6,813 research outputs found
Arbitrary Steady-State Solutions with the K-epsilon Model
Widely-used forms of the K-epsilon turbulence model are shown to yield arbitrary steady-state converged solutions that are highly dependent on numerical considerations such as initial conditions and solution procedure. These solutions contain pseudo-laminar regions of varying size. By applying a nullcline analysis to the equation set, it is possible to clearly demonstrate the reasons for the anomalous behavior. In summary, the degenerate solution acts as a stable fixed point under certain conditions, causing the numerical method to converge there. The analysis also suggests a methodology for preventing the anomalous behavior in steady-state computations
Impact of Escherichia coli on Urine Citrate and Urease-Induced Crystallization
Escherichia coli (E. coli) is usually not a urease producer. It is, however, often cultured in urinary phosphate containing calculi including ammonium magnesium phosphate stones. This suggests the possibility that E. coli might be involved in stone forming process. The effect of E. coli on urine citrate and urease-induced crystallization in human urine has been studied in vitro. E. coli was found to strongly reduce urine citrate (after 48 hours). In the E. coli inoculated samples, the urease-induced crystallization was increased. There was a strong correlation, r = 0.8, between the citrate decrease and the increase in calcium precipitation. The results indicate that E. coli and the reduced urine citrate influences urease-induced crystallization in vitro
SOTER on ROS: A Run-Time Assurance Framework on the Robot Operating System
We present an implementation of SOTER, a run-time assurance framework for
building safe distributed mobile robotic (DMR) systems, on top of the Robot
Operating System (ROS). The safety of DMR systems cannot always be guaranteed
at design time, especially when complex, off-the-shelf components are used that
cannot be verified easily. SOTER addresses this by providing a language-based
approach for run-time assurance for DMR systems. SOTER implements the reactive
robotic software using the language P, a domain-specific language designed for
implementing asynchronous event-driven systems, along with an integrated
run-time assurance system that allows programmers to use unfortified components
but still provide safety guarantees. We describe an implementation of SOTER for
ROS and demonstrate its efficacy using a multi-robot surveillance case study,
with multiple run-time assurance modules. Through rigorous simulation, we show
that SOTER enabled systems ensure safety, even when using unknown and untrusted
components.Comment: 20th International Conference on Runtime Verificatio
The dissipative linear Boltzmann equation for hard spheres
We prove the existence and uniqueness of an equilibrium state with unit mass
to the dissipative linear Boltzmann equation with hard--spheres collision
kernel describing inelastic interactions of a gas particles with a fixed
background. The equilibrium state is a universal Maxwellian distribution
function with the same velocity as field particles and with a non--zero
temperature lower than the background one, which depends on the details of the
binary collision. Thanks to the H--theorem we then prove strong convergence of
the solution to the Boltzmann equation towards the equilibrium.Comment: 17 pages, submitted to Journal of Statistical Physic
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