53,248 research outputs found
Determining WWW User's Next Access and Its Application to Pre-fetching
World-Wide Web (WWW) services have grown to levels where significant delays are expected to happen. Techniques like pre-fetching are likely to help users to personalize their needs, reducing their waiting times. However, pre-fetching is only effective if the right documents are identified and if user's move is correctly predicted. Otherwise, pre-fetching will only waste bandwidth. Therefore, it is productive to determine whether a revisit will occur or not, before starting pre-fetching.
In this paper we develop two user models that help determining user's next move. One model uses Random Walk approximation and the other is based on Digital Signal Processing techniques. We also give hints on how to use such models with a simple pre-fetching technique that we are developing.CNP
Wiggly tails: a gravitational wave signature of massive fields around black holes
Massive fields can exist in long-lived configurations around black holes. We
examine how the gravitational wave signal of a perturbed black hole is affected
by such `dirtiness' within linear theory. As a concrete example, we consider
the gravitational radiation emitted by the infall of a massive scalar field
into a Schwarzschild black hole. Whereas part of the scalar field is
absorbed/scattered by the black hole and triggers gravitational wave emission,
another part lingers in long-lived quasi-bound states. Solving numerically the
Teukolsky master equation for gravitational perturbations coupled to the
massive Klein-Gordon equation, we find a characteristic gravitational wave
signal, composed by a quasi-normal ringing followed by a late time tail. In
contrast to `clean' black holes, however, the late time tail contains small
amplitude wiggles with the frequency of the dominating quasi-bound state.
Additionally, an observer dependent beating pattern may also be seen. These
features were already observed in fully non-linear studies; our analysis shows
they are present at linear level, and, since it reduces to a 1+1 dimensional
numerical problem, allows for cleaner numerical data. Moreover, we discuss the
power law of the tail and that it only becomes universal sufficiently far away
from the `dirty' black hole. The wiggly tails, by constrast, are a generic
feature that may be used as a smoking gun for the presence of massive fields
around black holes, either as a linear cloud or as fully non-linear hair.Comment: 6 pages, 4 figure
Berends-Giele recursion for double-color-ordered amplitudes
Tree-level double-color-ordered amplitudes are computed using Berends--Giele
recursion relations applied to the bi-adjoint cubic scalar theory. The standard
notion of Berends--Giele currents is generalized to double-currents and their
recursions are derived from a perturbiner expansion of linearized fields that
solve the non-linear field equations. Two applications are given. Firstly, we
prove that the entries of the inverse KLT matrix are equal to Berends--Giele
double-currents (and are therefore easy to compute). And secondly, a simple
formula to generate tree-level BCJ-satisfying numerators for arbitrary
multiplicity is proposed by evaluating the field-theory limit of tree-level
string amplitudes for various color orderings using double-color-ordered
amplitudes.Comment: 15 pages, harvmac TeX, v2: published versio
The political dimension of animal ethics in the context of bioethics: problems of integration and future challenges
Animal ethics has reached a new phase with the development of animal ethical thinking. Topics and problems previously discussed in terms of moral theories and ethical concepts are now being reformulated in terms of political theory and political action. This constitutes a paradigm shift for Animal Ethics. It indicates the transition from a field focused on relations between individuals (humans and animals) to a new viewpoint that incorporates the political dimensions of the relationships between human communities and non-human animals. Animals are no longer seen as a heterogeneous group of sentient beings or simply as species, but as part of a common good that is simultaneously human and animal. In order to participate in this new phase, bioethics will have to face a series of challenges that have hindered the integration of animal ethics within its field. It will also need the development of a new theoretical framework based on relations between communities of individuals. This framework will be able to highlight the ethical and political dimensions that arise from interactions between human communities, non-human animals and the ecosystem
Simplifying the Tree-level Superstring Massless Five-point Amplitude
We use the pure spinor formalism to obtain the supersymmetric massless
five-point amplitude at tree-level in a streamlined fashion. We also prove the
equivalence of an OPE identity in string theory with a subset of the
Bern-Carrasco-Johansson five-point kinematic relations, and demonstrate how the
remaining BCJ identities follow from the different integration regions over the
open string world-sheet, therefore providing a first principles derivation of
the (supersymmetric) BCJ identities.Comment: 19 pages, harvmac TeX, v2: Fix and add references, fix typos and add
(3.16
PSS: A FORM Program to Evaluate Pure Spinor Superspace Expressions
A FORM program which is used to efficiently expand in components pure spinor
superfield expressions of kinematic factors is presented and comments on how it
works are made. It is highly customizable using the standard features of FORM
and can be used to help obtaining superstring effective actions from the
scattering amplitudes computed with the pure spinor formalism.Comment: 16 pages, harvma
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