1,089 research outputs found
Age and size at maturity: sex, environmental variability and developmental thresholds
In most organisms, transitions between different life-history stages occur later and at smaller sizes as growth conditions deteriorate. Day and Rowe recently proposed that this pattern could be explained by the existence of developmental thresholds (minimum sizes or levels of condition below which transitions are unable to proceed). The developmental-threshold model predicts that the reaction norm of age and size at maturity will rotate in an anticlockwise manner from positive to a shallow negative slope if: (i) initial body size or condition is reduced; and/or (ii) some individuals encounter poor growth conditions at increasingly early developmental stages. We tested these predictions by rearing replicated populations of soil mites Sancassania berlesei (Michael) under different growth conditions. High-food environments produced a vertical relationship between age and size at maturity. The slope became increasingly shallow as food was reduced. By contrast, high food in the maternal environment reduced the slope of the reaction norm of age and size at maturity, whereas low food increased it. Overall, the reaction norm of age and size at maturity in S. berlesei was significantly nonlinear and differed for males and females. We describe how growth conditions, mother's environment and sex determine age and size at maturity in S. berlesei
Description of Nuclear Structure Effects in Subbarrier Fusion by the Interacting Boson Model
Recent theoretical developments in using the Interacting Boson Model to
describe nuclear structure effects in fusion reactions below the Coulomb
barrier are reviewed. Methods dealing with linear and all orders coupling
between the nuclear excitations and the translational motion are discussed, and
the latter is found to lead to a better description of the barrier distribution
data. A systematic study of the available data (cross sections, barrier and
spin distributions) in rare-earth nuclei is presented.Comment: 9 pages + 2 Figures (in eps form). To be published in the Proceedings
of the FUSION97 Conference, South Durras, Australia, March 1997 (J. Phys. G).
Full text and figures are also available at
http://nucth.physics.wisc.edu/preprints/mad-nt-97-01.abs.htm
Exploring context dependency in ecoâevolutionary patterns with the stick insect Timema cristinae
Rapid evolution can influence the ecology of populations, communities, and ecosystems, but the importance of evolution for ecological dynamics remains unclear, largely because the contexts in which evolution is powerful are poorly resolved. Here, we carry out a large observational study to test hypotheses about context dependency of ecoâevolutionary patterns previously identified on the stick insect Timema cristinae . Experiments and observations conducted in 2011 and 2012 documented predatorâmediated negative effects of camouflage maladaptation (i.e., evolutionary dynamics) on: (a) T. cristinae abundance and, (b) species richness and abundance of other arthropods. Here we show that camouflage maladaptation does not correlate with T. cristinae abundance and, instead, is associated with increased abundance and species richness of cohabitating arthropods. We furthermore find that plants with high levels of Timema maladaptation tend to have higher foliar nitrogen, that is, higher nutritional value, and more positive massâabundance slopes in the coexisting arthropod communities. We propose explanations for the observed contrasting results, such as negative densityâ and frequencyâdependent selection, feedbacks between herbivore abundance and plant nutritional quality, and common effects of predation pressure on selection and prey abundance. Our results demonstrate the utility of observational studies to assess the context dependency of ecoâevolutionary dynamics patterns and provide testable hypotheses for future work
Path integral approach to no-Coriolis approximation in heavy-ion collisions
We use the two time influence functional method of the path integral approach
in order to reduce the dimension of the coupled-channels equations for
heavy-ion reactions based on the no-Coriolis approximation. Our method is
superior to other methods in that it easily enables us to study the cases where
the initial spin of the colliding particle is not zero. It can also be easily
applied to the cases where the internal degrees of freedom are not necessarily
collective coordinates. We also clarify the underlying assumptions in our
approach.Comment: 11 pages, Latex, Phys. Rev. C in pres
Mutant p53 establishes targetable tumor dependency by promoting unscheduled replication
Gain-of-function (GOF) p53 mutations are observed frequently in most intractable human cancers and establish dependency for tumor maintenance and progression. While some of the genes induced by GOF p53 have been implicated in more rapid cell proliferation compared with p53-null cancer cells, the mechanism for dependency of tumor growth on mutant p53 is unknown. This report reveals a therapeutically targetable mechanism for GOF p53 dependency. We have shown that GOF p53 increases DNA replication origin firing, stabilizes replication forks, and promotes micronuclei formation, thus facilitating the proliferation of cells with genomic abnormalities. In contrast, absence or depletion of GOF p53 leads to decreased origin firing and a higher frequency of fork collapse in isogenic cells, explaining their poorer proliferation rate. Following genome-wide analyses utilizing ChIP-Seq and RNA-Seq, GOF p53âinduced origin firing, micronuclei formation, and fork protection were traced to the ability of GOF p53 to transactivate cyclin A and CHK1. Highlighting the therapeutic potential of CHK1âs role in GOF p53 dependency, experiments in cell culture and mouse xenografts demonstrated that inhibition of CHK1 selectively blocked proliferation of cells and tumors expressing GOF p53. Our data suggest the possibility that checkpoint inhibitors could efficiently and selectively target cancers expressing GOF p53 alleles
Probing anharmonic properties of nuclear surface vibration by heavy-ion fusion reactions
Describing fusion reactions between ^{16}O and ^{154}Dy and, between ^{16}O
and ^{144}Sm by the and interacting boson model, we show that
heavy-ion fusion reactions are strongly affected by anharmonic properties of
nuclear surface vibrations and nuclear shape, and thus provide a powerful
method to study details of nuclear structure and dynamics.Comment: 8 pages, 5 figures, To be published in the Proceedings of the FUSION
97 Conference, South Durras, Australia, March 1997 (J. Phys. G
A kilobit hidden SNFS discrete logarithm computation
We perform a special number field sieve discrete logarithm computation in a
1024-bit prime field. To our knowledge, this is the first kilobit-sized
discrete logarithm computation ever reported for prime fields. This computation
took a little over two months of calendar time on an academic cluster using the
open-source CADO-NFS software. Our chosen prime looks random, and
has a 160-bit prime factor, in line with recommended parameters for the Digital
Signature Algorithm. However, our p has been trapdoored in such a way that the
special number field sieve can be used to compute discrete logarithms in
, yet detecting that p has this trapdoor seems out of reach.
Twenty-five years ago, there was considerable controversy around the
possibility of back-doored parameters for DSA. Our computations show that
trapdoored primes are entirely feasible with current computing technology. We
also describe special number field sieve discrete log computations carried out
for multiple weak primes found in use in the wild. As can be expected from a
trapdoor mechanism which we say is hard to detect, our research did not reveal
any trapdoored prime in wide use. The only way for a user to defend against a
hypothetical trapdoor of this kind is to require verifiably random primes
An Improved Quantum Molecular Dynamics Model and its Applications to Fusion Reaction near Barrier
An improved Quantum Molecular Dynamics model is proposed. By using this
model, the properties of ground state of nuclei from Li to Pb can
be described very well with one set of parameters. The fusion reactions for
Ca+Zr, Ca+Zr and Ca+Zr at energy near
barrier are studied by this model. The experimental data of the fusion cross
sections for Ca+Zr at the energy near barrier can be
reproduced remarkably well without introducing any new parameters. The
mechanism for the enhancement of fusion probability for fusion reactions with
neutron-rich projectile or target is analyzed.Comment: 20 pages, 12 figures, 3 table
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