13,277 research outputs found
Development of a Security-Focused Multi-Channel Communication Protocol and Associated Quality of Secure Service (QoSS) Metrics
The threat of eavesdropping, and the challenge of recognizing and correcting for corrupted or suppressed information in communication systems is a consistent challenge. Effectively managing protection mechanisms requires an ability to accurately gauge the likelihood or severity of a threat, and adapt the security features available in a system to mitigate the threat. This research focuses on the design and development of a security-focused communication protocol at the session-layer based on a re-prioritized communication architecture model and associated metrics. From a probabilistic model that considers data leakage and data corruption as surrogates for breaches of confidentiality and integrity, a set of metrics allows the direct and repeatable quantification of the security available in single- or multi-channel networks. The quantification of security is based directly upon the probabilities that adversarial listeners and malicious disruptors are able to gain access to or change the original message. Fragmenting data across multiple channels demonstrates potential improvements to confidentiality, while duplication improves the integrity of the data against disruptions. Finally, the model and metrics are exercised in simulation. The ultimate goal is to minimize the information available to adversaries
Fluctuation, dissipation, and thermalization in non-equilibrium AdS_5 black hole geometries
We give a simple recipe for computing dissipation and fluctuations
(commutator and anti-commutator correlation functions) for non-equilibrium
black hole geometries. The recipe formulates Hawking radiation as an initial
value problem, and is suitable for numerical work. We show how to package the
fluctuation and dissipation near the event horizon into correlators on the
stretched horizon. These horizon correlators determine the bulk and boundary
field theory correlation functions. In addition, the horizon correlators are
the components of a horizon effective action which provides a quantum
generalization of the membrane paradigm. In equilibrium, the analysis
reproduces previous results on the Brownian motion of a heavy quark. Out of
equilibrium, Wigner transforms of commutator and anti-commutator correlation
functions obey a fluctuation-dissipation relation at high frequency.Comment: 28 pages, 6 figure
Exempting low-risk health and medical research from ethics reviews: Comparing Australia, the United Kingdom, the United States and the Netherlands
Background: Disproportionate regulation of health and medical research contributes to research waste. Better understanding of exemptions of research from ethics review in different jurisdictions may help to guide modification of review processes and reduce research waste. Our aim was to identify examples of low-risk human health and medical research exempt from ethics reviews in Australia, the United Kingdom, the United States and the Netherlands. Methods: We examined documents providing national guidance on research ethics in each country, including those authored by the National Health and Medical Research Council (Australia), National Health Service (United Kingdom), the Office for Human Research Protections (United States) and the Central Committee on Research Involving Humans (the Netherlands). Examples and types of research projects exempt from ethics reviews were identified, and similar examples and types were grouped together. Results: Nine categories of research were exempt from ethics reviews across the four countries; these were existing data or specimen, questionnaire or survey, interview, post-marketing study, evaluation of public benefit or service programme, randomised controlled trials, research with staff in their professional role, audit and service evaluation, and other exemptions. Existing non-identifiable data and specimens were exempt in all countries. Four categories - evaluation of public benefit or service programme, randomised controlled trials, research with staff in their professional role, and audit and service evaluation - were exempted by one country each. The remaining categories were exempted by two or three countries. Conclusions: Examples and types of research exempt from research ethics reviews varied considerably. Given the considerable costs and burdens on researchers and ethics committees, it would be worthwhile to develop and provide clearer guidance on exemptions, illustrated with examples, with transparent underpinning rationales
Identification of a functional genetic variant driving racially dimorphic platelet gene expression of the thrombin receptor regulator, PCTP.
Platelet activation in response to stimulation of the Protease Activated Receptor 4 (PAR4) receptor differs by race. One factor that contributes to this difference is the expression level of Phosphatidylcholine Transfer Protein (PCTP), a regulator of platelet PAR4 function. We have conducted an expression Quantitative Trait Locus (eQTL) analysis that identifies single nucleotide polymorphisms (SNPs) linked to the expression level of platelet genes. This analysis revealed 26 SNPs associated with the expression level of PCTP at genome-wide significance (p \u3c 5Γ10(-8)). Using annotation from ENCODE and other public data we prioritised one of these SNPs, rs2912553, for functional testing. The allelic frequency of rs2912553 is racially-dimorphic, in concordance with the racially differential expression of PCTP. Reporter gene assays confirmed that the single nucleotide change caused by rs2912553 altered the transcriptional potency of the surrounding genomic locus. Electromobility shift assays, luciferase assays, and overexpression studies indicated a role for the megakaryocytic transcription factor GATA1. In summary, we have integrated multi-omic data to identify and functionalise an eQTL. This, along with the previously described relationship between PCTP and PAR4 function, allows us to characterise a genotype-phenotype relationship through the mechanism of gene expression
Dark-ages Reionization & Galaxy Formation Simulation VIII. Suppressed growth of dark matter halos during the Epoch of Reionization
We investigate how the hydrostatic suppression of baryonic accretion affects
the growth rate of dark matter halos during the Epoch of Reionization. By
comparing halo properties in a simplistic hydrodynamic simulation in which gas
only cools adiabatically, with its collisionless equivalent, we find that halo
growth is slowed as hydrostatic forces prevent gas from collapsing. In our
simulations, at the high redshifts relevant for reionization (between
