1,493 research outputs found
On the universality of science and technology
Wissenschaft und Technik als kulturelle Werte betrachtet sind niemandes Eigentum und auch nicht Eigentum einer einzelnen Kultur. Sie sind insofern universell, als die Suche nach Wahrheit und Effektivität jeder Kultur eigen ist. So gibt es keine Veranlassung, daß sich irgendein Land gegenüber "westlichen Wissenschaften" unterlegen fühlen müßte. Im Gegenteil, im Licht dieser Universalität darf man Forschung und Wissenschaft nicht dem Westen überlassen, sondern muß unabhängig selbstbewußt theoretische Forschung entwickeln, um die Natur um uns, unsere je eigene Geschichte und das gemeinsame zukünftige Schicksal zu meistern. (psz
Microlensing towards M31 with MDM data
We report the final analysis of a search for microlensing events in the
direction of the Andromeda galaxy, which aimed to probe the MACHO composition
of the M31 halo using data collected during the 1998-99 observational campaign
at the MDM observatory. In a previous paper, we discussed the results from a
first set of observations. Here, we deal with the complete data set, and we
take advantage of some INT observations in the 1999-2000 seasons. This merging
of data sets taken by different instruments turns out to be very useful, the
study of the longer baseline available allowing us to test the uniqueness
characteristic of microlensing events. As a result, all the candidate
microlensing events previously reported turn out to be variable stars. We
further discuss a selection based on different criteria, aimed at the detection
of short--duration events. We find three candidates whose positions are
consistent with self--lensing events, although the available data do not allow
us to conclude unambiguously that they are due to microlensing.Comment: Accepted for publication in Astronomy and Astrophysic
Affine actions on non-archimedean trees
We initiate the study of affine actions of groups on -trees for a
general ordered abelian group ; these are actions by dilations rather
than isometries. This gives a common generalisation of isometric action on a
-tree, and affine action on an -tree as studied by I. Liousse. The
duality between based length functions and actions on -trees is
generalised to this setting. We are led to consider a new class of groups:
those that admit a free affine action on a -tree for some .
Examples of such groups are presented, including soluble Baumslag-Solitar
groups and the discrete Heisenberg group.Comment: 27 pages. Section 1.4 expanded, typos corrected from previous versio
Pear breeding and selection for Fire blight resistance
I.I.F - I.I.R. Commission C2Pear breeding and selection for Fire blight resistance. Working Group "Pears
The POINT-AGAPE survey II: An Unrestricted Search for Microlensing Events towards M31
An automated search is carried out for microlensing events using a catalogue
of 44554 variable superpixel lightcurves derived from our three-year monitoring
program of M31. Each step of our candidate selection is objective and
reproducible by a computer. Our search is unrestricted, in the sense that it
has no explicit timescale cut. So, it must overcome the awkward problem of
distinguishing long-timescale microlensing events from long-period stellar
variables. The basis of the selection algorithm is the fitting of the
superpixel lightcurves to two different theoretical models, using variable star
and blended microlensing templates. Only if microlensing is preferred is an
event retained as a possible candidate. Further cuts are made with regard to
(i) sampling, (ii) goodness of fit of the peak to a Paczynski curve, (iii)
consistency of the microlensing hypothesis with the absence of a resolved
source, (iv) achromaticity, (v) position in the colour-magnitude diagram and
(vi) signal-to-noise ratio. Our results are reported in terms of first-level
candidates, which are the most trustworthy, and second-level candidates, which
are possible microlensing but have lower signal-to-noise and are more
questionable. The pipeline leaves just 3 first-level candidates, all of which
have very short full-width half-maximum timescale (<5 days) and 3 second-level
candidates, which have timescales of 31, 36 and 51 days respectively. We also
show 16 third-level lightcurves, as an illustration of the events that just
fail the threshold for designation as microlensing candidates. They are almost
certainly mainly variable stars. Two of the 3 first-level candidates correspond
to known events (PA 00-S3 and PA 00-S4) already reported by the POINT-AGAPE
project. The remaining first-level candidate is new.Comment: 22 pages, 18 figures, MNRAS, to appea
Boundary sentinels in cylindrical domains
We study a model describing vibrations of a cylindrical domain with thickness e > 0. A characteristic of this model is that it contains “pollution terms” in the boundary data and “missing terms” in the initial data. The “method of sentinels” of J.L. Lions [7] is followed to construct a sentinel using the observed vibrations on the boundary. Such a sentinel, by construction, provides information on pollution terms independent of missing terms. This requires resolution of initial-boundary value problems with nonzero boundary data of mixed type and an exact controllability problem. Further, we characterize so called “stealthy pollution terms” present in the model
Exact controllability of vibrations of thin bodies
In this paper, we address the problem of exact controllability of the wave equation in three dimensional domains which are thin in one direction. We prove the existence of exact controls and analyze their asymptotic behaviour as thickness parameter goes to zero. We characterize their limit as the solution of an exact controllability problem in two dimension
Force-directed scheduling in automatic data path synthesis
The HAL system performs data path synthesis using a new scheduling algorithm that 1s part Of an interdependent scheduling and allocation scheme. This scheme uses an BStl-mate of the hardware allocation to guide and optimiza the scheduling subtask. The allocation information includes the number. type. speed and cost of hardware modules as well as the associated multiplexer and interconnect costs. The iterative force-directed scheduling algorithm attempts to balance the distribution of operations that make use Of the same hardware resources:. Every feasible control step assignment is evaluated at each iteration, for a11 operations.. The associated side-effects on all the predecessor and successor operations are taken Into account.. All the decisions are global.. The algorithm has O(n*) complexity. We review and compare existing scheduling techniques. Mod-erate and difficult examples are used to illustrate the ef-fectiveness of the approach. 1
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