8,708 research outputs found
Coccolithophore fluxes in the open tropical North Atlantic: influence of thermocline depth, Amazon water, and Saharan dust
Coccolithophores are calcifying phytoplankton and major contributors to both the organic and inorganic oceanic carbon pumps. Their export fluxes, species composition, and seasonal patterns were determined in two sediment trap moorings (M4 at 12 degrees N, 49 degrees W and M2 at 14 degrees N, 37 degrees W) collecting settling particles synchronously from October 2012 to November 2013 at 1200 m of water depth in the open equatorial North Atlantic. The two trap locations showed a similar seasonal pattern in total coccolith export fluxes and a predominantly tropical coccolithophore settling assemblage. Species fluxes were dominated throughout the year by lower photic zone (LPZ) taxa (Florisphaera profunda, Gladiolithus flabellatus) but also included upper photic zone (UPZ) taxa (Umbellosphaera spp., Rhabdosphaera spp., Umbilicosphaera spp., Helicosphaera spp.). The LPZ flora was most abundant during fall 2012, whereas the UPZ flora was more important during summer. In spite of these similarities, the western part of the study area produced persistently higher fluxes, averaging 241 x 10(7) +/- 76 x 10(7) coccoliths m(-2) d(-1) at station M4 compared to only 66 x 10(7) +/- 31 x 10(7) coccoliths m(-2) d(-1) at station M2. Higher fluxes at M4 were mainly produced by the LPZ species, favoured by the westward deepening of the thermocline and nutricline. Still, most UPZ species also contributed to higher fluxes, reflecting enhanced productivity in the western equatorial North Atlantic. Such was the case of two marked flux peaks of the more opportunistic species Gephyrocapsa muellerae and Emiliania huxleyi in January and April 2013 at M4, indicating a fast response to the nutrient enrichment of the UPZ, probably by wind-forced mixing. Later, increased fluxes of G. oceanica and E. huxleyi in October-November 2013 coincided with the occurrence of Amazon-River-affected surface waters. Since the spring and fall events of 2013 were also accompanied by two dust flux peaks, we propose a scenario in which atmospheric dust also provided fertilizing nutrients to this area. Enhanced surface buoyancy associated with the river plume indicates that the Amazon acted not only as a nutrient source, but also as a surface density retainer for nutrients supplied from the atmosphere. Nevertheless, lower total coccolith fluxes during these events compared to the maxima recorded in November 2012 and July 2013 indicate that transient productivity by opportunistic species was less important than "background" tropical productivity in the equatorial North Atlantic. This study illustrates how two apparently similar sites in the tropical open ocean actually differ greatly in ecological and oceanographic terms. The results presented here provide valuable insights into the processes governing the ecological dynamics and the downward export of coccolithophores in the tropical North Atlantic.Netherlands Organization for Scientific Research (NWO) [822.01.008]; European Research Council (ERC) [311152]; University of Bremen; European Union [600411]info:eu-repo/semantics/publishedVersio
NMR implementation of Factoring Large Numbers with Gau\ss{}Sums: Suppression of Ghost Factors
Finding the factors of an integer can be achieved by various experimental
techniques, based on an algorithm developed by Schleich et al., which uses
specific properties of Gau\ss{}sums. Experimental limitations usually require
truncation of these series, but if the truncation parameter is too small, it is
no longer possible to distinguish between factors and so-called "ghost"
factors. Here, we discuss two techniques for distinguishing between true
factors and ghost factors while keeping the number of terms in the sum constant
or only slowly increasing. We experimentally test these modified algorithms in
a nuclear spin system, using NMR.Comment: 4 pages, 5 figure
An initial intercomparison of atmospheric and oceanic climatology for the ICE-5G and ICE-4G models of LGM paleotopography
This paper investigates the impact of the new ICE-5G paleotopography dataset for Last Glacial Maximum (LGM) conditions on a coupled model simulation of the thermal and dynamical state of the glacial atmosphere and on both land surface and sea surface conditions. The study is based upon coupled climate simulations performed with the oceanâatmosphereâsea ice model of intermediate-complexity Climate de Bilt-coupled large-scale iceâocean (ECBilt-Clio) model. Four simulations focusing on the Last Glacial Maximum [21 000 calendar years before present (BP)] have been analyzed: a first simulation (LGM-4G) that employed the original ICE-4G ice sheet topography and albedo, and a second simulation (LGM-5G) that employed the newly constructed ice sheet topography, denoted ICE-5G, and its respective albedo. Intercomparison of the results obtained in these experiments demonstrates that the