Elevated pCO2 enhances bacterioplankton removal of organic carbon.

Factors that affect the removal of organic carbon by heterotrophic bacterioplankton can impact the rate and magnitude of organic carbon loss in the ocean through the conversion of a portion of consumed organic carbon to CO2. Through enhanced rates of consumption, surface bacterioplankton communities can also reduce the amount of dissolved organic carbon (DOC) available for export from the surface ocean. The present study investigated the direct effects of elevated pCO2 on bacterioplankton removal of several forms of DOC ranging from glucose to complex phytoplankton exudate and lysate, and naturally occurring DOC. Elevated pCO2 (1000-1500 ppm) enhanced both the rate and magnitude of organic carbon removal by bacterioplankton communities compared to low (pre-industrial and ambient) pCO2 (250 -~400 ppm). The increased removal was largely due to enhanced respiration, rather than enhanced production of bacterioplankton biomass. The results suggest that elevated pCO2 can increase DOC consumption and decrease bacterioplankton growth efficiency, ultimately decreasing the amount of DOC available for vertical export and increasing the production of CO2 in the surface ocean

Monolithic Arrays of Grating-Surface-Emitting Diode Lasers and Quantum Well Modulators for Optical Communications

The electro-optic switching properties of injection-coupled coherent 2-D grating-surface-emitting laser arrays with multiple gain sections and quantum well active layers are discussed and demonstrated. Within such an array of injection-coupled grating-surface-emitting lasers, a single gain section can be operated as intra-cavity saturable loss element that can modulate the output of the entire array. Experimental results demonstrate efficient sub-nanosecond switching of high power grading-surface-emitting laser arrays by using only one gain section as an intra-cavity loss modulator

The Electromagnetic Self-Energy Contribution to M_p - M_n and the Isovector Nucleon Magnetic Polarizability

We update the determination of the isovector nucleon electromagnetic self-energy, valid to leading order in QED. A technical oversight in the literature concerning the elastic contribution to Cottingham's formula is corrected and modern knowledge of the structure functions is used to precisely determine the inelastic contribution. We find \delta M_{p-n}^\gamma = 1.30(03)(47) MeV. The largest uncertainty arises from a subtraction term required in the dispersive analysis, which can be related to the isovector magnetic polarizability. With plausible model assumptions, we can combine our calculation with additional input from lattice QCD to constrain this polarizability as: \beta_{p-n} = -0.87(85) x 10^{-4} fm^3.Comment: 5 pages, version accepted for publication in PR

Ab initio calculation of the electromagnetic and neutral-weak response functions of 4He and 12C

Precise measurement of neutrino oscillations, and hence the determination of their masses demands a quantitative understanding of neutrino-nucleus interactions. To this aim, two-body meson-exchange currents have to be accounted for along within realistic models of nuclear dynamics. We summarize our progresses towards the construction of a consistent framework, based on quantum Monte Carlo methods and on the spectral function approach, that can be exploited to accurately describe neutrino interactions with atomic nuclei over the broad kinematical region covered by neutrino experiments.Comment: 8 pages, 4 figure, Proceedings of the 21st International Conference on Few-Body Problems in Physics, Chicago, Illinois, US

Vanadium-chromium alloy system

On the basis of data obtaiined from melting point determinations, microscopic examination, and x-ray investigations, a phase I diagram is proposed for the V -Cr alloy system. The system forms a complete series of solid solutions with a minimum occurring in the solidus at 1750°C and approximately 70 w/o Cr. No intermediate phases were found in this system. Hardness and corrosion data are presented as a function of alloying composition

Relativistic electrons from sparks in the laboratory

Discharge experiments were carried out at the Eindhoven University of Technology in 2013. The experimental setup was designed to search for electrons produced in meter-scale sparks using a 1 MV Marx generator. Negative voltage was applied to the high voltage (HV) electrode. Five thin (1 mm) plastic detectors (5 $\rm cm^2$ each) were distributed in various configurations close to the spark gap. Earlier studies have shown (for HV negative) that X-rays are produced when a cloud of streamers is developed 30-60 cm from the negative electrode. This indicates that the electrons producing the X-rays are also accelerated at this location, that could be in the strong electric field from counterstreamers of opposite polarity. Comparing our measurements with modeling results, we find that $\sim$300 keV electrons produced about 30-60 cm from the negative electrode are the most likely source of our measurements. A statistical analysis of expected detection of photon bursts by these fiber detectors indicates that only 20%-45% of the detected bursts could be from soft ($\sim$10 keV) photons, which further supports that the majority of detected bursts are produced by relativistic electrons

Scaling and Duality in Semi-exclusive Processes

We discuss extending scaling and duality studies to semi-exclusive processes. We show that semi-exclusive hard pion photoproduction should exhibit scaling behavior in kinematic regions where the photon and pion both interact directly with the same quark. We show that such kinematic regions exist. We also show that the constancy with changing momentum transfer of the resonance peak/scaling curve ratio, familiar for many resonances in deep inelastic scattering, is also expected in the semi-exclusive case.Comment: 8 pages, 4 figures, submitted to Phys.Rev.

Quantum Monte Carlo Calculations of A≤6A\leq6 Nuclei

The energies of $^{3}H$, $^{3}He$, and $^{4}He$ ground states, the ${\frac{3}{2}}^{-}$ and ${\frac{1}{2}}^{-}$ scattering states of $^{5}He$, the ground states of $^{6}He$, $^{6}Li$, and $^{6}Be$ and the $3^{+}$ and $0^{+}$ excited states of $^{6}Li$ have been accurately calculated with the Green's function Monte Carlo method using realistic models of two- and three-nucleon interactions. The splitting of the $A=3$ isospin $T=\frac{1}{2}$ and $A=6$ isospin $T=1$, $J^{\pi} = 0^{+}$ multiplets is also studied. The observed energies and radii are generally well reproduced, however, some definite differences between theory and experiment can be identified.Comment: 12 pages, 1 figur

Masses of the 70- Baryons in Large Nc QCD

The masses of the negative parity 70-plet baryons are analyzed in large N_c QCD to order 1/N_c and to first order in SU(3) symmetry breaking. The existing experimental data are well reproduced and twenty new observables are predicted. The leading order SU(6) spin-flavor symmetry breaking is small and, as it occurs in the quark model, the subleading in 1/N_c hyperfine interaction is the dominant source of the breaking. It is found that the Lambda(1405) and Lambda(1520) are well described as three-quark states and spin-orbit partners. New relations between splittings in different SU(3) multiplets are found.Comment: 11 pages; references were added and a couple of improvements to the text were mad