24,104 research outputs found
CMB Likelihood Functions for Beginners and Experts
Although the broad outlines of the appropriate pipeline for cosmological
likelihood analysis with CMB data has been known for several years, only
recently have we had to contend with the full, large-scale, computationally
challenging problem involving both highly-correlated noise and extremely large
datasets (). In this talk we concentrate on the beginning and end of
this process. First, we discuss estimating the noise covariance from the data
itself in a rigorous and unbiased way; this is essentially an iterated
minimum-variance mapmaking approach. We also discuss the unbiased determination
of cosmological parameters from estimates of the power spectrum or experimental
bandpowers.Comment: Long-delayed submission. In AIP Conference Proceedings "3K Cosmology"
held in Rome, Oct 5-10, 1998, edited by Luciano Maiani, Francesco Melchiorri
and Nicola Vittorio, 343-347, New York, American Institute of Physics 199
Thermal inactivation of Byssochlamys nivea in pineapple nectar combined with preliminary high pressure treatments
Byssochlamys nivea is a thermal resistant filamentous fungi and potential micotoxin producer. Recent studies have verified the presence of ascospores of such microorganism in samples of pineapple nectars. Although the majority of filamentous fungi have limited heat resistance and are easily destroyed by heat, Byssochlamys nivea ascospores have shown high thermal resistance. The aim of this work was to evaluate the application of linear and Weibull models on thermal inactivation (70, 80 and 90ºC) of Byssochlamys nivea ascospores in pineapple nectar after pretreatment with high pressure (550MPa or 650MPa during 15min). Following the treatments, survival curves were built up for each processing temperature and adjusted for both models. It was observed that survival curves at 90°C after high pressure pretreatment at 550 MPa/15 min did not fit well to linear and Weibull models. For all the other treatments, the Weibull model presented a better fit. At 90ºC without pressure treatment, the Weibull model also showed a better adjustment, having a larger R2 and a smaller RMSE. Regarding the process effectiveness, a 5-log reduction (t5), as recommended for pasteurization, was only achieved for Byssochlamys nivea ascospores presented in pineapple nectar at 90ºC/10.7 min with previous high pressure treatment of 650 MPa for 15 min. Considering the high intensity and energy demanding process with possibly product damage, other preventive and alternative treatments are being investigated
Seismic vulnerability of churches in Faial and Pico islands, Azores
Earthquakes represent one of the main cause of serious damage and loss of historic and architectural heritage. Interventions to preserve these building should start with a careful knowledge and assessment of their seismic vulnerability, in order to support any needed retrofitting and strengthening measures.
This paper proposes a procedure to register and diagnose of the level of damage on churches after the occurrence of an earthquake, and also to assess the seismic vulnerability of this type of construction. This procedure was applied to sixteen churches in the Azores islands which were hit by the July 9th 1998 earthquake.
Belfries of church towers are elements with a particular seismic vulnerability. For this reason, and based on the Italian methodology proposed by the Linee Guida (2006), it is applied to belfries of two churches from Pico (Azores), a simplified mechanical model for assessment of seismic vulnerability of this type of structures
Efficient graphene-based photodetector with two cavities
We present an efficient graphene-based photodetector with two Fabri-P\'erot
cavities. It is shown that the absorption can reach almost 100% around a given
frequency, which is determined by the two-cavity lengths. It is also shown that
hysteresis in the absorbance is possible, with the transmittance amplitude of
the mirrors working as an external driving field. The role of non-linear
contributions to the optical susceptibility of graphene is discussed.Comment: 10 pages, 8 figures. published version: minor revisio
Outflows and Jets from Collapsing Magnetized Cloud Cores
Star formation is usually accompanied by outflow phenomena. There is strong
evidence that these outflows and jets are launched from the protostellar disk
by magneto-rotational processes. Here, we report on our three dimensional,
adaptive mesh, magneto-hydrodynamic simulations of collapsing, rotating,
magnetized Bonnor-Ebert-Spheres whose properties are taken directly from
observations. In contrast to the pure hydro case where no outflows are seen,
our present simulations show an outflow from the protodisk surface at ~ AU and
a jet at ~ 0.07 AU after a strong toroidal magnetic field build up. The large
scale outflow, which extends up to ~ AU at the end of our simulation, is driven
by toroidal magnetic pressure (spring), whereas the jet is powered by
magneto-centrifugal force (fling). At the final stage of our simulation these
winds are still confined within two respective shock fronts. Furthermore, we
find that the jet-wind and the disk-anchored magnetic field extracts a
considerable amount of angular momentum from the protostellar disk. The initial
spin of our cloud core was chosen high enough to produce a binary system. We
indeed find a close binary system (separation ~ 3 R_sol) which results from the
fragmentation of an earlier formed ring structure. The magnetic field strength
in these protostars reaches ~ 3 kG and becomes about 3 G at 1 AU from the
center in agreement with recent observational results.Comment: revised version, accepted for publication in ApJ, a higher resolution
version of this paper can be downloaded at
http://www.physics.mcmaster.ca/~banerjee/outflows.pd
Jet Collimation by Small-Scale Magnetic Fields
A popular model for jet collimation is associated with the presence of a
large-scale and predominantly toroidal magnetic field originating from the
central engine (a star, a black hole, or an accretion disk). Besides the
problem of how such a large-scale magnetic field is generated, in this model
the jet suffers from the fatal long-wave mode kink magnetohydrodynamic
instability. In this paper we explore an alternative model: jet collimation by
small-scale magnetic fields. These magnetic fields are assumed to be local,
chaotic, tangled, but are dominated by toroidal components. Just as in the case
of a large-scale toroidal magnetic field, we show that the ``hoop stress'' of
the tangled toroidal magnetic fields exerts an inward force which confines and
collimates the jet. The magnetic ``hoop stress'' is balanced either by the gas
pressure of the jet, or by the centrifugal force if the jet is spinning. Since
the length-scale of the magnetic field is small (< the cross-sectional radius
of the jet << the length of the jet), in this model the jet does not suffer
from the long-wave mode kink instability. Many other problems associated with
the large-scale magnetic field are also eliminated or alleviated for
small-scale magnetic fields. Though it remains an open question how to generate
and maintain the required small-scale magnetic fields in a jet, the scenario of
jet collimation by small-scale magnetic fields is favored by the current study
on disk dynamo which indicates that small-scale magnetic fields are much easier
to generate than large-scale magnetic fields.Comment: 14 pages, no figur
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