title: Reprocessing of wood fibre reinforced polypropylene composites. Part I: Effects on physical and mechanical properties

authors: Beg, Mohammad Dalour Hossen

subjects: natural fibre composites

abstract: This paper describes the effects of reprocessing on the physical and mechanical properties of composites based on radiata pine (Pinus radiata) fibre in a polypropylene (PP) matrix. Composites, containing either 40 wt% or 50 wt% fibre with 4 wt% maleated polypropylene (MAPP) as a coupling agent, were reprocessed up to eight times. For composites with 40 wt% fibre, tensile strength (TS) and Young’s modulus (YM) were found to decrease with increased reprocessing by up to 25% for TS and 17% for YM (after reprocessed eight times). Flexural tests were also carried out for 40 wt% fibre composites and flexural strength and modulus were found to decrease with increased reprocessing. Although, TS was lower for virgin composites with 50 wt% fibre than for those with 40 wt% fibre, this initially increased with reprocessing by up to 14% (after reprocessed two times), but then decreased with further reprocessing, and an overall 11% reduction of TS was found after reprocessing eight times compared to the virgin composites. YM was higher for virgin composites with 50 wt% than those with for 40 wt% fibre and also initially increased with reprocessing but decreased upon further reprocessing. Reprocessing was found to increase thermal stability. The TS of composites made by combining reprocessed with virgin materials was also assessed.

text: Reprocessing of wood fibre reinforced polypropylene composites. Part I: Effects on physical and mechanical properties This paper describes the effects of reprocessing on the physical and mechanical properties of composites based on radiata pine (Pinus radiata) fibre in a polypropylene (PP) matrix. Composites, containing either 40 wt% or 50 wt% fibre with 4 wt% maleated polypropylene (MAPP) as a coupling agent, were reprocessed up to eight times. For composites with 40 wt% fibre, tensile strength (TS) and Young’s modulus (YM) were found to decrease with increased reprocessing by up to 25% for TS and 17% for YM (after reprocessed eight times). Flexural tests were also carried out for 40 wt% fibre composites and flexural strength and modulus were found to decrease with increased reprocessing. Although, TS was lower for virgin composites with 50 wt% fibre than for those with 40 wt% fibre, this initially increased with reprocessing by up to 14% (after reprocessed two times), but then decreased with further reprocessing, and an overall 11% reduction of TS was found after reprocessing eight times compared to the virgin composites. YM was higher for virgin composites with 50 wt% than those with for 40 wt% fibre and also initially increased with reprocessing but decreased upon further reprocessing. Reprocessing was found to increase thermal stability. The TS of composites made by combining reprocessed with virgin materials was also assessed.

year: 2008

title: White-noise susceptibility and critical slowing in neurons near spiking threshold

authors: Steyn-Ross, D. Alistair

subjects: neuron

abstract: We present mathematical and simulation analyses of the below-threshold noisy response of two biophysically motivated models for excitable membrane due to H. R. Wilson: a squid axon (“resonator”) and a human cortical neuron (“integrator”). When stimulated with a low-intensity white noise superimposed on a dc control current, both membrane types generate voltage fluctuations that exhibit critical slowing down—that is, the voltage responsiveness to noisy input currents grows in amplitude while slowing in frequency—as the membrane approaches spiking threshold from below. We define threshold unambiguously as that dc current that renders a zero real eigenvalue for the Jacobian matrix for the integrator neuron, and, for the resonator neuron, as the dc current that gives a complex eigenvalue pair whose real part is zero. Using a linear Ornstein-Uhlenbeck analysis, we give exact small-noise expressions for the variance, power spectrum, and correlation function of the voltage fluctuations, and we derive the scaling laws for the divergence of susceptibility and correlation times for approach to threshold. We compare these predictions with numerical simulations of the nonlinear stochastic equations, and demonstrate that, provided the white-noise perturbations are kept sufficiently small, the linearized theory works well. These predictions should be testable in the laboratory using a current-clamped cell configuration. If confirmed, then the proximity of a neuron to its spike-transition point can be judged by measuring its subthreshold susceptibility to white-noise stimulation. We postulate that such temporally correlated fluctuations could provide a means of subthreshold signaling via gap-junction connections with neighboring neurons.

