382 research outputs found
Photoproduction of in NRQCD
We present a calculation for the photoproduction of under the
framework of NRQCD factorization formalism. We find a quite unique feature that
the color-singlet contribution to this process vanishes at not only the leading
order but also the next to leading order perturbative QCD calculations and that
the dominant contribution comes from the color-octet
subprocess. The nonperturbative color-octet matrix element of
of is related to that of of by the heavy
quark spin symmetry, and the latter can be determined from the direct
production of at large transverse momentum at the Fermilib Tevatron.
We then conclude that the measurement of this process may clarify the existing
conflict between the color-octet prediction and the experimental result on the
photoprodution.Comment: 11 pages, revtex, 4 ps figure
Stable Learning via Sample Reweighting
We consider the problem of learning linear prediction models with model
misspecification bias. In such case, the collinearity among input variables may
inflate the error of parameter estimation, resulting in instability of
prediction results when training and test distributions do not match. In this
paper we theoretically analyze this fundamental problem and propose a sample
reweighting method that reduces collinearity among input variables. Our method
can be seen as a pretreatment of data to improve the condition of design
matrix, and it can then be combined with any standard learning method for
parameter estimation and variable selection. Empirical studies on both
simulation and real datasets demonstrate the effectiveness of our method in
terms of more stable performance across different distributed data.Comment: Accepted as poster paper at AAAI202
Inelastic electroproduction of at ep colliders
Using the nonrelativistic QCD factorization formalism, we calculate the
electroproduction cross sections of in ep collisions, including the
contribution from both the transverse photon and the longitudinal photon. For
this process the color-singlet contribution vanishes up to the next to leading
order perturbative QCD calculations. The dominant contribution comes from the
color-octet subprocess. The nonperturbative color-octet matrix
element of of is related to that of of
by heavy quark spin symmetry, and the latter can be determined from
the direct production of at large transverse momentum at the Fermilab
Tevatron. The measurement of this process at DESY HERA can be viewed as another
independent test for the color-octet production mechanismComment: 17 pages, 5 figures, final version to appear in Phys. Rev.
Qualitative analysis of housing demand using Google trends data
Big data analytics often refer to the breakdown of huge amounts of data into a more readable and useful format. This study utilises Google Trends big data as a proxy for an analysis of housing demand. We employ a qualitative method (fuzzy set/Qualitative Comparative Analysis, fsQCA), instead of a quantitative method, for our estimate and forecast. The empirical results show that fsQCA successfully forecasts seasonal time series, even though the dataset is small in size. Our findings fill the gap in the qualitative and time series forecasting literature, and the forecasting procedure herein also offers a good standard for industry
Stable Prediction with Model Misspecification and Agnostic Distribution Shift
For many machine learning algorithms, two main assumptions are required to
guarantee performance. One is that the test data are drawn from the same
distribution as the training data, and the other is that the model is correctly
specified. In real applications, however, we often have little prior knowledge
on the test data and on the underlying true model. Under model
misspecification, agnostic distribution shift between training and test data
leads to inaccuracy of parameter estimation and instability of prediction
across unknown test data. To address these problems, we propose a novel
Decorrelated Weighting Regression (DWR) algorithm which jointly optimizes a
variable decorrelation regularizer and a weighted regression model. The
variable decorrelation regularizer estimates a weight for each sample such that
variables are decorrelated on the weighted training data. Then, these weights
are used in the weighted regression to improve the accuracy of estimation on
the effect of each variable, thus help to improve the stability of prediction
across unknown test data. Extensive experiments clearly demonstrate that our
DWR algorithm can significantly improve the accuracy of parameter estimation
and stability of prediction with model misspecification and agnostic
distribution shift
Hierarchical Topological Ordering with Conditional Independence Test for Limited Time Series
Learning directed acyclic graphs (DAGs) to identify causal relations
underlying observational data is crucial but also poses significant challenges.
Recently, topology-based methods have emerged as a two-step approach to
discovering DAGs by first learning the topological ordering of variables and
then eliminating redundant edges, while ensuring that the graph remains
acyclic. However, one limitation is that these methods would generate numerous
spurious edges that require subsequent pruning. To overcome this limitation, in
this paper, we propose an improvement to topology-based methods by introducing
limited time series data, consisting of only two cross-sectional records that
need not be adjacent in time and are subject to flexible timing. By
incorporating conditional instrumental variables as exogenous interventions, we
aim to identify descendant nodes for each variable. Following this line, we
propose a hierarchical topological ordering algorithm with conditional
independence test (HT-CIT), which enables the efficient learning of sparse DAGs
with a smaller search space compared to other popular approaches. The HT-CIT
algorithm greatly reduces the number of edges that need to be pruned. Empirical
results from synthetic and real-world datasets demonstrate the superiority of
the proposed HT-CIT algorithm
MEDOE: A Multi-Expert Decoder and Output Ensemble Framework for Long-tailed Semantic Segmentation
Long-tailed distribution of semantic categories, which has been often ignored
in conventional methods, causes unsatisfactory performance in semantic
segmentation on tail categories. In this paper, we focus on the problem of
long-tailed semantic segmentation. Although some long-tailed recognition
methods (e.g., re-sampling/re-weighting) have been proposed in other problems,
they can probably compromise crucial contextual information and are thus hardly
adaptable to the problem of long-tailed semantic segmentation. To address this
issue, we propose MEDOE, a novel framework for long-tailed semantic
segmentation via contextual information ensemble-and-grouping. The proposed
two-sage framework comprises a multi-expert decoder (MED) and a multi-expert
output ensemble (MOE). Specifically, the MED includes several "experts". Based
on the pixel frequency distribution, each expert takes the dataset masked
according to the specific categories as input and generates contextual
information self-adaptively for classification; The MOE adopts learnable
decision weights for the ensemble of the experts' outputs. As a model-agnostic
framework, our MEDOE can be flexibly and efficiently coupled with various
popular deep neural networks (e.g., DeepLabv3+, OCRNet, and PSPNet) to improve
their performance in long-tailed semantic segmentation. Experimental results
show that the proposed framework outperforms the current methods on both
Cityscapes and ADE20K datasets by up to 1.78% in mIoU and 5.89% in mAcc.Comment: 18 pages, 9 figure
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