2,287 research outputs found
UFO: A unified method for controlling Understandability and Faithfulness Objectives in concept-based explanations for CNNs
Concept-based explanations for convolutional neural networks (CNNs) aim to
explain model behavior and outputs using a pre-defined set of semantic concepts
(e.g., the model recognizes scene class ``bedroom'' based on the presence of
concepts ``bed'' and ``pillow''). However, they often do not faithfully (i.e.,
accurately) characterize the model's behavior and can be too complex for people
to understand. Further, little is known about how faithful and understandable
different explanation methods are, and how to control these two properties. In
this work, we propose UFO, a unified method for controlling Understandability
and Faithfulness Objectives in concept-based explanations. UFO formalizes
understandability and faithfulness as mathematical objectives and unifies most
existing concept-based explanations methods for CNNs. Using UFO, we
systematically investigate how explanations change as we turn the knobs of
faithfulness and understandability. Our experiments demonstrate a
faithfulness-vs-understandability tradeoff: increasing understandability
reduces faithfulness. We also provide insights into the ``disagreement
problem'' in explainable machine learning, by analyzing when and how
concept-based explanations disagree with each other
Magnetic resonance peak and nonmagnetic impurities
Nonmagnetic Zn impurities are known to strongly suppress superconductivity.
We review their effects on the spin excitation spectrum in , as investigated by inelastic neutron scattering measurements.Comment: Proceedings of Mato Advanced Research Workshop BLED 2000. To appear
in Nato Science Series: B Physic
"Help Me Help the AI": Understanding How Explainability Can Support Human-AI Interaction
Despite the proliferation of explainable AI (XAI) methods, little is
understood about end-users' explainability needs. This gap is critical, because
end-users may have needs that XAI methods should but don't yet support. To
address this gap and contribute to understanding how explainability can support
human-AI interaction, we conducted a study of a real-world AI application via
interviews with 20 end-users of Merlin, a bird-identification app. We found
that people express a need for practically useful information that can improve
their collaboration with the AI system, and intend to use XAI explanations for
calibrating trust, improving their task skills, changing their behavior to
supply better inputs to the AI system, and giving constructive feedback to
developers. We also assessed end-users' perceptions of existing XAI approaches,
finding that they prefer part-based explanations. Finally, we discuss
implications of our findings and provide recommendations for future designs of
XAI, specifically XAI for human-AI collaboration
Towards spin-polarized two-dimensional electron gas at a surface of an antiferromagnetic insulating oxide
The surfaces of transition-metal oxides with the perovskite structure are fertile grounds for the discovery of novel electronic and magnetic phenomena. In this article, we combine scanning transmission electron microscopy (STEM) with density functional theory (DFT) calculations to obtain the electronic and magnetic properties of the (001) surface of a
(
LaFe
O
3
)
8
/
(
SrFe
O
3
)
1
superlattice film capped with four layers of
LaFe
O
3
. Simultaneously acquired STEM images and electron-energy-loss spectra reveal the surface structure and a reduction in the oxidation state of iron from
F
e
3
+
in the bulk to
F
e
2
+
at the surface, extending over several atomic layers, which signals the presence of oxygen vacancies. The DFT calculations confirm the reduction in terms of oxygen vacancies and further demonstrate the stabilization of an exotic phase in which the surface layer is half metallic and ferromagnetic, while the bulk remains antiferromagnetic and insulating. Based on the calculations, we predict that the surface magnetism and conductivity can be controlled by tuning the partial pressure of oxygen
N\'eel transition, spin fluctuations, and pseudogap in underdoped cuprates by a Lorentz invariant four-fermion model in 2+1 dimensions
We show that the N\'eel transition and spin fluctuations near the N\'eel
transition in planar cuprates can be described by an SU(2) invariant
relativistic four-fermion model in 2+1 dimensions. Features of the pseudogap
phenomenon are naturally described by the appearance of an anomalous dimension
for the spinon propagator.Comment: 5 pages, 2 figures (revtex4). Final revised and corrected versio
Towards spin-polarized two-dimensional electron gas at a surface of an antiferromagnetic insulating oxide
The surfaces of transition-metal oxides with the perovskite structure are fertile grounds for the discovery of novel electronic and magnetic phenomena. In this article, we combine scanning transmission electron microscopy (STEM) with density functional theory (DFT) calculations to obtain the electronic and magnetic properties of the (001) surface of a
(
LaFe
O
3
)
8
/
(
SrFe
O
3
)
1
superlattice film capped with four layers of
LaFe
O
3
. Simultaneously acquired STEM images and electron-energy-loss spectra reveal the surface structure and a reduction in the oxidation state of iron from
F
e
3
+
in the bulk to
F
e
2
+
