3,051 research outputs found
Drying of Heat Sensitive Materials of High Moisture Content in Mechanically Spouted Bed of Inert Particles
In drying operation the material characteristics such as heat sensitivity, moisture content
and particle size are of great importance, which should be taken into account in selection of proper
design and conditions for the process. Rigorous quality requirements, i.e. gentle drying of heat
sensitive materials, stable, well-controlled and economic operation can be fulfilled by using
Mechanically Spouted Bed (MSB) dryer with inert particles developed to eliminate some
drawbacks of the conventional spouted bed dryers. In this paper the construction and the main
features of MSB-dryer are presented. Different tasks with special quality demands, namely drying
of bovine serum albumin and moisture removal from tomato pulp of thermoplastic behaviour, and a
method to accomplish these requirements are shown
Block partitions: an extended view
Given a sequence , a block of is a
subsequence . The size of a block is the sum
of its elements. It is proved in [1] that for each positive integer , there
is a partition of into blocks with for every . In this paper, we consider a generalization of the problem
in higher dimensions
Statistical mechanical systems on complete graphs, infinite exchangeability, finite extensions and a discrete finite moment problem
We show that a large collection of statistical mechanical systems with
quadratically represented Hamiltonians on the complete graph can be extended to
infinite exchangeable processes. This extends a known result for the
ferromagnetic Curie--Weiss Ising model and includes as well all ferromagnetic
Curie--Weiss Potts and Curie--Weiss Heisenberg models. By de Finetti's theorem,
this is equivalent to showing that these probability measures can be expressed
as averages of product measures. We provide examples showing that
``ferromagnetism'' is not however in itself sufficient and also study in some
detail the Curie--Weiss Ising model with an additional 3-body interaction.
Finally, we study the question of how much the antiferromagnetic Curie--Weiss
Ising model can be extended. In this direction, we obtain sharp asymptotic
results via a solution to a new moment problem. We also obtain a ``formula''
for the extension which is valid in many cases.Comment: Published at http://dx.doi.org/10.1214/009117906000001033 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Sums of products of Ramanujan sums
The Ramanujan sum is defined as the sum of -th powers of the
primitive -th roots of unity. We investigate arithmetic functions of
variables defined as certain sums of the products
, where are polynomials with
integer coefficients. A modified orthogonality relation of the Ramanujan sums
is also derived.Comment: 13 pages, revise
Pulsar wind nebulae in supernova remnants
A spherically symmetric model is presented for the interaction of a pulsar
wind with the associated supernova remnant. This results in a pulsar wind
nebula whose evolution is coupled to the evolution of the surrounding supernova
remnant. This evolution can be divided in three stages. The first stage is
characterised by a supersonic expansion of the pulsar wind nebula into the
freely expanding ejecta of the progenitor star. In the next stage the pulsar
wind nebula is not steady; the pulsar wind nebula oscillates between
contraction and expansion due to interaction with the reverse shock of the
supernova remnant: reverberations which propagate forward and backward in the
remnant. After the reverberations of the reverse shock have almost completely
vanished and the supernova remnant has relaxed to a Sedov solution, the
expansion of the pulsar wind nebula proceeds subsonically. In this paper we
present results from hydrodynamical simulations of a pulsar wind nebula through
all these stages in its evolution. The simulations were carried out with the
Versatile Advection Code.Comment: 10 pages, 9 figures, submitted to Astronomy and Astrophysic
On the decay of Burgers turbulence
This work is devoted to the decay ofrandom solutions of the unforced Burgers
equation in one dimension in the limit of vanishing viscosity. The initial
velocity is homogeneous and Gaussian with a spectrum proportional to at
small wavenumbers and falling off quickly at large wavenumbers. In physical
space, at sufficiently large distances, there is an ``outer region'', where the
velocity correlation function preserves exactly its initial form (a power law)
when is not an even integer. When the spectrum, at long times, has
three scaling regions : first, a region at very small \ms1 with a
time-independent constant, stemming from this outer region, in which the
initial conditions are essentially frozen; second, a region at
intermediate wavenumbers, related to a self-similarly evolving ``inner region''
in physical space and, finally, the usual region, associated to the
shocks. The switching from the to the region occurs around a wave
number , while the switching from to
occurs around (ignoring logarithmic
corrections in both instances). The key element in the derivation of the
results is an extension of the Kida (1979) log-corrected law for the
energy decay when to the case of arbitrary integer or non-integer .
A systematic derivation is given in which both the leading term and estimates
of higher order corrections can be obtained. High-resolution numerical
simulations are presented which support our findings.Comment: In LaTeX with 11 PostScript figures. 56 pages. One figure contributed
by Alain Noullez (Observatoire de Nice, France
Individual foraging, activity level and longevity in the stingless bee Melipona beecheii in Costa Rica (Hymenoptera, Apidae, Meliponinae)
Foraging behaviour of individually marked workers of Melipona beecheii (Meliponinae) was
monitored in Costa Rica to investigate individual specialisation for different materials and how
this influences foraging longevity. The majority of the individuals harvested one commodity
(pollen, nectar or resin) during a single day. Half of the age-marked foragers specialised on nectar
or pollen during their complete foraging career, the other half collected two or three commodities.
Most members of the latter group switched daily from early morning pollen (or resin) collecting to
nectar collecting. Life-long foraging of one-material collectors was not more efficient than that of
two-material collectors. The groups of foragers differed significantly in activity patterns and
longevity: activity was traded off with longevity. Nectar foragers were active all day and died after
an average of 3 foraging days. Pollen foragers were active for 1-3 hours per day, but lived for
12 days on average. However, pollen foragers and nectar foragers performed a similar number of
flights in their career.
How bees become pollen, nectar or mixed foragers is not clear. Age and performance of
pre-foraging hive tasks did not influence forager specialisation in M. beecheii
Effect of particle size on the surface properties and morphology of ground flax
Flax fibers were ground with a ball-mill and four fractions with different size ranges were collected by sieving. These were tested for water sorption, degree of polymerization (DP), copper number, hydroxyl number and analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and inverse gas chromatography (IGC). Significant differences were found between the properties of the flax fiber and those of the ground versions, including fragmentation of fibers, increase of water sorption, copper number, hydroxyl number and surface O/C ratio, and decrease of DP, crystallite size and dispersive component of surface energy (gammasd). Some parameters depended on the particle size: O/C ratio and hydroxyl number had local maxima at 315-630 μm, while gammasd increased steadily with the decrease of particle size. These relationships were explained by fiber disintegration, destruction of waxy surface layer, exposure of cellulosic components, increase of surface area and crystalline imperfections
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