2,220 research outputs found
The correct estimate of the probability of false detection of the matched filter in the detection of weak signals. II. (Further results with application to a set of ALMA and ATCA data)
The matched filter (MF) is one of the most popular and reliable techniques to
the detect signals of known structure and amplitude smaller than the level of
the contaminating noise. Under the assumption of stationary Gaussian noise, MF
maximizes the probability of detection subject to a constant probability of
false detection or false alarm (PFA). This property relies upon a priori
knowledge of the position of the searched signals, which is usually not
available. Recently, it has been shown that when applied in its standard form,
MF may severely underestimate the PFA. As a consequence the statistical
significance of features that belong to noise is overestimated and the
resulting detections are actually spurious. For this reason, an alternative
method of computing the PFA has been proposed that is based on the probability
density function (PDF) of the peaks of an isotropic Gaussian random field. In
this paper we further develop this method. In particular, we discuss the
statistical meaning of the PFA and show that, although useful as a preliminary
step in a detection procedure, it is not able to quantify the actual
reliability of a specific detection. For this reason, a new quantity is
introduced called the specific probability of false alarm (SPFA), which is able
to carry out this computation. We show how this method works in targeted
simulations and apply it to a few interferometric maps taken with the Atacama
Large Millimeter/submillimeter Array (ALMA) and the Australia Telescope Compact
Array (ATCA). We select a few potential new point sources and assign an
accurate detection reliability to these sources.Comment: 28 pages, 20 figures, Astronomy & Astrophysics, Minor changes and
some typos correcte
Head up, foot down : object words orient attention to the objects' typical location
Many objects typically occur in particular locations, and object words encode these spatial associations. We tested whether such object words (e.g., head, foot) orient attention toward the location where the denoted object typically occurs (i.e., up, down). Because object words elicit perceptual simulations of the denoted objects (i.e., the representations acquired during actual perception are reactivated), we predicted that an object word would interfere with identification of an unrelated visual target subsequently presented in the object's typical location. Consistent with this prediction, three experiments demonstrated that words denoting objects that typically occur high in the visual field hindered identification of targets appearing at the top of the display, whereas words denoting low objects hindered target identification at the bottom of the display. Thus, object words oriented attention to and activated perceptual simulations in the objects' typical locations. These results shed new light on how language affects perception
Lattice-Spin Mechanism in Colossal Magnetoresistant Manganites
We present a single-orbital double-exchange model, coupled with cooperative
phonons (the so called breathing-modes of the oxygen octahedra in manganites).
The model is studied with Monte Carlo simulations. For a finite range of doping
and coupling constants, a first-order Metal-Insulator phase transition is
found, that coincides with the Paramagnetic-Ferromagnetic phase transition. The
insulating state is due to the self-trapping of every carrier within an oxygen
octahedron distortion.Comment: 4 pages, 5 figures, ReVTeX macro, accepted for publication in PR
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