4,082 research outputs found
Central limit theorems for Gaussian polytopes
Choose random, independent points in according to the standard
normal distribution. Their convex hull is the {\sl Gaussian random
polytope}. We prove that the volume and the number of faces of satisfy
the central limit theorem, settling a well known conjecture in the field.Comment: to appear in Annals of Probabilit
On the deformation morphology of bulk metallic glasses underneath a Vickers indentation
16th International Symposium on Metastable, Amorphous and Nanostructured Materials, Beijing, PEOPLES R CHINA, JUL 05-09, 2009International audienceThe techniques commonly used for observing the deformation mechanisms underneath a Vickers indentation in metallic glasses (chemical etching, bonded interface) induce artefacts such as cracks or semi-circular shear-bands. We propose an alternative technique based on the propagation of indentation corner cracks through a pre-existing imprint, which is possible in metallic glasses such as iron-based compositions. With this procedure, only radial shear-bands are observed. Comparisons between the chemical etching or the bonded interface techniques and the new technique are made. (C) 2010 Elsevier B.V. All rights reserved
Circular strings in Kerr- black holes
The quest for extension of holographic correspondence to the case of finite
temperature naturally includes Kerr-AdS black holes and their field theory
duals. We probe the five-dimensional Kerr-AdS space time by pulsating strings.
First we find particular pulsating string solutions and then semi-classically
quantize the theory. For the string with large values of energy, we use the
Bohr-Sommerfeld analysis to find the energy of the string as a function of a
large quantum number. We obtain the wave function of the problem and thoroughly
study the corrections to the energy, which according to the holographic
dictionary are related to anomalous dimensions of certain operators in the dual
gauge theory. The interpretation of results from holographic point of view is
not straightforward since the dual theory is at finite temperature.
Nevertheless, near or at conformal point the expressions can be thought of as
the dispersion relations of stationary states.Comment: 32 pp, 1 figure; v2: Sec.3 improved, Sec.4 recalculated for a general
case, typos corrected, Appendix B included; v3: Sec.3 corrected, new figure
of an effective potential added, typos correcte
Accounting-based variables as an early warning indicator of financial distress in crisis and non-crisis periods
Financial integration in the Association of Southeast Asian Nations (ASEAN) region is a key focus of the ASEAN Economic Community. Whereas many studies focus on modelling corporate default, this paper identifies early warning indicators of financial distress before a default, using multiple discriminant analysis (MDA) models with a sample of listed and delisted companies in the ASEAN region. The analysis examines 720 companies in 10 different industries across six ASEAN countries from 1997 to 2016. The study constructs individual models for each country as well as an overall model for the entire region, using both in-sample and out-of-sample approaches. This overall model could be useful for an integrated banking system. To ensure robustness, the study also separately examines the predictive performance of the MDA models across different economic crises: the Asian financial crisis (AFC) from 1997 to 2000, the global financial crisis (GFC) from 2007 to 2009 and their pre- and post-crisis periods. We find that profitability ratios are the best indicators of financial distress in the ASEAN region, followed by liquidity and leverage ratios. In addition, our findings reveal common indicators that can be used to predict financial distress across ASEAN countries. The single model performs reasonably well in predicting financial distress 1 year ahead. In addition, the model is extended to incorporate a market-based indicator into the MDA models, the distance to default. However, the inclusion of this indicator does not significantly improve the accuracy of the models in predicting financial distress at listed firms in the ASEAN region
Zooming in on local level statistics by supersymmetric extension of free probability
We consider unitary ensembles of Hermitian NxN matrices H with a confining
potential NV where V is analytic and uniformly convex. From work by
Zinn-Justin, Collins, and Guionnet and Maida it is known that the large-N limit
of the characteristic function for a finite-rank Fourier variable K is
determined by the Voiculescu R-transform, a key object in free probability
theory. Going beyond these results, we argue that the same holds true when the
finite-rank operator K has the form that is required by the Wegner-Efetov
supersymmetry method of integration over commuting and anti-commuting
variables. This insight leads to a potent new technique for the study of local
statistics, e.g., level correlations. We illustrate the new technique by
demonstrating universality in a random matrix model of stochastic scattering.Comment: 38 pages, 3 figures, published version, minor changes in Section
Empirical Evaluation of Pre-trained Transformers for Human-Level NLP: The Role of Sample Size and Dimensionality
In human-level NLP tasks, such as predicting mental health, personality, or
demographics, the number of observations is often smaller than the standard
768+ hidden state sizes of each layer within modern transformer-based language
models, limiting the ability to effectively leverage transformers. Here, we
provide a systematic study on the role of dimension reduction methods
(principal components analysis, factorization techniques, or multi-layer
auto-encoders) as well as the dimensionality of embedding vectors and sample
sizes as a function of predictive performance. We first find that fine-tuning
large models with a limited amount of data pose a significant difficulty which
can be overcome with a pre-trained dimension reduction regime. RoBERTa
consistently achieves top performance in human-level tasks, with PCA giving
benefit over other reduction methods in better handling users that write longer
texts. Finally, we observe that a majority of the tasks achieve results
comparable to the best performance with just of the embedding
dimensions.Comment: 2021 Annual Conference of the North American Chapter of the
Association for Computational Linguistics (NAACL-HLT
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