11,155 research outputs found
Financial Liberalization and Monetary Policy Cooperation in East Asia
As the countries in East Asia embark on financial liberalization, a key issue that confronts policymakers is the greater complexity of risks that is injected into the financial system. In particular, capital account liberalization may potentially increase the vulnerability of individual countries to external financial shocks. This paper advocates the optimally cascading of financial liberalization that is consistent across three dimensions: extent of domestic financial liberalization; the degree of exchange rate flexibility; and the scope of capital account liberalization. Unless the process of liberalization is properly managed, it could provoke destabilizing capital flows and lead to volatile exchange rates. Smooth responses to fluctuating capital flows require accelerated institutional reforms in individual countries and an upgraded regional financial infrastructure. We argue that informal monetary arrangements, sequenced from simple to more intensive commitments, can go a long way in improving sovereign and regional institutions both to handle ongoing financial liberalization and to promote intra-regional currency stability.
Exciton band topology in spontaneous quantum anomalous Hall insulators: applications to twisted bilayer graphene
We uncover topological features of neutral particle-hole pair excitations of
correlated quantum anomalous Hall (QAH) insulators whose approximately flat
conduction and valence bands have equal and opposite non-zero Chern number.
Using an exactly solvable model we show that the underlying band topology
affects both the center-of-mass and relative motion of particle-hole bound
states. This leads to the formation of topological exciton bands whose features
are robust to nonuniformity of both the dispersion and the Berry curvature. We
apply these ideas to recently-reported broken-symmetry spontaneous QAH
insulators in substrate aligned magic-angle twisted bilayer graphene.Comment: 5+10 pages, 2+2 figures; improved treatment of interaction effects,
leading to |C|=1 exciton
Large-scale Bias and Efficient Generation of Initial Conditions for Non-Local Primordial Non-Gaussianity
We study the scale-dependence of halo bias in generic (non-local) primordial
non-Gaussian (PNG) initial conditions of the type motivated by inflation,
parametrized by an arbitrary quadratic kernel. We first show how to generate
non-local PNG initial conditions with minimal overhead compared to local PNG
models for a general class of primordial bispectra that can be written as
linear combinations of separable templates. We run cosmological simulations for
the local, and non-local equilateral and orthogonal models and present results
on the scale-dependence of halo bias. We also derive a general formula for the
Fourier-space bias using the peak-background split (PBS) in the context of the
excursion set approach to halos and discuss the difference and similarities
with the known corresponding result from local bias models. Our PBS bias
formula generalizes previous results in the literature to include non-Markovian
effects and non-universality of the mass function and are in better agreement
with measurements in numerical simulations than previous results for a variety
of halo masses, redshifts and halo definitions. We also derive for the first
time quadratic bias results for arbitrary non-local PNG, and show that
non-linear bias loops give small corrections at large-scales. The resulting
well-behaved perturbation theory paves the way to constrain non-local PNG from
measurements of the power spectrum and bispectrum in galaxy redshift surveys.Comment: 43 pages, 10 figures. v2: references added. 2LPT parallel code for
generating non-local PNG initial conditions available at
http://cosmo.nyu.edu/roman/2LP
Photooxidation of 2-methyl-3-buten-2-ol (MBO) as a potential source of secondary organic aerosol
2-Methyl-3-buten-2-ol (MBO) is an important biogenic hydrocarbon emitted in large quantities by pine forests. Atmospheric photooxidation of MBO is known to lead to oxygenated compounds, such as glycolaldehyde, which is the precursor to glyoxal. Recent studies have shown that the reactive uptake of glyoxal onto aqueous particles can lead to formation of secondary organic aerosol (SOA). In this work, MBO photooxidation under high- and low-NO_x conditions was performed in dual laboratory chambers to quantify the yield of glyoxal and investigate the potential for SOA formation. The yields of glycolaldehyde and 2-hydroxy-2-methylpropanal (HMPR), fragmentation products of MBO photooxidation, were observed to be lower at lower NO_x concentrations. Overall, the glyoxal yield from MBO photooxidation was 25% under high-NO_x and 4% under low-NO_x conditions. In the presence of wet ammonium sulfate seed and under high-NO_x conditions, glyoxal