123 research outputs found
Covariate assisted screening and estimation
Consider a linear model , where and .
The vector is unknown but is sparse in the sense that most of its
coordinates are . The main interest is to separate its nonzero coordinates
from the zero ones (i.e., variable selection). Motivated by examples in
long-memory time series (Fan and Yao [Nonlinear Time Series: Nonparametric and
Parametric Methods (2003) Springer]) and the change-point problem (Bhattacharya
[In Change-Point Problems (South Hadley, MA, 1992) (1994) 28-56 IMS]), we are
primarily interested in the case where the Gram matrix is nonsparse but
sparsifiable by a finite order linear filter. We focus on the regime where
signals are both rare and weak so that successful variable selection is very
challenging but is still possible. We approach this problem by a new procedure
called the covariate assisted screening and estimation (CASE). CASE first uses
a linear filtering to reduce the original setting to a new regression model
where the corresponding Gram (covariance) matrix is sparse. The new covariance
matrix induces a sparse graph, which guides us to conduct multivariate
screening without visiting all the submodels. By interacting with the signal
sparsity, the graph enables us to decompose the original problem into many
separated small-size subproblems (if only we know where they are!). Linear
filtering also induces a so-called problem of information leakage, which can be
overcome by the newly introduced patching technique. Together, these give rise
to CASE, which is a two-stage screen and clean [Fan and Song Ann. Statist. 38
(2010) 3567-3604; Wasserman and Roeder Ann. Statist. 37 (2009) 2178-2201]
procedure, where we first identify candidates of these submodels by patching
and screening, and then re-examine each candidate to remove false positives.Comment: Published in at http://dx.doi.org/10.1214/14-AOS1243 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Maximum Likelihood Estimation is All You Need for Well-Specified Covariate Shift
A key challenge of modern machine learning systems is to achieve
Out-of-Distribution (OOD) generalization -- generalizing to target data whose
distribution differs from that of source data. Despite its significant
importance, the fundamental question of ``what are the most effective
algorithms for OOD generalization'' remains open even under the standard
setting of covariate shift. This paper addresses this fundamental question by
proving that, surprisingly, classical Maximum Likelihood Estimation (MLE)
purely using source data (without any modification) achieves the minimax
optimality for covariate shift under the well-specified setting. That is, no
algorithm performs better than MLE in this setting (up to a constant factor),
justifying MLE is all you need. Our result holds for a very rich class of
parametric models, and does not require any boundedness condition on the
density ratio. We illustrate the wide applicability of our framework by
instantiating it to three concrete examples -- linear regression, logistic
regression, and phase retrieval. This paper further complement the study by
proving that, under the misspecified setting, MLE is no longer the optimal
choice, whereas Maximum Weighted Likelihood Estimator (MWLE) emerges as minimax
optimal in certain scenarios
Novel Insights into the Role of the Cytoskeleton in Cancer
The cytoskeleton is a complex network of highly ordered intracellular filaments that plays a central role in controlling cell shape, division, functions, and interactions in human organs and tissues, but dysregulation of this network can contribute to numerous human diseases, including cancer. To clarify the various functions of the cytoskeleton and its role in cancer progression, in this chapter, we will discuss the microfilament (actin cytoskeleton), microtubule (β‐tubulin), and intermediate filament (keratins, cytokeratins, vimentin, and lamins) cytoskeletal structures; analyze the physiological functions of the cytoskeleton and its regulation of cell differentiation; and investigate the roles of the cytoskeleton in cancer progression, the epithelial‐mesenchymal transition process (EMT), and the mechanisms of multidrug resistance (MDR) in relation to the cytoskeleton. Importantly, the cytoskeleton, as a key regulator of the transcription and expression of many genes, is known to be involved in various physiological and pathological processes, which makes the cytoskeleton a novel and highly effective target for assessing the response to antitumor therapy in cancer
Novel Implications of Exosomes and lncRNAs in the Diagnosis and Treatment of Pancreatic Cancer
Pancreatic cancer remains a leading cause of cancer-related deaths. Most patients are present with advanced stages of the disease at the time of diagnosis; thus, surgery, which is the best curative option for this malignancy, is no longer an effective treatment modality for affected individuals. As a likely source of “liquid biopsies,” exosomes, which are secreted by fusing intracellular multivesicular bodies with cell membranes, have relative stability and composition, allowing them to cover the entire range of cancer-related biomarkers, including cellular proteins, lipids, DNA, RNA, miRNA, and long non-coding RNAs (lncRNAs). To explore the early detection biomarkers of pancreatic cancer and to develop successful therapeutic intervention for this disease, assessing the implications of exosomes in pancreatic cancer patients is essential. In this chapter, we wish to focus on the possibility of using exosomes and lncRNAs in the clinical management of patients with pancreatic cancer. We will discuss the mechanisms of tumor formation under the exosomal action, demonstrate how circulating exosomes and lncRNAs have come into the research spotlight as likely biomarkers of pancreatic cancer, and discuss the applications of exosomes as transfer vectors in tumor therapeutics
