580 research outputs found
Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water System
©2019. American Geophysical Union. All Rights Reserved.Subglacial water ïŹow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5â to 10âHz seismic tremor that we associate with subglacial water ïŹow,
that is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequencyâdependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in meltâwater
input. We suggest that conduit formation requires sustained water input and that multiconduit ïŹow paths can be distinguished from singleâconduit ïŹow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely ïŹows through a singleâconduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable conïŹgurations that last 3â7 days, while tremor produced by singleâconduit ïŹow remains more stationary.
We also ïŹnd that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2â6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system.Raw seismic data described in this paper are available through the Incorporated Research Institutions for Seismology Data Management Center (http://ds.iris.edu/mda/ZQ? timewindow=2015â2016; Amundson et al., 2015). The raw weather data used in this paper can be found through the Arctic Data Center (https://doi.org/ 10.18739/A2H98ZC7V; Bartholomaus & Walter, 2018). Python code developed to carry out the analyses presented here is available at https://github.com/ voremargot/SeismicâTremorâRevealsâ SpatialâOrganizationâandâTemporalâ Changesâof SubglacialâWaterâSystem and https://github.com/ tbartholomaus/med_spec. This study was made possible with support from the University of Texas Institute for Geophysics and the University of Idaho. We thank Ginny Catania for the loan of weather stations. J. P. W.'s and J. M. A.'s contributions to this work were supported by the U.S. National Science Foundation (OPPâ1337548 and OPPâ 1303895). T. C. B. thanks Dylan Mikesell for an early conversation, which inspired the analysis presented here.Ye
Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water System
©2019. American Geophysical Union. All Rights Reserved.Subglacial water ïŹow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5â to 10âHz seismic tremor that we associate with subglacial water ïŹow,
that is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequencyâdependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in meltâwater
input. We suggest that conduit formation requires sustained water input and that multiconduit ïŹow paths can be distinguished from singleâconduit ïŹow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely ïŹows through a singleâconduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable conïŹgurations that last 3â7 days, while tremor produced by singleâconduit ïŹow remains more stationary.
We also ïŹnd that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2â6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system.Raw seismic data described in this paper are available through the Incorporated Research Institutions for Seismology Data Management Center (http://ds.iris.edu/mda/ZQ? timewindow=2015â2016; Amundson et al., 2015). The raw weather data used in this paper can be found through the Arctic Data Center (https://doi.org/ 10.18739/A2H98ZC7V; Bartholomaus & Walter, 2018). Python code developed to carry out the analyses presented here is available at https://github.com/ voremargot/SeismicâTremorâRevealsâ SpatialâOrganizationâandâTemporalâ Changesâof SubglacialâWaterâSystem and https://github.com/ tbartholomaus/med_spec. This study was made possible with support from the University of Texas Institute for Geophysics and the University of Idaho. We thank Ginny Catania for the loan of weather stations. J. P. W.'s and J. M. A.'s contributions to this work were supported by the U.S. National Science Foundation (OPPâ1337548 and OPPâ 1303895). T. C. B. thanks Dylan Mikesell for an early conversation, which inspired the analysis presented here.Ye
Open Heavy Flavor Production in QCD -- Conceptual Framework and Implementation Issues
Heavy flavor production is an important QCD process both in its own right and
as a key component of precision global QCD analysis. Apparent disagreements
between fixed-flavor scheme calculations of b-production rate with experimental
measurements in hadro-, lepto-, and photo-production provide new impetus to a
thorough examination of the theory and phenomenology of this process. We review
existing methods of calculation, and place them in the context of the general
PQCD framework of Collins. A distinction is drawn between scheme dependence and
implementation issues related to quark mass effects near threshold. We point
out a so far overlooked kinematic constraint on the threshold behavior, which
greatly simplifies the variable flavor number scheme. It obviates the need for
the elaborate existing prescriptions, and leads to robust predictions. It can
facilitate the study of current issues on heavy flavor production as well as
precision global QCD analysis.Comment: 13 pages, 10 figures, Proceedings of Ringberg Workshop: New Trends in
HERA Physics 2001, Munich, German
Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water System