LGM-5G simulation delivers significantly enhanced cooling over Canada compared to the LGM-4G simulation whereas positive temperature anomalies are simulated over southern North America and the northern Atlantic. Moreover, introduction of the ICE-5G topography is shown to lead to a deceleration of the subtropical westerlies and to the development of an intensified ridge over North America, which has a profound effect upon the hydrological cycle. Additionally, two flat ice sheet experiments were carried out to investigate the impact of the ice sheet albedo on global climate. By comparing these experiments with the full LGM simulations, it becomes evident that the climate anomalies between LGM-5G and LGM-4G are mainly driven by changes of the earthâs topography
High Fidelity Quantum Gates in the Presence of Dispersion
We numerically demonstrate the control of motional degrees of freedom of an
ensemble of neutral atoms in an optical lattice with a shallow trapping
potential. Taking into account the range of quasimomenta across different
Brillouin zones results in an ensemble whose members effectively have
inhomogeneous control fields as well as spectrally distinct control
Hamiltonians. We present an ensemble-averaged optimal control technique that
yields high fidelity control pulses, irrespective of quasimomentum, with
average fidelities above 98%. The resulting controls show a broadband spectrum
with gate times in the order of several free oscillations to optimize gates
with up to 13.2% dispersion in the energies from the band structure. This can
be seen as a model system for the prospects of robust quantum control. This
result explores the limits of discretizing a continuous ensemble for control
theory
Quantum control of the hyperfine-coupled electron and nuclear spins in alkali atoms
We study quantum control of the full hyperfine manifold in the
ground-electronic state of alkali atoms based on applied radio frequency and
microwave fields. Such interactions should allow essentially decoherence-free
dynamics and the application of techniques for robust control developed for NMR
spectroscopy. We establish the conditions under which the system is
controllable in the sense that one can generate an arbitrary unitary on the
system. We apply this to the case of Cs with its dimensional
Hilbert space of magnetic sublevels in the state, and design control
waveforms that generate an arbitrary target state from an initial fiducial
state. We develop a generalized Wigner function representation for this space
consisting of the direct sum of two irreducible representation of SU(2),
allowing us to visualize these states. The performance of different control
scenarios is evaluated based on the ability to generate high-fidelity operation
in an allotted time with the available resources. We find good operating points
commensurate with modest laboratory requirements.Comment: 14 pages, 7 figures; corrected typo
Relating particle hygroscopicity and CCN activity to chemical composition during the HCCT-2010 field campaign
Particle hygroscopic growth at 90% RH (relative humidity), cloud condensation nuclei (CCN) activity, and size-resolved chemical composition were concurrently measured in the ThĂŒringer Wald mid-level mountain range in central Germany in the fall of 2010. The median hygroscopicity parameter values, Îș, of 50, 75, 100, 150, 200, and 250 nm particles derived from hygroscopicity measurements are respectively 0.14, 0.14, 0.17, 0.21, 0.24, and 0.28 during the sampling period. The closure between HTDMA (Hygroscopicity Tandem Differential Mobility Analyzers)-measured (ÎșHTDMA) and chemical composition-derived (Îșchem) hygroscopicity parameters was performed based on the ZdanovskiiâStokesâRobinson (ZSR) mixing rule. Using size-averaged chemical composition, the Îș values are substantially overpredicted (30 and 40% for 150 and 100 nm particles). Introducing size-resolved chemical composition substantially improved closure. We found that the evaporation of NH4NO3, which may happen in a HTDMA system, could lead to a discrepancy in predicted and measured particle hygroscopic growth. The hygroscopic parameter of the organic fraction, Îșorg, is positively correlated with the O : C ratio (Îșorg = 0.19 Ă (O : C) â 0.03). Such correlation is helpful to define the Îșorg value in the closure study. Îș derived from CCN measurement was around 30% (varied with particle diameters) higher than that determined from particle hygroscopic growth measurements (here, hydrophilic mode is considered only). This difference might be explained by the surface tension effects, solution non-ideality, gas-particle partitioning of semivolatile compounds, and the partial solubility of constituents or non-dissolved particle matter. Therefore, extrapolating from HTDMA data to properties at the point of activation should be done with great care. Finally, closure study between CCNc (cloud condensation nucleus counter)-measured (ÎșCCN) and chemical composition (ÎșCCN, chem) was performed using CCNc-derived Îș values for individual components. The results show that the ÎșCCN can be well predicted using particle size-resolved chemical composition and the ZSR mixing rule
