Search results for " Sam"
showing 10 items of 1096 documents
A new strategy for effective learning in population Monte Carlo sampling
2016
In this work, we focus on advancing the theory and practice of a class of Monte Carlo methods, population Monte Carlo (PMC) sampling, for dealing with inference problems with static parameters. We devise a new method for efficient adaptive learning from past samples and weights to construct improved proposal functions. It is based on assuming that, at each iteration, there is an intermediate target and that this target is gradually getting closer to the true one. Computer simulations show and confirm the improvement of the proposed strategy compared to the traditional PMC method on a simple considered scenario.
Cross-entropy-based adaptive optimization of simulation parameters for Markovian-driven service systems
2005
Abstract Markov fluid models represent a general description of the process of service request arrivals to service systems. The solution of performance analysis problems incorporating them often calls for a simulation approach, for which a reference methodology is Importance Sampling. However, in this case the appropriate choice of the biasing conditions is a problem in itself. In this paper an iterative method based on the cross-entropy is proposed for this choice. The equations are given that allow to derive the biasing conditions from the simulation itself. The application of the proposed method to three different sample cases, referring to one transient scenario (finite time horizon and…
A Quick Simulation Technique for a Fluid Information Storage Problem
2001
Summary In this paper we present an application of Importance Sampling (IS) for quick simulation of buffer overflow probability in a statistical multiplexer loaded with a number of independent Markov modulated fluid sources. Runtime improvement is deducible from NMCσ2(p) and NISσ2(p*) that characterize the trade-offs between sample size and variance of the estimators of buffer overflow probability experienced in Monte Carlo (MC) and Importance Sampling simulations. By assuming that the same precision is achieved for the two kinds of simulations if σ2(p)=σ2(p*), an approximate closed form expression for the ratio NIS/NMC is derived, and it is minimized with respect to the load of the multipl…
Anti-tempered Layered Adaptive Importance Sampling
2017
Monte Carlo (MC) methods are widely used for Bayesian inference in signal processing, machine learning and statistics. In this work, we introduce an adaptive importance sampler which mixes together the benefits of the Importance Sampling (IS) and Markov Chain Monte Carlo (MCMC) approaches. Different parallel MCMC chains provide the location parameters of the proposal probability density functions (pdfs) used in an IS method. The MCMC algorithms consider a tempered version of the posterior distribution as invariant density. We also provide an exhaustive theoretical support explaining why, in the presented technique, even an anti-tempering strategy (reducing the scaling of the posterior) can …
La trascrivibilità del matrimonio tra identità personale e circolazione dello status coniugale
2015
Lo scritto affronta il tema della (in)trascrivibilità degli atti di matrimonio same-sex celebrati all’estero alla luce della più recente giurisprudenza interna e sovranazionale. Esaminati criticamente gli argomenti a sostegno della soluzione negativa e, in particolare, quello della contrarietà all’ordine pubblico vista la indefettibile struttura eterosessuale del matrimonio in Italia, le Autrici giungono alla conclusione che sia applicabile analogicamente la disciplina dei diritti e doveri nascenti dal matrimonio. Alla base della proposta interpretativa sta la primazia dei diritti fondamentali in un sistema di fonti multilivello. The paper deals with the (non-)registrability of same-sex mar…
Influences on the Development of Economic Knowledge over the First Academic Year
2020
Despite significant research, it remains unclear whether the goal of developing domain-specific knowledge in higher education is actually being achieved. This is also true for the internationally most popular study domain of business and economics. In Germany, a test for measuring economic knowledge was validated, enabling the analysis of change in knowledge over the course of studies. Business and economics students from across Germany were surveyed over the course of one study year: 7,111 beginning students in the winter term of 2016/2017, and 1,705 third semester students in the winter term of 2017/2018. Investigating the longitudinal matched sample of 734 students who took part at both …
<p>Preoperative Anemia and Iron Deficiency Screening, Evaluation and Management: Barrier Identification and Implementation Strategy Mapping<…
2020
Introduction and aims: Patients undergoing major surgery risk significant blood loss and transfusion, which increases substantially if they have pre-existing anemia. Preoperative Anemia and Iron Deficiency Screening, Evaluation and Management Pathways (PAIDSEM-P) outline recommended blood tests and treatment to optimize patients before surgery. Documented success using PAIDSEM-P to reduce transfusions and improve patient outcomes exists, but the reporting quality of such studies is suboptimal. It remains unclear what implementation strategies best support the implementation of PAIDSEM-P. Method: Maximum variation, purposive sampling was used to recruit a total of 15 partici-pants, including…
Comparing cetacean abundance estimates derived from spatial models and design-based line transect methods
2007
Spatial modelling is increasingly being used as an alternative to conventional design- based line transect sampling to estimate cetacean abundance. This new method combines line transect sampling with spatial analysis to predict animal abundance based on the relationship of ani- mals observed to environmental factors. It presents several advantages including: (1) the ability to use data collected from 'platforms of opportunity', (2) the ability to estimate abundance for any defined subarea within the study area, and (3) the possibility for increased precision if covariates explain sufficient variability in the data. One study has been conducted to compare spatial modelling with conventional…
Assessing persistent organic pollutants (POPS) in the sicily island atmosphere, mediterranean, using PUF disk passive air samplers
2016
In this study, PUF disk passive air samplers were deployed at eight sites, during two sampling periods, on the Island of Sicily in the Mediterranean basin. Samples were screened for a number of persistent organic pollutants (POPs) including polychlorinated biphenyls (PCBs) (n = 28 congeners), organochlorine pesticides (OCPs) (n = 16 compounds), and polybrominated biphenyl ethers (PBDEs n = 28) using GC-MS. PCB concentrations in air ranged ~10-300 pg m-3. The PCB pattern was dominated by lower to middle molecular weight PCBs (Cl3-5) and PCB-28 and PCB-52 were the most abundant congeners. α- and γ-Hexachlorocyclohexanes (HCHs) concentrations in air were relatively high ~420 ± 320 (50-1000) an…
Bactericidal activity of human milk: stability during storage
2016
Human milk provides infants with defensive factors against many illnesses. This study aims to analyse global bactericidal activity in fresh human milk and evaluate its stability in relation to milk manipulation and its possible alteration following refrigeration. Nineteen milk samples (mature milk) from 19 healthy women are analysed. Viability testing involving a strain of Escherichia coli NCTC 9111, serovar O111:K58(B4):H- was used to determine the bactericidal effect of human milk. Degree of bacteriolysis is calculated as the difference between E. coli counts in controls and in milk samples, expressed as a percentage of the control sample counts. An evaluation of the effect of refrigerati…