Longitudinal and Transverse Form Factors from 12^{12}C

Electron scattering form factors from $^{12}$C have been studied in the framework of the particle-hole shell model. Higher configurations are taken into account by allowing particle-hole excitations from the 1$s$ and 1$p$ shells core orbits up to the 1$f-2p$ shell. The inclusion of the higher configurations modifies the form factors markedly and describes the experimental data very well in all momentum transfer regions.Comment: 5 pages, 5 figures, 3 tables, late

Isospin-projected nuclear level densities by the shell model Monte Carlo method

We have developed an efficient isospin projection method in the shell model Monte Carlo approach for isospin-conserving Hamiltonians. For isoscalar observables this projection method has the advantage of being exact sample by sample. The isospin projection method allows us to take into account the proper isospin dependence of the nuclear interaction, thus avoiding a sign problem that such an interaction introduces in unprojected calculations. We apply our method in the calculation of the isospin dependence of level densities in the complete $pf+g_{9/2}$ shell. We find that isospin-dependent corrections to the total level density are particularly important for $N \sim Z$ nuclei.Comment: 5 pages including 4 figure

Dipole and Quadrupole electroexcitations of the isovector T=1 particle-hole states in C-12

Electroexcitations of the dominantly T=1 particle-hole states of C-12 are studied in the framework of the harmonic oscillator shell model. All possible T=1 single-particle-hole states of all allowed angular momenta are considered in a basis including single-particle states up to the 1f-2p shell. The Hamiltonian is diagnoalized in this space in the presence of the modified surface delta interaction. Correlation in the ground state wave functions by mixing more than one configuration is considered and shows a major contribution that leads to enhance the calculations of the form factors. A comparison with the experiment shows that this model is able to fit the location of states and a simple scaling of the results give a good fit to the experimental form factors.Comment: 5 pages, 4 figures, 5 tables, Late

Marine viruses:key players in marine ecosystems

Viruses were recognized as the causative agents of fish diseases, such as infectious pancreatic necrosis and Oregon sockeye disease, in the early 1960s [1], and have since been shown to be responsible for diseases in all marine life from bacteria to protists, mollusks, crustaceans, fish and mammals [2].[...

Re-appearance of the pairing correlations at finite temperature

Rotational and deformation dependence of isovector and isoscalar pairing correlations at finite temperature are studied in an exactly solvable cranked deformed shell model Hamiltonian. It is shown that isovector pairing correlations, as expected, decrease with increasing deformation and the isoscalar pairing correlations remain constant at temperature, T=0. However, it is observed that at finite temperature both isovector and isoscalar pairing correlations are enhanced with increasing deformation, which contradict the mean-field predictions. It is also demonstrated that the pair correlations, which are quenched at T=0 and high rotational frequency re-appear at finite temperature. The changes in the individual multipole pairing fields as a function of rotation and deformation are analyzed in detail.Comment: 16 pages 6 figure

The effect of core polarization on longitudinal form factors in 10^{10}B

Electron scattering Coulomb form factors for the single-particle quadrupole transitions in $p$-shell $^{10}$B nucleus have been studied. Core polarization effects are included through a microscopic theory that includes excitations from the core orbits up to higher orbits with 2$\hbar$$\omega$ excitations. The modified surface delta interaction (MSDI) is employed as a residual interaction. The effect of core polarization is found essential in both the transition strengths and momentum transfer dependence of form factors, and gives a remarkably good agreement with the measured data with no adjustable parameters.Comment: 4 pages, 5 figure

Effective operators from exact many-body renormalization

We construct effective two-body Hamiltonians and E2 operators for the p-shell by performing $16\hbar\Omega$ ab initio no-core shell model (NCSM) calculations for A=5 and A=6 nuclei and explicitly projecting the many-body Hamiltonians and E2 operator onto the $0\hbar\Omega$ space. We then separate the effective E2 operator into one-body and two-body contributions employing the two-body valence cluster approximation. We analyze the convergence of proton and neutron valence one-body contributions with increasing model space size and explore the role of valence two-body contributions. We show that the constructed effective E2 operator can be parametrized in terms of one-body effective charges giving a good estimate of the NCSM result for heavier p-shell nuclei.Comment: 9 pages, 8 figure

Alterations in microbial community composition with increasing fCO2: a mesocosm study in the eastern Baltic Sea

Ocean acidification resulting from the uptake of anthropogenic carbon dioxide (CO₂) by the ocean is considered a major threat to marine ecosystems. Here we examined the effects of ocean acidification on microbial community dynamics in the eastern Baltic Sea during the summer of 2012 when inorganic nitrogen and phosphorus were strongly depleted. Large-volume in situ mesocosms were employed to mimic present, future and far future CO₂ scenarios. All six groups of phytoplankton enumerated by flow cytometry ( &lt;  20 µm cell diameter) showed distinct trends in net growth and abundance with CO₂ enrichment. The picoeukaryotic phytoplankton groups Pico-I and Pico-II displayed enhanced abundances, whilst Pico-III, <i>Synechococcus</i> and the nanoeukaryotic phytoplankton groups were negatively affected by elevated fugacity of CO₂ (<i>f</i>CO₂). Specifically, the numerically dominant eukaryote, Pico-I, demonstrated increases in gross growth rate with increasing <i>f</i>CO₂ sufficient to double its abundance. The dynamics of the prokaryote community closely followed trends in total algal biomass despite differential effects of <i>f</i>CO₂ on algal groups. Similarly, viral abundances corresponded to prokaryotic host population dynamics. Viral lysis and grazing were both important in controlling microbial abundances. Overall our results point to a shift, with increasing <i>f</i>CO₂, towards a more regenerative system with production dominated by small picoeukaryotic phytoplankton.</p