Steering time-dependent estimation of posteriors with hyperparameter indexing in Bayesian topic models

This paper provides a new approach to topical trend analysis. Our aim is to improve the generalization power of latent Dirichlet allocation (LDA) by using document timestamps. Many previous works model topical trends by making latent topic distributions time-dependent. We propose a straightforward approach by preparing a different word multinomial distribution for each time point. Since this approach increases the number of parameters, overfitting becomes a critical issue. Our contribution to this issue is two-fold. First, we propose an effective way of defining Dirichlet priors over the word multinomials. Second, we propose a special scheduling of variational Bayesian (VB) inference. Comprehensive experiments with six datasets prove that our approach can improve LDA and also Topics over Time, a well-known variant of LDA, in terms of test data perplexity in the framework of VB inference

Bag of Timestamps: A Simple and Efficient Bayesian Chronological Mining

In this paper, we propose a new probabilistic model, Bag of Timestamps (BoT), for chronological text mining. BoT is an extension of latent Dirichlet allocation (LDA), and has two remarkable features when compared with a previously proposed Topics over Time (ToT), which is also an extension of LDA. First, we can avoid overfitting to temporal data, because temporal data are modeled in a Bayesian manner similar to word frequencies. Second, BoT has a conditional probability where no functions requiring time-consuming computations appear. The experiments using newswire documents show that BoT achieves more moderate fitting to temporal data in shorter execution time than ToT.Advances in Data and Web Management. Joint International Conferences, APWeb/WAIM 2009 Suzhou, China, April 2-4, 2009 Proceeding

Modeling topical trends over continuous time with priors

In this paper, we propose a new method for topical trend analysis. We model topical trends by per-topic Beta distributions as in Topics over Time (TOT), proposed as an extension of latent Dirichlet allocation (LDA). However, TOT is likely to overfit to timestamp data in extracting latent topics. Therefore, we apply prior distributions to Beta distributions in TOT. Since Beta distribution has no conjugate prior, we devise a trick, where we set one among the two parameters of each per-topic Beta distribution to one based on a Bernoulli trial and apply Gamma distribution as a conjugate prior. Consequently, we can marginalize out the parameters of Beta distributions and thus treat timestamp data in a Bayesian fashion. In the evaluation experiment, we compare our method with LDA and TOT in link detection task on TDT4 dataset. We use word predictive probabilities as term weights and estimate document similarities by using those weights in a TFIDF-like scheme. The results show that our method achieves a moderate fitting to timestamp data.Advances in Neural Networks - ISNN 2010 : 7th International Symposium on Neural Networks, ISNN 2010, Shanghai, China, June 6-9, 2010, Proceedings, Part IIThe original publication is available at www.springerlink.co

Dynamic hyperparameter optimization for bayesian topical trend analysis

This paper presents a new Bayesian topical trend analysis. We regard the parameters of topic Dirichlet priors in latent Dirichlet allocation as a function of document timestamps and optimize the parameters by a gradient-based algorithm. Since our method gives similar hyperparameters to the documents having similar timestamps, topic assignment in collapsed Gibbs sampling is affected by timestamp similarities. We compute TFIDF-based document similarities by using a result of collapsed Gibbs sampling and evaluate our proposal by link detection task of Topic Detection and Tracking.Proceeding of the 18th ACM conference : Hong Kong, China, 2009.11.02-2009.11.0

STRAD Project for Systematic Treatments of Radioactive Liquid Wastes Generated in Nuclear Facilities

A new collaborative research project for systematic treatments of radioactive liquid wastes containing various reagents generating in nuclear facilities was started from 2018 initiated by Japan Atomic Energy Agency. The project was named as STRAD (Systematic Treatments of RAdioactive liquid wastes for Decommissioning) project. Tentative targets to be studied under the project are aqueous and organic liquid wastes which have been generated by experiments and analyses in a reprocessing experimental laboratory of JAEA. Currently fundamental studies for treatments of the liquid wastes with complicated compositions are underway. In the STRAD project, process flow for treatment of ammonium ion involved in aqueous waste was designed though the inactive experiments, and decomposition of ammonium ion using catalysis will be carried out soon. Adsorbents for recovery of U and Pu from spent solvent were also developed. Demonstration experiments on genuine spent solvent is under planning

Effect of Flowing Water on Sr Sorption Changes of Hydrous Sodium Titanate

Radioactive contaminated water has been generated at the Fukushima Daiichi Nuclear Power station (F1NPS). Hydrous sodium titanate (SrTreat (R)) is able to remove radioactive Strontium (Sr) from this water. Knowing the amount of radioactive nuclides in the used as-received SrTreat (R) is important for effective disposal and deposition of the F1NPS waste. This study investigated changes in the ability of SrTreat (R) to sorb Sr, and to understand the causes of changes in the sorbing. An investigation of the Sr sorption ability of SrTreat (R) is important for calculating the initial radioactive inventory of used SrTreat (R). This study carries out Sr sorption studies with acid-base titrations and X-ray photoelectron spectroscopy (XPS) to characterize the properties. After exposure to simulated treated water for 99 h, the surface structure of the SrTreat (R) was changed, and the percentage of sorbed Sr and the buffer capacity for protons decreased. When the amount of radioactive nuclides contained in the used SrTreat (R) is calculated from the sorption data of the as-received SrTreat (R), the radioactive Sr content will be overestimated with a concomitant increase in the deposition and disposal costs of the used SrTreat (R)

