1,015 research outputs found
Automorphic forms and rational homology 3–spheres
We investigate a question of Cooper adjacent to the Virtual Haken Conjecture. Assuming certain conjectures in number theory, we show that there exist hyperbolic rational homology 3–spheres with arbitrarily large injectivity radius. These examples come from a tower of abelian covers of an explicit arithmetic 3–manifold. The conjectures
we must assume are the Generalized Riemann Hypothesis and a mild strengthening of results of Taylor et al on part of the Langlands Program for GL2 of an imaginary quadratic field.
The proof of this theorem involves ruling out the existence of an irreducible two dimensional Galois representation rho of Gal(Qbar/Qsqrt-2) satisfying certain prescribed ramification conditions. In contrast to similar questions of this form, rho is allowed to have arbitrary ramification at some prime pi of Z[sqrt -2].
In the next paper in this volume, Boston and Ellenberg apply pro–p techniques to our examples and show that our result is true unconditionally. Here, we give additional examples where their techniques apply, including some non-arithmetic examples.
Finally, we investigate the congruence covers of twist-knot orbifolds. Our experimental evidence suggests that these topologically similar orbifolds have rather different behavior depending on whether or not they are arithmetic. In particular, the congruence covers of the non-arithmetic orbifolds have a paucity of homology
Une étude de cas : examen de l’effet de la pluie sur neige à l’aide des micro-ondes passives
Abstract: The environmental and anthropocentric forcings have a significant impact on climate change and the rate at which it is happening. Even if the rain on snow (ROS) events are known to be an important part of the previously mentioned forcings, they are not taken into consideration in global climate models given the absence of a yet reliable empiric method for detecting their occurrence. Previous research has shown that the 19 GHz and 37 GHz passive microwave frequencies are highly sensitive to presence of liquid water within the snow column. By examining the normalized gradient (GR) of the polarized components, horizontal (H) and vertical (V), of the previously mentioned frequencies, we have created a ROS detection approach using the gradient ratios between GRV and GRH gradients. The validation of the approach using AMSR-E data over known ROS events (in-situ observed meteorological data) demonstrates the promising potential of the index and suggests that further research into this subject might allow us to create a reliable and operational remote sensing ROS detection method.L’Arctique est une des régions de notre planète les plus sensibles au réchauffement climatique. Les effets de pluie sur neige ne sont pas pris en considération dans les modèles climatiques globaux ainsi augmentant leurs incertitudes. La présence de l’eau dans une colonne de neige a un impact direct sur l’albédo ainsi que sur les propriétés diélectriques de la neige. Même si ces effets ont un impact direct sur les propriétés de la neige, ce qui contribue d’une manière positive au réchauffement climatique, il n’existe pas une méthode empirique de détection de ce phénomène. Des recherches précédentes sur ce sujet on démontrée que les fréquences de 19 et 37 GHz dans les micro-ondes passives sont d’une grande sensibilité a la présence de l’eau dans la neige. Cet essai propose, analyse et réalise un test validation d’une méthode qui met en relation les polarisations verticales et horizontales des fréquences mentionnées précédemment [...] pour les fins de détection de phénomène de pluie sur neige. La présence de l’eau dans une colonne de neige va augmenter la température de brillance dans le 19V, 37H et 37H, mais pas pour le 19H. La température de brillance de ce dernier va diminuer. En créant un ratio de gradient entre les deux polarisations [...] le phénomène de pluie sur neige va provoquer des valeurs négatives de ce dernier, tandis que les valeurs positives indiqueront des circonstances météorologiques normales ou de fonte (non liée à la pluie sur neige). La validation de cette méthode, en utilisant des données d’AMSR-E et des observations météorologique humaines de l’Environnement Canada, indique des résultats prometteurs avec des faibles valeurs d’omission, de commission, et d’inexactitude. Une étude plus poussée permettra de réduire l’inexactitude de l’index proposé et nous permettra d’obtenir une méthode empirique viable pour détecter le phénomène de pluie sur neige. [Symboles non conformes
Governance of territorial and urban policies
ESPON project 2.3.2Governance of Territorial and Urban Policies from EU to Local Level holds an important position in the definition and elaboration of a common ground for investigating the institutional, instrumental ans procedural aspects of territorial and urban policies in Europe. The project focuses on the question how effective different systems are, e.g. considering a policy mix of spatial planning (in different forms implemented by Member States), local government powers and taxation policy in defining common spatial development strategies and objectives such as a polycentric urban system, balancing urban-rural needs, reviving derelict urban areas, urban regeneration, sustainable management of the natural and cultural assets. In that perspective, an analysis based on a comparative review of the instruments used, and stakeholders involved in various policy areas and processes, is being undertaken to draw some valuable