Generalized Category Discovery in Semantic Segmentation
This paper explores a novel setting called Generalized Category Discovery in
Semantic Segmentation (GCDSS), aiming to segment unlabeled images given prior
knowledge from a labeled set of base classes. The unlabeled images contain
pixels of the base class or novel class. In contrast to Novel Category
Discovery in Semantic Segmentation (NCDSS), there is no prerequisite for prior
knowledge mandating the existence of at least one novel class in each unlabeled
image. Besides, we broaden the segmentation scope beyond foreground objects to
include the entire image. Existing NCDSS methods rely on the aforementioned
priors, making them challenging to truly apply in real-world situations. We
propose a straightforward yet effective framework that reinterprets the GCDSS
challenge as a task of mask classification. Additionally, we construct a
baseline method and introduce the Neighborhood Relations-Guided Mask Clustering
Algorithm (NeRG-MaskCA) for mask categorization to address the fragmentation in
semantic representation. A benchmark dataset, Cityscapes-GCD, derived from the
Cityscapes dataset, is established to evaluate the GCDSS framework. Our method
demonstrates the feasibility of the GCDSS problem and the potential for
discovering and segmenting novel object classes in unlabeled images. We employ
the generated pseudo-labels from our approach as ground truth to supervise the
training of other models, thereby enabling them with the ability to segment
novel classes. It paves the way for further research in generalized category
discovery, broadening the horizons of semantic segmentation and its
applications. For details, please visit https://github.com/JethroPeng/GCDS
A Sphingosine Kinase Form 2 Knockout Sensitizes Mouse Myocardium to Ischemia/Reoxygenation Injury and Diminishes Responsiveness to Ischemic Preconditioning
Sphingosine kinase (SphK) exhibits two isoforms, SphK1 and SphK2. Both forms catalyze the synthesis of sphingosine 1-phosphate (S1P), a sphingolipid involved in ischemic
preconditioning (IPC). Since the ratio of SphK1 : SphK2 changes dramatically with aging, it is important to assess the role of SphK2 in IR injury and IPC. Langendorff mouse hearts were subjected to IR (30 min
equilibration, 50 min global ischemia, and 40 min reperfusion). IPC consisted of 2 min of ischemia and 2 min of reperfusion for two cycles. At baseline, there were no differences in left ventricular developed pressure (LVDP), ± dP/dtmax, and heart rate between SphK2 null (KO)
and wild-type (WT) hearts. In KO hearts, SphK2 activity was undetectable, and SphK1 activity was unchanged compared to WT. Total SphK activity was reduced by 53%. SphK2 KO hearts subjected to IR exhibited significantly more cardiac damage (37 ± 1%
infarct size) compared with WT (28 ± 1% infarct size); postischemic recovery of LVDP
was lower in KO hearts. IPC exerted cardioprotection in WT hearts. The protective
effect of IPC against IR was diminished in KO hearts which had much higher infarction sizes (35 ± 2%) compared to the IPC/IR group in control hearts (12 ± 1%). Western analysis revealed that KO
hearts had substantial levels of phosphorylated p38 which could predispose the
heart to IR injury. Thus, deletion of the SphK2 gene sensitizes the myocardium to IR injury and
diminishes the protective effect of IPC
Dispersion characteristics of double-corrugated rectangular waveguide for terahertz vacuum devices
An analytical study on the dispersion of the double-corrugated waveguide for THz vacuum devices is presented. The boundary element method (BEM) is introduced to improve the accuracy of the dispersion. The results are compared with the 3D electromagnetic simulations
Laboratory-Evolved Mutants of an Exogenous Global Regulator, IrrE from Deinococcus radiodurans, Enhance Stress Tolerances of Escherichia coli
The tolerance of cells toward different stresses is very important for industrial strains of microbes, but difficult to improve by the manipulation of single genes. Traditional methods for enhancing cellular tolerances are inefficient and time-consuming. Recently, approaches employing global transcriptional or translational engineering methods have been increasingly explored. We found that an exogenous global regulator, irrE from an extremely radiation-resistant bacterium, Deinococcus radiodurans, has the potential to act as a global regulator in Escherichia coli, and that laboratory-evolution might be applied to alter this regulator to elicit different phenotypes for E. coli.To extend the methodology for strain improvement and to obtain higher tolerances toward different stresses, we here describe an approach of engineering irrE gene in E. coli. An irrE library was constructed by randomly mutating the gene, and this library was then selected for tolerance to ethanol, butanol and acetate stresses. Several mutants showing significant tolerances were obtained and characterized. The tolerances of E. coli cells containing these mutants were enhanced 2 to 50-fold, based on cell growth tests using different concentrations of alcohols or acetate, and enhanced 10 to 100-fold based on ethanol or butanol shock experiments. Intracellular reactive oxygen species (ROS) assays showed that intracellular ROS levels were sharply reduced for cells containing the irrE mutants. Sequence analysis of the mutants revealed that the mutations distribute cross all three domains of the protein.To our knowledge, this is the first time that an exogenous global regulator has been artificially evolved to suit its new host. The successes suggest the possibility of improving tolerances of industrial strains by introducing and engineering exogenous global regulators, such as those from extremophiles. This new approach can be applied alone or in combination with other global methods, such as global transcriptional machinery engineering (gTME) for strain improvements
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