18,313 research outputs found
Direct calculation of the critical Casimir force in a binary fluid
We show that critical Casimir effects can be accessed through direct
simulation of a model binary fluid passing through the demixing transition. We
work in the semi grand canonical ensemble, in slab geometry, in which the
Casimir force appears as the excess of the generalized pressure,
. The excesses of the perpendicular pressure, , and of
, are individually of much larger amplitude. A critical pressure
anisotropy is observed between forces parallel and perpendicular to the
confinement direction, which collapses onto a universal scaling function
closely related to that of the critical Casimir force
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
Dormência em sementes de hortaliças.
A presente revisão de literatura objetivou os fatores que induzem a dormência, as categorias e mecanismos de dormência, assim como, métodos para superar a dormência em sementes de hortaliças.bitstream/item/72481/1/doc-1361.pd
Peletização de sementes de hortaliças.
A presente revisão de literatura objetivou divulgar a técnica de peletização de sementes de hortaliças desenvolvida pela Embrapa Hortaliças, para melhorara a semeadura e/ou o desenvolvimento ou sobrevivência de espécies cultivads, a fim de reduzir os custos com as operações de transplante.bitstream/item/72475/1/doc-1371.pd
The young massive stellar cluster associated to RCW121
We report NIR broad and narrow band photometric observations in the direction
of the IRAS17149-3916 source that reveal the presence of a young cluster of
massive stars embedded in an HII region coincident with RCW121. These
observations, together with published radio data, MSX and Spitzer images were
used to determine some of the physical parameters of the region. We found 96
cluster member candidates in an area of about 1.5 x 2.0 square arcmin, 30% of
them showing excess emission in the NIR. IRS 1, the strongest source in the
cluster with an estimated spectral type of O5V-O6V ZAMS based on the
color-magnitude diagram, is probably the main ionizing source of the HII region
detected at radio wavelengths. Using the integrated Brgamma and the 5 GHz flux
densities, we derived a mean visual extinction AV=5.49 magnitudes. From the
observed size of the Brgamma extended emission, we calculated the emission
measure E and the electron density ne, characteristic of compact HII regions.Comment: 18 pages, 8 figures, accepted for publication on AJ (February/2006
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