1,400 research outputs found
A continuum model (PSUMEL1) of ice mélange and its role during retreat of the Antarctic Ice Sheet
Rapidly retreating thick ice fronts can generate large amounts of mélange
(floating ice debris), which may affect episodes of rapid retreat of
Antarctic marine ice. In modern Greenland fjords, mélange provides
substantial back pressure on calving ice faces, which slows ice front calving
rates. On the much larger scales of West Antarctica, it is unknown if
mélange could clog seaways and provide enough back pressure to act as a
negative feedback slowing retreat. Here we describe a new mélange model,
using a continuum-mechanical formulation that is computationally feasible for
long-term continental Antarctic applications. It is tested in an idealized
rectangular channel and calibrated very basically using observed modern
conditions in Jakobshavn fjord, West Greenland. The model is then applied to
drastic retreat of Antarctic ice in response to warm mid-Pliocene climate.
With mélange parameter values that yield reasonable modern Jakobshavn
results, Antarctic marine ice still retreats drastically in the Pliocene
simulations, with little slowdown despite the huge amounts of mélange
generated. This holds both for the rapid early collapse of West Antarctica
and for later retreat into major East Antarctic basins. If parameter values
are changed to make the mélange much more resistive to flow, far outside
the range for reasonable Jakobshavn results, West Antarctica still collapses
and retreat is slowed or prevented only in a few East Antarctic basins.</p
Geologic application of thermal inertia imaging using HCMM data
Three test sites in the western US were selected to discriminate among surface geologic materials on the basis of their thermal properties as determined from HCMM data. Attempts to determine quantitatively accurate thermal inertia values from HCMM digital data met with only partial success due to the effects of sensor miscalibrations, radiative transfer in the atmosphere, and varying meteorology and elevation across a scene. In most instances, apparent thermal inertia was found to be an excellent qualitative representation of true thermal inertia. Computer processing of digital day and night HCMM data allowed construction of geologically useful images. At some test sites, more information was provided by data than LANDSAT data. Soil moisture effects and differences in spectrally dark materials were more effectively displayed using the thermal data
Twin Ice Cores from Greenland Reveal History of Climate Change, More
Two projects conducted from 1989 to 1993 collected parallel ice cores—just 30 km apart— from the central part of the Greenland ice sheet. Each core is more than 3 km deep and extends back 110,000 years. In short, the ice cores tell a clear story: humans came of age agriculturally and industrially during the most stable climatic regime recorded in the cores. Change—large, rapid, and global—is more characteristic of the Earth\u27s climate than is stasis
High-accuracy global time and frequency transfer with a space-borne hydrogen maser clock
A proposed system for high-accuracy global time and frequency transfer using a hydrogen maser clock in a space vehicle is discussed. Direct frequency transfer with a accuracy of 10 to the minus 14th power and time transfer with an estimated accuracy of 1 nsec are provided by a 3-link microwave system. A short pulse laser system is included for subnanosecond time transfer and system calibration. The results of studies including operational aspects, error sources, data flow, system configuration, and implementation requirements for an initial demonstration experiment using the Space Shuttle are discussed
Diffusion, Fragmentation and Coagulation Processes: Analytical and Numerical Results
We formulate dynamical rate equations for physical processes driven by a
combination of diffusive growth, size fragmentation and fragment coagulation.
Initially, we consider processes where coagulation is absent. In this case we
solve the rate equation exactly leading to size distributions of Bessel type
which fall off as for large -values. Moreover, we provide
explicit formulas for the expansion coefficients in terms of Airy functions.
Introducing the coagulation term, the full non-linear model is mapped exactly
onto a Riccati equation that enables us to derive various asymptotic solutions
for the distribution function. In particular, we find a standard exponential
decay, , for large , and observe a crossover from the Bessel
function for intermediate values of . These findings are checked by
numerical simulations and we find perfect agreement between the theoretical
predictions and numerical results.Comment: (28 pages, 6 figures, v2+v3 minor corrections
Evaluation of thermal data for geologic applications
Sensitivity studies using thermal models indicated sources of errors in the determination of thermal inertia from HCMM data. Apparent thermal inertia, with only simple atmospheric radiance corrections to the measured surface temperature, would be sufficient for most operational requirements for surface thermal inertia. Thermal data does have additional information about the nature of surface material that is not available in visible and near infrared reflectance data. Color composites of daytime temperature, nighttime temperature, and albedo were often more useful than thermal inertia images alone for discrimination of lithologic boundaries. A modeling study, using the annual heating cycle, indicated the feasibility of looking for geologic features buried under as much as a meter of alluvial material. The spatial resolution of HCMM data is a major limiting factor in the usefulness of the data for geologic applications. Future thermal infrared satellite sensors should provide spatial resolution comparable to that of the LANDSAT data
Comment on Catastrophic Ice Shelf Breakup as the Source of Heinrich Event Icebergs\u27\u27 by C. L. Hulbe et al.
Comment on Catastrophic Ice Shelf Breakup as the Source of Heinrich Event Icebergs\u27\u27 by C. L. Hulbe et al.
Cosmological test of the Yilmaz theory of gravity
We test the Yilmaz theory of gravitation by working out the corresponding
Friedmann-type equations generated by assuming the Friedmann-Robertson-Walker
cosmological metrics. In the case that space is flat the theory is consistent
only with either a completely empty universe or a negative energy vacuum that
decays to produce a constant density of matter. In both cases the total energy
remains zero at all times, and in the latter case the acceleration of the
expansion is always negative. To obtain a more flexible and potentially more
realistic cosmology, the equation of state relating the pressure and energy
density of the matter creation process must be different from the vacuum, as
for example is the case in the steady-state models of Gold, Bondi, Hoyle and
others. The theory does not support the cosmological principle for curved space
K =/= 0 cosmological metrics
A Comparison of Youths Who Have Committed Delinquent Acts with Learning Disabled, Low-Achieving, and Normally Achieving Adolescents
This research was published by the KU Center for Research on Learning, formerly known as the University of Kansas Institute for Research in Learning Disabilities.This study compared a group of youths who had committed delinquent acts with LD, low-achieving, and normally-achieving adolescents. Youths who had committed delinquent acts most resembled the low-achieving group based on student and parent interview responses. The delinquent youth group generally indicated below average grade point averages; however, their achievement test scores were average. In addition, family relationships and difficulty in problem solving appeared to distinguish this group from all three groups
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