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