20,993 research outputs found
A study of BPS and near-BPS black holes via AdS/CFT
In the settings of various AdS/CFT dual pairs, we use results from supersymmetric localiza tion to gain insights into the physics of asymptotically-AdS, BPS black holes in 5 dimensions,
and near-BPS black holes in 4 dimensions.
We first begin with BPS black holes embedded in the known examples of AdS5/CFT4
dualities. Using the Bethe Ansatz formulation, we compute the superconformal index at large
N with arbitrary chemical potentials for all charges and angular momenta, for general N = 1
four-dimensional conformal theories with a holographic dual. We conjecture and bring some
evidence that a particular universal contribution to the sum over Bethe vacua dominates the
index at large N. For N = 4 SYM, this contribution correctly leads to the entropy of BPS
Kerr-Newman black holes in AdS5 × S
5
for arbitrary values of the conserved charges, thus
completing the microscopic derivation of their microstates. We also consider theories dual
to AdS5 × SE5, where SE5 is a Sasaki-Einstein manifold. We first check our results against
the so-called universal black hole. We then explicitly construct the near-horizon geometry
of BPS Kerr-Newman black holes in AdS5 × T
1,1
, charged under the baryonic symmetry
of the conifold theory and with equal angular momenta. We compute the entropy of these
black holes using the attractor mechanism and find complete agreement with field theory
predictions.
Next, we consider the 3d Chern-Simons matter theory that is holographically dual to
massive Type IIA string theory on AdS4 × S
6
. By Kaluza-Klein reducing on S
2 with a
background that is dual to the asymptotics of static dyonic BPS black holes in AdS4, we
construct a N = 2 supersymmetric gauged quantum mechanics whose ground-state degener acy reproduces the entropy of BPS black holes. We expect its low-lying spectrum to contain
information about near-extremal horizons. Interestingly, the model has a large number of
statistically-distributed couplings, reminiscent of SYK models
The key role of Lagrangian multiplier in mimetic gravitational theory in the frame of isotropic compact star
Recently, the mimetic gravitational theory has gained much attention in the
frame of cosmology as well as in the domain of astrophysics. In this study, we
show that in the frame of mimetic gravitation theory we are not able to derive
an isotropic model. As a result, our focus shifts towards combining mimetic
gravitational theory with the Lagrangian multiplier. The field equations of a
static isotropic gravitational system that controls the geometry and dynamics
of star structure are studied in the frame of mimetic theory coupled with a
Lagrangian multiplier using a non-linear equation of state. An energy density
is assumed from where all the other unknowns are fixed and a new isotropic
model is derived. The physical analysis of this model is studied from different
viewpoints and consistent results compatible with a realistic isotropic star
are investigated analytically and graphically. Ultimately, we demonstrate the
stability of the model in question by employing the adiabatic index technique.Comment: 12 pages 6 figure
Emergence of Adaptive Circadian Rhythms in Deep Reinforcement Learning
Adapting to regularities of the environment is critical for biological
organisms to anticipate events and plan. A prominent example is the circadian
rhythm corresponding to the internalization by organisms of the -hour
period of the Earth's rotation. In this work, we study the emergence of
circadian-like rhythms in deep reinforcement learning agents. In particular, we
deployed agents in an environment with a reliable periodic variation while
solving a foraging task. We systematically characterize the agent's behavior
during learning and demonstrate the emergence of a rhythm that is endogenous
and entrainable. Interestingly, the internal rhythm adapts to shifts in the
phase of the environmental signal without any re-training. Furthermore, we show
via bifurcation and phase response curve analyses how artificial neurons
develop dynamics to support the internalization of the environmental rhythm.
