title: Reprocessing of wood fibre reinforced polypropylene composites. Part II: Hygrothermal ageing and its effects

authors: Beg, Mohammad Dalour Hossen

subjects: A. Natural fibre composites

abstract: In this paper, hygrothermal ageing behaviour of virgin and reprocessed composites based on radiata pine (Pinus Radiata) wood fibre with a polypropylene (PP) matrix were investigated. Composites were produced with 40 wt% fibre and 4 wt% maleated polypropylene (MAPP) coupling agent using extrusion followed by injection moulding. Composites reprocessing was carried out using repeated pelletising and injection moulding for up to eight times. Hygrothermal ageing was carried out by immersing specimens in distilled water at 50 °C over a 9 month period. The diffusion coefficient of moisture absorption was obtained for composites by measuring water uptake of specimens at regular time intervals. It was found that the diffusion coefficient and the equilibrium moisture contents of composites decreased with increased number of times the materials were reprocessed. After hygrothermal ageing, tensile strength (TS), Young’s modulus (YM) and hardness of both virgin and reprocessed composites were found to decrease, but impact strength (IS) and failure strain (FS) increased. The thermal stability of both virgin and reprocessed composites was found to decrease after hygrothermal ageing.

text: Reprocessing of wood fibre reinforced polypropylene composites. Part II: Hygrothermal ageing and its effects In this paper, hygrothermal ageing behaviour of virgin and reprocessed composites based on radiata pine (Pinus Radiata) wood fibre with a polypropylene (PP) matrix were investigated. Composites were produced with 40 wt% fibre and 4 wt% maleated polypropylene (MAPP) coupling agent using extrusion followed by injection moulding. Composites reprocessing was carried out using repeated pelletising and injection moulding for up to eight times. Hygrothermal ageing was carried out by immersing specimens in distilled water at 50 °C over a 9 month period. The diffusion coefficient of moisture absorption was obtained for composites by measuring water uptake of specimens at regular time intervals. It was found that the diffusion coefficient and the equilibrium moisture contents of composites decreased with increased number of times the materials were reprocessed. After hygrothermal ageing, tensile strength (TS), Young’s modulus (YM) and hardness of both virgin and reprocessed composites were found to decrease, but impact strength (IS) and failure strain (FS) increased. The thermal stability of both virgin and reprocessed composites was found to decrease after hygrothermal ageing.

year: 2008

title: Modeling motor-evoked potentials from neural field simulations of transcranial magnetic stimulation

authors: Wilson, Marcus T.

subjects: Science & Technology

abstract: Objective
To develop a population-based biophysical model of motor-evoked potentials (MEPs) following transcranial magnetic stimulation (TMS).

Methods
We combined an existing MEP model with population-based cortical modeling. Layer 2/3 excitatory and inhibitory neural populations, modeled with neural-field theory, are stimulated with TMS and feed layer 5 corticospinal neurons, which also couple directly but weakly to the TMS pulse. The layer 5 output controls mean motoneuron responses, which generate a series of single motor-unit action potentials that are summed to estimate a MEP.

Results
A MEP waveform was generated comparable to those observed experimentally. The model captured TMS phenomena including a sigmoidal input–output curve, common paired pulse effects (short interval intracortical inhibition, intracortical facilitation, long interval intracortical inhibition) including responses to pharmacological interventions, and a cortical silent period. Changes in MEP amplitude following theta burst paradigms were observed including variability in outcome direction.

Conclusions
The model reproduces effects seen in common TMS paradigms.

Significance
The model allows population-based modeling of changes in cortical dynamics due to TMS protocols to be assessed in terms of changes in MEPs, thus allowing a clear comparison between population-based modeling predictions and typical experimental outcome measures.

text: Modeling motor-evoked potentials from neural field simulations of transcranial magnetic stimulation Objective
To develop a population-based biophysical model of motor-evoked potentials (MEPs) following transcranial magnetic stimulation (TMS).

Methods
We combined an existing MEP model with population-based cortical modeling. Layer 2/3 excitatory and inhibitory neural populations, modeled with neural-field theory, are stimulated with TMS and feed layer 5 corticospinal neurons, which also couple directly but weakly to the TMS pulse. The layer 5 output controls mean motoneuron responses, which generate a series of single motor-unit action potentials that are summed to estimate a MEP.

Results
A MEP waveform was generated comparable to those observed experimentally. The model captured TMS phenomena including a sigmoidal input–output curve, common paired pulse effects (short interval intracortical inhibition, intracortical facilitation, long interval intracortical inhibition) including responses to pharmacological interventions, and a cortical silent period. Changes in MEP amplitude following theta burst paradigms were observed including variability in outcome direction.

Conclusions
The model reproduces effects seen in common TMS paradigms.

