277 research outputs found
Statistical properties of genealogical trees
We analyse the statistical properties of genealogical trees in a neutral
model of a closed population with sexual reproduction and non-overlapping
generations. By reconstructing the genealogy of an individual from the
population evolution, we measure the distribution of ancestors appearing more
than once in a given tree. After a transient time, the probability of
repetition follows, up to a rescaling, a stationary distribution which we
calculate both numerically and analytically. This distribution exhibits a
universal shape with a non-trivial power law which can be understood by an
exact, though simple, renormalization calculation. Some real data on human
genealogy illustrate the problem, which is relevant to the study of the real
degree of diversity in closed interbreeding communities.Comment: Accepted for publication in Phys. Rev. Let
The properties of the three-nucleon system with the dressed-bag model for nn interaction. I: New scalar three-body force
A multi-component formalism is developed to describe three-body systems with
nonstatic pairwise interactions and non-nucleonic degrees of freedom. The
dressed-bag model for interaction based on the formation of an
intermediate six-quark bag dressed by a -field is applied to the
system, where it results in a new three-body force between the six-quark bag
and a third nucleon. Concise variational calculations of bound states are
carried out in the dressed-bag model including the new three-body force. It is
shown that this three-body force gives at least half the total binding
energy, while the weight of non-nucleonic components in the H and He
wavefunctions can exceed 10%. The new force model provides a very good
description of bound states with a reasonable magnitude of the
coupling constant. The model can serve as a natural bridge between dynamical
description of few-nucleon systems and the very successful Walecka approach to
heavy nuclei and nuclear matter.Comment: 26 pages, Latex, 7 figure
Tumor suppression in mice lacking GABARAP, an Atg8/LC3 family member implicated in autophagy, is associated with alterations in cytokine secretion and cell death
GABARAP belongs to an evolutionary highly conserved gene family that has a
fundamental role in autophagy. There is ample evidence for a crosstalk between
autophagy and apoptosis as well as the immune response. However, the molecular
details for these interactions are not fully characterized. Here, we report
that the ablation of murine GABARAP, a member of the Atg8/LC3 family that is
central to autophagosome formation, suppresses the incidence of tumor
formation mediated by the carcinogen DMBA and results in an enhancement of the
immune response through increased secretion of IL-1ÎČ, IL-6, IL-2 and IFN-Îł
from stimulated macrophages and lymphocytes. In contrast, TGF-ÎČ1 was
significantly reduced in the serum of these knockout mice. Further, DMBA
treatment of these GABARAP knockout mice reduced the cellularity of the spleen
and the growth of mammary glands through the induction of apoptosis. Gene
expression profiling of mammary glands revealed significantly elevated levels
of Xaf1, an apoptotic inducer and tumor-suppressor gene, in knockout mice.
Furthermore, DMBA treatment triggered the upregulation of pro-apoptotic (Bid,
Apaf1, Bax), cell death (Tnfrsf10b, Ripk1) and cell cycle inhibitor (Cdkn1a,
Cdkn2c) genes in the mammary glands. Finally, tumor growth of B16 melanoma
cells after subcutaneous inoculation was inhibited in GABARAP-deficient mice.
Together, these data provide strong evidence for the involvement of GABARAP in
tumorigenesis in vivo by delaying cell death and its associated immune-related
response
Moscow-type NN-potentials and three-nucleon bound states
A detailed description of Moscow-type (M-type) potential models for the NN
interaction is given. The microscopic foundation of these models, which appear
as a consequence of the composite quark structure of nucleons, is discussed.
M-type models are shown to arise naturally in a coupled channel approach when
compound or bag-like six-quark states, strongly coupled to the NN channel, are
eliminated from the complete multiquark wave function. The role of the
deep-lying bound states that appear in these models is elucidated. By
introducing additional conditions of orthogonality to these compound six-quark
states, a continuous series of almost on-shell equivalent nonlocal interaction
models, characterized by a strong reduction or full absence of a local
repulsive core (M-type models), is generated. The predictions of these
interaction models for 3N systems are analyzed in detail. It is shown that
M-type models give, under certain conditions, a stronger binding of the 3N
system than the original phase-equivalent model with nodeless wave functions.
An analysis of the 3N system with the new versions of the Moscow NN potential
describing also the higher even partial waves is presented. Large deviations
from conventional NN force models are found for the momentum distribution in
the high momentum region. In particular, the Coulomb displacement energy for
nuclei ^3He - ^3H displays a promising agreement with experiment when the ^3H
binding energy is extrapolated to the experimental value.Comment: 23 pages Latex, 9 figures, to appear in Phys.Rev.
Granular Solid Hydrodynamics
Granular elasticity, an elasticity theory useful for calculating static
stress distribution in granular media, is generalized to the dynamic case by
including the plastic contribution of the strain. A complete hydrodynamic
theory is derived based on the hypothesis that granular medium turns
transiently elastic when deformed. This theory includes both the true and the
granular temperatures, and employs a free energy expression that encapsulates a
full jamming phase diagram, in the space spanned by pressure, shear stress,
density and granular temperature. For the special case of stationary granular
temperatures, the derived hydrodynamic theory reduces to {\em hypoplasticity},
a state-of-the-art engineering model.Comment: 42 pages 3 fi
Why do dogs (Canis familiaris) select the empty container in an observational learning task?
Many argue that dogs show unique susceptibility to human communicative signals that make them suitable for being engaged in complex co-operation with humans. It has also been revealed that socially provided information is particularly effective in influencing the behaviour of dogs even when the humanâs action demonstration conveys inefficient or mistaken solution of task. It is unclear, however, how the communicative nature of the demonstration context and the presence of the human demonstrator affect the dogsâ object-choice behaviour in observational learning situations. In order to unfold the effects of these factors, 76 adult pet dogs could observe a communicative or a non-communicative demonstration in which the human retrieved a tennis ball from under an opaque container while manipulating another distant and obviously empty (transparent) one. Subjects were then allowed to choose either in the presence of the demonstrator or after she left the room. Results showed a significant main effect of the demonstration context (presence or absence of the humanâs communicative signals), and we also found some evidence for the response-modifying effect of the presence of the human demonstrator during the dogsâ choice. That is, dogs predominantly chose the baited container, but if the demonstration context was communicative and the human was present during the dogsâ choice, subjectsâ tendency to select the baited container has been reduced. In agreement with the studies showing sensitivity to humanâs communicative signals in dogs, these findings point to a special form of social influence in observational learning situations when it comes to learning about causally opaque and less efficient (compared to what comes natural to the dog) action demonstrations
Measurement of the J/Psi Production Cross Section in 920 GeV/c Fixed-Target Proton-Nucleus Interactions
The mid-rapidity (dsigma_(pN)/dy at y=0) and total sigma_(pN) production
cross sections of J/Psi mesons are measured in proton-nucleus interactions.
Data collected by the HERA-B experiment in interactions of 920 GeV/c protons
with carbon, titanium and tungsten targets are used for this analysis. The
J/Psi mesons are reconstructed by their decay into lepton pairs. The total
production cross section obtained is sigma_(pN)(J/Psi) = 663 +- 74 +- 46
nb/nucleon. In addition, our result is compared with previous measurements
Search for the Flavor-Changing Neutral Current Decay with the HERA-B Detector
We report on a search for the flavor-changing neutral current decay using events recorded with a dimuon trigger in
interactions of 920 GeV protons with nuclei by the HERA-B experiment. We find
no evidence for such decays and set a 90% confidence level upper limit on the
branching fraction .Comment: 17 pages, 4 figures (of which 1 double), paper to be submitted to
Physics Letters
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