1,540 research outputs found
Association of acute disseminated encephalomyelitis (ADEM) and COVID-19 in a pediatric patient
Cases of acute disseminated encephalomyelitis (ADEM) and its hyperacute form, acute hemorrhagic leukoencephalitis (AHLE), have been reported in coronavirus disease 2019 (COVID-19) patients as rare, but most severe neurological complications. However, histopathologic evaluations of ADEM/AHLE pathology in COVID patients are extremely limited, so far having only been reported in a few adult autopsy cases. Here we compare the findings with an ADEM-like pathology in a pediatric patient taken through a biopsy procedure. Understanding the neuropathology may shed informative light on the autoimmune process affecting COVID-19 patients and provide critical information to guide the clinical management
Oil Prices, Profits, and Recessions : An Inquiry Using Terrorism as an Instrumental Variable
Nearly all post-war recessions have been preceded by oil-price shocks, but is this because spikes in the price of petroleum cause economic downturns? Most research has ignored an identification problem : oil prices and the state of the world economy are endogenously determined. This paper uses terrorist incidents as an instrumental variable. In an international panel of industries, we show that after correction for simultaneity bias — though not before — the price of oil has large negative effects upon profitability. Our results seem to lend support to the claim that oil-price spikes can be a source of recessions.
The AdS Propagator and the Fate of Locality
We recently used Virasoro symmetry considerations to propose an exact formula
for a bulk proto-field in AdS. In this paper we study the propagator
. We show that many techniques from the study of
conformal blocks can be generalized to compute it, including the semiclassical
monodromy method and both forms of the Zamolodchikov recursion relations. When
the results from recursion are expanded at large central charge, they match
gravitational perturbation theory for a free scalar field coupled to gravity in
our chosen gauge.
We find that although the propagator is finite and well-defined at long
distances, its perturbative expansion in exhibits UV/IR
mixing effects. If we nevertheless interpret as a
probe of bulk locality, then when locality breaks down at
the new short-distance scale . For
with very large bulk mass, or at small central charge, bulk locality
fails at the AdS length scale. In all cases, locality `breakdown' manifests as
singularities or branch cuts at spacelike separation arising from
non-perturbative quantum gravitational effects.Comment: 42+17 pages, 7 figure
The Bulk-to-Boundary Propagator in Black Hole Microstate Backgrounds
First-quantized propagation in quantum gravitational AdS backgrounds can
be exactly reconstructed using CFT data and Virasoro symmetry. We develop
methods to compute the bulk-to-boundary propagator in a black hole microstate,
, at finite
central charge. As a first application, we show that the semiclassical theory
on the Euclidean BTZ solution sharply disagrees with the exact description, as
expected based on the resolution of forbidden thermal singularities, though
this effect may appear exponentially small for physical observers.Comment: 34+27 pages, 7 figures; v2: typos correcte
Degenerate Operators and the Expansion: Lorentzian Resummations, High Order Computations, and Super-Virasoro Blocks
One can obtain exact information about Virasoro conformal blocks by
analytically continuing the correlators of degenerate operators. We argued in
recent work that this technique can be used to explicitly resolve information
loss problems in AdS/CFT. In this paper we use the technique to perform
calculations in the small expansion: (1) we prove the
all-orders resummation of logarithmic factors in
the Lorentzian regime, demonstrating that corrections directly shift
Lyapunov exponents associated with chaos, as claimed in prior work, (2) we
perform another all-orders resummation in the limit of large with fixed
, interpolating between the early onset of chaos and late time behavior,
(3) we explicitly compute the Virasoro vacuum block to order and
, corresponding to and loop calculations in AdS, and (4) we
derive the heavy-light vacuum blocks in theories with
superconformal symmetry.Comment: 34+20 pages, 2 figure
- …