title: Modelling single cell electroporation with bipolar pulse: Simulating dependance of electroporated fractional pore area on the bipolar field frequency

authors: Talele, Sadhana

subjects: electroporation

abstract: Electroporation EP, in which external electric field pulses create transient pores in a cell membrane, is an important technique for delivery of DNA and drugs into the cell. To enable entry of DNA into cells, the pores should have sufficiently large radii, remain open long enough for the DNA chain to enter the cell, and should not cause membrane rupture. A numerical model for a single spherical cell electroporated by application of direct and/or alternating external electric field pulses has been developed. The model is used to calculate the transmembrane potential, the number of pores and the the fraction of area occupied by the pores (fractional pore area FPA) in response to the various electric field pulses. Presented here are simulation results used to compare the extent of electroporation (fractional pore area FPA) in response to eletric field pulses of different frequencies in a range of extracellular conductivity for two cell raii. It is also observed that a 1 MHz bipolar sinusoidal applied electric field pulse reduces the relative difference in fractional pore area between the two cell sizes compared to a 100 kHz pulse.

text: Modelling single cell electroporation with bipolar pulse: Simulating dependance of electroporated fractional pore area on the bipolar field frequency Electroporation EP, in which external electric field pulses create transient pores in a cell membrane, is an important technique for delivery of DNA and drugs into the cell. To enable entry of DNA into cells, the pores should have sufficiently large radii, remain open long enough for the DNA chain to enter the cell, and should not cause membrane rupture. A numerical model for a single spherical cell electroporated by application of direct and/or alternating external electric field pulses has been developed. The model is used to calculate the transmembrane potential, the number of pores and the the fraction of area occupied by the pores (fractional pore area FPA) in response to the various electric field pulses. Presented here are simulation results used to compare the extent of electroporation (fractional pore area FPA) in response to eletric field pulses of different frequencies in a range of extracellular conductivity for two cell raii. It is also observed that a 1 MHz bipolar sinusoidal applied electric field pulse reduces the relative difference in fractional pore area between the two cell sizes compared to a 100 kHz pulse.

year: 2010

title: Peak Shift in Remembering

authors: Hoan, Andros

subjects: memory trace

abstract: If remembering is discriminative behaviour along the dimension of time and if, as Sargisson and White (2001) argued, generalisation around a peak can occur in this behaviour, then the peak shift which has been shown in discrimination along so many other stimulus dimensions, might also occur in remembering. To examine this hypothesis, 6 hens were trained in a delayed matching-to-sample procedure at delays of 2 and 4 s. The probability of reinforcement for correct responses was initially 0.9 at both delays until performance stabilised. A generalisation probe was then carried out by inserting unreinforced trials at delays of 0, 1, 1.5, 2.5, 3, 3.5, 4.5, 5 and 6 s in a session amongst normal training delay trials. The generalisation functions had a slight peak around 2 s. After further training, a second generalisation probe showed a slightly declining function. The probability of reinforcement at the 2 s delay was then dropped to 0.1, so that in the terms of the classical generalisation/peak shift paradigm, 2-s delay trials became S- and 4-s delay trials became S+. A third generalisation probe then was conducted. This resulted in a flat function from 0 s to 3 s, and a large, clear peak in discriminative performance at 4.5 s over all hens. After more of the same differential reinforcement training, a fourth generalisation probe showed a broad curve peaking at 3 s, with minima at 1 s and 6 s and a global maximum at 0 s. Another training condition was then run, with the probability of reinforcement at the 2-s delay dropped to 0, to see if increasing the "aversiveness" of S- would again result in a peak shift. A fifth generalisation probe was then conducted. This showed a sharp decline in discriminability at shorter delays, a dip around 2 s, and a very small area shift beyond 4 s, but no clear peak shift. This was interpreted as being due to overlearning, with the consequences of remembering at S- no longer significantly affecting performance at S+. A final training condition was then run, with S- moved from 2 s to 3 s with zero probability of reinforcement, and for only a short period, to prevent overlearning. It was predicted that this would cause peak shift to re-occur. A sixth generalisation probe was then conducted. This found a further decline in discriminability at shorter delays, a shift in the dip from 2 s to 3 s, and a large, clear peak at 4.5 s. This demonstration of peak shift in a remembering process would not have been predicted by any traditional theory of memory, but strongly supports the conception of remembering as discriminative behaviour along the stimulus dimension of time.

