8,278 research outputs found
Is the Theta+ a K pi N bound state?
Following a recent suggestion that the could be a bound
state we perform an investigation under the light of the meson meson and meson
baryon dynamics provided by the chiral Lagrangians and using methods currently
employed to dynamically generate meson and baryon resonances by means of
unitary extensions of chiral perturbation theory. We consider two body and
three body forces and examine the possibility of a bound state below the three
particle pion-kaon-nucleon and above the kaon-nucleon thresholds. Although we
find indeed an attractive interaction in the case of isospin I=0 and
spin-parity , the interaction is too weak to bind the system. If we
arbitrarily add to the physically motivated potential the needed strength to
bind the system and with such strong attraction evaluate the decay width into
, this turns out to be small. A discussion on further work in this
direction is done.Comment: Change of title and few sentences, size of two graphs. References
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A statistical mechanics description of environmental variability in metabolic networks
Many of the chemical reactions that take place within a living cell are irreversible. Due to evolutionary pressures, the number of allowable reactions within these systems are highly constrained and thus the resulting metabolic networks display considerable asymmetry. In this paper, we explore possible evolutionary factors pertaining to the reduced symmetry observed in these networks, and demonstrate the important role environmental variability plays in shaping their structural organization. Interpreting the returnability index as an equilibrium constant for a reaction network in equilibrium with a hypothetical reference system, enables us to quantify the extent to which a metabolic network is in disequilibrium. Further, by introducing a new directed centrality measure via an extension of the subgraph centrality metric to directed networks, we are able to characterise individual metabolites by their participation within metabolic pathways. To demonstrate these ideas, we study 116 metabolic networks of bacteria. In particular, we find that the equilibrium constant for the metabolic networks decreases significantly in-line with variability in bacterial habitats, supporting the view that environmental variability promotes disequilibrium within these biochemical reaction system
Distributional versions of Littlewood's Tauberian theorem
We provide several general versions of Littlewood's Tauberian theorem. These
versions are applicable to Laplace transforms of Schwartz distributions. We
apply these Tauberian results to deduce a number of Tauberian theorems for
power series where Ces\`{a}ro summability follows from Abel summability. We
also use our general results to give a new simple proof of the classical
Littlewood one-sided Tauberian theorem for power series.Comment: 15 page
"Clumpiness" Mixing in Complex Networks
Three measures of clumpiness of complex networks are introduced. The measures
quantify how most central nodes of a network are clumped together. The
assortativity coefficient defined in a previous study measures a similar
characteristic, but accounts only for the clumpiness of the central nodes that
are directly connected to each other. The clumpiness coefficient defined in the
present paper also takes into account the cases where central nodes are
separated by a few links. The definition is based on the node degrees and the
distances between pairs of nodes. The clumpiness coefficient together with the
assortativity coefficient can define four classes of network. Numerical
calculations demonstrate that the classification scheme successfully
categorizes 30 real-world networks into the four classes: clumped assortative,
clumped disassortative, loose assortative and loose disassortative networks.
The clumpiness coefficient also differentiates the Erdos-Renyi model from the
Barabasi-Albert model, which the assortativity coefficient could not
differentiate. In addition, the bounds of the clumpiness coefficient as well as
the relationships between the three measures of clumpiness are discussed.Comment: 47 pages, 11 figure
"Clumpiness" Mixing in Complex Networks
Three measures of clumpiness of complex networks are introduced. The measures
quantify how most central nodes of a network are clumped together. The
assortativity coefficient defined in a previous study measures a similar
characteristic, but accounts only for the clumpiness of the central nodes that
are directly connected to each other. The clumpiness coefficient defined in the
present paper also takes into account the cases where central nodes are
separated by a few links. The definition is based on the node degrees and the
distances between pairs of nodes. The clumpiness coefficient together with the
assortativity coefficient can define four classes of network. Numerical
calculations demonstrate that the classification scheme successfully
categorizes 30 real-world networks into the four classes: clumped assortative,
clumped disassortative, loose assortative and loose disassortative networks.