Radioactive contamination of several materials following the Fukushima Daiichi Nuclear Power Station accident

Following the 2011 accident at the Fukushima Daiichi Nuclear Power Station (NPS), which is owned by Tokyo Electric Power Co., radioactive nuclides were released into the environment and heavily contaminated the NPS site. In this study, the contamination behavior of radioactive nuclides in accumulated water, rubble, soil, and vegetation is discussed. Activity concentrations are converted to a “transport ratio,” which is the activity concentration ratio normalized using the activity in the source term for the nuclides of interest and a selected standard. The transport ratio of Sr to rubble and soil by way of air was approximately 10−2 to 10−3, and the successive transport to accumulated water was comparable with Cs (except for the initial release). Transport of Pu, Am, and Cm was lower than for Sr regardless of the transport process (air or water), whereas those of I, Se, and Te were comparable or greater. Contamination with 3H and 14C was independent of 137Cs, 90Sr, and TRU nuclides and was likely a result of different transport process

Influence of plutonium content in dissolver solutions derived from irradiated fast reactor fuels on plutonium stripping in multistage countercurrent liquid–liquid extraction with acid split flowsheet

In the acid split flowsheet, the Pu content in the dissolver solution of nuclear fuel has a significant impact on the configuration of flowsheet and the Pu content in the products. The influence of Pu content in dissolver solutions of nuclear fuel on the Pu stripping has been studied. The decontamination performance of Cs as major fission products was assessed, and Cs was decontaminated well in the acid split flowsheet. High HNO3 concentration in the feed solution and at the co-decontamination section was adjusted for the co-recovery of Np with U and Pu, contributing to Np oxidation and the increase in the distribution ratio of Np. The experimental results demonstrate that the Pu content in the U/Pu and U products increased with an increase in the Pu content in the feed solution. The calculated results indicate that the Pu leakage into the U product is suppressed with the Pu stripping solution only at low temperature under our experimental conditions, and Pu is recovered into the U/Pu product efficiently. This study proves that the Pu leakage into the U product is controlled and the acid split flowsheet is flexible with change in the Pu content in the feed solution.</p

Oxidative decomposition of ammonium ion with ozone in the presence of cobalt and chloride ions for the treatment of radioactive liquid waste

To prevent unexpected accidents at nuclear facilities caused by accumulated ammonium nitrate in an aqueous liquid waste containing ammonium salts and nitric acid, NH4+ in the liquid waste must be decomposed under mild reaction conditions. In this study, we investigated the oxidative decomposition of NH4+ with O-3 at 333 K in the presence of a homogeneous Co2+ catalyst and Cl in the wide pH range of the test solution. The reaction behavior was greatly affected by pH of the test solution. In a basic solution at pH 12, high conversion of NH4+ was obtained even in the absence of Co2+ and Cl, and the main product was NO3. However, Co2+ and Cl in the solution greatly enhanced the decomposition rate of NH4+ in acidic to mild basic solutions (pH 1-8), while only low conversion of NH4+ was observed unless both Co2+ and Cl were present. For the reaction with Co2+ and Cl in the solutions, NH4+ was transformed mainly into chloramines (NHxCl3 x, x = 1-3) by the reaction with HClO, which was formed by the reaction of Cl with O-3 catalyzed by the homogeneous Co2+ catalyst, and led to the high decomposition rate of NH4+. Cl suppressed the formation of the precipitate CoO(OH) during the reaction and consequently the Co2+ catalyst stably existed in the reaction solution, which was another reason for the high decomposition rate of NH4+ in the presence of Cl. Owing to the swift decomposition of NH4+ under mild reaction conditions and small formation of secondary waste, the oxidative decomposition of NH4+ in the presence of the homogeneous Co2+ catalyst and Cl is suitable and applicable for the treatment of the aqueous liquid waste containing ammonium salts and nitric acid

Semi-supervised bibliographic element segmentation with latent permutations

This paper proposes a semi-supervised bibliographic element segmentation. Our input data is a large scale set of bibliographic references each given as an unsegmented sequence of word tokens. Our problem is to segment each reference into bibliographic elements, e.g. authors, title, journal, pages, etc. We solve this problem with an LDA-like topic model by assigning each word token to a topic so that the word tokens assigned to the same topic refer to the same bibliographic element. Topic assignments should satisfy contiguity constraint, i.e., the constraint that the word tokens assigned to the same topic should be contiguous. Therefore, we proposed a topic model in our preceding work [8] based on the topic model devised by Chen et al. [3]. Our model extends LDA and realizes unsupervised topic assignments satisfying contiguity constraint. The main contribution of this paper is the proposal of a semi-supervised learning for our proposed model. We assume that at most one third of word tokens are already labeled. In addition, we assume that a few percent of the labels may be incorrect. The experiment showed that our semi-supervised learning improved the unsupervised learning by a large margin and achieved an over 90% segmentation accuracy.13th International Conference on Asia-Pacific Digital Libraries, ICADL 2011; Beijing; 24 October 2011 through 27 October 201