2,025 research outputs found
Towards Mutual Learning with the Rising Powers
Mutual learning is emerging as a new way of talking about the ‘how’ of development cooperation, particularly in contexts of rapid change, with countries increasingly recognising that they have much to learn from each other’s experience. Achieving the promise of universal development within the ambitious and complex framework of the Global Goals agreed in 2015 will require much more systematic and strategic efforts to learn from and share the development policy innovations of rising powers such as China and Brazil. This should include exploring opportunities for other countries to engage with the rising powers’ experiences through more structured processes of mutual learning
Edge states in graphene quantum dots: Fractional quantum Hall effect analogies and differences at zero magnetic field
We investigate the way that the degenerate manifold of midgap edge states in
quasicircular graphene quantum dots with zig-zag boundaries supports, under
free-magnetic-field conditions, strongly correlated many-body behavior
analogous to the fractional quantum Hall effect (FQHE), familiar from the case
of semiconductor heterostructures in high magnetic fields. Systematic
exact-diagonalization (EXD) numerical studies are presented for the first time
for 5 <= N <= 8 fully spin-polarized electrons and for total angular momenta in
the range of N(N-1)/2 <= L <= 150. We present a derivation of a
rotating-electron-molecule (REM) type wave function based on the methodology
introduced earlier [C. Yannouleas and U. Landman, Phys. Rev. B 66, 115315
(2002)] in the context of the FQHE in two-dimensional semiconductor quantum
dots. The EXD wave functions are compared with FQHE trial functions of the
Laughlin and the derived REM types. It is found that a variational extension of
the REM offers a better description for all fractional fillings compared with
that of the Laughlin functions (including total energies and overlaps), a fact
that reflects the strong azimuthal localization of the edge electrons. In
contrast with the multiring arrangements of electrons in circular semiconductor
quantum dots, the graphene REMs exhibit in all instances a single (0,N)
polygonal-ring molecular (crystalline) structure, with all the electrons
localized on the edge. Disruptions in the zig-zag boundary condition along the
circular edge act effectively as impurities that pin the electron molecule,
yielding single-particle densities with broken rotational symmetry that portray
directly the azimuthal localization of the edge electrons.Comment: Revtex. 14 pages with 13 figures and 2 tables. Physical Review B, in
press. For related papers, see http://www.prism.gatech.edu/~ph274cy
Strongly correlated wave functions for artificial atoms and molecules
A method for constructing semianalytical strongly correlated wave functions
for single and molecular quantum dots is presented. It employs a two-step
approach of symmetry breaking at the Hartree-Fock level and of subsequent
restoration of total spin and angular momentum symmetries via Projection
Techniques. Illustrative applications are presented for the case of a
two-electron helium-like single quantum dot and a hydrogen-like quantum dot
molecule.Comment: 9 pages. Revtex with 2 GIF and 1 EPS figures. Published version with
extensive clarifications. A version of the manuscript with high quality
figures incorporated in the text is available at
http://calcite.physics.gatech.edu/~costas/qdhelproj.html For related papers,
see http://www.prism.gatech.edu/~ph274c
Ordering our world: the quest for traces of temporal organization in autobiographical memory
An experiment examined the idea, derived from the Self Memory System model (Conway & Pleydell-Pearce, 2000), that autobiographical events are sometimes tagged in memory with labels reflecting the life era in which an event occurred. The presence of such labels should affect the ease of judgments of the order in which life events occurred. Accordingly, 39 participants judged the order of two autobiographical events. Latency data consistently showed that between-era judgments were faster than within-era judgments, when the eras were defined in terms of either: (a) college versus high school, (b) academic quarter within year, or (c) academic year within school. The accuracy data similarly supported the presence of a between-era judgment effect for the college versus high school dichotomy
A uvbyCaHbeta CCD Analysis of the Open Cluster Standard, M67,and its Relation to NGC 752
Precision CCD uvbyCaHbeta photometry is presented of the old cluster, M67,
covering one square degree with typical internal precision at the 0.005-0.020
mag level to V~17. The photometry is calibrated using standards over a wide
range in luminosity and temperature from NGC 752 and zeroed to the standard
system via published photoelectric observations. Relative to NGC 752,
differential offsets in reddening and metallicity are derived using astrometric
members, supplemented by radial-velocity information. From single-star members,
offsets in the sense (M67 - NGC 752) are Delta E(b-y) = -0.005 +/-0.001 (sem)
mag from 327 F/G dwarfs and Delta [Fe/H] = 0.062 +/- 0.006 (sem) dex from the
combined m1 and hk indices of 249 F dwarfs, leading to E(b-y) = 0.021 +/- 0.004
(sem), and [Fe/H] = +0.030 +/- 0.016 (sem) for M67, assuming [Fe/H]{Hyades} =
+0.12. With probable binaries eliminated using c1,(b-y) indices, 83 members
with relative parallax errors < 0.02 generate (m-M)_0 = 8.220 +/- 0.005 (sem)
for NGC 752 and an isochronal age of 1.45 +/- 0.05 Gyr. Using the same parallax
restriction for 312 stars, M67 has (m-M) = 9.77 +/- 0.02 (sem), leading to an
age tied solely to the luminosity of the subgiant branch of 3.70 +/- 0.03 Gyr.
