Primordial black holes in non-Gaussian regimes

Primordial black holes (PBHs) can form in the early Universe from the collapse of rare, large density fluctuations. They have never been observed, but this fact is enough to constrain the amplitude of fluctuations on very small scales which cannot be otherwise probed. Because PBHs form only in very rare large fluctuations, the number of PBHs formed is extremely sensitive to changes in the shape of the tail of the fluctuation distribution - which depends on the amount of non-Gaussianity present. We first study how local non-Gaussianity of arbitrary size up to fifth order affects the abundance and constraints from PBHs, finding that they depend strongly on even small amounts of non-Gaussianity and the upper bound on the allowed amplitude of the power spectrum can vary by several orders of magnitude. The sign of the non-linearity parameters (f_{NL}, g_{NL}, etc) are particularly important. We also study the abundance and constraints from PBHs in the curvaton scenario, in which case the complete non-linear probability distribution is known, and find that truncating to any given order (i.e. to order f_{NL} or g_{NL}, etc) does not give accurate results

Long-short wavelength mode coupling tightens primordial black hole constraints

The effects of non-Gaussianity on the constraints on the primordial curvature perturbation power spectrum from primordial black holes (PBHs) are considered. We extend previous analyses to include the effects of coupling between the modes of the horizon scale at the time the PBH forms and superhorizon modes. We consider terms of up to third order in the Gaussian perturbation. For the weakest constraints on the abundance of PBHs in the early universe (corresponding to a fractional energy density of PBHs of 10−5 at the time of formation), in the case of Gaussian perturbations, constraints on the power spectrum are Pζ<0.05 but can be significantly tighter when even a small amount of non-Gaussianity is considered, to Pζ<0.01, and become approximately Pζ<0.003 in more special cases. Surprisingly, even when there is negative skew (which naively would suggest fewer areas of high density, leading to weaker constraints), we find that the constraints on the power spectrum become tighter than the purely Gaussian case—in strong contrast with previous results. We find that the constraints are highly sensitive to both the non-Gaussianity parameters as well as the amplitude of superhorizon perturbations

Review of local non-Gaussianity from multi-field inflation

We review models which generate a large non-Gaussianity of the local form. We first briefly consider three models which generate the non-Gaussianity either at or after the end of inflation; the curvaton scenario, modulated (p)reheating and an inhomogeneous end of inflation. We then focus on ways of generating the non-Gaussianity during inflation. We derive general conditions which a product or sum separable potential must satisfy in order to generate a large local bispectrum during slow-roll inflation. As an application we consider two-field hybrid inflation. We then derive a formalism not based on slow roll which can be applied to models in which the slow-roll parameters become large before inflation ends. An exactly soluble two-field model is given in which this happens. Finally we also consider further non-Gaussian observables; a scale dependence of f_NL and the trispectrum.Comment: 22 pages, 2 figures. Invited review for the special issue "Testing the Gaussianity and Statistical Isotropy of the Universe" for Advances in Astronomy. v2: Numerous references and comments adde

Magnetofection potentiates gene delivery to cultured endothelial cells

Modification of cellular functions by overexpression of genes is increasingly practised for research of signalling pathways, but restricted by limitations of low efficiency. We investigated whether the novel technique of magnetofection (MF) could enhance gene transfer to cultured primary endothelial cells. MF of human umbilical vein endothelial cells (HUVEC) increased transfection efficiency of a luciferase reporter gene up to 360-fold compared to various conventional transfection systems. In contrast, there was only an up to 1.6-fold increase in toxicity caused by MF suggesting that the advantages of MF outbalanced the increase in toxicity. MF efficiently increased transfection efficiency using several commercially available cationic lipid transfection reagents and polyethyleneimine (PEI). Using PEI, even confluent HUVEC could be efficiently transfected to express luciferase activity. Using a green fluorescent protein vector maximum percentages of transfected cells amounted up to 38.7% while PEI without MF resulted in only 1.3% transfected cells. Likewise, in porcine aortic endothelial cells MF increased expression of a luciferase or beta-galactosidase reporter, reaching an efficiency of 37.5% of cells. MF is an effective tool for pDNA transfection of endothelial cells allowing high efficiencies. It may be of great use for investigating protein function in cell culture experiments