uptake and SOA formation were not observed conclusively, due to relatively low (<30 ppb) glyoxal concentrations. Slight aerosol formation was observed under low-NO_x and dry conditions, with aerosol mass yields on the order of 0.1%. The small amount of SOA was not related to glyoxal uptake, but is likely a result of reactions similar to those that generate isoprene SOA under low-NO_x conditions. The difference in aerosol yields between MBO and isoprene photooxidation under low-NO_x conditions is consistent with the difference in vapor pressures between triols (from MBO) and tetrols (from isoprene). Despite its structural similarity to isoprene, photooxidation of MBO is not expected to make a significant contribution to SOA formation
Counterposition and negative phase velocity in uniformly moving dissipative materials
The Lorentz transformations of electric and magnetic fields were implemented
to study (i) the refraction of linearly polarized plane waves into a half-space
occupied by a uniformly moving material, and (ii) the traversal of linearly
polarized Gaussian beams through a uniformly moving slab. Motion was taken to
occur tangentially to the interface(s) and in the plane of incidence. The
moving materials were assumed to be isotropic, homogeneous, dissipative
dielectric materials from the perspective of a co-moving observer. Two
different moving materials were considered: from the perspective of a co-moving
observer, material A supports planewave propagation with only positive phase
velocity, whereas material B supports planewave propagation with both positive
and negative phase velocity, depending on the polarization state. For both
materials A and B, the sense of the phase velocity and whether or not
counterposition occurred, as perceived by a nonco-moving observer, could be
altered by varying the observer's velocity. Furthermore, the lateral position
of a beam upon propagating through a uniformly moving slab made of material A,
as perceived by a nonco-moving observer, could be controlled by varying the
observer's velocity. In particular, at certain velocities, the transmitted beam
emerged from the slab laterally displaced in the direction opposite to the
direction of incident beam. The transmittances of a uniformly moving slab made
of material B were very small and the energy density of the transmitted beam
was largely concentrated in the direction normal to the slab, regardless of the
observer's velocity
Supersymmetry on the honeycomb lattice: resonating charge stripes, superfrustration, and domain walls
We study a model of spinless fermions on the honeycomb lattice with
nearest-neighbor exclusion and extended repulsive interactions that exhibits
`lattice supersymmetry' [P. Fendley, K. Schoutens, and J. de Boer, Phys. Rev.
Lett. 90, 120402 (2003)]. Using a combination of exact diagonalization of large
( site) systems, mean-field numerics, and symmetry analysis, we
establish a rich phase structure as a function of fermion density, that
includes non-Fermi liquid behavior, resonating charge stripes, domain-wall and
bubble physics, and identify a finite range of fillings with extensive ground
state degeneracy and both gapped and gapless spectra. We comment on the
stability of our results to relaxing the stringent requirements for
supersymmetry, and on their possible broader relevance to systems of
strongly-correlated electrons with extended repulsive interactions.Comment: 15 pages, 12 figures, 1 tabl
Coarse-Grained MD Simulations Reveal Beta-Amyloid Fibrils of Various Sizes Bind to Interfacial Liquid-Ordered and Liquid-Disordered Regions in Phase Separated Lipid Rafts with Diverse Membrane-Bound Conformational States
The membrane binding behaviors of beta-amyloid fibrils, dimers to pentamers, from solution to lipid raft surfaces, were investigated using coarse-grained (CG) MD simulations. Our CG rafts contain phospholipid, cholesterol (with or without tail- or headgroup modifications), and with or without asymmetrically distributed monosialotetrahexosylganglioside (GM1). All rafts exhibited liquid-ordered (Lo), liquid-disordered (Ld), and interfacial Lo/Ld (Lod) domains, with domain sizes depending on cholesterol structure. For rafts without GM1, all fibrils bound to the Lod domains. Specifically, dimer fibrils bound exclusively via the C-terminal, while larger fibrils could bind via other protein regions. Interestingly, a membrane-inserted state was detected for a trimer fibril in a raft with tail-group modified cholesterol. For rafts containing GM1, fibrils bound either to the GM1-clusters, with numerous membrane-bound conformations, or to the non-GM1-containing-Lod domains via the C-terminal. Our results indicate beta-amyloid fibrils bind to Lod domains or GM1, with diversified membrane-bound conformations, in structurally heterogeneous lipid membranes
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