conclusions of practical relevance on governance. The report sums up the main overall findings of the ESPON 2.3.2 project and presents in more detail the contributions delivered by IRPUD. The structure of this report is as follows. Part 1 summarizes the project in terms of research aims, hypotheses and key findings. The following parts present research work done by IRPUD. It starts with a German National Overview on the application of governance practices (part 2) and two case studies for urban and territorial governance (part 3). The second half of the report presents on a quantitative analysis of several indicators. Part 4 on data and indicators discusses data quality and develops the quantitative approach for measuring governance. In part 5 the report draws a synthesis of governance trends identified in the national case studies
Singularities of moduli spaces of sheaves on K3 surfaces and Nakajima quiver varieties
The aim of this paper is to study the singularities of certain moduli spaces
of sheaves on K3 surfaces by means of Nakajima quiver varieties. The
singularities in question arise from the choice of a non--generic polarization,
with respect to which we consider stability, and admit natural symplectic
resolutions corresponding to choices of general polarizations. For sheaves that
are pure of dimension one, we show that these moduli spaces are, locally around
a singular point, isomorphic to a quiver variety and that, via this
isomorphism, the natural symplectic resolutions correspond to variations of GIT
quotients of the quiver variety.Comment: 40 pages; final version; As pointed out to us by Z. Zhang, we prove
quadraticity and not formality of the Kuranishi family. Quadraticity is all
we need for our main theorem. The current version reflects this correction. A
few other improvements in exposition and correction of typo
GMRT Radio Halo Survey in galaxy clusters at z = 0.2 -- 0.4. II.The eBCS clusters and analysis of the complete sample
We present the results of the GMRT cluster radio halo survey. The main
purposes of our observational project are to measure which fraction of massive
galaxy clusters in the redshift range z=0.2--0.4 hosts a radio halo, and to
constrain the expectations of the particle re--acceleration model for the
origin of the non--thermal radio emission. We selected a complete sample of 50
clusters in the X-ray band from the REFLEX (27) and the eBCS (23) catalogues.
In this paper we present Giant Metrewave Radio Telescope (GMRT) observations at
610 MHz for all clusters still lacking high sensitivity radio information, i.e.
16 eBCS and 7 REFLEX clusters, thus completing the radio information for the
whole sample. The typical sensitivity in our images is in the range 1Jy b. We found a radio halo in A697, a diffuse
peripheral source of unclear nature in A781, a core--halo source in Z7160, a
candidate radio halo in A1682 and ``suspect'' central emission in Z2661.
Including the literature information, a total of 10 clusters in the sample host
a radio halo. A very important result of our work is that 25 out of the 34
clusters observed with the GMRT do not host extended central emission at the
sensitivity level of our observations, and for 20 of them firm upper limits to
the radio power of a giant radio halo were derived. The GMRT Radio Halo Survey
shows that radio halos are not common, and our findings on the fraction of
giant radio halos in massive clusters are consistent with the statistical
expectations based on the re--acceleration model. Our results favour primary to
secondary electron models.Comment: A&A in press, 17 pages, 12 figures, 4 tables Version with high
quality figures available on web at
http://www.ira.inaf.it/~tventuri/pap/Venturi_web.pd
Standard Errors: How Budget Rules Distort Lawmaking
The article argues that the Congress’s budget process has invisibly influenced its legislative activities and structurally skewed its policy choices. The budgetary structure and tools as they affect lawmaking are largely unanalyzed. Until they are widely appreciated, they may often be random, inefficient, unrepresentative, and even deceptive. Review, critique, and change are overdue in any case. Inasmuch as the Congress is now, after a period of budget anarchy, debating how to refocus on the budget, this is a particularly good time for such activities.
The article also argues that additional structures are needed to “counter-balance” both the skewing that results from the current rules and the sheer centrality of the budget in policymaking. In a fundamental way, Congress should review its simplistic focus on the restraint of monetary deficits alone. In the long run, future generations may be equally or better served by the creation of budget-like restraints on non-monetary deficits, such as increased disability, diminished public health, or permanent environmental damage. The structures that have shaped financial decisions in the past may offer solutions to these problems in the future.
The article is laid out in four parts. Part One provides a brief historical background of the Congressional budget process, including its roots in Public Choice Theory. Part Two consists of an explanation of four non-obvious concepts essential to understanding the basics of the budget process. Part Three is a series of observations of some serious effects of the process in lawmaking. Part Four lays out suggestions for “counter-balancing” the budget process, including extension some of the Public-Choice remedies to non-monetary measures
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