title: Time-dependent particle acceleration in a Fermi reservoir

authors: Litvinenko, Yuri E.

subjects: acceleration of particles

abstract: Context. A steady model was presented by Burn, in which energy conservation is used to constrain the parameters of stochastic Fermi acceleration. A steady model, however, is unlikely to be adequate for particle acceleration in impulsive solar flares.
Aims. This paper describes a time-dependent model for particle acceleration in a Fermi reservoir 
Methods. The calculation is based on the original formulation of stochastic acceleration by Fermi, with additional physically motivated assumptions about the turbulent and particle energy densities within the reservoir, that are similar to those of the steady analysis. The problem is reduced to an integro-differential equation that possesses an analytical solution. 
Results. The model predicts the formation of a power-law differential energy spectrum N(E) similar to E-2, that is observable outside the reservoir. The predicted spectral index is independent of the parameters of the model. The results may help in understanding particle acceleration in solar flares and other astrophysical applications.

text: Time-dependent particle acceleration in a Fermi reservoir Context. A steady model was presented by Burn, in which energy conservation is used to constrain the parameters of stochastic Fermi acceleration. A steady model, however, is unlikely to be adequate for particle acceleration in impulsive solar flares.
Aims. This paper describes a time-dependent model for particle acceleration in a Fermi reservoir 
Methods. The calculation is based on the original formulation of stochastic acceleration by Fermi, with additional physically motivated assumptions about the turbulent and particle energy densities within the reservoir, that are similar to those of the steady analysis. The problem is reduced to an integro-differential equation that possesses an analytical solution. 
Results. The model predicts the formation of a power-law differential energy spectrum N(E) similar to E-2, that is observable outside the reservoir. The predicted spectral index is independent of the parameters of the model. The results may help in understanding particle acceleration in solar flares and other astrophysical applications.

year: 2012

title: A two-level learning method for generalized multi-instance problems

authors: Weidmann, Nils

subjects: computer science

abstract: In traditional multi-instance (MI) learning, a single positive instance in a bag produces a positive class label. Hence, the learner knows how the bags class label depends on the labels of the instances in the bag and can explicitly use this information to solve the learning task. In this paper we investigate a generalized view of the MI problem where this simple assumption no longer holds. We assume that an interaction between instances in a bag determines the class label. Our two-level learning method for this type of problem transforms an MI bag into a single meta-instance that can be learned by a standard propositional method. The meta-instance indicates which regions in the instance space are covered by instances of the bag. Results on both artificial and real-world data show that this two-level classification approach is well suited for generalized MI problems.

text: A two-level learning method for generalized multi-instance problems In traditional multi-instance (MI) learning, a single positive instance in a bag produces a positive class label. Hence, the learner knows how the bags class label depends on the labels of the instances in the bag and can explicitly use this information to solve the learning task. In this paper we investigate a generalized view of the MI problem where this simple assumption no longer holds. We assume that an interaction between instances in a bag determines the class label. Our two-level learning method for this type of problem transforms an MI bag into a single meta-instance that can be learned by a standard propositional method. The meta-instance indicates which regions in the instance space are covered by instances of the bag. Results on both artificial and real-world data show that this two-level classification approach is well suited for generalized MI problems.

year: 2003

title: Cultural identity and academic achievement among Māori undergraduate university students

authors: Bennett, Simon T.

subjects: Maori

abstract: Cultural identity and academic achievement were investigated among a nonrandom
sample of 72 undergraduate Māori university students studying at Massey
University. Student problems were examined to identify the types of difficulties
most prevalent among this population. The degree to which cultural identity
moderates the relationship between student problems and academic achievement
was then examined. Major findings were that (a) there is a consistent negative
relationship between student problems and academic achievement; and (b) cultural
identity moderates the effect of student problems on academic achievement, in that:
a high degree of problems were associated with decreases in grade point average
among respondents with low cultural identity; while among respondents with high
cultural identity, high levels of student problems had little negative effect on grade
point average. Despite the study having limitations, the findings have important
implications for Māori students, deliverers of tertiary education, tertiary education
providers, and those involved in the development and implementation of tertiary
education policy.

text: Cultural identity and academic achievement among Māori undergraduate university students Cultural identity and academic achievement were investigated among a nonrandom
sample of 72 undergraduate Māori university students studying at Massey
University. Student problems were examined to identify the types of difficulties
most prevalent among this population. The degree to which cultural identity
moderates the relationship between student problems and academic achievement
was then examined. Major findings were that (a) there is a consistent negative
relationship between student problems and academic achievement; and (b) cultural
identity moderates the effect of student problems on academic achievement, in that:
a high degree of problems were associated with decreases in grade point average
among respondents with low cultural identity; while among respondents with high
cultural identity, high levels of student problems had little negative effect on grade
point average. Despite the study having limitations, the findings have important
implications for Māori students, deliverers of tertiary education, tertiary education
providers, and those involved in the development and implementation of tertiary
education policy.

year: 2003