text: White-noise susceptibility and critical slowing in neurons near spiking threshold We present mathematical and simulation analyses of the below-threshold noisy response of two biophysically motivated models for excitable membrane due to H. R. Wilson: a squid axon (“resonator”) and a human cortical neuron (“integrator”). When stimulated with a low-intensity white noise superimposed on a dc control current, both membrane types generate voltage fluctuations that exhibit critical slowing down—that is, the voltage responsiveness to noisy input currents grows in amplitude while slowing in frequency—as the membrane approaches spiking threshold from below. We define threshold unambiguously as that dc current that renders a zero real eigenvalue for the Jacobian matrix for the integrator neuron, and, for the resonator neuron, as the dc current that gives a complex eigenvalue pair whose real part is zero. Using a linear Ornstein-Uhlenbeck analysis, we give exact small-noise expressions for the variance, power spectrum, and correlation function of the voltage fluctuations, and we derive the scaling laws for the divergence of susceptibility and correlation times for approach to threshold. We compare these predictions with numerical simulations of the nonlinear stochastic equations, and demonstrate that, provided the white-noise perturbations are kept sufficiently small, the linearized theory works well. These predictions should be testable in the laboratory using a current-clamped cell configuration. If confirmed, then the proximity of a neuron to its spike-transition point can be judged by measuring its subthreshold susceptibility to white-noise stimulation. We postulate that such temporally correlated fluctuations could provide a means of subthreshold signaling via gap-junction connections with neighboring neurons.

year: 2006

title: Final arrangements following death: Maori indigenous decision making and tangi

authors: Nikora, Linda Waimarie

subjects: Maori death rituals

abstract: Death is a universal event. It will happen to all of us, yet how we respond to death is particular and influenced by our cultural worlds. This study offers an investigation of the idiographic, of how one woman responded to, and made arrangements to, mourn and bury her mother. Specifically, we explore how she and her whanau (family) under pressure of time and grief and in the absence of clear final wishes, met to consider issues and make decisions about the situation they were confronted with. This case forms part of a much larger programme of research into Maori death rituals, change and adaption. Informing a scholarly audience unfamiliar with the Maori world requires a significant amount of contextual information. The case study is a powerful strategy to achieve this and one that draws readers into deep understanding (Willig, 2008). This case provides insight into the struggles of an indigenous fourth-world people living within the heterogeneity of Aotearoa/New Zealand society; it demonstrates how values change across generations as people live their lives increasingly away from their ancestral homelands; and how traditionally defined roles and responsibilities within the whanau (family) are challenged by members living away from each other.

text: Final arrangements following death: Maori indigenous decision making and tangi Death is a universal event. It will happen to all of us, yet how we respond to death is particular and influenced by our cultural worlds. This study offers an investigation of the idiographic, of how one woman responded to, and made arrangements to, mourn and bury her mother. Specifically, we explore how she and her whanau (family) under pressure of time and grief and in the absence of clear final wishes, met to consider issues and make decisions about the situation they were confronted with. This case forms part of a much larger programme of research into Maori death rituals, change and adaption. Informing a scholarly audience unfamiliar with the Maori world requires a significant amount of contextual information. The case study is a powerful strategy to achieve this and one that draws readers into deep understanding (Willig, 2008). This case provides insight into the struggles of an indigenous fourth-world people living within the heterogeneity of Aotearoa/New Zealand society; it demonstrates how values change across generations as people live their lives increasingly away from their ancestral homelands; and how traditionally defined roles and responsibilities within the whanau (family) are challenged by members living away from each other.

year: 2012-03