5,267 research outputs found
Why Engage the Public Sector and How?
This article, co-authored by Maximilian Martin, Global Head, UBS Philanthropy Services, and Greg Hills explores different ways in which foundations can interact with governments in order to achieve social impact. By the nature of the scale and authority of government institutions, changes in the formulation or execution of public policy can contribute to widespread social benefit and systemic change. Many people feel that foundations are well-positioned to influence these changes in public policy, and this article investigates different approaches that foundations can take in order to achieve this change
Learning Tuple Probabilities
Learning the parameters of complex probabilistic-relational models from
labeled training data is a standard technique in machine learning, which has
been intensively studied in the subfield of Statistical Relational Learning
(SRL), but---so far---this is still an under-investigated topic in the context
of Probabilistic Databases (PDBs). In this paper, we focus on learning the
probability values of base tuples in a PDB from labeled lineage formulas. The
resulting learning problem can be viewed as the inverse problem to confidence
computations in PDBs: given a set of labeled query answers, learn the
probability values of the base tuples, such that the marginal probabilities of
the query answers again yield in the assigned probability labels. We analyze
the learning problem from a theoretical perspective, cast it into an
optimization problem, and provide an algorithm based on stochastic gradient
descent. Finally, we conclude by an experimental evaluation on three real-world
and one synthetic dataset, thus comparing our approach to various techniques
from SRL, reasoning in information extraction, and optimization
-Analysis Minimization and Generalized (Co-)Sparsity: When Does Recovery Succeed?
This paper investigates the problem of signal estimation from undersampled
noisy sub-Gaussian measurements under the assumption of a cosparse model. Based
on generalized notions of sparsity, we derive novel recovery guarantees for the
-analysis basis pursuit, enabling highly accurate predictions of its
sample complexity. The corresponding bounds on the number of required
measurements do explicitly depend on the Gram matrix of the analysis operator
and therefore particularly account for its mutual coherence structure. Our
findings defy conventional wisdom which promotes the sparsity of analysis
coefficients as the crucial quantity to study. In fact, this common paradigm
breaks down completely in many situations of practical interest, for instance,
when applying a redundant (multilevel) frame as analysis prior. By extensive
numerical experiments, we demonstrate that, in contrast, our theoretical
sampling-rate bounds reliably capture the recovery capability of various
examples, such as redundant Haar wavelets systems, total variation, or random
frames. The proofs of our main results build upon recent achievements in the
convex geometry of data mining problems. More precisely, we establish a
sophisticated upper bound on the conic Gaussian mean width that is associated
with the underlying -analysis polytope. Due to a novel localization
argument, it turns out that the presented framework naturally extends to stable
recovery, allowing us to incorporate compressible coefficient sequences as
well
Four Revolutions in Global Philanthropy
Philanthropy is currently undergoing four revolutions in parallel. This paper identifies and analyzes the four main fault lines which will influence the next decades of global philanthropy. All are related to what we can refer to as the market revolution in global philanthropy. As global philanthropy moves beyond grantmaking, into investment approaches that produce a social as well as a financial return, this accelerates the mainstreaming of a variety of niche activities. They marry effectiveness, social impact, and market mechanisms
Real-space imaging of a topological protected edge state with ultracold atoms in an amplitude-chirped optical lattice
Topological states of matter, as quantum Hall systems or topological
insulators, cannot be distinguished from ordinary matter by local measurements
in the bulk of the material. Instead, global measurements are required,
revealing topological invariants as the Chern number. At the heart of
topological materials are topologically protected edge states that occur at the
intersection between regions of different topological order. Ultracold atomic
gases in optical lattices are promising new platforms for topological states of
matter, though the observation of edge states has so far been restricted in
these systems to the state space imposed by the internal atomic structure. Here
we report on the observation of an edge state between two topological distinct
phases of an atomic physics system in real space using optical microscopy. An
interface between two spatial regions of different topological order is
realized in a one-dimensional optical lattice of spatially chirped amplitude.
To reach this, a magnetic field gradient causes a spatial variation of the
Raman detuning in an atomic rubidium three- level system and a corresponding
spatial variation of the coupling between momentum eigenstates. This novel
experimental technique realizes a cold atom system described by a Dirac
equation with an inhomogeneous mass term closely related to the SSH-model. The
observed edge state is characterized by measuring the overlap to various
initial states, revealing that this topological state has singlet nature in
contrast to the other system eigenstates, which occur pairwise. We also
determine the size of the energy gap to the adjacent eigenstate doublet. Our
findings hold prospects for the spectroscopy of surface states in topological
matter and for the quantum simulation of interacting Dirac systems
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