Changing ocean chemistry : an introduction to this special issue

Author Posting. © The Oceanography Society, 2014. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 27, no. 1 (2014): 12–15, doi:10.5670/oceanog.2014.03.The modern industrialized and urbanized world, dubbed the "Anthropocene" by Paul Crutzen (2006), includes the past 250 years of multiple human impacts. Nobel Prize winner and atmospheric chemist Crutzen states: During the past 3 centuries human population increased tenfold to 6,000 million, growing by a factor of four during the past century alone. More than half of all accessible fresh water is used by mankind. Fisheries remove more than 25% of the primary production of the oceans in the upwelling regions and 35% in the temperature continental shelf regions. 30–50% of the world's land surface has been transformed by human action. Coastal wetlands have lost 50% of the world's mangroves. More nitrogen is now fixed synthetically and applied as fertilizers in agriculture than fixed naturally in all terrestrial ecosystems. Many of the world's rivers have been dammed or diverted.US National Science Foundation for funding this special issue

Variational calculations for the hydrogen-antihydrogen system with a mass-scaled Born-Oppenheimer potential

The problem of proton-antiproton motion in the ${\rm H}$--${\rm \bar{H}}$ system is investigated by means of the variational method. We introduce a modified nuclear interaction through mass-scaling of the Born-Oppenheimer potential. This improved treatment of the interaction includes the nondivergent part of the otherwise divergent adiabatic correction and shows the correct threshold behavior. Using this potential we calculate the vibrational energy levels with angular momentum 0 and 1 and the corresponding nuclear wave functions, as well as the S-wave scattering length. We obtain a full set of all bound states together with a large number of discretized continuum states that might be utilized in variational four-body calculations. The results of our calculations gives an indication of resonance states in the hydrogen-antihydrogen system

Time dependence of breakdown in a global fiber-bundle model with continuous damage

A time-dependent global fiber-bundle model of fracture with continuous damage is formulated in terms of a set of coupled non-linear differential equations. A first integral of this set is analytically obtained. The time evolution of the system is studied by applying a discrete probabilistic method. Several results are discussed emphasizing their differences with the standard time-dependent model. The results obtained show that with this simple model a variety of experimental observations can be qualitatively reproduced.Comment: APS style, two columns, 4 figures. To appear in Phys. Rev.

Computer analysis of cardiac radionuclide data

Gamma-camera tomography gives uniform in-plane and cross-plane resolution with propagation of the defect from one plane to another determined only by the usual camera-collimator resolution. These images may be reformatted by computer to portray slices in any orientation. Cross plane resolution is slightly worse than for the other methods, but it is uniform. The efficiency is less than either quadrant slant hole or seven pinhole apertures. Rotating cameras are not portable nor can they be used for dynamic studies.Both slant hole collimators and seven pinhole apertures distort the object in the depth dimension because of the limited viewing angle. The slant hole geometry provides somewhat better sampling and less plane-to-plane cross talk especially for the more distant planes. The full width half maximum of the depth response is not a sensitive indicator of this problem because the depth response function has very long tails.To date, best overall performance of the limited angle methods is offered by the 40[deg] slant hole collimator on a large field-of-view camera. This, however, is not a portable unit and has a field-of-view too small for about 10% of the patients.Seven pinhole imaging offers the advantage of having been well studied by a number of institution.87-90 A large pool of normal patient studies exists and the performance is well documented. Although the seven pinhole alone is suited to dynamic studies, any of the methods may be adapted to multigated studies.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25165/1/0000603.pd

Nitrous oxide cycling in the Arabian Sea

Depth profiles of dissolved nitrous oxide (N2O) were measured in the central and western Arabian Sea during four cruises in May and July–August 1995 and May–July 1997 as part of the German contribution to the Arabian Sea Process Study of the Joint Global Ocean Flux Study. The vertical distribution of N2O in the water column on a transect along 65°E showed a characteristic double-peak structure, indicating production of N2O associated with steep oxygen gradients at the top and bottom of the oxygen minimum zone. We propose a general scheme consisting of four ocean compartments to explain the N2O cycling as a result of nitrification and denitrification processes in the water column of the Arabian Sea. We observed a seasonal N2O accumulation at 600–800 m near the shelf break in the western Arabian Sea. We propose that, in the western Arabian Sea, N2O might also be formed during bacterial oxidation of organic matter by the reduction of IO3 − to I−, indicating that the biogeochemical cycling of N2O in the Arabian Sea during the SW monsoon might be more complex than previously thought. A compilation of sources and sinks of N2O in the Arabian Sea suggested that the N2O budget is reasonably balanced

