Gross and net production during the spring bloom along the Western Antarctic Peninsula

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of New Phytologist Trust for personal use, not for redistribution. The definitive version was published in New Phytologist 205 (2015): 182-191, doi:10.1111/nph.13125.This study explores some of the physiological mechanisms responsible for high productivity near the shelf in the Western Antarctic Peninsula despite a short growing season and cold temperature. We measured gross and net primary production at Palmer Station during the summer 2012/2013 via three different techniques: 1) incubation with H218O; 2) incubation with 14CO2; and 3) in situ measurements of O2/Ar and triple oxygen isotope. Additional laboratory experiments were performed with the psychrophilic diatom Fragilariopsis cylindrus. During the spring bloom, which accounted for more than half of the seasonal gross production at Palmer Station, the ratio of net to gross production reached a maximum greater than ~60%, among the highest ever reported. The use of multiple-techniques showed that these high ratios resulted from low heterotrophic respiration and very low daylight autotrophic respiration. Laboratory experiments revealed a similar ratio of net to gross O2 production in F.cylindrus and provided the first experimental evidence for an important level of cyclic electron flow (CEF) in this organism. The low ratio of community respiration to gross primary production observed during the bloom at Palmer Station may be characteristic of high latitude coastal ecosystems and partially supported by a very active CEF in psychrophilic phytoplankton.This study was supported by funds from the US National Science Foundation (Award numbers 1040965 and 1043593). Funding to PDT was provided by the Natural Science and Engineering Research Council of Canada

Quantum point contact on graphite surface

The conductance through a quantum point contact created by a sharp and hard metal tip on the graphite surface has features which to our knowledge have not been encountered so far in metal contacts or in nanowires. In this paper we first investigate these features which emerge from the strongly directional bonding and electronic structure of graphite, and provide a theoretical understanding for the electronic conduction through quantum point contacts. Our study involves the molecular-dynamics simulations to reveal the variation of interlayer distances and atomic structure at the proximity of the contact that evolves by the tip pressing toward the surface. The effects of the elastic deformation on the electronic structure, state density at the Fermi level, and crystal potential are analyzed by performing self-consistent-field pseudopotential calculations within the local-density approximation. It is found that the metallicity of graphite increases under the uniaxial compressive strain perpendicular to the basal plane. The quantum point contact is modeled by a constriction with a realistic potential. The conductance is calculated by representing the current transporting states in Laue representation, and the variation of conductance with the evolution of contact is explained by taking the characteristic features of graphite into account. It is shown that the sequential puncturing of the layers characterizes the conductance.Comment: LaTeX, 11 pages, 9 figures (included), to be published in Phys. Rev. B, tentatively scheduled for 15 September 1998 (Volume 58, Number 12

Hamlet and the fall of the Berlin wall : the myth of interventionist Shakespeare performance

The critical reception of Heiner Müller’s 1990 Hamlet/Maschine at the Deutsches Theater in East Berlin epitomizes a trend of crediting GDR Shakespeare performance with political influence. Drawing on rehearsal notes and reviews, Oliver challenges the interventionist Shakespeare myth, contrasting the Deutsches Theater’s political involvement with the impact of its Hamlet production on events surrounding the fall of the Berlin Wall. Shakespeare’s capacity for political intervention at this point was limited by theater practitioners’ reliance on public funding, their close relationships with governmental authority, and an underlying distrust of the masses. Ultimately, GDR artists proved useful to the 1989 protest movement because they occupied a unique position at the interface of dissidence and power

Metabolic balance of coastal Antarctic waters revealed by autonomous pCO2 and ΔO2/Ar measurements

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 41 (2014): 6803–6810, doi:10.1002/2014GL061266.We use autonomous gas measurements to examine the metabolic balance (photosynthesis minus respiration) of coastal Antarctic waters during the spring/summer growth season. Our observations capture the development of a massive phytoplankton bloom and reveal striking variability in pCO2 and biological oxygen saturation (ΔO2/Ar) resulting from large shifts in community metabolism on time scales ranging from hours to weeks. Diel oscillations in surface gases are used to derive a high-resolution time series of net community production (NCP) that is consistent with 14C-based primary productivity estimates and with the observed seasonal evolution of phytoplankton biomass. A combination of physical mixing, grazing, and light availability appears to drive variability in coastal Antarctic NCP, leading to strong shifts between net autotrophy and heterotrophy on various time scales. Our approach provides insight into the metabolic responses of polar ocean ecosystems to environmental forcing and could be employed to autonomously detect climate-dependent changes in marine primary productivity.This study was supported by funds from the U.S. National Science Foundation (OPP awards ANT-0823101, ANT-1043559, ANT-1043593, and ANT-1043532) as well as support for PDT and ECA from the National Science and Engineering Research Council of Canada.2015-04-0

The Gas Content in Galactic Disks: Correlation with Kinematics

We consider the relationship between the total HI mass in late-type galaxies and the kinematic properties of their disks. The mass $M_HI$ for galaxies with a wide variety of properties, from dwarf dIrr galaxies with active star formation to giant low-brightness galaxies, is shown to correlate with the product $V_c R_0$ ($V_c$ is the rotational velocity, and $R_0$ is the radial photometric disks scale length), which characterizes the specific angular momentum of the disk. This relationship, along with the anticorrelation between the relative mass of HI in a galaxy and $V_c$, can be explained in terms of the previously made assumption that the gas density in the disks of most galaxies is maintained at a level close to the threshold (marginal) stability of a gaseous layer to local gravitational perturbations. In this case, the regulation mechanism of the star formation rate associated with the growth of local gravitational instability in the gaseous layer must play a crucial role in the evolution of the gas content in the galactic disk.Comment: revised version to appear in Astronomy Letters, 8 pages, 5 EPS figure