2,879 research outputs found
Focused Fluid Flow along the Nootka Fault Zone and Continental slope, ExplorerâJuan de Fuca Plate Boundary
Key Points:
- Fluid flow is focused along Nootka Fault traces resulting in shallow bright spots
- Two seafloor mounds are the result of basaltic intrusions in the Nootka Fault zone
- Gas hydrates occur at the Nootka Slope and are imaged seismically as bottom-
simulating reflectors suggesting a regional heat-flow of ~80 mW/m2 along the slope
Abstract
Geophysical and geochemical data indicate there is abundant fluid expulsion in the Nootka fault zone (NFZ) between the Juan de Fuca and Explorer plates and the Nootka continental slope. Here we combine observations from > 20 years of investigations to demonstrate the nature of fluidâflow along the NFZ, which is the seismically most active region off Vancouver Island. Seismicity reaching down to the upper mantle is linked to nearâseafloor manifestation of fluid flow through a network of faults. Along the two main fault traces, seismic reflection data imaged bright spots 100 â 300 m below seafloor that lie above changes in basement topography. The bright spots are conformable to sediment layering, show oppositeâtoâseafloor reflection polarity, and are associated with frequencyâreduction and velocity pushâdown indicating the presence of gas in the sediments. Two seafloor mounds ~15 km seaward of the Nootka slope are underlain by deep, nonâconformable high amplitude reflective zones. Measurements in the water column above one mound revealed a plume of warm water, and bottomâvideo observations imaged hydrothermal vent system biota. Pore fluids from a core at this mound contain predominately microbial methane (C1) with a high proportion of ethane (C2) yielding C1/C2 ratios < 500 indicating a possible slight contribution from a deep source. We infer the reflective zones beneath the two mounds are basaltic intrusions that create hydrothermal circulation within the overlying sediments. Across the Nootka continental slope, gas hydrate related bottomâsimulating reflectors are widespread and occur at depths indicating heatâflow values of 80 â 90 mW/m2
Practical Implementations of Twirl Operations
Twirl operations, which convert impure singlet states into Werner states,
play an important role in many schemes for entanglement purification. In this
paper we describe strategies for implementing twirl operations, with an
emphasis on methods suitable for ensemble quantum information processors such
as nuclear magnetic resonance (NMR) quantum computers. We implement our twirl
operation on a general two-spin mixed state using liquid state NMR techniques,
demonstrating that we can obtain the singlet Werner state with high fidelity.Comment: 6 pages RevTex4 including 2 figures (fig 1 low quality to save space
Shell Model Monte Carlo Investigation of Rare Earth Nuclei
We utilize the Shell Model Monte Carlo (SMMC) method to study the structure
of rare earth nuclei. This work demonstrates the first systematic ``full
oscillator shell plus intruder'' calculations in such heavy nuclei. Exact
solutions of a pairing plus quadrupole hamiltonian are compared with mean field
and SPA approximations in several Dysprosium isotopes from A=152-162, including
the odd mass A=153. Basic properties of these nuclei at various temperatures
and spin are explored. These include energy, deformation, moments of inertia,
pairing channel strengths, band crossing, and evolution of shell model
occupation numbers. Exact level densities are also calculated and, in the case
of 162 Dy, compared with experimental data.Comment: 40 pages; 24 figures; 2 tables. Update includes correction of figure
labe
Dynamical heterogeneities in a supercooled Lennard-Jones liquid
We present the results of a large scale molecular dynamics computer
simulation study in which we investigate whether a supercooled Lennard-Jones
liquid exhibits dynamical heterogeneities. We evaluate the non-Gaussian
parameter for the self part of the van Hove correlation function and use it to
identify ``mobile'' particles. We find that these particles form clusters whose
size grows with decreasing temperature. We also find that the relaxation time
of the mobile particles is significantly shorter than that of the bulk, and
that this difference increases with decreasing temperature.Comment: 8 pages of RevTex, 4 ps figure
Water Chemisorption and Reconstruction of the MgO Surface
The observed reactivity of MgO with water is in apparent conflict with
theoretical calculations which show that molecular dissociation does not occur
on a perfect (001) surface. We have performed ab-initio total energy
calculations which show that a chemisorption reaction involving a
reconstruction to form a (111) hydroxyl surface is strongly preferred with
Delta E = -90.2kJ/mol. We conclude that protonation stabilizes the otherwise
unstable (111) surface and that this, not the bare (001), is the most stable
surface of MgO under ambient conditions.Comment: RevTeX, 4 pages, 1 Encapsulated Postscript Figur
Alpine Glacier Reveals Ecosystem Impacts of Europeâs Prosperity and Peril Over the Last Millennium
