617 research outputs found
Extracellular DNA provides structural integrity to a Micrococcus luteus biofilm
Force spectroscopy was used to show that extracellular DNA (eDNA) has a pre-eminent structural role in a biofilm. The adhesive behavior of extracellular polymeric substances to poly(ethylene terephthalate), a model hydrophobic surface, was measured in response to their degradation by hydrolytic enzymes known for their biofilm dispersion potential: DNaseI, protease, cellulase, and mannanase. Only treatment with DNaseI significantly decreased the adhesive force of the model bacterium Micrococcus luteus with the surface, and furthermore this treatment almost completely eliminated any components of the biofilm maintaining the adhesion, establishing a key structural role for eDNA
Matone's Relation in the Presence of Gravitational Couplings
The prepotential in N=2 SUSY Yang-Mills theories enjoys remarkable
properties. One of the most interesting is its relation to the coordinate on
the quantum moduli space that results into recursion
equations for the coefficients of the prepotential due to instantons. In this
work we show, with an explicit multi-instanton computation, that this relation
holds true at arbitrary winding numbers. Even more interestingly we show that
its validity extends to the case in which gravitational corrections are taken
into account if the correlators are suitably modified. These results apply also
to the cases in which matter in the fundamental and in the adjoint is included.
We also check that the expressions we find satisfy the chiral ring relations
for the gauge case and compute the first gravitational correction.Comment: 21 page
N=1 Superpotentials from Multi-Instanton Calculus
In this paper we compute gaugino and scalar condensates in N=1 supersymmetric
gauge theories with and without massive adjoint matter, using localization
formulae over the multi--instanton moduli space. Furthermore we compute the
chiral ring relations among the correlators of the theory and check
this result against the multi-instanton computation finding agreement.Comment: 31 pages, uses youngtab.sty, some explanations added, version to
appear in JHE
Instanton on toric singularities and black hole countings
We compute the instanton partition function for U(N) gauge
theories living on toric varieties, mainly of type
including or O_{\PP_1}(-p) surfaces. The results provide
microscopic formulas for the partition functions of black holes made out of
D4-D2-D0 bound states wrapping four-dimensional toric varieties inside a
Calabi-Yau. The partition function gets contributions from regular and
fractional instantons. Regular instantons are described in terms of symmetric
products of the four-dimensional variety. Fractional instantons are built out
of elementary self-dual connections with no moduli carrying non-trivial fluxes
along the exceptional cycles of the variety. The fractional instanton
contribution agrees with recent results based on 2d SYM analysis. The partition
function, in the large charge limit, reproduces the supergravity macroscopic
formulae for the D4-D2-D0 black hole entropy.Comment: 29 pages, 3 fig Section 5 is improved by the inclusion of a detailed
comparison between the instanton partition function and the D4-D2-D0 black
hole entropy formula coming from supergravit
Decline of genetic diversity in ancient domestic stallions in Europe.
Present-day domestic horses are immensely diverse in their maternally inherited mitochondrial DNA, yet they show very little variation on their paternally inherited Y chromosome. Although it has recently been shown that Y chromosomal diversity in domestic horses was higher at least until the Iron Age, when and why this diversity disappeared remain controversial questions. We genotyped 16 recently discovered Y chromosomal single-nucleotide polymorphisms in 96 ancient Eurasian stallions spanning the early domestication stages (Copper and Bronze Age) to the Middle Ages. Using this Y chromosomal time series, which covers nearly the entire history of horse domestication, we reveal how Y chromosomal diversity changed over time. Our results also show that the lack of multiple stallion lineages in the extant domestic population is caused by neither a founder effect nor random demographic effects but instead is the result of artificial selection-initially during the Iron Age by nomadic people from the Eurasian steppes and later during the Roman period. Moreover, the modern domestic haplotype probably derived from another, already advantageous, haplotype, most likely after the beginning of the domestication. In line with recent findings indicating that the Przewalski and domestic horse lineages remained connected by gene flow after they diverged about 45,000 years ago, we present evidence for Y chromosomal introgression of Przewalski horses into the gene pool of European domestic horses at least until medieval times
D-brane Instantons on the T^6/Z_3 orientifold
We give a detailed microscopic derivation of gauge and stringy instanton
generated superpotentials for gauge theories living on D3-branes at
Z_3-orientifold singularities. Gauge instantons are generated by D(-1)-branes
and lead to Affleck, Dine and Seiberg (ADS) like superpotentials in the
effective N=1 gauge theories with three generations of bifundamental and
anti/symmetric matter. Stringy instanton effects are generated by Euclidean
ED3-branes wrapping four-cycles on T^6/\Z_3. They give rise to Majorana masses
in one case and non-renormalizable superpotentials for the other cases. Finally
we determine the conditions under which ADS like superpotentials are generated
in N=1 gauge theories with adjoints, fundamentals, symmetric and antisymmetric
chiral matter.Comment: 31 pages, no figure
The long-lived Type IIn SN 2015da: Infrared echoes and strong interaction within an extended massive shell star star star
In this paper we report the results of the first similar to four years of spectroscopic and photometric monitoring of the Type IIn supernova SN 2015da (also known as PSN J13522411+3941286, or iPTF16tu). The supernova exploded in the nearby spiral galaxy NGC 5337 in a relatively highly extinguished environment. The transient showed prominent narrow Balmer lines in emission at all times and a slow rise to maximum in all bands. In addition, early observations performed by amateur astronomers give a very well-constrained explosion epoch. The observables are consistent with continuous interaction between the supernova ejecta and a dense and extended H-rich circumstellar medium. The presence of such an extended and dense medium is difficult to reconcile with standard stellar evolution models, since the metallicity at the position of SN 2015da seems to be slightly subsolar. Interaction is likely the mechanism powering the light curve, as confirmed by the analysis of the pseudo bolometric light curve, which gives a total radiated energy greater than or similar to 10(51) erg. Modeling the light curve in the context of a supernova shock breakout through a dense circumstellar medium allowed us to infer the mass of the prexisting gas to be similar or equal to 8 M-circle dot, with an extreme mass-loss rate for the progenitor star similar or equal to 0.6 M-circle dot yr(-1), suggesting that most of the circumstellar gas was produced during multiple eruptive events. Near- and mid-infrared observations reveal a fluxexcess in these domains, similar to those observed in SN 2010jl and other interacting transients, likely due to preexisting radiatively heated dust surrounding the supernova. By modeling the infrared excess, we infer a mass greater than or similar to 0.4 x 10(-3) M-circle dot for the dustSpanish MICINN gran
Manipulating the Tomonaga-Luttinger exponent by electric field modulation
We establish a theoretical framework for artificial control of the power-law
singularities in Tomonaga-Luttinger liquid states. The exponent governing the
power-law behaviors is found to increase significantly with an increase in the
amplitude of the periodic electric field modulation applied externally to the
system. This field-induced shift in the exponent indicates the tunability of
the transport properties of quasi-one-dimensional electron systems.Comment: 7 pages, 3 figure
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