The clumpiness coefficient also differentiates the Erdos-Renyi model from the
Barabasi-Albert model, which the assortativity coefficient could not
differentiate. In addition, the bounds of the clumpiness coefficient as well as
the relationships between the three measures of clumpiness are discussed.Comment: 47 pages, 11 figure
On the determination of quantum numbers and other topics of exotic baryons
In this talk I look into three different topics, addressing first a method to
determine the quantum numbers of the , then exploiting the
possibility that the is a bound state of and in the third
place I present results on a new resonant exotic baryonic state which appears
as dynamically generated by the Weinberg Tomozawa interaction.Comment: 9 pags. Talk in the NSTAR04 Workshop, Grenoble, march 200
Hadronic aspects of exotic baryons
In this talk I look into three different topics, addressing first the
possibility that the is a bound state of , exploiting the
results of this study to find out the contribution of two meson and one baryon
components in the baryon antidecuplet and in the third place I present results
on a new resonant exotic baryonic state which appears as dynamically generated
by the Weinberg Tomozawa interaction.Comment: Talk at the International Workshop PENTAQUARK0
On the issue of imposing boundary conditions on quantum fields
An interesting example of the deep interrelation between Physics and
Mathematics is obtained when trying to impose mathematical boundary conditions
on physical quantum fields. This procedure has recently been re-examined with
care. Comments on that and previous analysis are here provided, together with
considerations on the results of the purely mathematical zeta-function method,
in an attempt at clarifying the issue. Hadamard regularization is invoked in
order to fill the gap between the infinities appearing in the QFT renormalized
results and the finite values obtained in the literature with other procedures.Comment: 13 pages, no figure
Cluster analysis for validated climatology stations using precipitation in Mexico
Annual average of daily precipitation was used to group climatological stations into clusters using the k-means procedure and principal component analysis with varimax rotation. After a careful selection of the stations deployed in Mexico since 1950, we selected 349 characterized by having 35 to 40 complete years of observations. The clustering of stations was performed three times: firstly according to the amount of precipitation; secondly according to their anomalies from the mean, resulting in their standard deviations grouping; and thirdly using the standardized anomalies, which resulted in a clustering according to the features of the trend and the structural changes of the series over the observing period. We identified two clusters that occupy northwestern and north-central Mexico; another at the center of the territory, between Sierra Madre Oriental and Sierra Madre Occidental; the following over the Sierra Madre Oriental; and a last one in the southeast of the territory, the southern coast of the Pacific Ocean and the Yucatán Peninsula, that overlaps with Sierra Madre Oriental group. Some stations of Yucatán Peninsula show similar characteristics to the northwestern cluster. The groupings were compared with the results of previous studies. The comparison indicates that regions are invariant in time and space and independent of the method of agregation and the stations sampled
Lice and ticks parasitizing Audouin's Gull Larus audouinii Payraudeau, 7826 (Aves, Laridae) in the Chafarinas Islands (W Mediterranean)
Data on lice and ticks parasitizing gulls are scarce. Here
data on 58 adult and 10 young Audouin's gulls from the Chafarinas lslands are provided. Three species of chewing lice Austromenopon transversum (prevalencelmean intensity: 20%-2), Koeniginirmus punctatus (100%-15.5). and Saemundssonia lari (10%-3.2) and one tick Ornithodoros maritimus (100%-18) were found. A. transversum, S. lari, and 0. maritimus are recorded for the first time for L. audouinii
Key words: Chewing lice, Ticks, Larus audouinii.Data on lice and ticks parasitizing gulls are scarce. Here
data on 58 adult and 10 young Audouin's gulls from the Chafarinas lslands are provided. Three species of chewing lice Austromenopon transversum (prevalencelmean intensity: 20%-2), Koeniginirmus punctatus (100%-15.5). and Saemundssonia lari (10%-3.2) and one tick Ornithodoros maritimus (100%-18) were found. A. transversum, S. lari, and 0. maritimus are recorded for the first time for L. audouinii
Key words: Chewing lice, Ticks, Larus audouinii.Data on lice and ticks parasitizing gulls are scarce. Here
data on 58 adult and 10 young Audouin's gulls from the Chafarinas lslands are provided. Three species of chewing lice Austromenopon transversum (prevalencelmean intensity: 20%-2), Koeniginirmus punctatus (100%-15.5). and Saemundssonia lari (10%-3.2) and one tick Ornithodoros maritimus (100%-18) were found. A. transversum, S. lari, and 0. maritimus are recorded for the first time for L. audouinii
Key words: Chewing lice, Ticks, Larus audouinii
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