236 research outputs found
A hyperbolic-elliptic PDE model and conservative numerical method for gravity-dominated variably-saturated groundwater flow
Richards equation is often used to represent two-phase fluid flow in an
unsaturated porous medium when one phase is much heavier and more viscous than
the other. However, it cannot describe the fully saturated flow due to
degeneracy in the capillary pressure term. Mathematically, gravity-driven
variably saturated flows are interesting because their governing partial
differential equation switches from hyperbolic in the unsaturated region to
elliptic in the saturated region. Moreover, the presence of wetting fronts
introduces strong spatial gradients often leading to numerical instability. In
this work, we develop a robust, multidimensional mathematical and computational
model for such variably saturated flow in the limit of negligible capillary
forces. The elliptic problem for saturated regions is built-in efficiently into
our framework for a reduced system corresponding to the saturated cells, with
the boundary condition of the fixed head at the unsaturated cells. In summary,
this coupled hyperbolic-elliptic PDE framework provides an efficient,
physics-based extension of the hyperbolic Richards equation to simulate fully
saturated regions. Finally, we provide a suite of easy-to-implement yet
challenging benchmark test problems involving saturated flows in one and two
dimensions. These simple problems, accompanied by their corresponding
analytical solutions, can prove to be pivotal for the code verification, model
validation (V&V) and performance comparison of such simulators. Our numerical
solutions show an excellent comparison with the analytical results for the
proposed problems. The last test problem on two-dimensional infiltration in a
stratified, heterogeneous soil shows the formation and evolution of multiple
disconnected saturated regions.Comment: 21 pages, 9 figure
Absarokites from the Western Mexican Volcanic Belt : constraints on mantle wedge conditions
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 2002We have investigated the near liquidus phase relations of a primitive absarokite from the
Mascota region in Western Mexico. Sample M.102 was chosen because it has high MgO contents, a
high Mg# and F090 olivine phenocrysts, indicating it is primitive mantle melt. High-pressure
experiments on a synthetic analogue of the absarokite composition with a H2O content of either
-1 7 wt% or -5.1 wt% were cared out in a piston cylinder apparatus. The composition with
-1.7 wt% H2O is multiply saturated with olivine and orthopyroxene as liquidus phases at 1.6 GPa
and 1400°C. At the same pressure clinopyroxene appears 30°C below the liquidus. With a H2O
content of -5.1 wt% composition M.102 is multiply saturated with olivine and orthopyroxene on the
liquidus at 1.7 GPa and 1300°C. Assuming batch melting, we suggest that absarokite M.102
segregated from a depleted lherzolite or harburgite residue at depth -50 km depth in the mantle
wedge. Unlike most lavas in the region, the absarokite has not ponded and fractionated at the crust
mantle interface (-35-40 km), and the temperatures of multiple saturation indicate that the mantle
wedge beneath the Jalisco block is hotter than previously thought. The low degree batch melting of
an original metasomatised harzburgite source, can produce the observed trace element abundances.
The liquidus phase relations are not consistent with the presence of non-peridotitic veins at the depth
of last equilibration. Therefore, we propose that the Mascota absarokites segregated at an apparent
melt fraction of less than 5% from a depleted peridotitic source. They initially formed by a small
degree of melting of a metasomatised original source at greater depth
In Stars We Trust – A Note on Reputation Portability Between Digital Platforms
Complementors accumulate reputation on an ever-increasing number of online platforms. While the effects of reputation within individual platforms are well-understood, its potential effectiveness across platform boundaries has received much less attention. This research note considers complementors’ ability to increase their trustworthiness in the eyes of prospective consumers by importing reputational data from another platform. The study evaluates this potential lever by means of an online experiment, during which specific combinations of on-site and imported rating scores are tested. Results reveal that importing reputation can be advantageous – but also detrimental, depending on ratings’ values. Implications for complementors, platform operators, and regulatory bodies concerned with online reputation are considered
Multisensory Assisted In-hand Manipulation of Objects with a Dexterous Hand
Korthals T, Melnik A, Hesse M, Leitner J. Multisensory Assisted In-hand Manipulation of Objects with a Dexterous Hand. 2019 IEEE International Conference on Robotics and Automation Workshop on Integrating Vision and Touch for Multimodal and Cross-modal Perception, (ViTac) 2019, Montreal, CA, May 20-25, 2019. 2019:1-2
Bidirectional UWB Localization: A Review on an Elastic Positioning Scheme for GNSS-deprived Zones
A bidirectional Ultra-Wideband (UWB) localization scheme is one of the three
widely deployed design integration processes ordinarily destined for time-based
UWB positioning systems. The key property of the bidirectional UWB localization
is its ability to serve both the navigation and tracking assignments on-demand
within a single localization scheme. Conventionally, the perspective of
navigation and tracking in wireless localization systems is viewed distinctly
as an individual system because different methodologies were required for the
implementation process. The ability to flexibly or elastically combine two
unique positioning perspectives (i.e., navigation and tracking) within a single
scheme is a paradigm shift in the way location-based services are observed.
Thus, this article addresses and pinpoints the potential of a bidirectional UWB
localization scheme. Regarding this, the complete system model of the
bidirectional UWB localization scheme was comprehensively described based on
modular processes in this article. The demonstrative evaluation results based
on two system integration processes as well as a SWOT (strengths, weaknesses,
opportunities, and threats) analysis of the scheme were also discussed.
Moreover, we argued that the presented bidirectional scheme can also be used as
a prospective topology for the realization of precise location estimation
processes in 5G/6G wireless mobile networks, as well as Wi-Fi fine-time
measurement-based positioning systems in this article.Comment: 30 pages, 12 figure
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