4,684 research outputs found
Abstracting Fairness: Oracles, Metrics, and Interpretability
It is well understood that classification algorithms, for example, for
deciding on loan applications, cannot be evaluated for fairness without taking
context into account. We examine what can be learned from a fairness oracle
equipped with an underlying understanding of ``true'' fairness. The oracle
takes as input a (context, classifier) pair satisfying an arbitrary fairness
definition, and accepts or rejects the pair according to whether the classifier
satisfies the underlying fairness truth. Our principal conceptual result is an
extraction procedure that learns the underlying truth; moreover, the procedure
can learn an approximation to this truth given access to a weak form of the
oracle. Since every ``truly fair'' classifier induces a coarse metric, in which
those receiving the same decision are at distance zero from one another and
those receiving different decisions are at distance one, this extraction
process provides the basis for ensuring a rough form of metric fairness, also
known as individual fairness. Our principal technical result is a higher
fidelity extractor under a mild technical constraint on the weak oracle's
conception of fairness. Our framework permits the scenario in which many
classifiers, with differing outcomes, may all be considered fair. Our results
have implications for interpretablity -- a highly desired but poorly defined
property of classification systems that endeavors to permit a human arbiter to
reject classifiers deemed to be ``unfair'' or illegitimately derived.Comment: 17 pages, 1 figur
Author Correction: Task-dependent representations of stimulus and choice in mouse parietal cortex.
In the original version of this Article, the Acknowledgements section was inadvertently omitted. This has now been corrected in both the PDF and HTML versions of the Article
New mechanism of generation of large-scale magnetic field in a sheared turbulent plasma
A review of recent studies on a new mechanism of generation of large-scale
magnetic field in a sheared turbulent plasma is presented. This mechanism is
associated with the shear-current effect which is related to the W x J-term in
the mean electromotive force. This effect causes the generation of the
large-scale magnetic field even in a nonrotating and nonhelical homogeneous
sheared turbulent convection whereby the alpha effect vanishes. It is found
that turbulent convection promotes the shear-current dynamo instability, i.e.,
the heat flux causes positive contribution to the shear-current effect.
However, there is no dynamo action due to the shear-current effect for small
hydrodynamic and magnetic Reynolds numbers even in a turbulent convection, if
the spatial scaling for the turbulent correlation time is k^{-2}, where k is
the small-scale wave number. We discuss here also the nonlinear mean-field
dynamo due to the shear-current effect and take into account the transport of
magnetic helicity as a dynamical nonlinearity. The magnetic helicity flux
strongly affects the magnetic field dynamics in the nonlinear stage of the
dynamo action. When the magnetic helicity flux is not small, the saturated
level of the mean magnetic field is of the order of the equipartition field
determined by the turbulent kinetic energy. The obtained results are important
for elucidation of origin of the large-scale magnetic fields in astrophysical
and cosmic sheared turbulent plasma.Comment: 7 pages, Planetory and Space Science, in pres
Three-coordinate iron(II) expanded ring N-heterocyclic carbene complexes
A sterically demanding seven-membered expanded ring N-heterocyclic carbene (NHC) ligand allows access to rare examples of three-coordinate iron(II)-NHC complexes incorporating only halide coligands of the general formula [Fe(NHC)X 2 ] (NHC = 7-DiPP; X = Br (1) Cl (2)). Reducing the steric influence of the ancillary NHC ligand through modulation of the N-aryl substituents leads to either four- or three-coordinate complexes of the general formula [Fe(NHC)Br 2 (THF)] (3) or [Fe(NHC)Br 2 ] (4) (NHC = 7-Mes), dependent upon the solvent of recrystallization. The further reduction of NHC steric influence results in four-coordinate geometries at iron in the form of the dimeric species [Fe(NHC)Br(μ-Br)] 2 (5) or [Fe(NHC)Br 2 (THF)] (6) (NHC = SDiPP), again dependent upon the solvent of recrystallization. Compounds 1-6 have been analyzed by 1 H NMR spectroscopy, X-ray crystallography, elemental microanalysis, Mössbauer spectroscopy (for 1 and 3-5), and Evans method magnetic susceptibility. In addition to these measurements the three-coordinate species 1 and 4 have been further analyzed by SQUID magnetometry and CASSCF calculations, which show significant magnetic anisotropy that is extremely sensitive to the coordination geometry
Cross helicity and turbulent magnetic diffusivity in the solar convection zone
In a density-stratified turbulent medium the cross helicity is
considered as a result of the interaction of the velocity fluctuations and a
large-scale magnetic field. By means of a quasilinear theory and by numerical
simulations we find the cross helicity and the mean vertical magnetic field
anti-correlated. In the high-conductivity limit the ratio of the helicity and
the mean magnetic field equals the ratio of the magnetic eddy diffusivity and
the (known) density scale height. The result can be used to predict that the
cross helicity at the solar surface exceeds the value of 1 Gauss km/s. Its sign
is anti-correlated with that of the radial mean magnetic field. Alternatively,
we can use our result to determine the value of the turbulent magnetic
diffusivity from observations of the cross helicity.Comment: 9 pages, 2 figures, submitted to Solar Physic
Kinematic alpha effect in isotropic turbulence simulations
Using numerical simulations at moderate magnetic Reynolds numbers up to 220
it is shown that in the kinematic regime, isotropic helical turbulence leads to
an alpha effect and a turbulent diffusivity whose values are independent of the
magnetic Reynolds number, \Rm, provided \Rm exceeds unity. These turbulent
coefficients are also consistent with expectations from the first order
smoothing approximation. For small values of \Rm, alpha and turbulent
diffusivity are proportional to \Rm. Over finite time intervals meaningful
values of alpha and turbulent diffusivity can be obtained even when there is
small-scale dynamo action that produces strong magnetic fluctuations. This
suggests that small-scale dynamo-generated fields do not make a correlated
contribution to the mean electromotive force.Comment: Accepted for publication in MNRAS Letter
Teaching Engineering Design Through Wearable Device Design Competition (Evaluation)
The Wearable Device Challenge was developed at the Nanosystems Engineering Research Center for Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST). The Challenge is rooted in the research and innovation ecosystem of the Center and its vision: to have a transformational impact on the way doctors and patients manage wellness through wearable, self-powered health and environmental monitoring systems. At its core, the program teaches middle and high school teachers and students how to apply the engineering design process to solve real-world problems through a project-based approach. The program impacts several hundred students in North Carolina annually through real-world, relevant, hands-on engineering design challenges. Teachers are empowered to introduce engineering design into a variety of both formal and informal educational settings, and students are given the opportunity to explore exciting, cutting-edge applications of science and technology that will inspire them to continue in science, technology, engineering, and mathematics fields
Power-law corrections to entanglement entropy of horizons
We re-examine the idea that the origin of black-hole entropy may lie in the
entanglement of quantum fields between inside and outside of the horizon.
Motivated by the observation that certain modes of gravitational fluctuations
in a black-hole background behave as scalar fields, we compute the entanglement
entropy of such a field, by tracing over its degrees of freedom inside a
sphere. We show that while this entropy is proportional to the area of the
sphere when the field is in its ground state, a correction term proportional to
a fractional power of area results when the field is in a superposition of
ground and excited states. The area law is thus recovered for large areas.
Further, we identify location of the degrees of freedom that give rise to the
above entropy.Comment: 16 pages, 6 figures, to appear in Phys. Rev.
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