44,139 research outputs found
Simulations for Multi-Object Spectrograph Planet Surveys
Radial velocity surveys for extra-solar planets generally require substantial
amounts of large telescope time in order to monitor a sufficient number of
stars. Two of the aspects which can limit such surveys are the single-object
capabilities of the spectrograph, and an inefficient observing strategy for a
given observing window. In addition, the detection rate of extra-solar planets
using the radial velocity method has thus far been relatively linear with time.
With the development of various multi-object Doppler survey instruments, there
is growing potential to dramatically increase the detection rate using the
Doppler method. Several of these instruments have already begun usage in large
scale surveys for extra-solar planets, such as FLAMES on the VLT and Keck ET on
the Sloan 2.5m wide-field telescope.
In order to plan an effective observing strategy for such a program, one must
examine the expected results based on a given observing window and target
selection. We present simulations of the expected results from a generic
multi-object survey based on calculated noise models and sensitivity for the
instrument and the known distribution of exoplanetary system parameters. We
have developed code for automatically sifting and fitting the planet candidates
produced by the survey to allow for fast follow-up observations to be
conducted. The techniques presented here may be applied to a wide range of
multi-object planet surveys.Comment: 15 pages, 10 figures, accepted for publication in MNRA
Typing Quantum Superpositions and Measurement
We propose a way to unify two approaches of non-cloning in quantum lambda-calculi. The first approach is to forbid duplicating variables, while the second is to consider all lambda-terms as algebraic-linear functions. We illustrate this idea by defining a quantum extension of first-order simply-typed lambda-calculus, where the type is linear on superposition, while allows cloning base vectors. In addition, we provide an interpretation of the calculus where superposed types are interpreted as vector spaces and non-superposed types as their basis.Fil: DĂaz Caro, Alejandro. Universidad Nacional de Quilmes. Departamento de Ciencia y TecnologĂa; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Dowek, Gilles. Institut National de Recherche en Informatique et en Automatique; Franci
Shear viscosity, instability and the upper bound of the Gauss-Bonnet coupling constant
We compute the dimensionality dependence of for charged black branes
with Gauss-Bonnet correction. We find that both causality and stability
constrain the value of Gauss-Bonnet coupling constant to be bounded by 1/4 in
the infinite dimensionality limit. We further show that higher dimensionality
stabilize the gravitational perturbation. The stabilization of the perturbation
in higher dimensional space-time is a straightforward consequence of the
Gauss-Bonnet coupling constant bound.Comment: 16 pages,3 figures+3 tables,typos corrected, published versio
A Model of Strongly Correlated Electrons with Condensed Resonating-Valence-Bond Ground States
We propose a new exactly solvable model of strongly correlated electrons. The
model is based on a - model of the CuO plane with infinitely large
repulsive interactions on Cu-sites, and it contains additional
correlated-hopping, pair-hopping and charge-charge interactions of electrons.
For even numbers of electrons less than or equal to 2/3-filling, we construct
the exact ground states of the model, all of which have the same energy and
each of which is the unique ground state for a fixed electron number. It is
shown that these ground states are the resonating-valence-bond states which are
also regarded as condensed states in which all electrons are in a single
two-electron state. We also show that the ground states exhibit off-diagonal
long-range order.Comment: 17 pages, 1 figure, v2: minor changes, v3: minor changes and typos
correction
Quantum Entanglement and Teleportation in Higher Dimensional Black Hole Spacetimes
We study the properties of quantum entanglement and teleportation in the
background of stationary and rotating curved space-times with extra dimensions.
We show that a maximally entangled Bell state in an inertial frame becomes less
entangled in curved space due to the well-known Hawking-Unruh effect. The
degree of entanglement is found to be degraded with increasing the extra
dimensions. For a finite black hole surface gravity, the observer may choose
higher frequency mode to keep high level entanglement. The fidelity of quantum
teleporation is also reduced because of the Hawking-Unruh effect. We discuss
the fidelity as a function of extra dimensions, mode frequency, black hole mass
and black hole angular momentum parameter for both bosonic and fermionic
resources.Comment: 15 pages, 10 figures,contents expande
Geoarchaeological evidence of the AD 1642 Yellow River flood that destroyed Kaifeng, a former capital of dynastic China
Rising global temperatures will increase the number of extreme weather events, creating new challenges for cities around the world. Archaeological research on the destruction and subsequent reoccupation of ancient cities has the potential to reveal geological and social dynamics that have historically contributed to making urban settings resilient to these extreme weather events. Using a combination of archaeological and geological methods, we examine how extreme flood events at Kaifeng, a former capital of dynastic China, have shaped the city’s urban resilience. Specifically, we focus on an extreme Yellow River flood event in AD 1642 that historical records suggest killed around 300,000 people living in Kaifeng. Our recent archaeological excavations have discovered compelling geological and archaeological evidence that corroborates these documents, revealing that the AD 1642 Yellow River flood destroyed Kaifeng’s inner city, entombing the city and its inhabitants within meters of silt and clay. We argue that the AD 1642 flood was extraordinarily catastrophic because Kaifeng’s city walls only partly collapsed, entrapping most of the flood waters within the city. Both the geology of the Yellow River floods as well as the socio-political context of Kaifeng shaped the city’s resilience to extreme flood events
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