3,485 research outputs found
The restricted EM algorithm under inequality restrictions on the parameters
AbstractOne of the most powerful algorithms for maximum likelihood estimation for many incomplete-data problems is the EM algorithm. The restricted EM algorithm for maximum likelihood estimation under linear restrictions on the parameters has been handled by Kim and Taylor (J. Amer. Statist. Assoc. 430 (1995) 708–716). This paper proposes an EM algorithm for maximum likelihood estimation under inequality restrictions A0β⩾0, where β is the parameter vector in a linear model W=Xβ+ε and ε is an error variable distributed normally with mean zero and a known or unknown variance matrix Σ>0. Some convergence properties of the EM sequence are discussed. Furthermore, we consider the consistency of the restricted EM estimator and a related testing problem
Properties of the FCC Catalyst Additive Prepared from Guizhou Kaoline
The properties of a FCC catalyst additive prepared from Guizhou kaoline were extensively investigated. The samples were characterized by N<sub>2 adsorption, X-ray diffraction, IR spectrometry, and scanning electron microscope (SEM). The results showed that the crystallinity of NaY zeolite synthesized from this kaoline was 25% and the silica alumina ratio was <sub>rk/s ˇ m </sub>= 5.05. The catalyst additive prepared from above crystallization product exhibited excellent performance of nickel and vanadium passivation, offered 21% lower coke versus base catalyst, while maintaining high bottoms upgrading selectivity
Svojstva aditiva FCC katalizatora pripravljenih iz Guizhou kaolina
The properties of a FCC catalyst additive prepared from Guizhou kaoline were extensively investigated. The samples were characterized by N2 adsorption, X-ray diffraction, IR spectrometry, and scanning electron microscope (SEM). The results showed that the crystallinity of NaY zeolite synthesized from this kaoline was 25% and the silica alumina ratio was rk/s ˇ m = 5.05. The catalyst additive prepared from above crystallization product exhibited excellent performance of nickel and vanadium passivation, offered 21% lower coke versus base catalyst, while maintaining high bottoms upgrading selectivity.U radu su opisana istraživanja svojstava aditiva FCC-katalizatora pripravljenih iz Guizhou kaolina. Aditivi su karakterizirani adsorpcijom N2, rengenskom difrakcijom praškastih uzoraka, IR-spektroskopijom i pretražnom elektronskom mikroskopijom. Rezultati ukazuju da kristaliničnost zeolita NaY pripravljenog iz Guizhou kaolina iznosi 25% te da je omjer silicijevog oksida (SiO2) i aluminijevog oksida (Al2O3) 5,05 (mol/mol). Aditiv iskazuje prestižna svojstva FCC-katalizatora prvenstveno pasivizacije nikla i vanadija, proizvodi 21% manje koksa, i održava visoku selektivnost destilacijskih ostataka
PPAR α and PPAR γ Polymorphisms as risk factors for Dyslipidemia in a Chinese han population
BACKGROUND: The PPAR α and PPAR γ are the key messengers responsible for the translation of nutritional stimuli into changes for the expression of genes, particularly genes involved in lipid metabolism. However, the associations between PPAR α / γ polymorphisms and lipid serum levels in the general population were rarely studied, and the conclusions were conflicting. The objective was to investigate the associations of the PPAR α and PPAR γ polymorphisms with dyslipidemia. METHODS: 820 subjects were randomly selected from the Prevention of Multiple Metabolic Disorders and MS in Jiangsu Province cohort populations. The logistic regression model was used to examine the association between these polymorphisms and dyslipidemia. SNPstats was used to explore the haplotype association analyses. RESULTS: In the codominant and log-additive models, rs1800206, rs1805192 and rs3856806 were all associated with dyslipidemia (P < 0.005). When the most common haplotype L-G (established by rs1800206, rs4253778) was treated as the reference group, the V-G haplotype was associated with dyslipidemia (P < 0.001), higher TC and TG levels (P < 0.01). Moreover, when compared to Pro-C haplotype (established by rs1805192, rs3856806), the Pro-T, Ala-C, Ala-T haplotypes were associated with dyslipidemia (p < 0.001). A-T haplotype was associated with higher TC levels, (p < 0.01), and the P-T, A-C, A-T haplotypes were associated with higher TG levels (p < 0.01). CONCLUSIONS: PPAR α and PPAR γ polymorphisms and haplotypes may be the genetic risk factors for dyslipidemia
Attack is Good Augmentation: Towards Skeleton-Contrastive Representation Learning
Contrastive learning, relying on effective positive and negative sample
pairs, is beneficial to learn informative skeleton representations in
unsupervised skeleton-based action recognition. To achieve these positive and
negative pairs, existing weak/strong data augmentation methods have to randomly
change the appearance of skeletons for indirectly pursuing semantic
perturbations. However, such approaches have two limitations: 1) solely
perturbing appearance cannot well capture the intrinsic semantic information of
skeletons, and 2) randomly perturbation may change the original
positive/negative pairs to soft positive/negative ones. To address the above
dilemma, we start the first attempt to explore an attack-based augmentation
scheme that additionally brings in direct semantic perturbation, for
constructing hard positive pairs and further assisting in constructing hard
negative pairs. In particular, we propose a novel Attack-Augmentation