The turnoff color spread implies +/- 0.1 Gyr, but the turnoff morphology
defines a younger age/higher mass for the stars, consistent with recent binary
analysis and broad-band photometry indicating possible missing physics in the
isochrones. Anomalous stars positioned blueward of the turnoff are discussed.Comment: 36 pages, 8 figures. Accepted for Astronomical Journa
General properties and analytical approximations of photorefractive solitons
We investigate general properties of spatial 1-dimensional bright
photorefractive solitons and suggest various analytical approximations for the
soliton profile and the half width, both depending on an intensity parameter r
Superflares on Ordinary Solar-Type Stars
Short duration flares are well known to occur on cool main-sequence stars as
well as on many types of `exotic' stars. Ordinary main-sequence stars are
usually pictured as being static on time scales of millions or billions of
years. Our sun has occasional flares involving up to ergs which
produce optical brightenings too small in amplitude to be detected in
disk-integrated brightness. However, we identify nine cases of superflares
involving to ergs on normal solar-type stars. That is,
these stars are on or near the main-sequence, are of spectral class from F8 to
G8, are single (or in very wide binaries), are not rapid rotators, and are not
exceedingly young in age. This class of stars includes many those recently
discovered to have planets as well as our own Sun, and the consequences for any
life on surrounding planets could be profound. For the case of the Sun,
historical records suggest that no superflares have occurred in the last two
millennia.Comment: 16 pages, accepted for publication in Ap
CT findings and patterns of e-cigarette or vaping product use-associated lung injury: A multicenter cohort of 160 cases
BACKGROUND: e-Cigarette or vaping-induced lung injury (EVALI) causes a spectrum of CT lung injury patterns. Relative frequencies and associations with vaping behavior are unknown.
RESEARCH QUESTION: What are the frequencies of imaging findings and CT patterns in EVALI and what is the relationship to vaping behavior?
STUDY DESIGN AND METHODS: CT scans of 160 subjects with EVALI from 15 institutions were retrospectively reviewed. CT findings and patterns were defined and agreed on via consensus. The parenchymal organizing pneumonia (OP) pattern was defined as regional or diffuse ground-glass opacity (GGO) ± consolidation without centrilobular nodules (CNs). An airway-centered OP pattern was defined as diffuse CNs with little or no GGO, whereas a mixed OP pattern was a combination of the two. Other patterns included diffuse alveolar damage (DAD), acute eosinophilic-like pneumonia, and pulmonary hemorrhage. Cases were classified as atypical if they did not fit into a pattern. Imaging findings, pattern frequencies, and injury severity were correlated with substance vaped (marijuana derives [tetrahydrocannabinol] [THC] only, nicotine derivates only, and both), vaping frequency, regional geography, and state recreational THC legality. One-way analysis of variance, χ
RESULTS: A total of 160 patients (79.4% men) with a mean age of 28.2 years (range, 15-68 years) with EVALI underwent CT scan. Seventy-seven (48.1%), 15 (9.4%), and 68 (42.5%) patients admitted to vaping THC, nicotine, or both, respectively. Common findings included diffuse or lower lobe GGO with subpleural (78.1%), lobular (59.4%), or peribronchovascular (PBV) sparing (40%). Septal thickening (50.6%), lymphadenopathy (63.1%), and CNs (36.3%) were common. PBV sparing was associated with younger age (P = .02). Of 160 subjects, 156 (97.5%) had one of six defined patterns. Parenchymal, airway-centered, and mixed OP patterns were seen in 89 (55.6%), 14 (8.8%), and 32 (20%) patients, respectively. Acute eosinophilic-like pneumonia (six of 160, 3.8%), DAD (nine of 160, 5.6%), pulmonary hemorrhage (six of 160, 3.8%), and atypical (four of 160, 2.5%) patterns were less common. Increased vaping frequency was associated with more severe injury (P = .008). Multivariable analysis showed a negative association between vaping for \u3e 6 months and DAD pattern (P = .03). Two subjects (1.25%) with DAD pattern died. There was no relation between pattern and injury severity, geographic location, and state legality of recreational use of THC.
INTERPRETATION: EVALI typically causes an OP pattern but exists on a spectrum of acute lung injury. Vaping habits do not correlate with CT patterns except for negative correlation between vaping \u3e 6 months and DAD pattern. PBV sparing, not previously described in acute lung injury, is a common finding
Theory and Applications of Robust Optimization
In this paper we survey the primary research, both theoretical and applied,
in the area of Robust Optimization (RO). Our focus is on the computational
attractiveness of RO approaches, as well as the modeling power and broad
applicability of the methodology. In addition to surveying prominent
theoretical results of RO, we also present some recent results linking RO to
adaptable models for multi-stage decision-making problems. Finally, we
highlight applications of RO across a wide spectrum of domains, including
finance, statistics, learning, and various areas of engineering.Comment: 50 page
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