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

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

Intruder level and deformation in the SD-pair shell model

The influence of the intruder level on nuclear deformation is studied within the framework of the nucleon-pair shell model truncated to an SD-pair subspace. The results suggest that the intruder level has a tendency to soften the deformation and plays an important role in determining the onset of rotational behavior.Comment: 2 input TeX files, 2 figures, submitted to Phys. Lett.

On the Solution of the Number-Projected Hartree-Fock-Bogoliubov Equations

The numerical solution of the recently formulated number-projected Hartree-Fock-Bogoliubov equations is studied in an exactly soluble cranked-deformed shell model Hamiltonian. It is found that the solution of these number-projected equations involve similar numerical effort as that of bare HFB. We consider that this is a significant progress in the mean-field studies of the quantum many-body systems. The results of the projected calculations are shown to be in almost complete agreement with the exact solutions of the model Hamiltonian. The phase transition obtained in the HFB theory as a function of the rotational frequency is shown to be smeared out with the projection.Comment: RevTeX, 11 pages, 3 figures. To be published in a special edition of Physics of Atomic Nuclei (former Sov. J. Nucl. Phys.) dedicated to the 90th birthday of A.B. Migda

Effect of CO2 enrichment on bacterial metabolism in an Arctic fjord

he anthropogenic increase of carbon dioxide (CO2) alters the seawater carbonate chemistry, with a decline of pH and an increase in the partial pressure of CO2 (pCO2). Although bacteria play a major role in carbon cycling, little is known about the impact of rising pCO2 on bacterial carbon metabolism, especially for natural bacterial communities. In this study, we investigated the effect of rising pCO2 on bacterial production (BP), bacterial respiration (BR) and bacterial carbon metabolism during a mesocosm experiment performed in Kongsfjorden (Svalbard) in 2010. Nine mesocosms with pCO2 levels ranging from ca. 180 to 1400 μatm were deployed in the fjord and monitored for 30 days. Generally BP gradually decreased in all mesocosms in an initial phase, showed a large (3.6-fold average) but temporary increase on day 10, and increased slightly after inorganic nutrient addition. Over the wide range of pCO2 investigated, the patterns in BP and growth rate of bulk and free-living communities were generally similar over time. However, BP of the bulk community significantly decreased with increasing pCO2 after nutrient addition (day 14). In addition, increasing pCO2 enhanced the leucine to thymidine (Leu : TdR) ratio at the end of experiment, suggesting that pCO2 may alter the growth balance of bacteria. Stepwise multiple regression analysis suggests that multiple factors, including pCO2, explained the changes of BP, growth rate and Leu : TdR ratio at the end of the experiment. In contrast to BP, no clear trend and effect of changes of pCO2 was observed for BR, bacterial carbon demand and bacterial growth efficiency. Overall, the results suggest that changes in pCO2 potentially influence bacterial production, growth rate and growth balance rather than the conversion of dissolved organic matter into CO2