Subglacial water flow impacts glacier dynamics and shapes the subglacial environment. However, due to the challenges of observing glacier beds, the spatial organization of subglacial water systems and the time scales of conduit evolution and migration are largely unknown. To address these questions, we analyze 1.5â to 10âHz seismic tremor that we associate with subglacial water flow, hat is, glaciohydraulic tremor, at Taku Glacier, Alaska, throughout the 2016 melt season. We use frequencyâdependent polarization analysis to estimate glaciohydraulic tremor propagation direction (related to the subglacial conduit location) and a degree day melt model to monitor variations in meltâwater input. We suggest that conduit formation requires sustained water input and that multiconduit flow paths can be distinguished from singleâconduit flow paths. Theoretical analysis supports our seismic interpretations that subglacial discharge likely flows through a singleâconduit in regions of steep hydraulic potential gradients but may be distributed among multiple conduits in regions with shallower potential gradients. Seismic tremor in regions with multiple conduits evolves through abrupt jumps between stable configurations that last 3â7 days, while tremor produced by singleâconduit flow remains more stationary. We also find that polarized glaciohydraulic tremor wave types are potentially linked to the distance from source to station and that multiple peak frequencies propagate from a similar direction. Tremor appears undetectable at distances beyond 2â6 km from the source. This new understanding of the spatial organization and temporal development of subglacial conduits informs our understanding of dynamism within the subglacial hydrologic system
Determining V(ub) from B+ --> D*+(s) e+ e- and B+ --> D*+ e+ e-
It was recently pointed out that the decays B^+ --> D^{*+}_s gamma and B^+
--> D^{*+} gamma can be used for an extraction of |V_{ub}|. The theory of these
decays is poorly understood. It was shown that in a world of almost degenerate
b and c-quarks the decay would be computable. The severe difficulties that are
encountered in the realistic calculation stem primarily from the very hard
photon produced in the two body decay. We point out that in the decays B^+ -->
D^{*+}_s e^+e^- and B^+ --> D^{*+} e^+e^- the photon vertex is soft when the
charmed meson is nearly at rest (in the B^+ rest frame). This allows us to
compute with some confidence the decay rate in a restricted but interesting
kinematic regime. Given enough data the extraction of V_{ub} with reasonably
small uncertainties could proceed through an analysis of these exclusive decays
much as is done in the determination of V_{cb}.Comment: 9 pages, latex (revtex), replaced with published versio
delta C-13 Analysis of Mars Analog Carbonates Using Evolved Gas Cavity - Ringdown Spectrometry on the 2010 Arctic Mars Analog Svalbard Expedition (AMASE)
The 2010 Arctic Mars Analog Svalbard Expedition (AMASE) investigated two distinct geologic settings on Svalbard, using instrumentation and techniques in development for future Mars missions, such as the Mars Science Laboratory (MSL), ExoMars, and Mars Sample Return (MSR). The Sample Analysis at Mars (SAM) instrument suite, which will fly on MSL, was developed at Goddard Space Flight Center (GSFC), together with several partners. SAM consists of a quadrupole mass spectrometer (QMS), a gas chromatograph CGC), and a tunable laser spectrometer (TLS), which all analyze gases created by evolved gas analysis (EGA). The two sites studied represent "biotic" and "abiotic" analogs; the "biotic" site being the Knorringfjell fossil methane seep, and the "abiotic" site being the basaltic Sigurdfjell vent complex. The data presented here represent experiments to measure the carbon isotopic composition of carbonates from these two analogs using evolved gas analysis coupled with a commercial cavity ringdown CO2 isotopic analyzer (Picarro) as a proxy for the TLS on SAM
Single Neutralino production at CERN LHC
The common belief that the lightest supersymmetric particle (LSP) might be a
neutralino, providing also the main Dark Matter (DM) component, calls for
maximal detail in the study of the neutralino properties. Motivated by this, we
consider the direct production of a single neutralino \tchi^0_i at a
high/energy hadron collider, focusing on the \tchi^0_1 and \tchi^0_2 cases.
At Born level, the relevant subprocesses are q\bar q\to \tchi^0_i \tilde g,
g q\to \tchi^0_i \tilde q_{L,R} and q\bar q'\to \tchi^0_i\tchi^\pm_j; while
at 1-loop, apart from radiative corrections to these processes, we consider
also gg\to \tchi^0_i\tilde{g}, for which a numerical code named PLATONgluino
is released. The relative importance of these channels turns out to be
extremely model dependent. Combining these results with an analogous study of
the direct \tchi^0_i\tchi^0_j pair production, should help in testing the
SUSY models and the Dark Matter assignment.Comment: 22 pages and 12 figures; version to appear in Phys.Rev.
Shear Alignment and Instability of Smectic Phases
We consider the shear flow of well-aligned one-component smectic phases, such
as thermotropic smectics and lamellar diblock copolymers, below the critical
region. We show that, as a result of thermal fluctuations of the layers,
parallel () alignment is generically unstable and perpendicular ()
alignment is stable against long-wavelength undulations. We also find,
surprisingly, that both and are stable for a narrow window of values
for the anisotropic viscosity.Comment: To appear in PRL. Revtex, 1 figure
Treatment of Heavy Quarks in Deeply Inelastic Scattering
We investigate a simplified version of the ACOT prescription for calculating
deeply inelastic scattering from Q^2 values near the squared mass M_H^2 of a
heavy quark to Q^2 much larger than M_H^2.Comment: 14 pages, 5 figure
Uncertainties of the Inclusive Higgs Production Cross Section at the Tevatron and the LHC
We study uncertainties of the predicted inclusive Higgs production cross
section due to the uncertainties of parton distribution functions (PDF).
Particular attention is given to bbH Yukawa coupling enhanced production
mechanisms in beyond SM scenarios, such as MSSM. The PDF uncertainties are
determined by the robust Lagrange Multiplier method within the CTEQ global
analysis framework. We show that PDF uncertainties dominate over theoretical
uncertainties of the perturbative calculation (usually estimated by the scale
dependence of the calculated cross sections), except for low Higgs masses at
LHC. Thus for the proper interpretation of any Higgs signal, and for better
understanding of the underlying electroweak symmetry breaking mechanism, it is
important to gain better control of the uncertainties of the PDFs.Comment: LaTeX, JHEP, 19 pages, 14 figure
- âŠ