417 research outputs found
A Quantum Window Onto Early Inflation
Inflation in the early Universe is one of the most promising probes of
gravity in the high-energy regime. However, observable scales give access to a
limited window in the inflationary dynamics. In this essay, we argue that
quantum corrections to the classical dynamics of cosmological fields allow us
to probe much earlier epochs of the inflationary phase and extend this window
by many orders of magnitude. We point out that both the statistics of
cosmological fluctuations at observable scales, and the field displacements
acquired by spectator fields that play an important role in many
post-inflationary processes, are sensitive to a much longer phase of the
inflationary epoch.Comment: 5 pages, 2 figures. Honourable Mention from the Gravity Research
Foundation 2017 Awards for Essays on Gravitation. Version to appear in
October 2017 Special Issue of the International Journal of Modern Physics D.
Updated to match the published versio
Renormalisation group improvement in the stochastic formalism
We investigate compatibility between the stochastic infrared (IR) resummation
of light test fields on inflationary spacetimes and renormalisation group
running of the ultra-violet (UV) physics. Using the Wilsonian approach, we
derive improved stochastic Langevin and Fokker-Planck equations which
consistently include the renormalisation group effects. With the exception of
stationary solutions, these differ from the naive approach of simply replacing
the classical potential in the standard stochastic equations with the
renormalisation group improved potential. Using this new formalism, we
exemplify the IR dynamics with the Yukawa theory during inflation, illustrating
the differences between the consistent implementation of the UV running and the
naive approach.Comment: 18 pages, 1 figure, 1 appendix, matches accepted version in JCA
Neurobehavioural representations of observed action viewpoint
This thesis examined whether the viewpoint from which an action was observed could modulate the behavioural and neural activity of the observer. Chapter 2 presents motion capture data from a manual prehension task which manipulated observed reach height. Actions were observed from two allocentric viewpoints. The data revealed no differences between viewpoints, but did reveal effects of relative spatial direction congruency. Chapter 3 further examined these direction congruency effects. Using simple arm movements, observed task and direction congruency were split. The data revealed effects of direction congruency dependent on observed action viewpoint. Chapter 4 presents experiments further examining the effects of observed action viewpoint. The data suggest participants considered observed actions in terms of agency; participants responded faster when observing egocentrically framed actions compared to allocentrically framed actions. Chapter 5 further examined this using functional Magnetic Resonance Imaging. The data suggest that stronger representations of observed actions are present for egocentric actions compared to allocentric actions. Collectively, this thesis demonstrates that relative spatial direction kinematics are a key factor in action observation, and that the viewpoint from which an action is observed can modulate participant behavioural responses and brain activity, as participants distinguish between egocentrically and allocentrically framed actions
Multiple spectator condensates from inflation
We investigate the development of spectator (light test) field condensates
due to their quantum fluctuations in a de Sitter inflationary background,
making use of the stochastic formalism to describe the system. In this context,
a condensate refers to the typical field value found after coarse-graining
using the Hubble scale , which can be essential to seed the initial
conditions required by various post-inflationary processes. We study models
with multiple coupled spectators and for the first time we demonstrate that new
forms of stationary solution exist (distinct from the standard exponential
form) when the potential is asymmetric. Furthermore, we find a critical value
for the inter-field coupling as a function of the number of fields above which
the formation of stationary condensates collapses to . Considering some
simple two-field example potentials, we are also able to derive a lower limit
on the coupling, below which the fluctuations are effectively decoupled, and
the standard stationary variance formulae for each field separately can be
trusted. These results are all numerically verified by a new publicly available
python class (https://github.com/umbralcalc/nfield) to solve the coupled
Langevin equations over a large number of fields, realisations and timescales.
Further applications of this new tool are also discussed.Comment: 18 pages, 10 figures, paragraph added to match published version in
JCA
Surface Structural Disordering in Graphite upon Lithium Intercalation/Deintercalation
We report on the origin of the surface structural disordering in graphite
anodes induced by lithium intercalation and deintercalation processes. Average
Raman spectra of graphitic anodes reveal that cycling at potentials that
correspond to low lithium concentrations in LixC (0 \leq x < 0.16) is
responsible for most of the structural damage observed at the graphite surface.
The extent of surface structural disorder in graphite is significantly reduced
for the anodes that were cycled at potentials where stage-1 and stage-2
compounds (x > 0.33) are present. Electrochemical impedance spectra show larger
interfacial impedance for the electrodes that were fully delithiated during
cycling as compared to electrodes that were cycled at lower potentials (U <
0.15 V vs. Li/Li+). Steep Li+ surface-bulk concentration gradients at the
surface of graphite during early stages of intercalation processes, and the
inherent increase of the LixC d-spacing tend to induce local stresses at the
edges of graphene layers, and lead to the breakage of C-C bonds. The exposed
graphite edge sites react with the electrolyte to (re)form the SEI layer, which
leads to gradual degradation of the graphite anode, and causes reversible
capacity loss in a lithium-ion battery.Comment: 12 pages, 5 figure
Findings and Recommendations of the Metropolitan Planning and Zoning Committee of the Jacksonville Chapter of the American Institute of Architects
Contained is a proposed bill that was introduced to the 1957 Florida Legislature concerning city development and zoning law
Resting state morphology predicts the effect of theta burst stimulation in false belief reasoning:ventrolateral prefrontal cortex in false belief reasoning
When required to represent a perspective that conflicts with one's own, functional magnetic resonance imaging (fMRI) suggests that the right ventrolateral prefrontal cortex (rvlPFC) supports the inhibition of that conflicting self-perspective. The present task dissociated inhibition of self-perspective from other executive control processes by contrasting belief reasoning-a cognitive state where the presence of conflicting perspectives was manipulated-with a conative desire state wherein no systematic conflict existed. Linear modeling was used to examine the effect of continuous theta burst stimulation (cTBS) to rvlPFC on participants' reaction times in belief and desire reasoning. It was anticipated that cTBS applied to rvlPFC would affect belief but not desire reasoning, by modulating activity in the Ventral Attention System (VAS). We further anticipated that this effect would be mediated by functional connectivity within this network, which was identified using resting state fMRI and an unbiased model-free approach. Simple reaction-time analysis failed to detect an effect of cTBS. However, by additionally modeling individual measures from within the stimulated network, the hypothesized effect of cTBS to belief (but, importantly, not desire) reasoning was demonstrated. Structural morphology within the stimulated region, rvlPFC, and right temporoparietal junction were demonstrated to underlie this effect. These data provide evidence that inconsistencies found with cTBS can be mediated by the composition of the functional network that is being stimulated. We suggest that the common claim that this network constitutes the VAS explains the effect of cTBS to this network on false belief reasoning. Hum Brain Mapp, 2016. © 2016 Wiley Periodicals, Inc
- …