7,485 research outputs found
QCD Factorization in Decays into
Based on the QCD factorization approach we analyse the branching ratios for
the channel . From the comparisons with experimental data
provided by CLEO, BELLE and BABAR we constrain the form factor and propose boundaries for this form factor depending on
the CKM matrix element parameters and .Comment: 11 pages, 9 figures. Talk presented at Fourth Tropical Workshop,
Cairns, Australia, 9--13 June 2003. Proceedings to be published by AI
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Introduction: Urban revolutions in the age of global urbanism
This special issue, papers presented at an Urban Studies Foundation-funded conference in Jakarta (March 2011), examines the current ‘urban century’ in terms of three revolutions. Revolutions from above index the logics and norms of mainstream global urbanism, particularly the form they have taken as policymakers work with municipal officials worldwide to organise urban development around neoliberal norms. Revolutions from below refer to the multifaceted contestations of global urbanism that take place in and around cities, ranging from urban street demonstrations and occupations (such as those riveting the world in early 2011 when these papers were written) to the quotidian actions of those pursuing politics and livelihoods that subvert the norms of mainstream global urbanism. It also highlights conceptual revolutions, referencing the ongoing challenge of reconceptualising urban theory from the South – not simply as a hemispheric location or geopolitical category but an epistemological stance, staged from many different locations but always fraught with the differentials of power and the weight of historical geographies. Drawing on the insights of scholars writing from, and not just about, such locations, a further iteration in this ‘southern’ turn of urban theorising is proposed. This spatio-temporal conjunctural approach emphasises how the specificity of cities – their existence as entities that are at once singular and universal – emerges from spatio-temporal dynamics, connectivities and horizontal and vertical relations. Practically, such scholarship entails taking the field seriously through collaborative work that is multi-sited, engages people along the spectrum of academics and activists, and is presented before and scrutinised by multiple publics
Unbounded Human Learning: Optimal Scheduling for Spaced Repetition
In the study of human learning, there is broad evidence that our ability to
retain information improves with repeated exposure and decays with delay since
last exposure. This plays a crucial role in the design of educational software,
leading to a trade-off between teaching new material and reviewing what has
already been taught. A common way to balance this trade-off is spaced
repetition, which uses periodic review of content to improve long-term
retention. Though spaced repetition is widely used in practice, e.g., in
electronic flashcard software, there is little formal understanding of the
design of these systems. Our paper addresses this gap in three ways. First, we
mine log data from spaced repetition software to establish the functional
dependence of retention on reinforcement and delay. Second, we use this memory
model to develop a stochastic model for spaced repetition systems. We propose a
queueing network model of the Leitner system for reviewing flashcards, along
with a heuristic approximation that admits a tractable optimization problem for
review scheduling. Finally, we empirically evaluate our queueing model through
a Mechanical Turk experiment, verifying a key qualitative prediction of our
model: the existence of a sharp phase transition in learning outcomes upon
increasing the rate of new item introductions.Comment: Accepted to the ACM SIGKDD Conference on Knowledge Discovery and Data
Mining 201
Structure of the solar photosphere studied from the radiation hydrodynamics code ANTARES
The ANTARES radiation hydrodynamics code is capable of simulating the solar
granulation in detail unequaled by direct observation. We introduce a
state-of-the-art numerical tool to the solar physics community and demonstrate
its applicability to model the solar granulation. The code is based on the
weighted essentially non-oscillatory finite volume method and by its
implementation of local mesh refinement is also capable of simulating turbulent
fluids. While the ANTARES code already provides promising insights into
small-scale dynamical processes occurring in the quiet-Sun photosphere, it will
soon be capable of modeling the latter in the scope of radiation
magnetohydrodynamics. In this first preliminary study we focus on the vertical
photospheric stratification by examining a 3-D model photosphere with an
evolution time much larger than the dynamical timescales of the solar
granulation and of particular large horizontal extent corresponding to on the solar surface to smooth out horizontal spatial
inhomogeneities separately for up- and downflows. The highly resolved Cartesian
grid thereby covers of the upper convection zone and the
adjacent photosphere. Correlation analysis, both local and two-point, provides
a suitable means to probe the photospheric structure and thereby to identify
several layers of characteristic dynamics: The thermal convection zone is found
to reach some ten kilometers above the solar surface, while convectively
overshooting gas penetrates even higher into the low photosphere. An wide transition layer separates the convective from the
oscillatory layers in the higher photosphere.Comment: Accepted for publication in Astrophysics and Space Science; 18 pages,
12 figures, 2 tables; typos correcte
Social marketing: Immunizing against unethical practice
A simple approach for the catalytic conversion of primary alcohols into their corresponding esters and amides, with evolution of H2 gas using in situ formed ruthenium PNP- and PNN-pincer catalysts, is presented. The evaluation showed conversions for the esterification with turnover numbers as high as 4300, and 4400 for the amidation
The Impact of Isospin Breaking on the Distribution of Transition Probabilities
In the present paper we investigate the effect of symmetry breaking in the
statistical distributions of reduced transition amplitudes and reduced
transition probabilities. These quantities are easier to access experimentally
than the components of the eigenvectors and were measured by Adams et al. for
the electromagnetic transitions in ^{26}Al. We focus on isospin symmetry
breaking described by a matrix model where both, the Hamiltonian and the
electromagnetic operator, break the symmetry. The results show that for partial
isospin conservation, the statistical distribution of the reduced transition
probability can considerably deviate from the Porter-Thomas distribution.Comment: 16 pages, 8 figures, submitted to PR
Electronic Correlations in Vanadium Revealed by Electron-Positron Annihilation Measurements
The electronic structure of vanadium measured by Angular Correlation of
electron-positron Annihilation Radiation (ACAR) is compared with the
predictions of the combined Density Functional and Dynamical Mean-Field Theory
(DMFT). Reconstructing the momentum density from five 2D projections we were
able to determine the full Fermi surface and found excellent agreement with the
DMFT calculations. In particular, we show that the local, dynamic self-energy
corrections contribute to the anisotropy of the momentum density and need to be
included to explain the experimental results
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