The Behavior of HEGY Tests for Quarterly Time Series with Seasonal Mean Shifts

This paper studies the behavior of the HEGY statistics for quarterly data, for seasonal autoregressive unit roots, when the analyzed time series is deterministic seasonal stationary but exhibits a change in the seasonal pattern. As a by-product we analyze also the HEGY test for the nonseasonal unit root, the data generation process being trend stationary too. Our results show that when the break magnitudes are finite the HEGY test statistics are not asymptotically biased towards the non-rejection of the seasonal and nonseasonal unit root hypotheses. However, the finite sample power properties may be substancially affected, the behavior of the tests depending on the type of the break. Hence, our results are also useful to understand and to predict this behavior under several circumstances.seasonality; unit roots; strctural breaks; HEGY tests

On the Numerical Accuracy of Spreadsheets

This paper discusses the numerical precision of five spreadsheets (Calc, Excel, Gnumeric, NeoOffice and Oleo) running on two hardware platforms (i386 and amd64) and on three operating systems (Windows Vista, Ubuntu Intrepid and Mac OS Leopard). The methodology consists of checking the number of correct significant digits returned by each spreadsheet when computing the sample mean, standard deviation, first-order autocorrelation, F statistic in ANOVA tests, linear and nonlinear regression and distribution functions. A discussion about the algorithms for pseudorandom number generation provided by these platforms is also conducted. We conclude that there is no safe choice among the spreadsheets here assessed: they all fail in nonlinear regression and they are not suited for Monte Carlo experiments.

Tell me who your friends are?! The mediating role of friends use in cannabis abuse

Objective: To evaluate the relationship between onset age of cannabis use and cannabis abuse testing the mediating role of the number of friends using cannabis with a sample of Portuguese cannabis users. Comparing men and women regarding these relationships. Method: A sample of 529 Portuguese cannabis users, composed of 276 men and 244 women, aged from 14 to 21 years, completed a sociodemographic questionnaire, the Cannabis Abuse Screening Test and four questions related to cannabis use. Data were analyzed using the PROCESS macro in SPSS version 26.0. Results: The onset age of cannabis use was negatively related to the number of friends using cannabis, while the number of friends using cannabis showed a positive relationship with cannabis abuse. As predicted, the number of friends using cannabis seems to have a mediating role in the relationship between the onset age of cannabis use and cannabis abuse since the indirect effect was found to be significant. The pattern of the relationships among the variables observed was found to be similar both for the male and women' samples. However, males reported higher cannabis abuse than females. Conclusion: Results highlight the mediating role of the friends' using cannabis in the relationship between the onset age of cannabis use and users' abuse. Results highlight the importance of early intervention to cannabis use. Particularly, the pattern of the relationships observed among the studied variables emphasized the need to monitor and peer training intervention or the promotion of social skills.info:eu-repo/semantics/acceptedVersio

On the Numerical Accuracy of Spreadsheets

This paper discusses the numerical precision of five spreadsheets (Calc, Excel, Gnumeric, NeoOffice and Oleo) running on two hardware platforms (i386 and amd64) and on three operating systems (Windows Vista, Ubuntu Intrepid and Mac OS Leopard). The methodology consists of checking the number of correct significant digits returned by each spreadsheet when computing the sample mean, standard deviation, first-order autocorrelation, F statistic in ANOVA tests, linear and nonlinear regression and distribution functions. A discussion about the algorithms for pseudorandom number generation provided by these platforms is also conducted. We conclude that there is no safe choice among the spreadsheets here assessed: they all fail in nonlinear regression and they are not suited for Monte Carlo experiments

Mathematical model of brain tumour with glia-neuron interactions and chemotherapy treatment

Acknowledgements This study was possible by partial financial support from the following Brazilian government agencies: Fundação Araucária, EPSRC-EP/I032606/1 and CNPq, CAPES and Science Without Borders Program Process nos. 17656125, 99999.010583/2013-00 and 245377/2012-3.Peer reviewedPreprin

Numerical study of the optimal nozzle width and jet orientation in a downward blowing air curtain

This paper presents a numerical study of the performance of an air curtain device (ACD) installed on top of the access door of a refrigerated room, aiming to quantify the influence of some parameters (nozzle width, initial orientation and discharge velocity of the jet) towards the maximization of the sealing effect. For this purpose, a numerical model was developed to simulate the turbulent non-isothermal 3D airflow generated by the ACD jet, focusing on the period after the door is opened. The situation when the ACD is switched off is taken as the reference for the performance evaluation. The results allow identifying an optimum jet nozzle width corresponding to maximum sealing efficiency and lower jet airflow rate (lower energy consumption in the air curtain operation). For the present conditions (ACD installed outside the refrigerated room), the sealing efficiency is highest with the ACD oriented vertically and is practically unaffected if the jet discharge is directed towards the warmer space. On the contrary, a jet discharged towards the cooler space is very detrimental to the ACD sealing effectinfo:eu-repo/semantics/publishedVersio

Validity and reliability of self-report instruments for measuring physical activity in adolescents: a systematic review

Realizou-se revisão sistemática de estudos de reprodutibilidade e validade de instrumentos de medida da atividade física do tipo self-report - medidas subjetivas, em adolescentes (10-19 anos). Buscas foram realizadas em bases de dados (MEDLINE, PsycInfo, SportsDiscus, Scopus, Web of Science, SciELO, Lilacs) e nas referências dos artigos localizados. Sessenta e seis estudos atenderam aos critérios de inclusão. A maioria deles foi realizada em países da América do Norte, apenas cinco no Brasil. Identificaram-se 52 instrumentos diferentes: 42 questionários, 6 diários e 4 entrevistas. A reprodutibilidade "teste-reteste" variou de 0,20 a 0,98; a maioria (28/50) dos coeficientes apresentou valores < 0,70. Os coeficientes de validade apresentaram ampla variação (-0,13 a 0,88), sendo a maioria deles (64/84) < 0,50. Apenas três instrumentos apresentaram correlações &gt; 0,70. Diversos instrumentos foram testados em adolescentes, especialmente questionários. Em geral, tais instrumentos demonstraram melhor reprodutibilidade "teste-reteste" do que validade.This was a systematic review of studies on the reliability and validity of self-report instruments for measuring physical activity, or subjective measurements, in adolescents (10-18 years). Searches were conducted in databases (MEDLINE, PsycInfo, SportsDiscus, Scopus, Web of Science, SciELO, Lilacs) and in the references of the retrieved articles. Sixty-six studies met the inclusion criteria. The majority were from North America, with only 5 from Brazil. Fifty-two different instruments were identified: 42 questionnaires, 6 diaries or logs, and 4 interviews. "Test-retest" reliability varied from 0.20 to 0.98; the majority (28/50) of the coefficients showed values < 0.70. Validity coefficients showed wide variation (-0.13 to 0.88), with the majority (64/84) < 0.50. Only 3 instruments displayed correlations &gt; 0.70. Various instruments were tested in adolescents, especially questionnaires. These instruments generally showed better "test-retest" reliability than validity.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES