20,005 research outputs found
Sanitizing the fortress: protection of ant brood and nest material by worker antibiotics
Social groups are at particular risk for parasite infection, which is heightened in eusocial insects by the low genetic diversity of individuals within a colony. To combat this, adult ants have evolved a suite of defenses to protect each other, including the production of antimicrobial secretions. However, it is the brood in a colony that are most vulnerable to parasites because their individual defenses are limited, and the nest material in which ants live is also likely to be prone to colonization by potential parasites. Here, we investigate in two ant species whether adult workers use their antimicrobial secretions not only to protect each other but also to sanitize the vulnerable brood and nest material. We find that, in both leaf-cutting ants and weaver ants, the survival of the brood was reduced and the sporulation of parasitic fungi from them increased, when the workers nursing them lacked functional antimicrobial-producing glands. This was the case for both larvae that were experimentally treated with a fungal parasite (Metarhizium) and control larvae which developed infections of an opportunistic fungal parasite (Aspergillus). Similarly, fungi were more likely to grow on the nest material of both ant species if the glands of attending workers were blocked. The results show that the defense of brood and sanitization of nest material are important functions of the antimicrobial secretions of adult ants and that ubiquitous, opportunistic fungi may be a more important driver of the evolution of these defenses than rarer, specialist parasites
Spermatocytic Seminoma: Clinical Case and Review
Introdução: O seminoma espermatocítico é um
diagnóstico incomum de tumores do testículo, frequentemente exuberantes na sua dimensão, mas com bom prognóstico. Apesar da designação errónea, trata-se de tumores de células germinativas do tipo não-seminoma.
Caso Clínico: Descreve-se o caso clínico de um homem de 49 anos de idade, com exuberante
aumento de volume escrotal de agravamento
recente, à custa de massa indolor do testículo direito.
Foi feita ecografia escrotal que mostrou hidrocelo e imagem sugestiva de massa atípica do epidídimo direito. TC torácica, abdominal e pélvica não mostrou adenomegalias retroperitoneais ou outra
alteração; os valores de LDH, αFP e βHCG eram
normais. Foi feita orquidectomia por via escrotal à direita, com excisão de uma ampla área do escroto.
Identificou-se na peça operatória, com 1375g,
seminoma espermatocítico com invasão vascular
da túnica albugínea (pT2). O doente iniciou quimioterapia com BEP (dois ciclos).
Discussão: O seminoma espermatocítico é raro,
com cerca de 2% de incidência, o diagnóstico
faz-se habitualmente na 6ª década de vida, e tem localização exclusivamente testicular. A orquidectomia é frequentemente curativa. Apesar de estarem descritos tumores de maior volume do que o seminoma clássico, destaca-se neste caso a exuberância clínica incomum pela dimensão do testículo, bem como do hidrocelo que o acompanhava
Renormalisation scheme for vector fields on T2 with a diophantine frequency
We construct a rigorous renormalisation scheme for analytic vector fields on
the 2-torus of Poincare type. We show that iterating this procedure there is
convergence to a limit set with a ``Gauss map'' dynamics on it, related to the
continued fraction expansion of the slope of the frequencies. This is valid for
diophantine frequency vectors.Comment: final versio
Vanishing Viscosity Limits and Boundary Layers for Circularly Symmetric 2D Flows
We continue the work of Lopes Filho, Mazzucato and Nussenzveig Lopes [LMN],
on the vanishing viscosity limit of circularly symmetric viscous flow in a disk
with rotating boundary, shown there to converge to the inviscid limit in
-norm as long as the prescribed angular velocity of the
boundary has bounded total variation. Here we establish convergence in stronger
and -Sobolev spaces, allow for more singular angular velocities
, and address the issue of analyzing the behavior of the boundary
layer. This includes an analysis of concentration of vorticity in the vanishing
viscosity limit. We also consider such flows on an annulus, whose two boundary
components rotate independently.
[LMN] Lopes Filho, M. C., Mazzucato, A. L. and Nussenzveig Lopes, H. J.,
Vanishing viscosity limit for incompressible flow inside a rotating circle,
preprint 2006
Modeling disorder in graphene
We present a study of different models of local disorder in graphene. Our
focus is on the main effects that vacancies -- random, compensated and
uncompensated --, local impurities and substitutional impurities bring into the
electronic structure of graphene. By exploring these types of disorder and
their connections, we show that they introduce dramatic changes in the low
energy spectrum of graphene, viz. localized zero modes, strong resonances, gap
and pseudogap behavior, and non-dispersive midgap zero modes.Comment: 16 pages, lower resolution figure
Nambu monopoles interacting with lattice defects in two-dimensional artificial square spin ice
The interactions between an excitation (similar to a pair of Nambu monopoles)
and a lattice defect are studied in an artificial two-dimensional square spin
ice. This is done by considering a square array of islands containing only one
island different from all others. This difference is incorporated in the
magnetic moment (spin) of the "imperfect" island and several cases are studied,
including the special situation in which this distinct spin is zero (vacancy).
We have shown that the two extreme points of a malformed island behave like two
opposite magnetic charges. Then, the effective interaction between a pair of
Nambu monopoles with the deformed island is a problem involving four magnetic
charges (two pairs of opposite poles) and a string. We also sketch the
configuration of the field lines of these four charges to confirm this picture.
The influence of the string on this interaction decays rapidly with the string
distance from the defect.Comment: 7 pages, 13 figure
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