Magnetic Field Stimulated Transitions of Excited States in Fast Muonic Helium Ions

It is shown that one can stimulate, by using the present-day laboratory magnetic fields, transitions between the $lm$ sub-levels of fast $\mu He^+$ ions formating in muon catalyzed fusion. Strong fields also cause the self-ionization from highly excited states of such muonic ions. Both effects are the consequence of the interaction of the bound muon with the oscillating field of the Stark term coupling the center-of-mass and muon motions of the $\mu He^+$ ion due to the non-separability of the collective and internal variables in this system. The performed calculations show a possibility to drive the population of the $lm$ sub-levels by applying a field of a few $Tesla$, which affects the reactivation rate and is especially important to the $K\alpha$ $x$-ray production in muon catalyzed fusion. It is also shown that the $2s-2p$ splitting in $\mu He^+$ due to the vacuum polarization slightly decreases the stimulated transition rates.Comment: 5 figure

X-ray emission during the muonic cascade in hydrogen

We report our investigations of X rays emitted during the muonic cascade in hydrogen employing charge coupled devices as X-ray detectors. The density dependence of the relative X-ray yields for the muonic hydrogen lines (K_alpha, K_beta, K_gamma) has been measured at densities between 0.00115 and 0.97 of liquid hydrogen density. In this density region collisional processes dominate the cascade down to low energy levels. A comparison with recent calculations is given in order to demonstrate the influence of Coulomb deexcitation.Comment: 5 pages, Tex, 4 figures, submitted to Physical Review Letter

Resonant Formation of dμtd\mu t Molecules in Deuterium: An Atomic Beam Measurement of Muon Catalyzed dt Fusion

Resonant formation of $d\mu t$ molecules in collisions of muonic tritium ($\mu t$) on D$_2$ was investigated using a beam of $\mu t$ atoms, demonstrating a new direct approach in muon catalyzed fusion studies. Strong epithermal resonances in $d\mu t$ formation were directly revealed for the first time. From the time-of-flight analysis of $2036\pm 116$ $dt$ fusion events, a formation rate consistent with $0.73\pm (0.16)_{meas} \pm (0.09)_{model}$ times the theoretical prediction was obtained. For the largest peak at a resonance energy of $0.423 \pm 0.037$ eV, this corresponds to a rate of $(7.1 \pm 1.8) \times 10^9$ s$^{-1}$, more than an order of magnitude larger than those at low energies.Comment: To appear in Phys. Rev. Let

Combined treatment with memantine and galantamine-CR compared with galantamine-CR only in antidementia drug naive patients with mild-to-moderate Alzheimer's disease

Introduction: Several studies have tested the N-methyl-D-aspartate–receptor antagonist memantine as an add-on to pre-existing treatment with acetylcholinesterase inhibitors. The objective of this study was to evaluate the efficacy and safety of a combined memantine and galantamine-CR de novo regimen compared with galantamine-CR only treatment in never treated patients with mild-to-moderate Alzheimer's disease (AD). Methods: Antidementia drug–naïve participants (n = 232) with probable, mild-to-moderate AD, and mini-mental state examination scores between 15 and 26 (inclusive) were randomized to receive either 20 mg/day memantine plus 24 mg/day galantamine-CR or 24 mg/day galantamine-CR plus placebo in a 52-week, prospective, double-blind, controlled trial. The primary outcome measurement was the change on the Alzheimer's disease assessment scale-cognition score. Secondary measures comprised the Alzheimer's Disease Cooperative Study-activities of daily living inventory and the clinical dementia rating. Results: At the end of the trial, there were no statistically significant differences between the galantamine-CR/memantine combination and galantamine-CR only group in primary and secondary outcome measurements. The incidence and the severity of adverse events were similar between the groups. Discussion: In this trial, memantine in combination with galantamine-CR did not show an advantage with respect to cognition, function, and behavior in previously never treated patients with mild-to-moderate AD. There were no significant differences in tolerability and safety between the groups. Thus, a de novo combination treatment results in no significant improvement in disease progression (current controlled trials number: NCT01921972)