15,543 research outputs found
CM cycles on Kuga–Sato varieties over Shimura curves and Selmer groups
Given a modular form f of even weight larger than two and an imaginary quadratic field K
satisfying a relaxed Heegner hypothesis, we construct a collection of CM cycles on a Kuga–Sato
variety over a suitable Shimura curve which gives rise to a system of Galois cohomology classes
attached to f enjoying the compatibility properties of an Euler system. Then we use Kolyvagin’s
method [21], as adapted by Nekova´¿r [28] to higher weight modular forms, to bound the size of the relevant Selmer group associated to f and K and prove the finiteness of the (primary part) of the Shafarevich–Tate group, provided that a suitable cohomology class does not vanish.Peer ReviewedPostprint (author's final draft
New bounds for truthful scheduling on two unrelated selfish machines
We consider the minimum makespan problem for tasks and two unrelated
parallel selfish machines. Let be the best approximation ratio of
randomized monotone scale-free algorithms. This class contains the most
efficient algorithms known for truthful scheduling on two machines. We propose
a new formulation for , as well as upper and lower bounds on
based on this formulation. For the lower bound, we exploit pointwise
approximations of cumulative distribution functions (CDFs). For the upper
bound, we construct randomized algorithms using distributions with piecewise
rational CDFs. Our method improves upon the existing bounds on for small
. In particular, we obtain almost tight bounds for showing that
.Comment: 28 pages, 3 tables, 1 figure. Theory Comput Syst (2019
Baseline report on the evaluation of Familias en Acción
This report describes the survey that was carried out in 122 communities in rural Colombia by the consortium formed by the Institute for Fiscal Studies, Econometria and SEI as the baseline for the impact evaluation of Familias en Acción, a programme to foster the accumulation of human capital in rural Colombia, run by the Colombian government.
In this report, we will not describe in detail the programme or the methodology of the proposed evaluation, as this was done in IFS-Econometria-SEI (2003a). The main aim of the document is to discuss the first, baseline survey that was collected for this evaluation. While the baseline survey cannot, by definition, be used to perform impact evaluation, towards the end of the report we exploit the slightly peculiar way in which the programme was started and
have a first very preliminary glance at some of the impacts that the programme might have.
The methodological caveats on interpreting these results should be taken very seriously.
This report does not contain an extensive ‘fieldwork’ report. This is included in SEI (2003).
Analogously, we do not discuss extensively the operation of the programme and the evidence that emerged on related issues and on targeting. These issues are covered in IFS-Econometria- SEI (2003b, 2003c). We will be referring to some of the issues raised in those reports, however.
This report is divided into five chapters. In Chapter 1, we briefly summarise the main features of the programme and its proposed evaluation. A more detailed description of both of these aspects is contained in IFS-Econometria-SEI (2003a). Here, however, we give some details on the expansion of the programme and on the features of this expansion that allow a first and preliminary analysis of the impact of the programme. In Chapter 2, we describe the statistical methodology that will be used in the report. This includes the methodology for the data description that constitutes the largest part of the report and for the preliminary impact evaluation. Chapter 3 describes the baseline survey. This chapter is divided into several
sections, each referring to a particular module. In each section, we first describe the ‘treatment’ population – that is, the households eligible for the programme that were living in villages targeted by the programme. We then move on to the population living in ‘control’ villages –
that is, in villages that were not targeted by the programme and yet are, nonetheless, reasonably similar to the treatment villages. Chapter 4 presents the preliminary impact evaluation
Using the BFKL resummation to fit DIS data: collinear and running coupling effects
The proton structure function F2 is studied in the low x regime using BFKL
evolution. The next to leading logarithmic (NLL) analysis requires the
inclusion of running coupling effects which lead to off-diagonal terms in the
evolution kernel. An all-orders resummation is used to improve the collinear
behavior of the NLL BFKL result. We emphasize the theoretical uncertainties
that appear throughout the analysis and give a comparison to the combined HERA
data.Comment: 4 pages, 5 figures, proceedings of the XX Workshop on Deep-Inelastic
Scattering and Related Subjects, 26-30 March, University of Bonn (2012
Interior Structures and Tidal Heating in the TRAPPIST-1 Planets
With seven planets, the TRAPPIST-1 system has the largest number of
exoplanets discovered in a single system so far. The system is of
astrobiological interest, because three of its planets orbit in the habitable
zone of the ultracool M dwarf. Assuming the planets are composed of
non-compressible iron, rock, and HO, we determine possible interior
structures for each planet. To determine how much tidal heat may be dissipated
within each planet, we construct a tidal heat generation model using a single
uniform viscosity and rigidity for each planet based on the planet's
composition. With the exception of TRAPPIST-1c, all seven of the planets have
densities low enough to indicate the presence of significant HO in some
form. Planets b and c experience enough heating from planetary tides to
maintain magma oceans in their rock mantles; planet c may have eruptions of
silicate magma on its surface, which may be detectable with next-generation
instrumentation. Tidal heat fluxes on planets d, e, and f are lower, but are
still twenty times higher than Earth's mean heat flow. Planets d and e are the
most likely to be habitable. Planet d avoids the runaway greenhouse state if
its albedo is 0.3. Determining the planet's masses within
to 0.5 Earth masses would confirm or rule out the presence of HO and/or
iron in each planet, and permit detailed models of heat production and
transport in each planet. Understanding the geodynamics of ice-rich planets f,
g, and h requires more sophisticated modeling that can self-consistently
balance heat production and transport in both rock and ice layers.Comment: 34 pages, 3 tables, 4 figures. Accepted for publication in Astronomy
& Astrophysics -- final version including corrections made in proof stag
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