961 research outputs found
Disruption of termite gut-microbiota and its prolonged fitness consequences
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of American Society for Microbiology for personal use, not for redistribution. The definitive version was published in Applied and Environmental Microbiology 77 (2011): 4303-4312, doi:10.1128/AEM.01886-10.The disruption of host-symbiont interactions through the use of antibiotics
can help elucidate microbial functions that go beyond short-term nutritional
value. Termite gut symbionts have been studied extensively, but little is
known about their impact on the termiteâs reproductive output. Here we
describe the effect that the antibiotic rifampin has not only on the gut
microbial diversity, but also on the longevity, fecundity, and weight of two
termite species - Zootermopsis angusticollis and Reticulitermes flavipes.
We report three key findings: (i) the antibiotic rifampin, when fed to
primary reproductives during the incipient stages of colony foundation,
causes a permanent reduction in the diversity of gut bacteria, and a
transitory effect on the density of the protozoan community, (ii) rifampin
treatment reduces oviposition rates of queens, translating into delayed
colony growth and ultimately reduced colony fitness and (iii) the initial
dosages of rifampin on reproduction and colony fitness had severe longterm fitness effects on Z. angusticollis survivorship and colony size. Taken
together, our findings demonstrate that the antibiotic-induced perturbation
of the microbial community associates with prolonged reductions in
longevity and fecundity. A causal relationship between these changes in the
gut microbial population structures and fitness is suggested by the
acquisition of opportunistic pathogens and incompetence of the termites to
restore a pre-treatment, native microbiota. Our results indicate that
antibiotic treatment significantly alters the termiteâs microbiota,
reproduction, colony establishment and ultimately, colony growth and
development. We discuss the implications for antimicrobials as a new
application to the control of termite pest species.This research was funded by the Louis Stokes Minority Program which
supported Jessica Dumas, NSF CAREER award DEB 0447316 to
Rosengaus RB, and NSF IOS-0852344 and NAI NNA04CC04A to
Bordenstein SR
Automated Certification of Authorisation Policy Resistance
Attribute-based Access Control (ABAC) extends traditional Access Control by
considering an access request as a set of pairs attribute name-value, making it
particularly useful in the context of open and distributed systems, where
security relevant information can be collected from different sources. However,
ABAC enables attribute hiding attacks, allowing an attacker to gain some access
by withholding information. In this paper, we first introduce the notion of
policy resistance to attribute hiding attacks. We then propose the tool ATRAP
(Automatic Term Rewriting for Authorisation Policies), based on the recent
formal ABAC language PTaCL, which first automatically searches for resistance
counter-examples using Maude, and then automatically searches for an Isabelle
proof of resistance. We illustrate our approach with two simple examples of
policies and propose an evaluation of ATRAP performances.Comment: 20 pages, 4 figures, version including proofs of the paper that will
be presented at ESORICS 201
From Secure Business Process Models to Secure Artifact-Centric Specifications
Making today's systems secure is an extremely difficult and challenging problem. Socio and technical issues interplay and contribute in creating vulnerabilities that cannot be easily prevented without a comprehensive engineering method. This paper presents a novel approach to support process-aware secure systems modeling and automated generation of secure artifact-centric implementations. It combines social and technical perspectives in developing secure complex systems. This work is the result of an academic and industrial collaboration, where SecBPMN2, a research prototype, has been integrated with SAP River, an industrial artifact-centric language
âIn the darkâ: Voices of parents in marginalised stepfamilies: perceptions and experiences of their parenting support needs
The fastest growing family type in the UK is the stepfamily with social parenting an increasingly normal practice. Parenting policy and practice, which has increased exponentially over the last two decades, has historically been modelled on the biological nuclear family model with marginalised families the main recipients. The possibility that parents in marginalised stepfamilies might have separate and discrete parenting support needs to biological parents seems to be overlooked in policy, practice and research. Rather, the historical legacy of deficit, dysfunction and a âwhiffâ of poor parenting in marginalised stepfamilies lingers on. The focus of the research was to determine marginalised parentsâ perceptions and experiences of parenting in their stepfamily and their parenting support needs.
