Search results for "Statistical"
showing 10 items of 4960 documents
Dynamics of a Single Species in a Fluctuating Environment under Periodic Yield Harvesting
2013
We discuss the effect of a periodic yield harvesting on a single species population whose dynamics in a fluctuating environment is described by the logistic differential equation with periodic coefficients. This problem was studied by Brauer and Sánchez (2003) who attempted the proof of the existence of two positive periodic solutions; the flaw in their argument is corrected. We obtain estimates for positive attracting and repelling periodic solutions and describe behavior of other solutions. Extinction and blow-up times are evaluated for solutions with small and large initial data; dependence of the number of periodic solutions on the parameterσassociated with the intensity of harvesting i…
Statistical Analysis of the (In)efficiency of Bitcoin : A comparison of the weak form efficient market hypothesis in the US and Venezuela
2019
Master's thesis Business Administration BE501 - University of Agder 2019 Bitcoin is a phenomenon that has received a lot of attentionduringthe last years. Although the literature on the subject has expanded, there is still need for more research. This paper replicates the work of Urquhart (2016) and examines whether there isevidence ofweak form efficiency in the Bitcoin market. He found that the Bitcoin market in the US showed signs of moving towards weak form efficiency. We contribute to the existing literature by adding recentdata and comparing two different markets;the USand Venezuela. To obtain robustness of the results, the analysis is conducted by performing six different statistical …
Has the Introduction of Bitcoin Futures on Regulated Exchanges Decreased Price Volatility?
2019
Master's thesis Business Administration BE501 - University of Agder 2019 Bitcoin is a tremendously debated phenomenon in the world of finance and in recent the scientific literature on the topic has expanded. In this thesis,the bitcoin to US dollar exchange rate is examined through various conditional variance models to describe its highly volatile nature. We examine whether the introduction of bitcoin futurescontractsin late 2017 has had a decreasing impact on price volatility by estimatingthe unconditional variance. The log-return of the bitcoin exchange rate is analysed,and there is evidence of volatility clustering and time-varying volatility. Consequently, the variance is modelled thro…
Modalitātes lietojums tiešsaistes laikrakstu rakstos Lielbritānijā un ASV par politiskām tēmām
2020
Iepriekšējie pētījumi par modalitātes lietojumu laikrakstu rakstos atklāja, ka žurnālisti mēdz ietekmēt lasītājus un sniegt faktu subjektīvu interpretāciju, kad tiek gaidīts objektīvs notikumu atspoguļojums. Tāpēc šī darba mērķis bija analizēt modalitātes lietojumu septiņpadsmit tiešsaistes laikrakstu rakstos divos Lielbritānijas un divos ASV laikrakstos par Brexit. Pētījumā izmantotās metodes ir diskursa analīze un statistiskā analīze. Rezultāti liecina, ka visvairāk lietotais modālais darbības vārds abu valstu laikrakstos ir will, kas izteica pārliecības nozīmi ar pierādījumu palīdzību, un norādīja, ka priekšroka tiek dota patiesībai. Pārējie modālie darbības vārdi would un could dominēja…
Agritourism and local development: A methodology for assessing the role of public contributions in the creation of competitive advantage
2018
Abstract Agriculture has been an economic mainstay of countries throughout history. Recently, its importance and essential role in local and regional growth and development have also received due acknowledgment. However, agritourism entrepreneurs often lack the necessary means, when relying only on their own funds alone. For these reasons, targeted aid measures are provided at the regional, national and European levels, provided they fulfill specified subjective and objective eligibility criteria. This investigation aims at understanding the rationale, if any, according to which the Public Administration allots such contributions. To this end, a two-tiered analysis was conducted on the data…
Simultaneous optimization of mobile phase composition, column nature and length to analyse complex samples using serially coupled columns
2013
Abstract The combination of the selectivity of different columns serially coupled improves the separation expectancies with regard to the separation offered by each single column. In the reported approaches, either a pre-selected isocratic mobile phase composition or gradient program, giving rise to acceptable retention, is used. In previous work (JCA 1281 (2013) 94), we showed that the approach succeeds with conventional columns, assembled through zero-dead volume couplers. In this work, the simultaneous interpretive optimization of mobile phase composition and column nature and length, based on a limited number of experimental data, is demonstrated. This approach allows an impressive redu…
Fuzzy logic and meteorological variables: a case study of solar irradiance
2002
Solar irradiance is an extreme case of an uncertain variable when measured on an hourly, or shorter time interval. In this paper solar irradiance has been considered as a case study for physical fuzzy modelling of a climate variable. The uncertainty of the solar irradiance is treated as a fuzzy uncertainty whilst other variables are considered crisp. The approach is robust as it does not rely on statistical assumptions, and it is a possible alternative to modelling complex systems. To our knowledge, this is the first time that a physical model of a meteorological variable based on fuzzy numbers has been proposed. Previous rule-based fuzzy meteorological models are only descriptive, and cann…
Evaluation of the effect of chance correlations on variable selection using Partial Least Squares -Discriminant Analysis
2013
Variable subset selection is often mandatory in high throughput metabolomics and proteomics. However, depending on the variable to sample ratio there is a significant susceptibility of variable selection towards chance correlations. The evaluation of the predictive capabilities of PLSDA models estimated by cross-validation after feature selection provides overly optimistic results if the selection is performed on the entire set and no external validation set is available. In this work, a simulation of the statistical null hypothesis is proposed to test whether the discrimination capability of a PLSDA model after variable selection estimated by cross-validation is statistically higher than t…
Varying numbers of players in small-sided soccer games modifies action opportunities during training
2014
This study examined the effects of the numbers of players involved in small-sided team games (underloading and overloading) on opportunities for maintaining ball possession, shooting at goal and passing to teammates during training. These practice constraint manipulations were assumed to alter values of key performance variables identified in previous research, such as interpersonal distances between players and time to intercept shots and passes. Fifteen male soccer players (age: 19.60±1.99 years) were grouped into three teams and played against each other in different versions of small-sided soccer games, in which the number of players was manipulated in three different conditions: 5 vs. …
A Non-WSSUS Mobile-to-Mobile Channel Model Assuming Velocity Variations of the Mobile Stations
2017
This paper aims to characterize the effects that the velocity variations of the mobile stations (MSs) produce on the correlation properties of non-stationary time-frequency (TF) dispersive mobile- to-mobile (M2M) fading channels. Toward that end, we propose a novel geometrical model for non-wide-sense stationary uncorrelated scattering (non-WSSUS) M2M channels that incorporates such variations following a plane wave propagation approach. Capitalizing on the mathematical simplicity of this approach, we derive a general expression for the four-dimensional (4D) TF correlation function (TFCF) of the proposed channel model. From this expression, we analyze the influence of the MSs' acceleration#…