2,104 research outputs found
Arithmetic harmonic analysis for smooth quartic Weyl sums: three additive equations
We establish the non-singular Hasse principle for systems of three diagonal
quartic equations in 32 or more variables, subject to a certain rank condition.
Our methods employ the arithmetic harmonic analysis of smooth quartic Weyl sums
and also a new estimate for their tenth moment.Comment: 22 page
Correlation estimates for sums of three cubes
We establish estimates for linear correlation sums involving sums of three
positive integral cubes. Under appropriate conditions, the underlying methods
permit us to establish the solubility of systems of homogeneous linear
equations in sums of three positive cubes whenever these systems have more than
twice as many variables as equations.Comment: arXiv admin note: substantial text overlap with arXiv:1304.5165 25pp;
Revisions to sections 2 and 3 to address referee comment
Resolving the fine-scale structure in turbulent Rayleigh-Benard convection
We present high-resolution direct numerical simulation studies of turbulent
Rayleigh-Benard convection in a closed cylindrical cell with an aspect ratio of
one. The focus of our analysis is on the finest scales of convective
turbulence, in particular the statistics of the kinetic energy and thermal
dissipation rates in the bulk and the whole cell. The fluctuations of the
energy dissipation field can directly be translated into a fluctuating local
dissipation scale which is found to develop ever finer fluctuations with
increasing Rayleigh number. The range of these scales as well as the
probability of high-amplitude dissipation events decreases with increasing
Prandtl number. In addition, we examine the joint statistics of the two
dissipation fields and the consequences of high-amplitude events. We also have
investigated the convergence properties of our spectral element method and have
found that both dissipation fields are very sensitive to insufficient
resolution. We demonstrate that global transport properties, such as the
Nusselt number, and the energy balances are partly insensitive to insufficient
resolution and yield correct results even when the dissipation fields are
under-resolved. Our present numerical framework is also compared with
high-resolution simulations which use a finite difference method. For most of
the compared quantities the agreement is found to be satisfactory.Comment: 33 pages, 24 figure
Radiative Corrections to Multi-Level Mollow-Type Spectra
This paper is concerned with two rather basic phenomena: the incoherent
fluorescence spectrum of an atom driven by an intense laser field and the
coupling of the atom to the (empty) modes of the radiation field. The sum of
the many-photon processes gives rise to the inelastic part of the atomic
fluorescence, which, for a two-level system, has a well-known characteristic
three-peak structure known as the Mollow spectrum. From a theoretical point of
view, the Mollow spectrum finds a natural interpretation in terms of
transitions among laser-dressed states which are the energy eigenstates of a
second-quantized two-level system strongly coupled to a driving laser field. As
recently shown, the quasi-energies of the laser-dressed states receive
radiative corrections which are nontrivially different from the results which
one would expect from an investigation of the coupling of the bare states to
the vacuum modes. In this article, we briefly review the basic elements
required for the analysis of the dynamic radiative corrections, and we
generalize the treatment of the radiative corrections to the incoherent part of
the steady-state fluorescence to a three-level system consisting of 1S, 3P and
2S states.Comment: Dedicated to Prof. H. Walther on the occasion of his 70th birthda
Clustering of Galaxies in a Hierarchical Universe: III. Mock Redshift Surveys
This is the third paper in a series which combines N-body simulations and
semi-analytic modelling to provide a fully spatially resolved simulation of the
galaxy formation and clustering processes. Here we extract mock redshift
surveys from our simulations: a Cold Dark Matter model with either Omega_0=1
(tauCDM) or Omega_0=0.3 and Lambda=0.7 (LambdaCDM). We compare the mock
catalogues with the northern region (CfA2N) of the Center for Astrophysics
(CfA) Redshift Surveys. We study the properties of galaxy groups and clusters
identified using standard observational techniques and we study the relation of
these groups to real virialised systems. Most features of CfA2N groups are
reproduced quite well by both models with no obvious dependence on Omega_0.
Redshift space correlations and pairwise velocities are also similar in the two
cosmologies. The luminosity functions predicted by our galaxy formation models
depend sensitively on the treatment of star formation and feedback. For the
particular choices of Paper I they agree poorly with the CfA survey. To isolate
the effect of this discrepancy on our mock redshift surveys, we modify galaxy
luminosities in our simulations to reproduce the CfA luminosity function
exactly. This adjustment improves agreement with the observed abundance of
groups, which depends primarily on the galaxy luminosity density, but other
statistics, connected more closely with the underlying mass distribution,
remain unaffected. Regardless of the luminosity function adopted, modest
differences with observation remain. These can be attributed to the presence of
the ``Great Wall'' in the CfA2N. It is unclear whether the greater coherence of
the real structure is a result of cosmic variance, given the relatively small
region studied, or reflects a physical deficiency of the models.Comment: 47 pages, LaTex, 17 figures, MNRAS, in press; one figure adde
Harmonising and formalising research administration profiles CASRAI / CERIF
CASRAI and CERIF are international standardisation initiatives in the domain of Research Information Management. CASRAI develops and maintains a standard extensible vocabulary and exchangeable data profiles that reflect the business requirements of involved stakeholders. A data profile specifies the maximal ideal space of its application with compliant data records. CERIF is a data model supplying standard formal syntax and declared semantics to preserve the meaning inherent in identified requirements. It enables the transformation of conceptual descriptions into formal representation thereof and thus their meaningful re-use as well as a semantically compliant and syntactically valid data interchange. With this paper we share the experience, and the lessons learned from the transformation of CASRAI profiles into CERIF XML through the example of an Abridged CV
Renormalization flow of QED
We investigate textbook QED in the framework of the exact renormalization
group. In the strong-coupling region, we study the influence of
fluctuation-induced photonic and fermionic self-interactions on the
nonperturbative running of the gauge coupling. Our findings confirm the
triviality hypothesis of complete charge screening if the ultraviolet cutoff is
sent to infinity. Though the Landau pole does not belong to the physical
coupling domain owing to spontaneous chiral symmetry breaking (chiSB), the
theory predicts a scale of maximal UV extension of the same order as the Landau
pole scale. In addition, we verify that the chiSB phase of the theory which is
characterized by a light fermion and a Goldstone boson also has a trivial
Yukawa coupling.Comment: 4 pages, 1 figur
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