583 research outputs found
A mechanized proof of loop freedom of the (untimed) AODV routing protocol
The Ad hoc On-demand Distance Vector (AODV) routing protocol allows the nodes
in a Mobile Ad hoc Network (MANET) or a Wireless Mesh Network (WMN) to know
where to forward data packets. Such a protocol is 'loop free' if it never leads
to routing decisions that forward packets in circles. This paper describes the
mechanization of an existing pen-and-paper proof of loop freedom of AODV in the
interactive theorem prover Isabelle/HOL. The mechanization relies on a novel
compositional approach for lifting invariants to networks of nodes. We exploit
the mechanization to analyse several improvements of AODV and show that
Isabelle/HOL can re-establish most proof obligations automatically and identify
exactly the steps that are no longer valid.Comment: The Isabelle/HOL source files, and a full proof document, are
available in the Archive of Formal Proofs, at
http://afp.sourceforge.net/entries/AODV.shtm
Mechanizing a Process Algebra for Network Protocols
This paper presents the mechanization of a process algebra for Mobile Ad hoc
Networks and Wireless Mesh Networks, and the development of a compositional
framework for proving invariant properties. Mechanizing the core process
algebra in Isabelle/HOL is relatively standard, but its layered structure
necessitates special treatment. The control states of reactive processes, such
as nodes in a network, are modelled by terms of the process algebra. We propose
a technique based on these terms to streamline proofs of inductive invariance.
This is not sufficient, however, to state and prove invariants that relate
states across multiple processes (entire networks). To this end, we propose a
novel compositional technique for lifting global invariants stated at the level
of individual nodes to networks of nodes.Comment: This paper is an extended version of arXiv:1407.3519. The
Isabelle/HOL source files, and a full proof document, are available in the
Archive of Formal Proofs, at http://afp.sourceforge.net/entries/AWN.shtm
Genetic mapping in polyploids
Many of our most important crop species are polyploid – an unusual phenomenon whereby each chromosome is present in multiple copies (more than the usual two copies). The most common such arrangement is tetraploidy, where each chromosome is present four times. Plant species can tolerate this condition quite well (the same cannot be said of animals or humans). In fact, polyploidy can confer certain advantages such as larger fruits and flowers, seedless fruits (useful for fruit growers) or improved tolerance to environmental stresses. However, carrying multiple copies of each chromosome complicates things, particularly when crop breeders would like to use DNA information to help inform selection decisions. This PhD project looked at how DNA information of polyploids should be best analysed, developing methods and new software tools to achieve this. We analysed DNA information from polyploid crops such as potato, rose and chrysanthemum, yielding many novel insights and important results.</p
Established liked versus disliked brands: brain activity, implicit associations and explicit
Consumers' attitudes towards established brands were tested using implicit and explicit measures. In particular, late positive potential (LPP) effects were assessed as an implicit physiological measure of motivational significance. The implicit Association Test (IAT) was used as an implicit behavioural measure of valence-related aspects (affective content) of brand attitude. We constructed individualised stimulus lists of liked and disliked brand types from participants' subjective pre-assessment. Participants then re-rated these visually presented brands whilst brain potential changes were recorded via electroencephalography (EEG). First, self-report measures during the test confirmed pre-assessed attitudes underlining consistent explicit rating performance. Second, liked brands elicited significantly more positive going waveforms (LPPs) than disliked brands over right parietal cortical areas starting at about 800 ms post stimulus onset (reaching statistical significance at around 1000 ms) and lasting until the end of the recording epoch (2000 ms). In accordance to the literature this finding is interpreted as reflecting positive affect-related motivational aspects of liked brands. Finally, the IAT revealed that both liked and disliked brands indeed are associated with affect-related valence. The increased levels of motivation associated with liked brands is interpreted as potentially reflecting increased purchasing intention, but this is of course only speculation at this stage. (authors' abstract
ATCA and Spitzer Observations of the Binary Protostellar Systems CG30 and BHR71
We present interferometric observations with resolution of ~3 arcsecs of the
isolated, low-mass protostellar double cores CG30 and BHR71 in the N2M_\odotSpitzerSpitzer$ observations, we construct spectral
energy distributions (SEDs) and derive temperatures and luminosities for all
cores. Based on the morphology and velocity structure, we suggest that the
sub-cores in CG30 were formed by initial fragmentation of a filamentary
prestellar core, while those in BHR71 could originate from rotational
fragmentation of a single collapsing protostellar core.Comment: 31 pages, 10 figures, to be published by ApJ in Sep. 200
Helminth coinfection and COVID-19: an alternate hypothesis
[Extract] In their recently published commentary, Bradbury and colleagues [1] drew attention to the possible negative interactions between helminth infection and COVID-19 severity in helminth-endemic regions. Helminth infections are known to be powerful modulators of the human immune response, and numerous studies now highlight the effects this may have on human infectious, inflammatory, and metabolic diseases. We believe, however, that any interaction between pre-existing helminth infection and the subsequent severity of COVID-19 need not necessarily be a negative one, and theoretical and empirical evidence suggests that helminths may indeed have a mitigating effect
The acute oncologist's role in managing patients with cancer and other co-morbidities
Background: An Acute Oncology Service (AOS) is paramount to providing timely and improved pathways
of care for patients who are admitted to hospital with cancer-related problems or suspected cancer. Objective:
To establish an AOS pilot study to decide how best to implement such a service locally. Methods: The AOS,
which included collaboration between the oncology and palliative care teams at the Northern General Hospital
in Sheffi eld, UK, ensured that the majority of oncology patients in the region received timely assessment
by an oncologist if they became acutely unwell as a result of their cancer or its treatment. The AOS consisted
of a thrice-weekly ward round, and daily telephone advice service. Results: We report on patient data during
the fi rst 12 months of the pilot study. Delivery of the AOS enhanced communication between the services
and provided inter-professional education and support, resulting in earlier oncological team involvement in the
management of patients with cancer admitted under other teams, as well as provision of advice to patients and
their caregivers and families. Provision of the AOS shortened the mean length of hospital stay by 6 days. Two
case studies are presented to illustrate the typical challenges faced when managing these patients. Conclusions:
Establishment of the AOS enabled effective collaboration between the oncology and other clinical teams to
provide a rapid and streamlined referral pathway of patients to the AOS. Locally, this process has been supported
by the development of acute oncology protocols, which are now in use across the local cancer network
Researching teacher educators’ preparedness to teach to and about diversity : Investigating epistemic reflexivity as a new conceptual framework
There is growing international concern about the extent to which teachers are prepared to work with an increasingly diverse student (and community) population. To date, research into the relationship between teacher preparation and preparedness to teach diverse learners has not focused on teacher educators’ understandings about teaching to/about diversity. Such understandings can be informed by epistemic aspects of professional work. Epistemic cognitions (cognitions about knowledge and knowing) allow professionals to generate perspectives necessary to tackle new and old challenges.
The social lab reported in this paper investigated 12 Australian teacher educators’ perspectives about teaching to/about diversity using the 3R-Epistemic Cognition (EC) framework. The findings showed that the 3R-EC framework could be useful for capturing epistemic reflexive dialogues about teaching to/about diversity, although some aspects of the framework were identified by the teacher educators as challenging. On the basis of these identified challenges, refinements concerning communication and use of the 3R-EC framework were identified. The feedback also led to some refinements of the social lab methodology for use in the larger national study
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