and ), halos that host dwarf galaxies () can be reduced by up to a factor of 2 in mass due to the
hydrostatic pressure of baryons. Consequently, the inclusion of baryonic
effects reduces the amplitude of the low mass tail of the halo mass function by
factors of 2 to 4. In addition, we find that the fraction of baryons in dark
matter halos hosting dwarf galaxies at high redshift never exceeds
of the cosmic baryon fraction. When implementing baryonic processes, including
cooling, star formation, supernova feedback and reionization, the suppression
effects become more significant with further reductions of to
60\%. Although convergence tests suggest that the suppression may become weaker
in higher resolution simulations, this suppressed growth will be important for
semi-analytic models of galaxy formation, in which the halo mass inherited from
an underlying N-body simulation directly determines galaxy properties. Based on
the adiabatic simulation, we provide tables to account for these effects in
N-body simulations, and present a modification of the halo mass function along
with explanatory analytic calculations.Comment: 17 pages, 11 figures; Updated to match the published version. Two
changes in Figures 1 and 3 in order to 1) correct bin sizes of the 10^8 and
10^8.5 Msol bins for NOSN_NOZCOOL_NoRe (was 0.5, should be 0.25); 2) include
stellar mass in baryon fraction (was missed in Fig. 3). Quantitative
description of Fig. 3 changed slightly in Section 2.2. All other results and
conclusions remain unchange
Dark-ages reionization and galaxy formation simulation--VII. The sizes of high-redshift galaxies
We investigate high-redshift galaxy sizes using a semi-analytic model
constructed for the Dark-ages Reionization And Galaxy-formation Observables
from Numerical Simulation project. Our fiducial model, including strong
feedback from supernovae and photoionization background, accurately reproduces
the evolution of the stellar mass function and UV luminosity function. Using
this model, we study the size--luminosity relation of galaxies and find that
the effective radius scales with UV luminosity as at --. We show that recently discovered very luminous
galaxies at (Bowler et al. 2016) and (Oesch et al. 2016)
lie on our predicted size--luminosity relations. We find that a significant
fraction of galaxies at will not be resolved by JWST, but GMT will have
the ability to resolve all galaxies in haloes above the atomic cooling limit.
We show that our fiducial model successfully reproduces the redshift evolution
of average galaxy sizes at . We also explore galaxy sizes in models
without supernova feedback. The no-supernova feedback models produce galaxy
sizes that are smaller than observations. We therefore confirm that supernova
feedback plays an important role in determining the size--luminosity relation
of galaxies and its redshift evolution during reionization.Comment: 10 pages, 4 figures, Accepted for publication in MNRA
Dark-ages Reionization and Galaxy Formation Simulation - X. The small contribution of quasars to reionization
Motivated by recent measurements of the number density of faint AGN at high
redshift, we investigate the contribution of quasars to reionization by
tracking the growth of central supermassive black holes in an update of the
Meraxes semi-analytic model. The model is calibrated against the observed
stellar mass function at , the black hole mass function at
, the global ionizing emissivity at and the Thomson
scattering optical depth. The model reproduces a Magorrian relation in
agreement with observations at and predicts a decreasing black hole
mass towards higher redshifts at fixed total stellar mass. With the
implementation of an opening angle of 80 deg for quasar radiation,
corresponding to an observable fraction of per cent due to
obscuration by dust, the model is able to reproduce the observed quasar
luminosity function at . The stellar light from galaxies hosting
faint AGN contributes a significant or dominant fraction of the UV flux. At
high redshift, the model is consistent with the bright end quasar luminosity
function and suggests that the recent faint AGN sample compiled by
Giallongo et al. (2015) includes a significant fraction of stellar light.
Direct application of this luminosity function to the calculation of AGN
ionizing emissivity consequently overestimates the number of ionizing photons
produced by quasars by a factor of 3 at . We conclude that quasars are
unlikely to make a significant contribution to reionization.Comment: 21 pages, 12 figures; Updated to match the published version. All
results and conclusions remain unchange
Establishment of Human Papillomavirus Infection Requires Cell Cycle Progression
Human papillomaviruses (HPVs) are DNA viruses associated with major human cancers. As such there is a strong interest in developing new means, such as vaccines and microbicides, to prevent HPV infections. Developing the latter requires a better understanding of the infectious life cycle of HPVs. The HPV infectious life cycle is closely linked to the differentiation state of the stratified epithelium it infects, with progeny virus only made in the terminally differentiating suprabasal compartment. It has long been recognized that HPV must first establish its infection within the basal layer of stratified epithelium, but why this is the case has not been understood. In part this restriction might reflect specificity of expression of entry receptors. However, this hypothesis could not fully explain the differentiation restriction of HPV infection, since many cell types can be infected with HPVs in monolayer cell culture. Here, we used chemical biology approaches to reveal that cell cycle progression through mitosis is critical for HPV infection. Using infectious HPV16 particles containing the intact viral genome, G1-synchronized human keratinocytes as hosts, and early viral gene expression as a readout for infection, we learned that the recipient cell must enter M phase (mitosis) for HPV infection to take place. Late M phase inhibitors had no effect on infection, whereas G1, S, G2, and early M phase cell cycle inhibitors efficiently prevented infection. We conclude that host cells need to pass through early prophase for successful onset of transcription of the HPV encapsidated genes. These findings provide one reason why HPVs initially establish infections in the basal compartment of stratified epithelia. Only this compartment of the epithelium contains cells progressing through the cell cycle, and therefore it is only in these cells that HPVs can establish their infection. By defining a major condition for cell susceptibility to HPV infection, these results also have potentially important implications for HPV control
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