340 research outputs found
Integers represented as a sum of primes and powers of two
It is shown that every sufficiently large even integer is a sum of two primes
and exactly 13 powers of 2. Under the Generalized Rieman Hypothesis one can
replace 13 by 7. Unlike previous work on this problem, the proof avoids
numerical calculations with explicit zero-free regions of Dirichlet
L-functions. The argument uses a new technique to bound the measure of the set
on which the exponential sum formed from powers of 2 is large.Comment: 32 Pages; typos correcte
Large normal subgroup growth and large characteristic subgroup growth
The maximal normal subgroup growth type of a finitely generated group is
. Very little is known about groups with this type of growth. In
particular, the following is a long standing problem: Let be a group
and a subgroup of finite index. Suppose has normal subgroup
growth of type , does has normal subgroup growth of type
? We give a positive answer in some cases, generalizing a result of
M\"uller and the second author and a result of Gerdau. For instance, suppose
is a profinite group and an open subgroup of . We show that if
is a generalized Golod-Shafarevich group, then has normal subgroup growth
of type of . We also use our methods to show that one can find a
group with characteristic subgroup growth of type
The irrationality of a number theoretical series
Denote by the sum of the -th powers of the divisors of ,
and let . We prove that Schinzel's
conjecture H implies that is irrational, and give an unconditional proof
for the case
The subgroup growth spectrum of virtually free groups
For a finitely generated group denote by the growth
coefficient of , that is, the infimum over all real numbers such
that . We show that the growth coefficient of a virtually
free group is always rational, and that every rational number occurs as growth
coefficient of some virtually free group. Moreover, we describe an algorithm to
compute
Involvement of the cohesin cofactor PDS5 (SPO76) during meiosis and DNA repair in Arabidopsis thaliana
Maintenance and precise regulation of sister chromatid cohesion is essential for faithful chromosome segregation during mitosis and meiosis. Cohesin cofactors contribute to cohesin dynamics and interact with cohesin complexes during cellcycle. One of these, PDS5, also known as SPO76, is essential during mitosis and meiosis in several organisms and also plays a role in DANN repair. In yeast, the complex Wapl-Pds5 controls cohesion maintenance and colocalizes with cohesin complexes into chromosomes. In Arabidopsis, AtWAPL proteins are essential during meiosis, however, the role of AtPDS5 remains to be ascertained. Here we have isolated mutants for each of the five AtPDS5 genes(A–E) and obtained, after different crosses between them, double,triple,and even quadruple mutants (Atpds5a Atpds5b Atpds5c Atpds5e). Depletion of AtPDS5 proteins has a weak impact on meiosis, but leads to severe effects on development, fertility, somatic homologous recombination (HR) and DANN repair. Furthermore, this cohesin cofactor could be important for the function of the AtSMC5/AtSMC6 complex. Contrarily to ist function in other species, our results suggest that AtPDS5 is dispensable during the meiotic division of Arabidopsis, although it plays an important role in DANN repair by HR
Irregular behaviour of class numbers and Euler-Kronecker constants of cyclotomic fields: the log log log devil at play
Kummer (1851) and, many years later, Ihara (2005) both posed conjectures on
invariants related to the cyclotomic field with a
prime. Kummer's conjecture concerns the asymptotic behaviour of the first
factor of the class number of and Ihara's the positivity
of the Euler-Kronecker constant of (the ratio of the
constant and the residue of the Laurent series of the Dedekind zeta function
at ). If certain standard conjectures in
analytic number theory hold true, then one can show that both conjectures are
true for a set of primes of natural density 1, but false in general.
Responsible for this are irregularities in the distribution of the primes. With
this survey we hope to convince the reader that the apparently dissimilar
mathematical objects studied by Kummer and Ihara actually display a very
similar behaviour.Comment: 20 pages, 1 figure, survey, to appear in `Irregularities in the
Distribution of Prime Numbers - Research Inspired by Maier's Matrix Method',
Eds. J. Pintz and M. Th. Rassia
One vertex spin-foams with the Dipole Cosmology boundary
We find all the spin-foams contributing in the first order of the vertex
expansion to the transition amplitude of the Bianchi-Rovelli-Vidotto Dipole
Cosmology model. Our algorithm is general and provides spin-foams of
arbitrarily given, fixed: boundary and, respectively, a number of internal
vertices. We use the recently introduced Operator Spin-Network Diagrams
framework.Comment: 23 pages, 30 figure
Engaging Without Exposing: Use of a Fictional Character to Facilitate Mental Health Talk in Focus Groups With Men Who Have Been Subject to the Criminal Justice System.
In an effort to encourage men with experience of being subject to the criminal justice system to contribute to focus group discussions on the sensitive topic of mental health, while also doing our utmost to protect them from discomfort or risk of exploitation, we used a novel technique involving the creation of a fictional character, supplemented by an audio-recorded vignette. We studied the role played by this technique in achieving our stated aims of "engaging without exposing." In this article, we report on the use of this technique in three focus groups, showing how in very different ways it shaped the interaction between participants and generated crucial insights into the lives and service needs of each group. We conclude that the technique may lend itself to being used in focus groups with other marginalized or seldom-heard populations
Feynman diagrammatic approach to spin foams
"The Spin Foams for People Without the 3d/4d Imagination" could be an
alternative title of our work. We derive spin foams from operator spin network
diagrams} we introduce. Our diagrams are the spin network analogy of the
Feynman diagrams. Their framework is compatible with the framework of Loop
Quantum Gravity. For every operator spin network diagram we construct a
corresponding operator spin foam. Admitting all the spin networks of LQG and
all possible diagrams leads to a clearly defined large class of operator spin
foams. In this way our framework provides a proposal for a class of 2-cell
complexes that should be used in the spin foam theories of LQG. Within this
class, our diagrams are just equivalent to the spin foams. The advantage,
however, in the diagram framework is, that it is self contained, all the
amplitudes can be calculated directly from the diagrams without explicit
visualization of the corresponding spin foams. The spin network diagram
operators and amplitudes are consistently defined on their own. Each diagram
encodes all the combinatorial information. We illustrate applications of our
diagrams: we introduce a diagram definition of Rovelli's surface amplitudes as
well as of the canonical transition amplitudes. Importantly, our operator spin
network diagrams are defined in a sufficiently general way to accommodate all
the versions of the EPRL or the FK model, as well as other possible models. The
diagrams are also compatible with the structure of the LQG Hamiltonian
operators, what is an additional advantage. Finally, a scheme for a complete
definition of a spin foam theory by declaring a set of interaction vertices
emerges from the examples presented at the end of the paper.Comment: 36 pages, 23 figure
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