atoms takes place. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mass spectrometric sequencing and acylation character analysis of C-terminal anchoring segment from Influenza A hemagglutinin

Influenza A virus hemagglutinin (HA) is a major envelope glycoprotein mediating viral and cell membrane fusion. HA is anchored in the viral envelope by a light HA(2) chain containing one transmembrane domain and a cytoplasmic tail. Three cysteine residues in the C-terminal region, one in the transmembrane domain and two in the cytoplasmic tail, are highly conserved and potentially palmitoylated in all HA subtypes. The HA(2) C- terminal anchoring segments were extracted to organic phase from the bromelain-digested viruses (subviral particles) of three strains: A/X-31 (H3 subtype), A/Puerto Rico/8/34 (H1 subtype) and A/FPV/Weybridge/34 (H7 subtype). Their primary structures were assessed by matrix-assisted laser desorption/ionization time-of-flight time-of- flight mass spectrometry (MALDI-ToF-ToF MS). Trypsin-type protease-cleaved peptides prevailed over bromelain- cleaved ones in the peptide mixtures. All of them included transmembrane domains. Several distinctive features of the C-terminal HA(2) peptides acylation character were discovered by MALDI-ToF MS: 1) the peptides isolated from the viruses, which were digested by bromelain in the absence of beta-mercaptoethanol, were predominantly triply acylated; 2) the peptides were acylated not only by palmitic, but also by stearic acid residues; 3) the palmitate/stearate ratio was different for the three strains studied; 4) the A/FPV/Weybridge/34 strain has a priority to stearate binding. This fatty acid residue was discovered at the first of three conservative cysteine residues located in the transmembrane domain. It was found that presence of thiol reagent during preparation of subviral particles led to the appearence of the C-terminal HA(2) peptides acylated to different degrees. Triply, doubly, mono- and even unacylated peptides were detected. It was demonstrated that the thioester bond in the isolated acylpeptides was extremely sensitive to thiol reagents.     

High-velocity components in exotic atoms,their origin and effects

The evolution of the kinetic energy distribution during the cascade is shown to play an important role for pionic and muonic atoms in hydrogen and deuterium. The kinetics of muon transfer in excited states is studied with a new cascade code and the results are compared with recent experimental data.     

Time-of-flight measurement of resonant molecular formation in muon-catalyzed dt fusion

Preliminary results are reported for an experiment at TRIUMF where a time-of-flight technique was tested for measuring the energy dependence of the rate for muon-catalyzed dt fusion. Muonic tritium atoms were created following transfer of negative muons from muonic protium in a layer of solid hydrogen (protium) containing a small fraction of tritium. The atoms escaped from the solid layer via the Ramsauer-Townsend mechanism, traversed a drift region of 18 mm, and then struck an adjacent layer of deuterium, where the muonic atom could form a molecular system. The time of detection of a fusion product (neutron or alpha) following muon arrival is dependent upon the energy of the muonic tritium atom as it traverses the drift region. By comparison of the time distribution of fusion events with a prediction based on the theoretical energy dependence of the rate, the strength of resonant formation can in principle be determined. The results extracted so far are discussed and the limitations of the method are examined.     

Molecular simulation of LiCl aqueous solutions

Non-primitive LiCl aqueous electrolyte solutions were studied at 1.0, 5.0 and 10.0 M concentrations by molecular dynamics simulations. It was observed that the ion hydration structure is progressively lost with increasing concentration. The ions are aggregated in small clusters at C = 1.0 M. However, at this concentration, two large clusters were detected that are an initial step in an aggregation process. At C = 5.0 M, the highly unstable ion clustering seems to correspond to an intermediary state between low concentration states with poor aggregation and states where the ions are highly aggregated, as observed at C = 10.0 M where almost all the ions are clustered in one cluster. This cluster does not present a crystal-like structure. The high solubility of LiCl in aqueous solutions can consequently be explained as a result of the large radii difference between the anion and the cation that results in the instability of the ionic aggregates, which makes the formation of crystal seeds difficult.     

Effect of the deletion of the C region on the structure and hydration of insulin-like growth factor 1: a molecular dynamics investigation

The structure and hydration of insulin-like growth factor 1 and an inactive mutant lacking the C region have been investigated in aqueous solution by molecular dynamics simulation. The overall structures of the two polypeptide resemble those determined by NMR spectroscopy. The deletion of the C region in the wild polypeptide introduces structural stability in the mutant, leading to a better definition of the secondary structure elements. A detailed hydration analysis was performed using the radial distribution functions and energy distributions. The backbone of the mutant is in general more solvent accessible than the wild polypeptide backbone. The structural rearrangements induced in the mutant led to changes in the solvent exposition of Tyr24 and Tyr60, which are residues important for ligand—receptor complex formation. Tyr24 exhibited a similar degree of solvent exposition in both IGF-I and in the mutant; however, its hydroxyl group in the wild polypeptide is better solvated than in the mutant. Tyr60 was found to be solvent exposed in the wild protein, while in the mutant the involvement of its hydroxyl group in intramolecular hydrogen bonds led to it being buried away from the solvent.     

The nuclear fusion in the muonic molecule ddμ and the charge symmetry violation in the low energy dd interaction

The rate λ_f = 1.0 × 10⁹ s^?1 of the nuclear fusion in the ddμ molecule is calculated. It is shown that the ratio of the neutron to the proton yield equals the ratio of the p-wave cross sections of the d(d,n)³ He and d(d,p)t reactions near the dd threshold.     

Muonic hydrogen and deuterium in H-D mixture and muon transfer in excited states

The deexcitation of µp and µd atoms in hydrogen-deuterium mixtures has been studied with a new kinetics model that takes the energy dependence of the cascade processes into account. The X-ray yields, the populations of atomic states, and the muon transfer from hydrogen to deuterium during the cascade have been calculated as functions of density and isotope fractions. The evolution of the kinetic energy distribution during the cascade is shown to play an important role in the transfer kinetics. The atomic energy distribution in the ground state is significantly changed by the transfer. The calculated X-ray yields and the muon transfer probabilities are in fair agreement with experimental data provided the current theoretical transfer rates are reduced by a factor of about 2.     

Measurement of absolute yields of Lyman transitions in pionic hydrogen and deuterium as a function of pressure

Absolute yields ofK X-ray transitions in pionic hydrogen and deuterium were determined with accuracies of typically ±10% at target pressures of 2.8, 15 and 40 bar and compared with the results of a recently developed cascade code.Deceased     

Measurement of the heavy neutrino admixture upper limit from muon capture by3He

The triton energy spectrum of the muon capture reaction µ³Het+_µ where µ³He is the ground state of muonic³He, has been measured by means of a high-pressure ionization chamber in order to investigate a possible heavyv admixture into the µ flavor with high sensitivity. The upper limit of the µ-heavy v_i mixing matrix element squared was obtained to be U_µi²10^–3 for heavy neutrino masses in the range of 25 E_0V75 MeV.