12,817 research outputs found
Bayesian Geoadditive Seemingly Unrelated Regression
Parametric seemingly unrelated regression (SUR) models are a common tool for multivariate regression analysis when error variables are reasonably correlated, so that separate univariate analysis may result in inefficient estimates of covariate effects. A weakness of parametric models is that they require strong assumptions on the functional form of possibly nonlinear effects of metrical covariates. In this paper, we develop a Bayesian semiparametric SUR model, where the usual linear predictors are replaced by more flexible additive predictors allowing for simultaneous nonparametric estimation of such covariate effects and of spatial effects. The approach is based on appropriate smoothness priors which allow different forms and degrees of smoothness in a general framework. Inference is fully Bayesian and uses recent Markov chain Monte Carlo techniques
Intrinsically Legal-For-Trade Objects by Digital Signatures
The established techniques for legal-for-trade registration of weight values
meet the legal requirements, but in praxis they show serious disadvantages. We
report on the first implementation of intrinsically legal-for-trade objects,
namely weight values signed by the scale, that is accepted by the approval
authority. The strict requirements from both the approval- and the
verification-authority as well as the limitations due to the hardware of the
scale were a special challenge. The presented solution fulfills all legal
requirements and eliminates the existing practical disadvantages.Comment: 4 pages, 0 figure
Twisting type-N vacuum fields with a group
We derive the equations corresponding to twisting type-N vacuum gravitational
fields with one Killing vector and one homothetic Killing vector by using the
same approach as that developed by one of us in order to treat the case with
two non-commuting Killing vectors. We study the case when the homothetic
parameter takes the value -1, which is shown to admit a reduction to a
third-order real ordinary differential equation for this problem, similar to
that previously obtained by one of us when two Killing vectors are present.Comment: LaTeX, 11 pages. To be published in Classical and Quantum Gravit
3D Model Atmospheres for Extremely Low-Mass White Dwarfs
We present an extended grid of mean three-dimensional (3D) spectra for
low-mass, pure-hydrogen atmosphere DA white dwarfs (WDs). We use CO5BOLD
radiation-hydrodynamics 3D simulations covering Teff = 6000-11,500 K and logg =
5-6.5 (cgs units) to derive analytical functions to convert spectroscopically
determined 1D temperatures and surface gravities to 3D atmospheric parameters.
Along with the previously published 3D models, the 1D to 3D corrections are now
available for essentially all known convective DA WDs (i.e., logg = 5-9). For
low-mass WDs, the correction in temperature is relatively small (a few per cent
at the most), but the surface gravities measured from the 3D models are lower
by as much as 0.35 dex. We revisit the spectroscopic analysis of the extremely
low-mass (ELM) WDs, and demonstrate that the 3D models largely resolve the
discrepancies seen in the radius and mass measurements for relatively cool ELM
WDs in eclipsing double WD and WD + milli-second pulsar binary systems. We also
use the 3D corrections to revise the boundaries of the ZZ Ceti instability
strip, including the recently found ELM pulsators.Comment: 11 pages, 8 figures, accepted for publication in the Astrophysical
Journa
Die Wirkung von Düngerart und Düngermenge auf die Partitionierung von Kohlenstoff und Stickstoff in Pools mit unterschiedlichem Umsatz
Type and rate of fertilizer influence the level of organic carbon and total nitrogen in the
soil markedly, but the effect on different pools is open to question. Soil samples were
taken from a sandy Cambisol at Darmstadt, Germany, after 27 years of different
fertilization treatments. The six treatments were: straw incorporation plus application
of mineral fertilizer (MSI) and application of farmyard manure (FYM) each at high (140
– 150 kg N ha-1 year-1), medium (100 kg N ha-1 year-1) and low (50 – 60 kg N ha-1
year-1) rates. After 266 days of incubation (10°C, 50% water-filled pore space)
mineralization of C (1130 – 1820 kg ha-1) and N (90 – 125 kg ha-1) depended on the
rate and not on the type of fertilizer. Very labile and labile pools were obtained by
fitting a two-pool model on the mineralization data. The very labile pool (turnover: 17
days, C/N ratio: 23) was unaffected by treatments. Storage of C (1.8 – 3.2 t ha-1) in the
labile pool (turnover 462 days, C/N ratio: 22) increased significantly with the rate of
fertilizer. The size of the intermediate pool was significantly higher in FYM (15 -18 t
ha-1) than in MSI treatments (12- 14 t ha-1). A passive pool, obtained by oxidation with
Na2S2O8, was independent of treatments. Our study shows that labile and
intermediate pools were affected differently by fertilization
Frame formalism for the N-dimensional quantum Euclidean spaces
We sketch our recent application of a non-commutative version of the Cartan
`moving-frame' formalism to the quantum Euclidean space , the space
which is covariant under the action of the quantum group . For each of
the two covariant differential calculi over based on the -matrix
formalism, we summarize our construction of a frame, the dual inner
derivations, a metric and two torsion-free almost metric compatible covariant
derivatives with a vanishing curvature. To obtain these results we have
developed a technique which fully exploits the quantum group covariance of
. We first find a frame in the larger algebra \Omega^*(R^N_q) \cocross
\uqs. Then we define homomorphisms from R^N_q \cocross U_q^{\pm}{so(N)} to
which we use to project this frame in .Comment: Latex file, 11 pages. Talks given at the Euroconference
``Non-commutative Geometry and Hopf Algebras in Field Theory and Particle
Physics'', Villa Gualino (Torino), Sept. 199
On a generalization of Jacobi's elliptic functions and the Double Sine-Gordon kink chain
A generalization of Jacobi's elliptic functions is introduced as inversions
of hyperelliptic integrals. We discuss the special properties of these
functions, present addition theorems and give a list of indefinite integrals.
As a physical application we show that periodic kink solutions (kink chains) of
the double sine-Gordon model can be described in a canonical form in terms of
generalized Jacobi functions.Comment: 18 pages, 9 figures, 3 table
Interpreting a conformally flat pure radiation space-time
A physical interpretation is presented of the general class of conformally
flat pure radiation metrics that has recently been identified by Edgar and
Ludwig. It is shown that, at least in the weak field limit, successive wave
surfaces can be represented as null (half) hyperplanes rolled around a
two-dimensional null cone. In the impulsive limit, the solution reduces to a
pp-wave whose direction of propagation depends on retarded time. In the general
case, there is a coordinate singularity which corresponds to an envelope of the
wave surfaces. The global structure is discussed and a possible vacuum
extension through the envelope is proposed.Comment: 9 pages, Plain TeX, 2 figures. To appear in Class. Quantum Grav.
Reference adde
- …