Search results for "sampling"

Event generation and statistical sampling for physics with deep generative models and a density information buffer

2021

Simulating nature and in particular processes in particle physics require expensive computations and sometimes would take much longer than scientists can afford. Here, we explore ways to a solution for this problem by investigating recent advances in generative modeling and present a study for the generation of events from a physical process with deep generative models. The simulation of physical processes requires not only the production of physical events, but to also ensure that these events occur with the correct frequencies. We investigate the feasibility of learning the event generation and the frequency of occurrence with several generative machine learning models to produce events l…

Green determination of the presence of volatile organic compounds in vehicle repair shops through passive sampling.

2012

A simple, fast and green direct analytical methodology has been developed to evaluate the concentration level of volatile organic compounds (VOCs) in indoor areas of vehicle repair shops using membrane devices as passive samplers. VOCs retained in the samplers were directly determined without any sample pre-treatment and avoiding the use of solvents by head space (HS) coupled to gas chromatography-mass spectrometry (GC-MS) in only 20 min. Benzene, toluene, tetrachloroethene, m,p-xylene and o-xylene were found at concentration levels from 0.1 to 11.2 mg m(-3).

New QM/MM implementation of the DFTB3 method in the gromacs package.

2015

The approximate density-functional tight-binding theory method DFTB3 has been implemented in the quantum mechanics/molecular mechanics (QM/MM) framework of the Gromacs molecular simulation package. We show that the efficient smooth particle–mesh Ewald implementation of Gromacs extends to the calculation of QM/MM electrostatic interactions. Further, we make use of the various free-energy functionalities provided by Gromacs and the PLUMED plugin. We exploit the versatility and performance of the current framework in three typical applications of QM/MM methods to solve biophysical problems: (i) ultrafast proton transfer in malonaldehyde, (ii) conformation of the alanine dipeptide, and (iii) el…

The Properties of Atmospheric Aerosol Particles as Functions of the Relative Humidity at Thermodynamic Equilibrium with the Surrounding Moist Air

1976

Publisher Summary The chapter addresses the problems in aerosol measuring techniques and selection of sampling and measuring methods. Theoretic evaluation of mass, size, mean density, and mean refractive index as functions of the relative humidity is discussed. The chapter also discusses techniques for measuring the mass as a function of the relative humidity; determination of the mean density; and measuring the mean complex index of refraction. Results of the measurements, discussion of the results, coefficients of mass increase, mean densities and real parts of the mean complex index of refractions, and applicability of the results are also described. Finally, the chapter then reviews the…

Validity of multiplex biomarker model of 6 genes for the differential diagnosis of thyroid nodules

2011

Abstract Background Currently the cytological examination of fine needle aspiration (FNA) biopsies is the standard technique for the pre-operative differential diagnosis of thyroid nodules. However, the results may be non-informative in ~20% of cases due to an inadequate sampling and the lack of highly specific, measurable cytological criteria, therefore ancillary biomarkers that could aid in these cases are clearly needed. The aim of our study was to evaluate the mRNA expression levels of 8 candidate marker genes as the diagnostic biomarkers for the discrimination of benign and malignant thyroid nodules and to find a combination of biomarkers with the highest diagnostic value. Materials an…

A note on the calibration of the tourists mobility in Sicily and Sardinia

2011

Multi-label Classification Using Stacked Hierarchical Dirichlet Processes with Reduced Sampling Complexity

2018

Nonparametric topic models based on hierarchical Dirichlet processes (HDPs) allow for the number of topics to be automatically discovered from the data. The computational complexity of standard Gibbs sampling techniques for model training is linear in the number of topics. Recently, it was reduced to be linear in the number of topics per word using a technique called alias sampling combined with Metropolis Hastings (MH) sampling. We propose a different proposal distribution for the MH step based on the observation that distributions on the upper hierarchy level change slower than the document-specific distributions at the lower level. This reduces the sampling complexity, making it linear i…

Online Sparse Collapsed Hybrid Variational-Gibbs Algorithm for Hierarchical Dirichlet Process Topic Models

2017

Topic models for text analysis are most commonly trained using either Gibbs sampling or variational Bayes. Recently, hybrid variational-Gibbs algorithms have been found to combine the best of both worlds. Variational algorithms are fast to converge and more efficient for inference on new documents. Gibbs sampling enables sparse updates since each token is only associated with one topic instead of a distribution over all topics. Additionally, Gibbs sampling is unbiased. Although Gibbs sampling takes longer to converge, it is guaranteed to arrive at the true posterior after infinitely many iterations. By combining the two methods it is possible to reduce the bias of variational methods while …

22. Administering Face-To-Face Structured Questionnaires In Tourism Research

2018

Non-sampling errors occur in all social sciences, tourism included. Apart from coverage and non-response, tourism research suffers from noteworthy measurement errors. The limitation and control of non-sampling errors plays a key role to prevent serious biases in research outputs. The entire survey design process could be based on the control and reduction of non-sampling errors. From this point of view, face-to-face interviewing represents an effective response to some common threats to data quality, particularly errors attributable to respondents and non-response.

Unobserved tourism

2015

Having more reliable statistics is essential for policy-makers to be able to make effective decisions. Nevertheless, measuring the number of tourists in a given destination is not an easy task. After reviewing the main problems affecting official statistics on tourism, this paper proposes a general framework by formalizing a theoretical model in which tourism nights and trips in a given destination are broken down into observed and unobserved components, according to the European system of tourism statistics. The main approaches related to the measurement of unobserved tourism are discussed, and some empirical findings in Sicily (Italy) are presented in order to highlight the actual magnitu…