From a dynamical systems view, we demonstrate that the adaptation proceeds by
the emergence of a stable periodic orbit in the neuron dynamics with a phase
response that allows an optimal phase synchronisation between the agent's
dynamics and the environmental rhythm.Comment: ICML 202
Memory Effects, Multiple Time Scales and Local Stability in Langevin Models of the S&P500 Market Correlation
The analysis of market correlations is crucial for optimal portfolio
selection of correlated assets, but their memory effects have often been
neglected. In this work, we analyse the mean market correlation of the S&P500
which corresponds to the main market mode in principle component analysis. We
fit a generalised Langevin equation (GLE) to the data whose memory kernel
implies that there is a significant memory effect in the market correlation
ranging back at least three trading weeks. The memory kernel improves the
forecasting accuracy of the GLE compared to models without memory and hence,
such a memory effect has to be taken into account for optimal portfolio
selection to minimise risk or for predicting future correlations. Moreover, a
Bayesian resilience estimation provides further evidence for non-Markovianity
in the data and suggests the existence of a hidden slow time scale that
operates on much slower times than the observed daily market data. Assuming
that such a slow time scale exists, our work supports previous research on the
existence of locally stable market states.Comment: 15 pages (excluding references and appendix
Drugs, techno and the ecstasy of queer bodies
This is the final version. Available from SAGE Publications via the DOI in this record. In Cruising Utopia, José Muñoz writes that “drugs are a surplus that pushes one off course, no longer able to contribute labor power at the proper tempo” (2009, p. 154). Their pharmacology of unproductive time also interacts in a “synergistic/synaesthetic” manner (Reynolds, 2012, p. xxx) with the hypnotic upbeat tempos of electronic dance genres like disco, house or techno. In the club, drugs enhance sensations and draw bodies close together, all while sound penetrates the ear, turning it into an “erotic orifice” (Schafer, 2004, p. 9). Central to countercultural histories of sexual liberation (Florêncio, 2021; Race, 2009), the club is a temple of queer world-making, a laboratory carrying out experiments with a queerness-yet-to-come. In this speculative autotheoretical essay, I explore the ethics and political value—as well as political ambivalence—of drug-fuelled techniques of self-invention encountered in the queer club. At once pharmacological, sexual, and biopolitical, these modes of becoming-queer of bodies flooded by sound, drugs, and sexual pleasure allude to the possibility of kinds of subjectivity and social relations that resonate with a narcofeminist ethics and veer away from neoliberal regimes of identity and belonging
Numerical modeling of thermal dust polarization from aligned grains in the envelope of evolved stars with updated POLARIS
Magnetic fields are thought to influence the formation and evolution of
evolved star envelopes. Thermal dust polarization from magnetically aligned
grains is potentially a powerful tool for probing magnetic fields and dust
properties in these circumstellar environments. In this paper, we present
numerical modeling of thermal dust polarization from the envelope of IK Tau
using the magnetically enhanced radiative torque (MRAT) alignment theory
implemented in our updated POLARIS code. Due to the strong stellar radiation
field, the minimum size required for RAT alignment of silicate grains is . Additionally, ordinary paramagnetic grains can achieve
perfect alignment by MRAT in the inner regions of due to
stronger magnetic fields of mG - 1G, producing thermal dust
polarization degree of . The polarization degree can be enhanced
to for grains with embedded iron inclusions. We also find that
the magnetic field geometry affects the alignment size and the resulting
polarization degree due to the projection effect in the plane-of-sky. We also
study the spectrum of polarized thermal dust emission and find the increased
polarization degree toward due to the alignment of
small grains by MRAT. Furthermore, we investigate the impact of rotational
disruption by RATs (RAT-D) and find the RAT-D effect cause a decrease in the
dust polarization fraction. Finally, we compare our numerical results with
available polarization data observed by SOFIA/HAWC+ for constraining dust
properties, suggesting grains are unlikely to have embedded iron clusters and
might have slightly elongated shapes. Our modeling results suggest further
observational studies at far-infrared/sub-millimeter wavelengths to understand
the properties of magnetic fields and dust in AGB envelopes.Comment: 27 pages, 23 figures, 1 table, to be submitte
Collective variables between large-scale states in turbulent convection
The dynamics in a confined turbulent convection flow is dominated by multiple
long-lived macroscopic circulation states, which are visited subsequently by
the system in a Markov-type hopping process. In the present work, we analyze
the short transition paths between these subsequent macroscopic system states
by a data-driven learning algorithm that extracts the low-dimensional
transition manifold and the related new coordinates, which we term collective
variables, in the state space of the complex turbulent flow. We therefore
transfer and extend concepts for conformation transitions in stochastic
microscopic systems, such as in the dynamics of macromolecules, to a
deterministic macroscopic flow. Our analysis is based on long-term direct
numerical simulation trajectories of turbulent convection in a closed cubic
cell at a Prandtl number and Rayleigh numbers and
for a time lag of convective free-fall time units. The simulations
resolve vortices and plumes of all physically relevant scales resulting in a
state space spanned by more than 3.5 million degrees of freedom. The transition
dynamics between the large-scale circulation states can be captured by the
transition manifold analysis with only two collective variables which implies a
reduction of the data dimension by a factor of more than a million. Our method
demonstrates that cessations and subsequent reversals of the large-scale flow
are unlikely in the present setup and thus paves the way to the development of
efficient reduced-order models of the macroscopic complex nonlinear dynamical
system.Comment: 24 pages, 12 Figures, 1 tabl
Unstable Periodic Orbits: a language to interpret the complexity of chaotic systems
Unstable periodic orbits (UPOs), exact periodic solutions of the evolution equation, offer a very
powerful framework for studying chaotic dynamical systems, as they allow one to dissect their
dynamical structure. UPOs can be considered the skeleton of chaotic dynamics, its essential
building blocks. In fact, it is possible to prove that in a chaotic system, UPOs are dense in
the attractor, meaning that it is always possible to find a UPO arbitrarily near any chaotic
trajectory. We can thus think of the chaotic trajectory as being approximated by different
UPOs as it evolves in time, jumping from one UPO to another as a result of their instability.
