17,506 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
Event-Driven Network Programming
Software-defined networking (SDN) programs must simultaneously describe
static forwarding behavior and dynamic updates in response to events.
Event-driven updates are critical to get right, but difficult to implement
correctly due to the high degree of concurrency in networks. Existing SDN
platforms offer weak guarantees that can break application invariants, leading
to problems such as dropped packets, degraded performance, security violations,
etc. This paper introduces EVENT-DRIVEN CONSISTENT UPDATES that are guaranteed
to preserve well-defined behaviors when transitioning between configurations in
response to events. We propose NETWORK EVENT STRUCTURES (NESs) to model
constraints on updates, such as which events can be enabled simultaneously and
causal dependencies between events. We define an extension of the NetKAT
language with mutable state, give semantics to stateful programs using NESs,
and discuss provably-correct strategies for implementing NESs in SDNs. Finally,
we evaluate our approach empirically, demonstrating that it gives well-defined
consistency guarantees while avoiding expensive synchronization and packet
buffering
The true nature of the alleged planetary nebula W16-185
We report the discovery of a small cluster of massive stars embedded in a NIR
nebula in the direction of the IRAS15411-5352 point source, which is related to
the alleged planetary nebula W16-185. The majority of the stars present large
NIR excess characteristic of young stellar objects and have bright counterparts
in the Spitzer IRAC images; the most luminous star (IRS1) is the NIR
counterpart of the IRAS source. We found very strong unresolved Brgamma
emission at the IRS1 position and more diluted and extended emission across the
continuum nebula. From the sizes and electron volume densities we concluded
that they represent ultra-compact and compact HII regions, respectively.
Comparing the Brgamma emission with the 7 mm free-free emission, we estimated
that the visual extinction ranges between 14 and 20 mag. We found that only one
star (IRS1) can provide the number of UV photons necessary to ionize the
nebula.Comment: 30 pages, 15 figures, 2 tables V3: minor grammatical changes. Figure
4 is available in pdf file. Accepted for publication in AJ, April / 200
Physiological seed quality of 'BRS Mari' hot pepper during seed development and maturation.
Abstract 78
Control Plane Compression
We develop an algorithm capable of compressing large networks into a smaller
ones with similar control plane behavior: For every stable routing solution in
the large, original network, there exists a corresponding solution in the
compressed network, and vice versa. Our compression algorithm preserves a wide
variety of network properties including reachability, loop freedom, and path
length. Consequently, operators may speed up network analysis, based on
simulation, emulation, or verification, by analyzing only the compressed
network. Our approach is based on a new theory of control plane equivalence. We
implement these ideas in a tool called Bonsai and apply it to real and
synthetic networks. Bonsai can shrink real networks by over a factor of 5 and
speed up analysis by several orders of magnitude.Comment: Extended version of the paper appearing in ACM SIGCOMM 201
Estrutura de renda dos produtores da Reserva Extrativista do Rio Cajari, Amapá.
Neste estudo caracterizou-se a estrutura de renda e a posse de bens das famílias residentes em três comunidades representativas do macro ambiente de terra firme da Reserva Extrativista do Rio Cajari no Estado do Amapá. A área de estudo abrangeu as comunidades de Açaizal, Marinho e Martins. Por meio de painéis temáticos e de questionários aplicados junto a 41 famílias selecionadas por amostragem, coletou-se dados que constituíram um cross section, ano agrícola 1999/2000. Constatou-se que, em média, a renda bruta familiar corresponde, em termos mensais, a 3,5 vezes o salário mínimo vigente no ano da pesquisa. Na composição dessa renda bruta, as atividades agrícolas participam com 38,9%, as ligadas ao extrativismo com 35,0%, a criação de pequenos animais com 2,9% e outras formas de renda com 23,1%. Em relação aos produtos do extrativismo, a comercialização e o consumo de 70 hectolitros de castanha-do-pará coletados por ano, por família, representam 25,7% da renda bruta e 31,6% da renda monetária. Quanto aos produtos agrícolas, a farinha de mandioca representa 14,6% da renda bruta e 11,6% da renda monetária, seguida pelas frutas que contribuem para a formação dessas rendas com 9,5% e 10,6%, respectivamente. Outras rendas como as provenientes de programas sociais governamentais, aposentadorias, salários de funcionários públicos, atividades mercantis e venda de mão-de-obra, representam 23,1% da renda bruta e 28,7% da renda monetária e, em média, por família, equivalem a um valor mensal igual a 0,8 vezes o salário mínimo vigente no ano da pesquisa. Fogão a gás, rádio, televisor com antena parabólica e geladeira/freezer são os bens que apresentam os maiores percentuais de posse por parte dos produtoresbitstream/CPAF-AP/7752/1/Boletim200255.PD
Modelling of integrated multi-energy systems : drivers, requirements, and opportunities
There is growing recognition that decarbonisation of existing uses of electricity is only ‘part of the story’ and that closer attention needs to be given to demand for energy in heating or cooling and in transport, and to all the energy vectors and infrastructures that supply the end-use demand. In this respect, concepts such as ‘multi-energy systems’ (MES) have been put forward and are gaining increasing momentum, with the aim of identifying how multiple energy systems that have been traditionally operated, planned and regulated in independent silos can be integrated to improve their collective technical, economic, and environmental performance. This paper addresses the need for modelling of MES which is capable of assessing interactions between different sectors and the energy vectors they are concerned with, so as to bring out the benefits and potential unforeseen or undesired drawbacks arising from energy systems integration. Drivers for MES modelling and the needs of different users of models are discussed, along with some of the practicalities of such modelling, including the choices to be made in respect of spatial and temporal dimensions, what these models might be used to quantify, and how they may be framed mathematically. Examples of existing MES models and tools and their capabilities, as well as of studies in which such models have been used in the authors’ own research, are provided to illustrate the general concepts discussed. Finally, challenges, opportunities and recommendations are summarised for the engagement of modellers in developing a new range of analytical capabilities that are needed to deal with the complexity of ME
A Dain Inequality with charge
We prove an upper bound for angular-momentum and charge in terms of the mass
for electro-vacuum asymptotically flat axisymmetric initial data sets with
simply connected orbit space
Horizontal Pressures in Cylindrical Metal Silos and Comparison with Different International Standards
The focus of this research was to evaluate the horizontal pressures on a cylindrical metal silo of corrugated walls and flat bottom with 1.82m diameter and 5.4m high, and to compare the values with those obtained theoretically by the ISO 11697, EP 433 and AS 3774 standards. The silo was symmetrically filled and constant speed with wheat cv. soft red for two different height/diameter ratios (H/D) and was unloaded through three orifices with a diameter of 71.6mm, one concentric and two eccentrics. Horizontal pressures were measured on the walls of the silo at three positions using hydraulic type pressure cells. The results showed that shortly after the start of the unloading, there was a mass flow above the quota of H/D = 1.2, whereas below this quota funnel flow occurred. It can be said that the EP 433 standard was more appropriate to predict horizontal pressures in silos in H/D ratio = 1.0, with eccentric unloading. For the H/D ratio = 1.5, AS 3774 standard was the one that produced values closer to the experimental
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