Information about past ecosystem dynamics and human activities is stored in the ice of Colle Gnifetti glacier in the Swiss Alps. Adverse climatic intervals incurred crop failures and famines and triggered reestablishment of forest vegetation but also societal resilience through innovation. Historical documents and lake sediments record these changes at localâregional scales but often struggle to comprehensively document continental-scale impacts on ecosystems. Here, we provide unique multiproxy evidence of broad-scale ecosystem, land use, and climate dynamics over the past millennium from a Colle Gnifetti microfossil and oxygen isotope record. Microfossil data indicate that before 1750 CE forests and fallow land rapidly replaced crop cultivation during historically documented societal crises caused by climate shifts and epidemics. Subsequently, with technology and the introduction of more resilient crops, European societies adapted to the Little Ice Age cold period, but resource overexploitation and industrialization led to new regional to global-scale environmental challenges
String-like Clusters and Cooperative Motion in a Model Glass-Forming Liquid
A large-scale molecular dynamics simulation is performed on a glass-forming
Lennard-Jones mixture to determine the nature of dynamical heterogeneities
which arise in this model fragile liquid. We observe that the most mobile
particles exhibit a cooperative motion in the form of string-like paths
(``strings'') whose mean length and radius of gyration increase as the liquid
is cooled. The length distribution of the strings is found to be similar to
that expected for the equilibrium polymerization of linear polymer chains.Comment: 6 pages of RevTex, 6 postscript figures, uses epsf.st
Nonlinear response of dense colloidal suspensions under oscillatory shear: Mode-coupling theory and FT-rheology experiments
Using a combination of theory, experiment and simulation we investigate the
nonlinear response of dense colloidal suspensions to large amplitude
oscillatory shear flow. The time-dependent stress response is calculated using
a recently developed schematic mode-coupling-type theory describing colloidal
suspensions under externally applied flow. For finite strain amplitudes the
theory generates a nonlinear response, characterized by significant higher
harmonic contributions. An important feature of the theory is the prediction of
an ideal glass transition at sufficiently strong coupling, which is accompanied
by the discontinuous appearance of a dynamic yield stress. For the oscillatory
shear flow under consideration we find that the yield stress plays an important
role in determining the non linearity of the time-dependent stress response.
Our theoretical findings are strongly supported by both large amplitude
oscillatory (LAOS) experiments (with FT-rheology analysis) on suspensions of
thermosensitive core-shell particles dispersed in water and Brownian dynamics
simulations performed on a two-dimensional binary hard-disc mixture. In
particular, theory predicts nontrivial values of the exponents governing the
final decay of the storage and loss moduli as a function of strain amplitude
which are in excellent agreement with both simulation and experiment. A
consistent set of parameters in the presented schematic model achieves to
jointly describe linear moduli, nonlinear flow curves and large amplitude
oscillatory spectroscopy
The Green Bank Northern Celestial Cap Pulsar Survey - I: Survey Description, Data Analysis, and Initial Results
We describe an ongoing search for pulsars and dispersed pulses of radio
emission, such as those from rotating radio transients (RRATs) and fast radio
bursts (FRBs), at 350 MHz using the Green Bank Telescope. With the Green Bank
Ultimate Pulsar Processing Instrument, we record 100 MHz of bandwidth divided
into 4,096 channels every 81.92 . This survey will cover the entire sky
visible to the Green Bank Telescope (, or 82% of the sky)
and outside of the Galactic Plane will be sensitive enough to detect slow
pulsars and low dispersion measure (30 ) millisecond
pulsars (MSPs) with a 0.08 duty cycle down to 1.1 mJy. For pulsars with a
spectral index of 1.6, we will be 2.5 times more sensitive than previous and
ongoing surveys over much of our survey region. Here we describe the survey,
the data analysis pipeline, initial discovery parameters for 62 pulsars, and
timing solutions for 5 new pulsars. PSR J02145222 is an MSP in a long-period
(512 days) orbit and has an optical counterpart identified in archival data.
PSR J06365129 is an MSP in a very short-period (96 minutes) orbit with a
very low mass companion (8 ). PSR J06455158 is an isolated MSP
with a timing residual RMS of 500 ns and has been added to pulsar timing array
experiments. PSR J14347257 is an isolated, intermediate-period pulsar that
has been partially recycled. PSR J18164510 is an eclipsing MSP in a
short-period orbit (8.7 hours) and may have recently completed its spin-up
phase.Comment: 18 pages, 10 figures, 5 tables, accepted by Ap
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