Mixing-Contrastive learning (AMC) to contrast hard positive features and
hard negative features for learning more robust skeleton representations. In
AMC, Attack-Augmentation (Att-Aug) is designed to collaboratively perform
targeted and untargeted perturbations of skeletons via attack and augmentation
respectively, for generating high-quality hard positive features. Meanwhile,
Positive-Negative Mixer (PNM) is presented to mix hard positive features and
negative features for generating hard negative features, which are adopted for
updating the mixed memory banks. Extensive experiments on three public datasets
demonstrate that AMC is competitive with the state-of-the-art methods
Deep Time-Stream Framework for Click-Through Rate Prediction by Tracking Interest Evolution
Click-through rate (CTR) prediction is an essential task in industrial
applications such as video recommendation. Recently, deep learning models have
been proposed to learn the representation of users' overall interests, while
ignoring the fact that interests may dynamically change over time. We argue
that it is necessary to consider the continuous-time information in CTR models
to track user interest trend from rich historical behaviors. In this paper, we
propose a novel Deep Time-Stream framework (DTS) which introduces the time
information by an ordinary differential equations (ODE). DTS continuously
models the evolution of interests using a neural network, and thus is able to
tackle the challenge of dynamically representing users' interests based on
their historical behaviors. In addition, our framework can be seamlessly
applied to any existing deep CTR models by leveraging the additional
Time-Stream Module, while no changes are made to the original CTR models.
Experiments on public dataset as well as real industry dataset with billions of
samples demonstrate the effectiveness of proposed approaches, which achieve
superior performance compared with existing methods.Comment: 8 pages. arXiv admin note: text overlap with arXiv:1809.03672 by
other author
A cross-species alignment tool (CAT)
<p>Abstract</p> <p>Background</p> <p>The main two sorts of automatic gene annotation frameworks are <it>ab initio </it>and alignment-based, the latter splitting into two sub-groups. The first group is used for intra-species alignments, among which are successful ones with high specificity and speed. The other group contains more sensitive methods which are usually applied in aligning inter-species sequences.</p> <p>Results</p> <p>Here we present a new algorithm called <it>CAT </it>(for Cross-species Alignment Tool). It is designed to align mRNA sequences to mammalian-sized genomes. <it>CAT </it>is implemented using C scripts and is freely available on the web at <url>http://xat.sourceforge.net/</url>.</p> <p>Conclusions</p> <p>Examined from different angles, <it>CAT </it>outperforms other extant alignment tools. Tested against all available mouse-human and zebrafish-human orthologs, we demonstrate that <it>CAT </it>combines the specificity and speed of the best intra-species algorithms, like <it>BLAT </it>and <it>sim4</it>, with the sensitivity of the best inter-species tools, like <it>GeneWise</it>.</p
Ionospheric Response to the Total Solar Eclipse of 22 July 2009 as Deduced from VLBI and GPS Data
A total solar eclipse occurred over China at latitudes of about 30 N on the morning of 22 July 2009, providing a unique opportunity to investigate the influence of the sun on the earth's upper ionosphere. GPS observations from Shanghai GPS Local Network and VLBI observations from stations Shanghai, Urumqi, and Kashima were used to observe the response of TEC to the total solar eclipse. From the GPS data reduction, the sudden decrease of TEC at the time of the eclipse, amounting to 2.8 TECU, and gradual increase of TEC after the eclipse were found by analyzing the diurnal variations. More distinctly, the variations of TEC were studied along individual satellite passes. The delay in reaching the minimum level of TEC with the maximum phase of eclipse was 5-10 min. Besides, we also compared the ionospheric activity derived from different VLBI stations with the GPS results and found a strong correlation between them
Localized-to-itinerant transition preceding antiferromagnetic quantum critical point and gapless superconductivity in CeRh0.5Ir0.5In5
A fundamental problem posed from the study of correlated electron compounds, of which heavy-fermion systems are prototypes, is the need to understand the physics of states near a quantum critical point (QCP). At a QCP, magnetic order is suppressed continuously to zero temperature and unconventional superconductivity often appears. Here, we report pressure T-c. (P)-dependent In-115 nuclear quadrupole resonance (NQR) measurements on heavy-fermion antiferromagnet CeRh0.5Ir0.5In5. These experiments reveal an antiferromagnetic (AF) QCP at P-c(AF) = 1.2 GPa where a dome of superconductivity reaches a maximum transition temperature Tc. Preceding P-c(AF), however, the NQR frequency nu(Q) undergoes an abrupt increase at P-c* = 0.8 GPa in the zero-temperature limit, indicating a change from localized to itinerant character of cerium's f-electron and associated small-to-large change in the Fermi surface. At P-c(AF) where T-c is optimized, there is an unusually large fraction of gapless excitations well below T-c that implicates spin-singlet, odd-frequency pairing symmetry
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