text: Peak Shift in Remembering If remembering is discriminative behaviour along the dimension of time and if, as Sargisson and White (2001) argued, generalisation around a peak can occur in this behaviour, then the peak shift which has been shown in discrimination along so many other stimulus dimensions, might also occur in remembering. To examine this hypothesis, 6 hens were trained in a delayed matching-to-sample procedure at delays of 2 and 4 s. The probability of reinforcement for correct responses was initially 0.9 at both delays until performance stabilised. A generalisation probe was then carried out by inserting unreinforced trials at delays of 0, 1, 1.5, 2.5, 3, 3.5, 4.5, 5 and 6 s in a session amongst normal training delay trials. The generalisation functions had a slight peak around 2 s. After further training, a second generalisation probe showed a slightly declining function. The probability of reinforcement at the 2 s delay was then dropped to 0.1, so that in the terms of the classical generalisation/peak shift paradigm, 2-s delay trials became S- and 4-s delay trials became S+. A third generalisation probe then was conducted. This resulted in a flat function from 0 s to 3 s, and a large, clear peak in discriminative performance at 4.5 s over all hens. After more of the same differential reinforcement training, a fourth generalisation probe showed a broad curve peaking at 3 s, with minima at 1 s and 6 s and a global maximum at 0 s. Another training condition was then run, with the probability of reinforcement at the 2-s delay dropped to 0, to see if increasing the "aversiveness" of S- would again result in a peak shift. A fifth generalisation probe was then conducted. This showed a sharp decline in discriminability at shorter delays, a dip around 2 s, and a very small area shift beyond 4 s, but no clear peak shift. This was interpreted as being due to overlearning, with the consequences of remembering at S- no longer significantly affecting performance at S+. A final training condition was then run, with S- moved from 2 s to 3 s with zero probability of reinforcement, and for only a short period, to prevent overlearning. It was predicted that this would cause peak shift to re-occur. A sixth generalisation probe was then conducted. This found a further decline in discriminability at shorter delays, a shift in the dip from 2 s to 3 s, and a large, clear peak at 4.5 s. This demonstration of peak shift in a remembering process would not have been predicted by any traditional theory of memory, but strongly supports the conception of remembering as discriminative behaviour along the stimulus dimension of time.

year: 2003

title: The intergenerational perpetuation of achievement messages in whānau

authors: Southey, Kim Marie

subjects: Maori

abstract: The current research is an open exploration of achievement messages that are carried from generation to generation in whānau, in relation to the mainstream education system of Aotearoa. Participant groups comprised of two to three generations within each whānau. A maximum of eight whānau will be asked to participate. A series of continuous conversations will be held with each member of the whānau, reminiscent of the narrative approach, but most recently described as a methodology that allows for ensuring that data is collected in its fullest form.
Differing views about achievement and how it is negotiated within whānau will be explored; along with issues on what, and who, within whānau are the most predominant indicators of achievement views. Detracting from an ethnocentric view of scholastic ability (a common marker for achievement) is done through abandoning mainstream ideals. This research favours an open exploration approach allowing for differing values about what constitutes achievement, and what context achievement is based in. Outcomes of the research are intended to show patterns within whānau and among Māori on the mainstream school system, and how this system has contributed to achievement messages. The positive or negative nature of the contribution from mainstream education is highly important and relevant to further research goals, including the ability to use outcomes to suggest social change in education provision for Māori.

text: The intergenerational perpetuation of achievement messages in whānau The current research is an open exploration of achievement messages that are carried from generation to generation in whānau, in relation to the mainstream education system of Aotearoa. Participant groups comprised of two to three generations within each whānau. A maximum of eight whānau will be asked to participate. A series of continuous conversations will be held with each member of the whānau, reminiscent of the narrative approach, but most recently described as a methodology that allows for ensuring that data is collected in its fullest form.
Differing views about achievement and how it is negotiated within whānau will be explored; along with issues on what, and who, within whānau are the most predominant indicators of achievement views. Detracting from an ethnocentric view of scholastic ability (a common marker for achievement) is done through abandoning mainstream ideals. This research favours an open exploration approach allowing for differing values about what constitutes achievement, and what context achievement is based in. Outcomes of the research are intended to show patterns within whānau and among Māori on the mainstream school system, and how this system has contributed to achievement messages. The positive or negative nature of the contribution from mainstream education is highly important and relevant to further research goals, including the ability to use outcomes to suggest social change in education provision for Māori.

year: 2003