Significance
The model allows population-based modeling of changes in cortical dynamics due to TMS protocols to be assessed in terms of changes in MEPs, thus allowing a clear comparison between population-based modeling predictions and typical experimental outcome measures.

year: 2021

title: Formulaic Discourse Patterning in Mōteatea

authors: Roa, Te Raukura o Te Rangimarie

subjects: mōteatea

abstract: Oral formulaic composition, which involves the use of communally owned formulae of various kinds, is a common feature of verbal arts produced in many different languages. It is particularly associated with pre-literate cultures and tends to be gradually replaced by more individualistic verbal art forms when societies become literate. There are very few publications in which the analysis of mōteatea (Māori laments) is linked explicitly to oral formulaic theory. Nevertheless, there is, I believe, sufficient evidence in published sources to indicate that traditional mōteatea (defined here as mōteatea that are not fundamentally influenced by European cultural beliefs and practices) exhibit evidence of regularly recurring, conventional themes (such as death, separation, loss and travel) and motifs (such as the setting sun, the presence of rain or mist and sleeplessness).  There is, however, considerably less evidence that traditional mōteatea make extensive use of verbal formulae, that is, of the same or very similar groups of words derived from a common store of poetic resources. Although there are references in the literature to the conventionalized use of language in mōteatea, and although it has been claimed that there are at least some commonly recurring verbal expressions, this is by no means evidence of reliance on a common stock of verbal formulae. Indeed, no attempt has hitherto been made to define precisely what might be meant by the term 'oral formula' in the context of compositions in te reo Māori, something that is clearly required in view, in particular, of the fact that the phrasal structure of the language means that certain groupings (e.g. i te X; ki te X) are very likely to occur in certain contexts irrespective of genre. Furthermore, in the literature on oral formulaic composition, oral formulae are generally linked to particular metrical conditions and there is, it is argued here, no convincing empirically-based evidence that mōteatea conform to any common metrical structure or structures (see Chapters 2 and 4).

In the context of a critical review of selected literature on oral formulaic theory (Chapter 2) and mōteatea (Chapter 3), this thesis sets out to test the hypothesis that traditional mōteatea were composed, in whole or in large part, from a common stock of oral formulae. The conclusion, based on analysis of a selection of mōteatea included in Ngā mōteatea, a collection initially established by Sir Apirana Ngata, is that this hypothesis must be rejected (Chapter 4). However, a model derived from a review of selected literature on discourse structure (Chapter 5) was also applied to the analysis of a sample of these mōteatea (Chapter 6). On the basis of this analysis, it is concluded that they exhibit one of two very similar discourse prototypes, each of which involves a particular combination of discourse elements. What distinguishes the two prototypes is the fact that only one of them is characterized by the inclusion of hortatory sections in which the poet urges one or more of the protagonists to undergo one or more steps or stages required to achieve a particular outcome, such as entry into the spirit world or vengeance for death and/ or humiliation.

text: Formulaic Discourse Patterning in Mōteatea Oral formulaic composition, which involves the use of communally owned formulae of various kinds, is a common feature of verbal arts produced in many different languages. It is particularly associated with pre-literate cultures and tends to be gradually replaced by more individualistic verbal art forms when societies become literate. There are very few publications in which the analysis of mōteatea (Māori laments) is linked explicitly to oral formulaic theory. Nevertheless, there is, I believe, sufficient evidence in published sources to indicate that traditional mōteatea (defined here as mōteatea that are not fundamentally influenced by European cultural beliefs and practices) exhibit evidence of regularly recurring, conventional themes (such as death, separation, loss and travel) and motifs (such as the setting sun, the presence of rain or mist and sleeplessness).  There is, however, considerably less evidence that traditional mōteatea make extensive use of verbal formulae, that is, of the same or very similar groups of words derived from a common store of poetic resources. Although there are references in the literature to the conventionalized use of language in mōteatea, and although it has been claimed that there are at least some commonly recurring verbal expressions, this is by no means evidence of reliance on a common stock of verbal formulae. Indeed, no attempt has hitherto been made to define precisely what might be meant by the term 'oral formula' in the context of compositions in te reo Māori, something that is clearly required in view, in particular, of the fact that the phrasal structure of the language means that certain groupings (e.g. i te X; ki te X) are very likely to occur in certain contexts irrespective of genre. Furthermore, in the literature on oral formulaic composition, oral formulae are generally linked to particular metrical conditions and there is, it is argued here, no convincing empirically-based evidence that mōteatea conform to any common metrical structure or structures (see Chapters 2 and 4).

In the context of a critical review of selected literature on oral formulaic theory (Chapter 2) and mōteatea (Chapter 3), this thesis sets out to test the hypothesis that traditional mōteatea were composed, in whole or in large part, from a common stock of oral formulae. The conclusion, based on analysis of a selection of mōteatea included in Ngā mōteatea, a collection initially established by Sir Apirana Ngata, is that this hypothesis must be rejected (Chapter 4). However, a model derived from a review of selected literature on discourse structure (Chapter 5) was also applied to the analysis of a sample of these mōteatea (Chapter 6). On the basis of this analysis, it is concluded that they exhibit one of two very similar discourse prototypes, each of which involves a particular combination of discourse elements. What distinguishes the two prototypes is the fact that only one of them is characterized by the inclusion of hortatory sections in which the poet urges one or more of the protagonists to undergo one or more steps or stages required to achieve a particular outcome, such as entry into the spirit world or vengeance for death and/ or humiliation.

year: 2008