1,474 research outputs found
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Configuration-specific attentional modulation of flanker target lateral interactions
Elements of a contour are often easier to detect when they possess collinearity, with their local orientations matching the global orientation of the contour. We recently reported attentional modulation of such lateral interactions between a central near-threshold target Gabor patch and flanking high-contrast patches (Freeman et al, 2001 Nature Neuroscience 4 1032-1036). Here, we examined whether such attentional effects reflect specific modulation of mechanisms sensitive to collinear configurations, or instead more general modulation of sensitivity to either the global or local orientation-components of the stimulus. Thresholds for detecting a central Gabor target were measured, while observers also judged the Vernier alignment between one pair of flankers and ignored a second flanker pair (when present). Target contrast-thresholds were facilitated only when attending collinear flankers. There was no facilitation when attending flankers that shared only local orientation with the target, or flankers that fell on a global axis aligned with target orientation but having orthogonal local orientation. Ignored collinear flankers had no effect on target thresholds. These results demonstrate strong and specific attentional modulation of contour-integration mechanisms in early vision sensitive to collinear configurations
Measurement of the Homogeneous Contact of a Unitary Fermi gas
By selectively probing the center of a trapped gas, we measure the local, or
homogeneous, contact of a unitary Fermi gas as a function of temperature. Tan's
contact, C, is proportional to the derivative of the energy with respect to the
interaction strength, and is thus an essential thermodynamic quantity for a gas
with short-range correlations. Theoretical predictions for the temperature
dependence of C differ substantially, especially near the superfluid
transition, Tc, where C is predicted to either sharply decrease, sharply
increase, or change very little. For T/T_F>0.4, our measurements of the
homogeneous gas contact show a gradual decrease of C with increasing
temperature, as predicted by theory. We observe a sharp decrease in C at
T/T_F=0.16, which may be due to the superfluid phase transition. While a sharp
decrease in C below Tc is predicted by some many-body theories, we find that
none of the predictions fully accounts for the data.Comment: 5 pages, including a supplementary material section (10 pages).
Rewriting of the introduction and discussion section
Desiderata for the Context Use of Question Answering Systems
Prior work has uncovered a set of common problems in state-of-the-art
context-based question answering (QA) systems: a lack of attention to the
context when the latter conflicts with a model's parametric knowledge, little
robustness to noise, and a lack of consistency with their answers. However,
most prior work focus on one or two of those problems in isolation, which makes
it difficult to see trends across them. We aim to close this gap, by first
outlining a set of -- previously discussed as well as novel -- desiderata for
QA models. We then survey relevant analysis and methods papers to provide an
overview of the state of the field. The second part of our work presents
experiments where we evaluate 15 QA systems on 5 datasets according to all
desiderata at once. We find many novel trends, including (1) systems that are
less susceptible to noise are not necessarily more consistent with their
answers when given irrelevant context; (2) most systems that are more
susceptible to noise are more likely to correctly answer according to a context
that conflicts with their parametric knowledge; and (3) the combination of
conflicting knowledge and noise can reduce system performance by up to 96%. As
such, our desiderata help increase our understanding of how these models work
and reveal potential avenues for improvements.Comment: Accepted to EACL 202
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Minimum Cost Flows in Graphs with Unit Capacities
We consider the minimum cost flow problem on graphs with unit capacities and its special cases. In previous studies, special purpose algorithms exploiting the fact that capacities are one have been developed.
In contrast, for maximum flow with unit capacities, the best bounds are proven for slight modifications of classical blocking flow and push-relabel algorithms.
In this paper we show that the classical cost scaling algorithms of Goldberg and Tarjan (for general integer capacities) applied to a problem with unit capacities achieve or improve the best known bounds.
For weighted bipartite matching we establish a bound of O(sqrt{rm}log C) on a slight variation of this algorithm. Here r is the size of the smaller side of the bipartite graph, m is the number of edges, and C is the largest absolute value of an arc-cost. This simplifies a result of [Duan et al. 2011] and improves the bound, answering an open question of [Tarjan and Ramshaw 2012]. For graphs with unit vertex capacities we establish a novel O(sqrt{n}mlog(nC)) bound. We also give the first cycle canceling algorithm for minimum cost flow with unit capacities. The algorithm naturally generalizes the single source shortest path algorithm of [Goldberg 1995]
Ramsey-like measurement of the decoherence rate between Zeeman sub-levels
Two-photon processes that involve different sub-levels of the ground state of
an atom, are highly sensitive to depopulation and decoherence within the ground
state. For example, the spectral width of electromagnetically induced
transparency resonances in type system, are strongly affected by the
ground state depopulation and decoherence rates. We present a direct
measurement of decay rates between hyperfine and Zeeman sub-levels in the
ground state of Rb vapor. Similar to the relaxation-in-the-dark
technique, pumping lasers are used to pre-align the atomic vapor in a well
defined quantum state. The free propagation of the atomic state is monitored
using a Ramsey-like method. Coherence times in the range 1-10 ms were measured
for room temperature atomic vapor. In the range of the experimental parameters
used in this study, the dominant process inducing Zeeman decoherence is the
spin-exchange collisions between rubidium atoms.Comment: 7 pages, 7 figure
Comparing Template-based and Template-free Language Model Probing
The differences between cloze-task language model (LM) probing with 1)
expert-made templates and 2) naturally-occurring text have often been
overlooked. Here, we evaluate 16 different LMs on 10 probing English datasets
-- 4 template-based and 6 template-free -- in general and biomedical domains to
answer the following research questions: (RQ1) Do model rankings differ between
the two approaches? (RQ2) Do models' absolute scores differ between the two
approaches? (RQ3) Do the answers to RQ1 and RQ2 differ between general and
domain-specific models? Our findings are: 1) Template-free and template-based
approaches often rank models differently, except for the top domain-specific
models. 2) Scores decrease by up to 42% Acc@1 when comparing parallel
template-free and template-based prompts. 3) Perplexity is negatively
correlated with accuracy in the template-free approach, but,
counter-intuitively, they are positively correlated for template-based probing.
4) Models tend to predict the same answers frequently across prompts for
template-based probing, which is less common when employing template-free
techniques.Comment: Accepted to EACL 202
Black Hole Thermodynamics and Lorentz Symmetry
Recent developments point to a breakdown in the generalized second law of
thermodynamics for theories with Lorentz symmetry violation. It appears
possible to construct a perpetual motion machine of the second kind in such
theories, using a black hole to catalyze the conversion of heat to work. Here
we describe and extend the arguments leading to that conclusion. We suggest the
inference that local Lorentz symmetry may be an emergent property of the
macroscopic world with origins in a microscopic second law of causal horizon
thermodynamics.Comment: 4 pages; v2: Version to appear in Foundations of Physics. Potential
counterexamples addressed, argument given applying to LV theories where all
speeds (or horizons) coincide, and editing for clarit
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