Development of a Portable, Tileable, Dual-Particle Radiography System

A scalable, portable, multi-particle neutron radiography device has been developed using commercial-off-the-shelf-parts. The IDEAS ROSSPAD readout module was selected for use in developing the radiography panel due to its single-wire Power-over-Ethernet (PoE) connectivity and its tileable form factor. Each ROSSPAD detector is paired with an 8 by 8 array of 6-mm-pitch Sensl J-Series silicon photomultipliers (SiPMs). With both single and multi-ROSSPAD testing, a detection package consisting of a 3-mm-thick sheet of EJ-200 plastic scintillator and a 3-mm-thick sheet of acrylic light spreader was coupled to the SiPM board face. After both quality assurance of the detector packages and the calibration of the raw data from the ROSSPADs, sub-SiPM spatial resolution was achieved. For the single- ROSSPAD setup, modulation transfer functions (MTFs) showed spatial resolutions of 2.32 line pairs per centimeter at 10% MTF for gamma rays and 3.35 line pairs per centimeter at 10% MTF for neutrons. The multi-ROSSPAD setups performed similarly with gammas at 2.09 line pairs per centimeter at 10% MTF, while the neutron images lost some spatial resolution with 10% MTF values ranging from 1.30 to 1.46 line pairs per centimeter. Based on the physical characteristics of the board, the raw board spatial resolution sits at 0.833 line pairs per centimeter, meaning all of the methods developed could resolve an object at a sub-SiPM pitch spatial resolution. Additionally, changes to the cutoff values for the full-panel radiography system showed little change to the spatial resolution of the full-panel images, suggesting that the loss is spatial resolution is external to the data collection outside of the number of events recorded. Overall, this research resulted in the development of a state-of-the-art scalable neutron radiography system

A Compositional Semantics for Stochastic Reo Connectors

In this paper we present a compositional semantics for the channel-based coordination language Reo which enables the analysis of quality of service (QoS) properties of service compositions. For this purpose, we annotate Reo channels with stochastic delay rates and explicitly model data-arrival rates at the boundary of a connector, to capture its interaction with the services that comprise its environment. We propose Stochastic Reo automata as an extension of Reo automata, in order to compositionally derive a QoS-aware semantics for Reo. We further present a translation of Stochastic Reo automata to Continuous-Time Markov Chains (CTMCs). This translation enables us to use third-party CTMC verification tools to do an end-to-end performance analysis of service compositions.Comment: In Proceedings FOCLASA 2010, arXiv:1007.499

The resilience of urban Aboriginal children and their caregivers

The current health and social disparities between Australian Aboriginal and non-Aboriginal people pose significant challenges for Aboriginal communities. These disparities are widely attributed to the historical and ongoing trauma associated with European colonisation, including catastrophic population loss, institutionalised discrimination, dispossession of land, loss of culture and language, and the removal of children. In the face of these challenges Aboriginal people have shown remarkable resilience. Resilience is commonly described as ‘positive adaption in the context of adversity’. Despite a rich history of resilience research, the scientific literature describing Aboriginal resilience is sparse. The aim of this research is to investigate resilience within an urban Aboriginal context and identify factors that promote it. This thesis includes a systematic review of the psychosocial correlates of mental health and resilience among Indigenous children from high-income countries, a mixed methods investigation of the resilience of children from four urban Australian communities, a cross-sectional assessment of the resilience of caregivers of Aboriginal children, and a systematic review of peer reviewed studies that evaluated social and emotional wellbeing (SEWB) programs for Aboriginal young people. For children, the presence of stable home environments, supportive social networks, connection to culture, regular exercise and the opportunity to set and attain positive goals were all seen to be associated with resilience. Caregivers who lived in stable home environments were more likely to be resilient; however, the poor physical health of caregivers and their families posed a significant threat to resilience. The number of evaluated SEWB programs was small, and the quality of evidence was predominantly low, reflecting the nascent stage of Aboriginal SEWB and resilience research. For Aboriginal families, this thesis highlights risks that are associated with higher order determinants of poor health. Greater provision of initiatives that can promote stable, strong, cohesive and physically healthy Aboriginal families are needed to build resilience. More rigorous program evaluations that have the power to inform large-scale strategies to enhance resilience are warranted