at the surface, extending over several atomic layers, which signals the presence of oxygen vacancies. The DFT calculations confirm the reduction in terms of oxygen vacancies and further demonstrate the stabilization of an exotic phase in which the surface layer is half metallic and ferromagnetic, while the bulk remains antiferromagnetic and insulating. Based on the calculations, we predict that the surface magnetism and conductivity can be controlled by tuning the partial pressure of oxygen
Incommensurate Charge and Spin Fluctuations in d-wave Superconductors
We show analytic results for the irreducible charge and spin
susceptibilities, , where is the momentum
transfer between the nodes in d-wave superconductors. Using the BCS theory and
a circular Fermi surface, we find that the singular behavior of the irreducible
charge susceptibility leads to the dynamic incommensurate charge collective
modes. The peaks in the charge structure factor occur at a set of wave vectors
which form an ellipse around and in
momentum space with momentum dependent spectral weight. It is also found that,
due to the non-singular irreducible spin susceptibility, an extremely strong
interaction via random phase approximation is required to support the magnetic
peaks near . Under certain conditions, the peaks in the magnetic
structure factor occur near and .Comment: 5 pages, 3 figure
Mean-Field Description of Phase String Effect in the Model
A mean-field treatment of the phase string effect in the model is
presented. Such a theory is able to unite the antiferromagnetic (AF) phase at
half-filling and metallic phase at finite doping within a single theoretical
framework. We find that the low-temperature occurrence of the AF long range
ordering (AFLRO) at half-filling and superconducting condensation in metallic
phase are all due to Bose condensations of spinons and holons, respectively, on
the top of a spin background described by bosonic resonating-valence-bond (RVB)
pairing. The fact that both spinon and holon here are bosonic objects, as the
result of the phase string effect, represents a crucial difference from the
conventional slave-boson and slave-fermion approaches. This theory also allows
an underdoped metallic regime where the Bose condensation of spinons can still
exist. Even though the AFLRO is gone here, such a regime corresponds to a
microscopic charge inhomogeneity with short-ranged spin ordering. We discuss
some characteristic experimental consequences for those different metallic
regimes. A perspective on broader issues based on the phase string theory is
also discussed.Comment: 18 pages, five figure
Renormalized mean-field theory of the neutron scattering in cuprate superconductors
The magnetic excitation spectrum of the t-t'-J-model is studied in mean-field
theory and compared to inelastic neutron-scattering (INS) experiments on YBCO
and BSCCO superconductors. Within the slave-particle formulation the dynamical
spin response is calculated from a renormalized Fermi liquid with an effective
interaction ~J in the magnetic particle--hole channel. We obtain the so-called
41meV resonance at wave vector (pi,pi) as a collective spin-1 excitation in the
d-wave superconducting state. It appears sharp (undamped), if the underlying
Fermi surface is hole-like with a sufficient next-nearest-neighbor hopping
t'<0. The double-layer structure of YBCO or BSCCO is not important for the
resonance to form. The resonance energy \omega_{res} and spectral weight at
optimal doping come out comparable to experiment. The observed qualitative
behavior of \omega_{res} with hole filling is reproduced in the underdoped as
well as overdoped regime. A second, much broader peak becomes visible in the
magnetic excitation spectrum if the 2D wave-vector is integrated over. It is
caused by excitations across the maximum gap, and in contrast to the resonance
its energy is almost independent of doping. At energies above or below
\omega_{res} the commensurate resonance splits into incommensurate peaks,
located off (pi,pi). Below \omega_{res} the intensity pattern is of `parallel'
type and the dispersion relation of incommensurate peaks has a negative
curvature. This is in accordance with recent INS experiments on YBCO.Comment: 17pp including 14 figure
A simple strategy guides the complex metabolic regulation in Escherichia coli
A way to decipher the complexity of the cellular metabolism is to study the effect of different external perturbations. Through an analysis over a sufficiently large set of gene knockouts and growing conditions, one aims to find a unifying principle that governs the metabolic regulation. For instance, it is known that the cessation of the microorganism proliferation after a gene deletion is only transient. However, we do not know the guiding principle that determines the partial or complete recovery of the growth rate, the corresponding redistribution of the metabolic fluxes and the possible different phenotypes. In spite of this large variety in the observed metabolic adjustments, we show that responses of E. coli to several different perturbations can always be derived from a sequence of greedy and myopic resilencings. This simple mechanism provides a detailed explanation for the experimental dynamics both at cellular (proliferation rate) and molecular level ((13)C-determined fluxes), also in case of appearance of multiple phenotypes. As additional support, we identified an example of a simple network motif that is capable of implementing this myopic greediness in the regulation of the metabolism
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