27 research outputs found
Î and X bandgap hydrostatic deformation potentials for epitaxial In<sub>0.52</sub>Al<sub>0.48</sub>As on InP(001)
The pressure dependence of the direct and indirect bandgap of epitaxial In0.52Al0.48As on InP(001) substrate has been measured using photoluminescence up to 92 kbar hydrostatic pressure. The bandgap changes from Î toX at an applied pressure of ⌠43 kbar. Hydrostatic deformation potentials for both the Î andX bandgaps are deduced, after correcting for the elastic constant (bulk modulus) mismatch between the epilayer and the substrate. For the epilayer we obtain (Îd+1/3Îuâa)asâ(6â
92+0â
3)eV and+(2.81±0.15)eV for the Î andX bandgaps respectively. From the pressure dependence of the normalized Î-bandgap photoluminescence intensity a Î-X lifetime ratio, (ÏÎ/ÏX), of 4.1Ă10â3 is deduced
Estimating global and North American methane emissions with high spatial resolution using GOSAT satellite data
We use 2009-2011 space-borne methane observations from the Greenhouse Gases Observing SATellite (GOSAT) to estimate global and North American methane emissions with 4° x 5° and up to 50 km x 50 km spatial resolution, respectively. GEOS-Chem and GOSAT data are first evaluated with atmospheric methane observations from surface and tower networks (NOAA/ESRL, TCCON) and aircraft (NOAA/ESRL, HIPPO), using the GEOS-Chem chemical transport model as a platform to facilitate comparison of GOSAT with in situ data. This identifies a high-latitude bias between the GOSAT data and GEOS-Chem that we correct via quadratic regression. Our global adjoint-based inversion yields a total methane source of 539 Tg aâ1 with some important regional corrections to the EDGARv4.2 inventory used as a prior. Results serve as dynamic boundary conditions for an analytical inversion of North American methane emissions using radial basis functions to achieve high resolution of large sources and provide error characterization. We infer a US anthropogenic methane source of 40.2-42.7 Tg aâ1, as compared to 24.9-27.0 Tg aâ1 in the EDGAR and EPA bottom-up inventories, and 30.0-44.5 Tg aâ1 in recent inverse studies. Our estimate is supported by independent surface and aircraft data and by previous inverse studies for California. We find that the emissions are highest in the southern-central US, the Central Valley of California, and Florida wetlands; large isolated point sources such as the US Four Corners also contribute. Using prior information on source locations, we attribute 29-44 % of US anthropogenic methane emissions to livestock, 22-31 % to oil/gas, 20 % to landfills/wastewater, and 11-15 % to coal. Wetlands contribute an additional 9.0-10.1 Tg aâ1
D-branes in Nongeometric Backgrounds
"T-fold" backgrounds are generically-nongeometric compactifications of string
theory, described by T^n fibrations over a base N with transition functions in
the perturbative T-duality group. We review Hull's doubled torus formalism,
which geometrizes these backgrounds, and use the formalism to constrain the
D-brane spectrum (to leading order in g_s and alpha') on T^n fibrations over
S^1 with O(n,n;Z) monodromy. We also discuss the (approximate) moduli space of
such branes and argue that it is always geometric. For a D-brane located at a
point on the base N, the classical ``D-geometry'' is a T^n fibration over a
multiple cover of N.Comment: 29 pages; uses harvmac.tex; v2: substantial revision throughou
Lectures on Nongeometric Flux Compactifications
These notes present a pedagogical review of nongeometric flux
compactifications. We begin by reviewing well-known geometric flux
compactifications in Type II string theory, and argue that one must include
nongeometric "fluxes" in order to have a superpotential which is invariant
under T-duality. Additionally, we discuss some elementary aspects of the
worldsheet description of nongeometric backgrounds. This review is based on
lectures given at the 2007 RTN Winter School at CERN.Comment: 31 pages, JHEP
Structure in 6D and 4D N=1 supergravity theories from F-theory
We explore some aspects of 4D supergravity theories and F-theory vacua that
are parallel to structures in the space of 6D theories. The spectrum and
topological terms in 4D supergravity theories correspond to topological data of
F-theory geometry, just as in six dimensions. In particular, topological
axion-curvature squared couplings appear in 4D theories; these couplings are
characterized by vectors in the dual to the lattice of axion shift symmetries
associated with string charges. These terms are analogous to the Green-Schwarz
terms of 6D supergravity theories, though in 4D the terms are not generally
linked with anomalies. We outline the correspondence between F-theory topology
and data of the corresponding 4D supergravity theories. The correspondence of
geometry with structure in the low-energy action illuminates topological
aspects of heterotic-F-theory duality in 4D as well as in 6D. The existence of
an F-theory realization also places geometrical constraints on the 4D
supergravity theory in the large-volume limit.Comment: 63 page
A ten-dimensional action for non-geometric fluxes
The NSNS Lagrangian of ten-dimensional supergravity is rewritten via a change
of field variables inspired by Generalized Complex Geometry. We obtain a new
metric and dilaton, together with an antisymmetric bivector field which leads
to a ten-dimensional version of the non-geometric Q-flux. Given the involved
global aspects of non-geometric situations, we prescribe to use this new
Lagrangian, whose associated action is well-defined in some examples
investigated here. This allows us to perform a standard dimensional reduction
and to recover the usual contribution of the Q-flux to the four-dimensional
scalar potential. An extension of this work to include the R-flux is discussed.
The paper also contains a brief review on non-geometry.Comment: 47 pages; v2: minor modifications, references added, version to be
published in JHE