28,105 research outputs found
Results from the NEMO 3 experiment
The aim of the NEMO 3 experiment is the search for neutrinoless double beta
decay and precise measurement of two-neutrino double beta decay of several
isotopes. The experiment has been taking data since 2003. Since no evidence for
neutrinoless double beta decay of Mo100 and Se82 has been found, a 90% C.L.
lower limit on the half-life of this process and corresponding upper limit on
the effective Majorana neutrino mass are derived. The data are also interpreted
in terms of alternative models, such as weak right-handed currents or Majoron
emission. In addition, NEMO 3 has performed precision measurements of the
two-neutrino double beta decay for seven different isotopes. The most recent
experimental results of NEMO 3 are presented in this paper.Comment: 5 pages, 2 tables, talk at the 10th ICATPP Conference (Como, Italy, 8
- 12 October 2007
Primordial magnetic fields constrained by CMB anisotropies and dynamo cosmology
Magneto-curvature stresses could deform magnetic field lines and this would
give rise to back reaction and restoring magnetic stresses [Tsagas, PRL
(2001)]. Barrow et al [PRD (2008)] have shown in Friedman universe the
expansion to be slow down in spatial section of negative Riemann curvatures.
From Chicone et al [CMP (1997)] paper, proved that fast dynamos in compact 2D
manifold implies negatively constant Riemannian curvature, here one applies the
Barrow-Tsagas ideas to cosmic dynamos. Fast dynamo covariant stretching of
Riemann slices of cosmic Lobachevsky plane is given. Inclusion of advection
term on dynamo equations [Clarkson et al, MNRAS (2005)] is considered. In
absence of advection a fast dynamo is also obtained. Viscous and restoring
forces on stretching particles decrease, as magnetic rates increase. From COBE
data (), one computes stretching
.
Zeldovich et al has computed the maximum magnetic growth rate as
. From COBE data one computes
a lower growth rate for the magnetic field as
, well-within Zeldovich et al
estimate. Instead of the Harrison value one obtains the
lower primordial field which yields the
at the Big Bang time.Comment: Dept of theoretical physics-UERJ-Brasi
Electrostatics in Periodic Slab Geometries I
We propose a new method to sum up electrostatic interactions in 2D slab
geometries. It consists of a combination of two recently proposed methods, the
3D Ewald variant of Yeh and Berkowitz, J. Chem. Phys. 111 (1999) 3155, and the
purely 2D method MMM2D by Arnold and Holm, to appear in Chem. Phys. Lett. 2002.
The basic idea involves two steps. First we use a three dimensional summation
method whose summation order is changed to sum up the interactions in a
slab-wise fashion. Second we subtract the unwanted interactions with the
replicated layers analytically. The resulting method has full control over the
introduced errors. The time to evaluate the layer correction term scales
linearly with the number of charges, so that the full method scales like an
ordinary 3D Ewald method, with an almost linear scaling in a mesh based
implementation. In this paper we will introduce the basic ideas, derive the
layer correction term and numerically verify our analytical results.Comment: 10 pages, 7 figure
Performance assessment of demand controlled ventilation controls concerning indoor VOC exposure based on a dynamic VOC emission model
The performance assessment of ventilation systems often focusses only on CO2 and humidity levels. The indoor Volatile Organic Compounds (VOC) emissions of building materials or other products is thereby overlooked. The new generation of ventilation systems, Demand Controlled Ventilation (DCV), are systems that do not supply the nominal airflow continuously but are controlled by CO2 or humidity sensors in order to save energy. This poses potential problems for exposure to VOCs. In this study, a dynamic VOC model, which takes into account changing temperature and humidity that was derived from literature, is implemented in a CONTAM model of the Belgian reference apartment. The impact of a DCV system on the indoor VOC levels is investigated. Results show that the use of a dynamic model is necessary compared to the previously used approximation of a constant emission. Furthermore, on a system level, the influence of the ventilation system control on the indoor VOC levels shows. The overall VOC concentration in the different rooms will be higher because of lowered ventilation rates. Especially in rooms that are often unoccupied during the day, the accumulation of VOCs shows. In the development of DCV system controls, the aspect of VOC exposure should not be overlooked to be able to benefit from both the energy savings and improved Indoor Air Quality (IAQ)
Electrostatics in Periodic Slab Geometries II
In a previous paper a method was developed to subtract the interactions due
to periodically replicated charges (or other long-range entities) in one
spatial dimension. The method constitutes a generalized "electrostatic layer
correction" (ELC) which adapts any standard 3D summation method to slab-like
conditions. Here the implementation of the layer correction is considered in
detail for the standard Ewald (EW3DLC) and the PPPM mesh Ewald (PPPMLC)
methods. In particular this method offers a strong control on the accuracy and
an improved computational complexity of O(N log N) for mesh-based
implementations. We derive anisotropic Ewald error formulas and give some
fundamental guidelines for optimization. A demonstration of the accuracy, error
formulas and computation times for typical systems is also presented.Comment: 14 pages, 7 figure
Adaptive Harmonic Analysis
In this paper we describe a new approach to the harmonic analysis of the tide. For a number of reasons the harmonic constants are not really constant but vary slowly in time. Therefore, we introduce a narrow-band noise process to model the time-varying behaviour of these harmonic parameters. Furthermore, since the measurements available are not perfect, we also introduce a, possibly time-varying, measurement noise process to model the errors associated with the measurement process. By employing a Kalman filter to estimate the harmonic parameters recursively, the estimates can be adapted contineously to chaning conditions. The adaptive harmonic analysis can be used for the on-line prediction of the astronomical tide or, since the Kalman filter also produces the covariance of the estimation error, to gain quantitative insight into the resolution of tidal constituents
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