1,539 research outputs found
Backward SDE Representation for Stochastic Control Problems with Non Dominated Controlled Intensity
We are interested in stochastic control problems coming from mathematical
finance and, in particular, related to model uncertainty, where the uncertainty
affects both volatility and intensity. This kind of stochastic control problems
is associated to a fully nonlinear integro-partial differential equation, which
has the peculiarity that the measure characterizing the
jump part is not fixed but depends on a parameter which lives in a compact
set of some Euclidean space . We do not assume that the family
is dominated. Moreover, the diffusive part can be
degenerate. Our aim is to give a BSDE representation, known as nonlinear
Feynman-Kac formula, for the value function associated to these control
problems. For this reason, we introduce a class of backward stochastic
differential equations with jumps and partially constrained diffusive part. We
look for the minimal solution to this family of BSDEs, for which we prove
uniqueness and existence by means of a penalization argument. We then show that
the minimal solution to our BSDE provides the unique viscosity solution to our
fully nonlinear integro-partial differential equation.Comment: arXiv admin note: text overlap with arXiv:1212.2000 by other author
Modeling, Stability Analysis, and Testing of a Hybrid Docking Simulator
A hybrid docking simulator is a hardware-in-the-loop (HIL) simulator that
includes a hardware element within a numerical simulation loop. One of the
goals of performing a HIL simulation at the European Proximity Operation
Simulator (EPOS) is the verification and validation of the docking phase in an
on-orbit servicing mission.....Comment: 30 papge
Analytical and experimental stability investigation of a hardware-in-the-loop satellite docking simulator
The European Proximity Operation Simulator (EPOS) of the DLR-German Aerospace
Center is a robotics-based simulator that aims at validating and verifying a
satellite docking phase. The generic concept features a robotics tracking
system working in closed loop with a force/torque feedback signal. Inherent
delays in the tracking system combined with typical high stiffness at contact
challenge the stability of the closed-loop system. The proposed concept of
operations is hybrid: the feedback signal is a superposition of a measured
value and of a virtual value that can be tuned in order to guarantee a desired
behavior. This paper is concerned with an analytical study of the system's
closed-loop stability, and with an experimental validation of the hybrid
concept of operations in one dimension (1D). The robotics simulator is modeled
as a second-order loop-delay system and closed-form expressions for the
critical delay and associated frequency are derived as a function of the
satellites' mass and the contact dynamics stiffness and damping parameters. A
numerical illustration sheds light on the impact of the parameters on the
stability regions. A first-order Pade approximation provides additional means
of stability investigation. Experiments were performed and tests results are
described for varying values of the mass and the damping coefficients. The
empirical determination of instability is based on the coefficient of
restitution and on the observed energy. There is a very good agreement between
the critical damping values predicted by the analysis and observed during the
tests...Comment: 16 page
Equilibrium composition between liquid and clathrate reservoirs on Titan
Hundreds of lakes and a few seas of liquid hydrocarbons have been observed by
the Cassini spacecraft to cover the polar regions of Titan. A significant
fraction of these lakes or seas could possibly be interconnected with
subsurface liquid reservoirs of alkanes. In this paper, we investigate the
interplay that would happen between a reservoir of liquid hydrocarbons located
in Titan's subsurface and a hypothetical clathrate reservoir that progressively
forms if the liquid mixture diffuses throughout a preexisting porous icy layer.
To do so, we use a statistical-thermodynamic model in order to compute the
composition of the clathrate reservoir that forms as a result of the
progressive entrapping of the liquid mixture. This study shows that clathrate
formation strongly fractionates the molecules between the liquid and the solid
phases. Depending on whether the structure I or structure II clathrate forms,
the present model predicts that the liquid reservoirs would be mainly composed
of either propane or ethane, respectively. The other molecules present in the
liquid are trapped in clathrates. Any river or lake emanating from subsurface
liquid reservoirs that significantly interacted with clathrate reservoirs
should present such composition. On the other hand, lakes and rivers sourced by
precipitation should contain higher fractions of methane and nitrogen, as well
as minor traces of argon and carbon monoxide.Comment: Accepted for publication in Icaru
High performance Tunnel Field Effect Transistors based on in-plane transition metal dichalcogenide heterojunctions
In-plane heterojunction tunnel field effect transistors based on monolayer
transition metal dichalcogenides are studied by means of self-consistent
non-equilibrium Green's functions simulations and an atomistic tight-binding
Hamiltonian. We start by comparing several heterojunctions before focusing on
the most promising ones, i.e WTe2-MoS2 and MoTe2-MoS2. The scalability of those
devices as a function of channel length is studied, and the influence of
backgate voltages on device performance is analysed. Our results indicate that,
by fine-tuning the design parameters, those devices can yield extremely low
sub-threshold swings (below 5mV/decade) and Ion/Ioff ratios higher than 1e8 at
a supply voltage of 0.3V, making them ideal for ultra-low power consumption.Comment: 10 page
Measurements of thermal properties of icy Mars regolith analogs
In a series of laboratory experiments, we measure thermal diffusivity, thermal conductivity, and heat capacity of icy regolith created by vapor deposition of water below its triple point and in a low pressure atmosphere. We find that an ice-regolith mixture prepared in this manner, which may be common on Mars, and potentially also present on the Moon, Mercury, comets and other bodies, has a thermal conductivity that increases approximately linearly with ice content. This trend differs substantially from thermal property models based of preferential formation of ice at grain contacts previously applied to both terrestrial and non-terrestrial subsurface ice. We describe the observed microphysical structure of ice responsible for these thermal properties, which displaces interstitial gases, traps bubbles, exhibits anisotropic growth, and bridges non-neighboring grains. We also consider the applicability of these measurements to subsurface ice on Mars and other solar system bodies
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