10 research outputs found
Adapting approximate memory potentials for time-dependent density functional theory
Frequency dependent exchange correlation kernels for time-dependent density
functional theory can be used to construct approximate exchange-correlation
potentials. The resulting potentials are usually not translationally covariant
nor do they obey the so-called zero-force condition. These two basic symme-try
requirements are essential for using the potentials in actual applications
(even within the linear re-sponse regime). We provide two pragmatic methods for
imposing these conditions. As an example we take the Gross and Kohn (GK)
frequency dependent XC functional (Phys. Rev.Lett. 55, 2850 (1985)), correct
it, and numerically test it on a sodium metal cluster. Violation of the basic
symme-tries causes instabilities or spurious low frequency modes
Faithful Explanations of Black-box NLP Models Using LLM-generated Counterfactuals
Causal explanations of the predictions of NLP systems are essential to ensure
safety and establish trust. Yet, existing methods often fall short of
explaining model predictions effectively or efficiently and are often
model-specific. In this paper, we address model-agnostic explanations,
proposing two approaches for counterfactual (CF) approximation. The first
approach is CF generation, where a large language model (LLM) is prompted to
change a specific text concept while keeping confounding concepts unchanged.
While this approach is demonstrated to be very effective, applying LLM at
inference-time is costly. We hence present a second approach based on matching,
and propose a method that is guided by an LLM at training-time and learns a
dedicated embedding space. This space is faithful to a given causal graph and
effectively serves to identify matches that approximate CFs. After showing
theoretically that approximating CFs is required in order to construct faithful
explanations, we benchmark our approaches and explain several models, including
LLMs with billions of parameters. Our empirical results demonstrate the
excellent performance of CF generation models as model-agnostic explainers.
Moreover, our matching approach, which requires far less test-time resources,
also provides effective explanations, surpassing many baselines. We also find
that Top-K techniques universally improve every tested method. Finally, we
showcase the potential of LLMs in constructing new benchmarks for model
explanation and subsequently validate our conclusions. Our work illuminates new
pathways for efficient and accurate approaches to interpreting NLP systems
Quantum memory effects on the dynamics of electrons in small gold clusters
Electron dynamics in metallic clusters are examined using a time-dependent
density functional theory that includes a 'memory term', i.e. attempts to
describe temporal non-local correlations. Using the Iwamoto, Gross and Kohn
exchange-correlation (XC) kernel we construct a translationally invariant
memory action from which an XC potential is derived that is translationally
covariant and exerts zero net force on the electrons. An efficient and stable
numerical method to solve the resulting Kohn-Sham equations is presented. Using
this framework, we study memory effects on electron dynamics in spherical
Jellium 'gold clusters'. We find memory significantly broadens the surface
plasmon absorption line, yet considerably less than measured in real gold
clusters, attributed to the inadequacy of the Jellium model. Two-dimensional
pump-probe spectroscopy is used to study the temporal decay profile of the
plasmon, finding a fast decay followed by slower tail. Finally, we examine
memory effects on high harmonic generation, finding memory narrows emission
lines
CEBaB: Estimating the Causal Effects of Real-World Concepts on NLP Model Behavior
The increasing size and complexity of modern ML systems has improved their
predictive capabilities but made their behavior harder to explain. Many
techniques for model explanation have been developed in response, but we lack
clear criteria for assessing these techniques. In this paper, we cast model
explanation as the causal inference problem of estimating causal effects of
real-world concepts on the output behavior of ML models given actual input
data. We introduce CEBaB, a new benchmark dataset for assessing concept-based
explanation methods in Natural Language Processing (NLP). CEBaB consists of
short restaurant reviews with human-generated counterfactual reviews in which
an aspect (food, noise, ambiance, service) of the dining experience was
modified. Original and counterfactual reviews are annotated with
multiply-validated sentiment ratings at the aspect-level and review-level. The
rich structure of CEBaB allows us to go beyond input features to study the
effects of abstract, real-world concepts on model behavior. We use CEBaB to
compare the quality of a range of concept-based explanation methods covering
different assumptions and conceptions of the problem, and we seek to establish
natural metrics for comparative assessments of these methods
Fecal microbiota of the synanthropic golden jackal (Canis aureus)
Abstract The golden jackal (Canis aureus), is a medium canid carnivore widespread throughout the Mediterranean region and expanding into Europe. This species thrives near human settlements and is implicated in zoonoses such as rabies. This study explores for the first time, the golden jackal fecal microbiota. We analyzed 111 fecal samples of wild golden jackals using 16S rRNA amplicon sequencing the connection of the microbiome to animal characteristics, burden of pathogens and geographic and climate characteristics. We further compared the fecal microbiota of the golden jackal to the black-backed jackal and domestic dog. We found that the golden jackal fecal microbiota is dominated by the phyla Bacteroidota, Fusobacteriota and Firmicutes. The golden jackal fecal microbiota was associated with different variables, including geographic region, age-class, exposure to rabies oral vaccine, fecal parasites and toxoplasmosis. A remarkable variation in the relative abundance of different taxa was also found associated with different variables, such as age-class. Linear discriminant analysis effect size (LEfSe) analysis found abundance of specific taxons in each region, Megasphaera genus in group 1, Megamonas genus in group 2 and Bacteroides coprocola species in group 3. We also found a different composition between the fecal microbiota of the golden jackal, blacked-backed jackal and the domestic dog. Furthermore, LEfSe analysis found abundance of Fusobacterium and Bacteroides genera in the golden jackal, Clostridia class in blacked-backed jackal and Megamonas genus in domestic dog. The golden jackal fecal microbiota is influenced by multiple factors including host traits and pathogen burden. The characterization of the microbiota of this thriving species may aid in mapping its spread and proximity to human settlements. Moreover, understanding the jackal microbiota could inform the study of potential animal and human health risks and inform control measures