New detectors for the kaon and hypernuclear experiments with KaoS at MAMI and with PANDA at GSI
The KaoS spectrometer at the Mainz Microtron MAMI, Germany, is perceived as
the ideal candidate for a dedicated spectrometer in kaon and hypernuclei
electroproduction. KaoS will be equipped with new read-out electronics, a
completely new focal plane detector package consisting of scintillating fibres,
and a new trigger system. First prototypes of the fibre detectors and the
associated new front-end electronics are shown in this contribution. The Mainz
hypernuclei research program will complement the hypernuclear experiments at
the planned FAIR facility at GSI, Germany. At the proposed antiproton storage
ring the spectroscopy of double Lambda hypernuclei is one of the four main
topics which will be addressed by the PANDA Collaboration. The experiments
require the operation of high purity germanium (HPGe) detectors in high
magnetic fields (B= 1T) in the presence of a large hadronic background. The
performance of high resolution Ge detectors in such an environment has been
investigated.Comment: Presentation at International Symposium on the Development of
Detectors for Particle, Astroparticle and Synchrotron Radiation Experiments,
Stanford, Ca (SNIC06), 6 pages, LaTeX, 11 eps figure
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Mobility particle size spectrometers: Calibration procedures and measurement uncertainties
Mobility particle size spectrometers (MPSS) belong to the essential instruments in aerosol science that determine the particle number size distribution (PNSD) in the submicrometer size range. Following calibration procedures and target uncertainties against standards and reference instruments are suggested for a complete MPSS quality assurance program: (a) calibration of the CPC counting efficiency curve (within 5% for the plateau counting efficiency; within 1 nm for the 50% detection efficiency diameter), (b) sizing calibration of the MPSS, using a certified polystyrene latex (PSL) particle size standard at 203 nm (within 3%), (c) intercomparison of the PNSD of the MPSS (within 10% and 20% of the dN/dlogDP concentration for the particle size range 20â200 and 200â800 nm, respectively), and (d) intercomparison of the integral PNC of the MPSS (within 10%). Furthermore, following measurement uncertainties have been investigated: (a) PSL particle size standards in the range from 100 to 500 nm match within 1% after sizing calibration at 203 nm. (b) Bipolar diffusion chargers based on the radioactive nuclides Kr85, Am241, and Ni63 and a new ionizer based on corona discharge follow the recommended bipolar charge distribution, while soft X-ray-based charges may alter faster than expected. (c) The use of a positive high voltage supply show a 10% better performance than a negative one. (d) The intercomparison of the integral PNC of an MPSS against the total number concentration is still within the target uncertainty at an ambient pressure of approximately 500 hPa. Copyright © 2018 Published with license by American Association for Aerosol Research
Mobility particle size spectrometers: Calibration procedures and measurement uncertainties
Mobility particle size spectrometers (MPSS) belong to the essential instruments in aerosol science that
determine the particle number size distribution (PNSD) in the submicrometer size range. Following
calibration procedures and target uncertainties against standards and reference instruments are
suggested for a complete MPSS quality assurance program: (a) calibration of the CPC counting efficiency
curve (within 5% for the plateau counting efficiency; within 1 nm for the 50% detection efficiency
diameter), (b) sizing calibration of the MPSS, using a certified polystyrene latex (PSL) particle size
standard at 203 nm (within 3%), (c) intercomparison of the PNSD of the MPSS (within 10% and 20% of
the dN/dlogDP concentration for the particle size range 20â200 and 200â800 nm, respectively), and (d)
intercomparison of the integral PNC of the MPSS (within 10%). Furthermore, following measurement
uncertainties have been investigated: (a) PSL particle size standards in the range from 100 to 500 nm
match within 1% after sizing calibration at 203 nm. (b) Bipolar diffusion chargers based on
the radioactive nuclides Kr85, Am241, and Ni63 and a new ionizer based on corona discharge follow the
recommended bipolar charge distribution, while soft X-ray-based charges may alter faster than
expected. (c) The use of a positive high voltage supply show a 10% better performance than a negative
one. (d) The intercomparison of the integral PNC of an MPSS against the total number concentration is
still within the target uncertainty at an ambient pressure of approximately 500 hPa
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