1,741 research outputs found
A Dynamically Adaptive Sparse Grid Method for Quasi-Optimal Interpolation of Multidimensional Analytic Functions
In this work we develop a dynamically adaptive sparse grids (SG) method for
quasi-optimal interpolation of multidimensional analytic functions defined over
a product of one dimensional bounded domains. The goal of such approach is to
construct an interpolant in space that corresponds to the "best -terms"
based on sharp a priori estimate of polynomial coefficients. In the past, SG
methods have been successful in achieving this, with a traditional construction
that relies on the solution to a Knapsack problem: only the most profitable
hierarchical surpluses are added to the SG. However, this approach requires
additional sharp estimates related to the size of the analytic region and the
norm of the interpolation operator, i.e., the Lebesgue constant. Instead, we
present an iterative SG procedure that adaptively refines an estimate of the
region and accounts for the effects of the Lebesgue constant. Our approach does
not require any a priori knowledge of the analyticity or operator norm, is
easily generalized to both affine and non-affine analytic functions, and can be
applied to sparse grids build from one dimensional rules with arbitrary growth
of the number of nodes. In several numerical examples, we utilize our
dynamically adaptive SG to interpolate quantities of interest related to the
solutions of parametrized elliptic and hyperbolic PDEs, and compare the
performance of our quasi-optimal interpolant to several alternative SG schemes
OPTIMAL WEIGHT AND DIALYSIS DOSE IN PATIENTS ON PERIODIC HEMODIALYSIS
Small patients tend to be better dialyzed than large ones. We analyzed the delivered dose of dialysis in two groups of patients - group A, body weight over 50 kg (n-39, m:f=28:l; 57,4 8,3 kg) and group B, body weight under 50 kg (n=15, m:f=6:9; 45,4 3,4 kg). We calculated KT/V and Time Average Concentration of urea (TAC) using two-pool method for urea kinetic modeling. The patients from group Ăâ had a higher KT/V urea =1,35 0,25 (p < 0,05) and lower TAC =13,7 2,72 (p < 0,05) with a shorter dialysis time. Mean serum protein and albumin levels for a year did not differ
Deep Reinforcement Learning for Concentric Tube Robot Control with a Goal-Based Curriculum
Concentric Tube Robots (CTRs), a type of continuum robot, are a collection of concentric, pre-curved tubes
composed of super elastic nickel titanium alloy. CTRs can
bend and twist from the interactions between neighboring tubes
causing the kinematics and therefore control of the end-effector
to be very challenging to model. In this paper, we develop a
control scheme for a CTR end-effector in Cartesian space with
no prior kinematic model using a deep reinforcement learning
(DRL) approach with a goal-based curriculum reward strategy.
We explore the use of curricula by changing the goal tolerance
through training with constant, linear and exponential decay
functions. Also, relative and absolute joint representations
as a way of improving training convergence are explored.
Quantitative comparisons for combinations of curricula and
joint representations are performed and the exponential decay
relative approach is used for training a robust policy in a
noise-induced simulation environment. Compared to a previous
DRL approach, our new method reduces training time and
employs a more complex simulation environment. We report
mean Cartesian errors of 1.29 mm and a success rate of 0.93
with a relative decay curriculum. In path following, we report
mean errors of 1.37 mm in a noise-induced path following task.
Albeit in simulation, these results indicate the promise of using
DRL in model free control of continuum robots and CTRs in
particular
Spectral observations of X Persei: Connection between H-alpha and X-ray emission
We present spectroscopic observations of the Be/X-ray binary X Per obtained
during the period 1999 - 2018. Using new and published data, we found that
during "disc-rise" the expansion velocity of the circumstellar disc is 0.4 -
0.7 km/s. Our results suggest that the disc radius in recent decades show
evidence of resonant truncation of the disc by resonances 10:1, 3:1, and 2:1,
while the maximum disc size is larger than the Roche lobe of the primary and
smaller than the closest approach of the neutron star. We find correlation
between equivalent width of H-alpha emission line () and the X-ray
flux, which is visible when . The
correlation is probably due to wind Roche lobe overflow.Comment: Accepted for publication in Astronomy & Astrophysic
Connection between orbital modulation of H-alpha and gamma-rays in the Be/X-ray binary LSI+61303
We studied the average orbital modulation of various parameters (gamma-ray
flux, H-alpha emission line, optical V band brightness) of the radio- and
gamma-ray emitting Be/X-ray binary LSI+61303. Using the Spearman rank
correlation test, we found highly significant correlations between the orbital
variability of the equivalent width of the blue hump of the H-alpha and
Fermi-LAT flux with a Spearman p-value 2e-5, and the equivalent widths ratio
EW_B/EW_R and Fermi-LAT flux with p-value 9e-5. We also found a significant
anti-correlation between Fermi-LAT flux and V band magnitude with p-value
7.10^{-4}.
All these correlations refer to the average orbital variability, and we
conclude that the H-alpha and gamma-ray emission processes in LSI+61303 are
connected. The possible physical scenario is briefly discussed.Comment: accepted as a Letter in Astronomy and Astrophysic
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