In this thesis we provide a contribution towards the use of UPOs as a tool to understand and
distill the dynamical structure of chaotic dynamical systems. We will focus on two models,
characterised by different properties, the Lorenz-63 and Lorenz-96 model.
The process of approximation of a chaotic trajectory in terms of UPOs will play a central role
in our investigation. In fact, we will use this tool to explore the properties of the attractor of
the system under the lens of its UPOs.
In the first part of the thesis we consider the Lorenz-63 model with the classic parameters’ value.
We investigate how a chaotic trajectory can be approximated using a complete set of UPOs
up to symbolic dynamics’ period 14. At each instant in time, we rank the UPOs according to
their proximity to the position of the orbit in the phase space. We study this process from
two different perspectives. First, we find that longer period UPOs overwhelmingly provide the
best local approximation to the trajectory. Second, we construct a finite-state Markov chain
by studying the scattering of the trajectory between the neighbourhood of the various UPOs.
Each UPO and its neighbourhood are taken as a possible state of the system. Through the
analysis of the subdominant eigenvectors of the corresponding stochastic matrix we provide a
different interpretation of the mixing processes occurring in the system by taking advantage of
the concept of quasi-invariant sets.
In the second part of the thesis we provide an extensive numerical investigation of the variability
of the dynamical properties across the attractor of the much studied Lorenz ’96 dynamical
system. By combining the Lyapunov analysis of the tangent space with the study of the
shadowing of the chaotic trajectory performed by a very large set of unstable periodic orbits,
we show that the observed variability in the number of unstable dimensions, which shows a
serious breakdown of hyperbolicity, is associated with the presence of a substantial number of
finite-time Lyapunov exponents that fluctuate about zero also when very long averaging times
are considered
Monotheism and the Suffering of Animals in Nature
This is the Submitted Manuscript Under Review. The final version is available from Cambridge University Press via the DOI in this recordThis Element concerns itself with a particular aspect of the problem posed to monotheistic religious thought by suffering, namely the suffering of non-human creatures in nature. It makes some comparisons between Judaism, Christianity, and Islam, and then explores the problem in depth within Christian thought. After clarification of the nature of the problem, the Element considers a range of possible responses, including those based on a fall-event, those based on freedom of process, and those hypothesising a constraint on the possibilities for God as creator. Proposals based on the motif of self-emptying are evaluated. Two other aspects of the question concern God's providential relationship to the evolving creation, and the possibility of resurrection lives for animals. After consideration of the possibility of combining different explanations, the Element ends its discussion by looking at two innovative proposals at the cutting-edge of the debate
Dissecting the mechanisms of transport of herpes simplex virus between Langerhans Cells & dendritic cells in epidermis and dermis following infection of human genital mucosa and skin
Herpes Simplex Virus (HSV) is a sexually transmitted infection (STI) that the World Health Organisation (WHO) has deemed a priority for a vaccine. CD8 and CD4T cells are important in the control and clearance of HSV, however no known vaccine has been able to stimulate CD8T cells. The dermal dendritic cells (dDCs) are suspected to play a role.
Previously the host lab has shown in human tissue that HSV-1 infection of Langerhans cells (LCs) caused apoptosis and migration of LCs to the dermis, where they were phagocytosed by dDCs (termed HSV viral relay). Very little is known about the mechanisms of this relay. The host lab has also identified a second resident epidermal immune cell, Epi-cDC2s, which are infectable by HSV. This thesis aims to unravel the mechanisms involved in the relay.
RNA-seq and cell surface phenotyping on human dDCs subsets showed that was differential chemokine receptor expression. Bead-based immunoassays were used to determine the chemokines produced by HSV-1 infected LCs and Epi-cDC2s,and showed HSV infected LCs produced increased CXCR3 ligands, while HSV infected Epi-cDC2s produced increased CCR5 ligands. The importance of these chemokine axes was investigated using chemotaxis assays.
An cyclic immunofluorescent microscopy panel was then developed to investigate whether this migration could be seen in situ in HSV infected foreskin explants. Underneath epidermal foci of infection, there was migration of both cDC1s and cDC2s towards the basement membrane. Under foci of infection there was a greater proportion of cDC2s clustering with LCs.
The uptake of HSV infected epidermal cells by the dDC subsets was examined using imaging cytometry. Preliminary results suggest that there were no significant differences between the ability of dDCs to phagocytose HSV infected epidermal cells.
Understanding the mechanisms and the role of each dDC subset in the HSV viral relay will determine which dDC subsets are crucial for CD8 and CD4 T cell stimulation
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