Thematic analysis of the data revealed accounts that were interwoven throughout with strong moral undertones which seemed to categorise their lives. The parenting issues were different and more complex than those they had encountered before. The parents adopted biological family identities, but these didnât fit with their social roles and often rendered them powerless in their relationships with stepchildren. This appeared to have a cumulative effect which impacted on the already fragile couple relationship.
Despite the parents easy articulation of the parenting issues there was a contrasting unease and ambivalence in discussing parenting support needs. Parenting support seemed to be an irrelevance that could be disregarded.
Ultimately the moral significance of the parents marginalised class positions appeared to be central to their lives, which has important implications for policy and practice
Crystal Structure of a Nonsymbiotic Plant Hemoglobin
Background: Nonsymbiotic hemoglobins (nsHbs) form a new class of plant proteins that is distinct genetically and structurally from leghemoglobins. They are found ubiquitously in plants and are expressed in low concentrations in a variety of tissues including roots and leaves. Their function involves a biochemical response to growth under limited O2 conditions. Results: The first X-ray crystal structure of a member of this class of proteins, riceHb1, has been determined to 2.4 Ă
resolution using a combination of phasing techniques. The active site of ferric riceHb1 differs significantly from those of traditional hemoglobins and myoglobins. The proximal and distal histidine sidechains coordinate directly to the heme iron, forming a hemichrome with spectral properties similar to those of cytochrome b5. The crystal structure also shows that riceHb1 is a dimer with a novel interface formed by close contacts between the G helix and the region between the B and C helices of the partner subunit. Conclusions: The bis-histidyl heme coordination found in riceHb1 is unusual for a protein that binds O2 reversibly. However, the distal His73 is rapidly displaced by ferrous ligands, and the overall O2 affinity is ultra-high (KD â 1 nM). Our crystallographic model suggests that ligand binding occurs by an upward and outward movement of the E helix, concomitant dissociation of the distal histidine, possible repacking of the CD corner and folding of the D helix. Although the functional relevance of quaternary structure in nsHbs is unclear, the role of two conserved residues in stabilizing the dimer interface has been identified
Rescheduling in passenger railways: the rolling stock rebalancing problem
This paper addresses the Rolling Stock Rebalancing Problem (RSRP) which arises within a passenger railway operator when the rolling stock has to be rescheduled due to changing circumstances. RSRP is relevant both in the short-term planning stage and in the real-time operations. RSRP has as input a timetable and a rolling stock circulation where the allocation of the rolling stock among the stations at the start or at the end of a certain planning period does not match with the allocation before or after that planning period. The problem is then to modify the input rolling stock circulation in such a way that the number of remaining off-balances is minimal. If all off-balances have been solved, then the obtained rolling stock circulation can be implemented in practice. For practical usage of solution approaches for RSRP, it is important to solve the problem quickly. Since we prove that RSRP is NP-hard, we focus on heuristic solution approaches: we describe two heuristics and compare them with each other on (variants of) real-life instances of NS, the main Dutch passenger railway operator. Finally, to get further insight in the quality of the proposed heuristics, we also compare their outcomes with optimal solutions obtained by solving an existing rolling stock circulation model
The trade off between diversity and quality for multi-objective workforce scheduling
In this paper we investigate and compare multi-objective and
weighted single objective approaches to a real world workforce scheduling
problem. For this difficult problem we consider the trade off in solution quality
versus population diversity, for different sets of fixed objective weights. Our
real-world workforce scheduling problem consists of assigning resources with
the appropriate skills to geographically dispersed task locations while satisfying
time window constraints. The problem is NP-Hard and contains the Resource
Constrained Project Scheduling Problem (RCPSP) as a sub problem. We investigate
a genetic algorithm and serial schedule generation scheme together with
various multi-objective approaches. We show that multi-objective genetic algorithms
can create solutions whose fitness is within 2% of genetic algorithms using
weighted sum objectives even though the multi-objective approaches know
nothing of the weights. The result is highly significant for complex real-world
problems where objective weights are seldom known in advance since it suggests
that a multi-objective approach can generate a solution close to the user
preferred one without having knowledge of user preferences
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