title: Measuring the electrical impedance of mouse brain tissue

authors: Wilson, Marcus T.

abstract: We report on an experimental method to measure conductivity of cortical tissue. We use a pair of 5mm diameter Ag/AgCl electrodes in a Perspex sandwich device that can be brought to a distance of 400 microns apart. The apparatus is brought to uniform temperature before use. Electrical impedance of a sample is measured across the frequency range 20 Hz-2.0 MHz with an Agilent 4980A four-point impedance monitor in a shielded room. The equipment has been used to measure the conductivity of mature mouse brain cortex in vitro. Slices 400 microns in thickness are prepared on a vibratome. Slices are bathed in artificial cerebrospinal fluid (ACSF) to keep them alive. Slices are removed from the ACSF and sections of cortical tissue approximately 2 mm times 2 mm are cut with a razor blade. The sections are photographed through a calibrated microscope to allow identification of their cross-sectional areas. Excess ACSF is removed from the sample and the sections places between the electrodes. The impedance is measured across the frequency range and electrical conductivity calculated. Results show two regions of dispersion. A low frequency region is evident below approximately 10 kHz, and a high frequency dispersion above this. Results at the higher frequencies show a good fit to the Cole-Cole model of impedance of biological tissue; this model consists of resistive and non-linear capacitive elements. Physically, these elements are likely to arise due to membrane polarization and migration of ions both intra- and extra-cellularly.

text: Measuring the electrical impedance of mouse brain tissue We report on an experimental method to measure conductivity of cortical tissue. We use a pair of 5mm diameter Ag/AgCl electrodes in a Perspex sandwich device that can be brought to a distance of 400 microns apart. The apparatus is brought to uniform temperature before use. Electrical impedance of a sample is measured across the frequency range 20 Hz-2.0 MHz with an Agilent 4980A four-point impedance monitor in a shielded room. The equipment has been used to measure the conductivity of mature mouse brain cortex in vitro. Slices 400 microns in thickness are prepared on a vibratome. Slices are bathed in artificial cerebrospinal fluid (ACSF) to keep them alive. Slices are removed from the ACSF and sections of cortical tissue approximately 2 mm times 2 mm are cut with a razor blade. The sections are photographed through a calibrated microscope to allow identification of their cross-sectional areas. Excess ACSF is removed from the sample and the sections places between the electrodes. The impedance is measured across the frequency range and electrical conductivity calculated. Results show two regions of dispersion. A low frequency region is evident below approximately 10 kHz, and a high frequency dispersion above this. Results at the higher frequencies show a good fit to the Cole-Cole model of impedance of biological tissue; this model consists of resistive and non-linear capacitive elements. Physically, these elements are likely to arise due to membrane polarization and migration of ions both intra- and extra-cellularly.

year: 2014

title: Two-state systems with non-Markovian thermal and squeezed quantum noise inputs

authors: Parkins, Andrew Scott

abstract: The effect of quantum noise on the two-state system is studied in the context of (i) coherent quantum tunnelling in a double-well system subject to low temperature quantum noise, and (ii) the two-level atom subject to finite bandwidth squeezed noise. Our approach to these problems is based on the adjoint equation, which describes the evolution of a quantum stochastic density operator. This equation is amenable to solution by ordinary stochastic methods, of which numerical simulation plays the most significant role in our calculations.
The dissipative double-well system is relevant to the search for macroscopic quantum coherence in superconducting quantum interference devices, and previous work, starting from a two-state model and using path integral methods, has established the so-called “noninteracting-blip approximation” as a central result. The adjoint equation, applied to this problem in the weak coupling limit, is shown to closely reproduce this result. The noninteracting-blip approximation entails a Markovian-type assumption about the noise, and, by means of stochastic simulation, we are able to check, and confirm, the validity of this assumption, even for the case of a zero-temperature bath.
Squeezed light, which has reduced quantum fluctuations in one quadrature phase, has been produced experimentally, and possible applications are under active consideration. Analyses of the effect of squeezed light on fundamental radiative processes in simple atoms have revealed interesting possibilities, most notably line-narrowing in the fluorescence spectrum. The original analyses in this field of research have been based on the assumption of broad bandwidth squeezing, and we review the primary results found in this limit. Also in this limit, we study in more detail the phenomenon of squeezed-light-induced photon echoes.
For broad bandwidth squeezing, line-narrowing in resonance fluorescence is restricted to the central fluorescence peak, while the Rabi sidebands exhibit broadening. We examine strongly driven resonance fluorescence for the case in which squeezing is confined to relatively small regions of frequency space about individual fluorescence peaks. It is shown that the noisy component associated with the unsqueezed quadrature phase can be effectively decoupled from the atomic dynamics, which allows narrowing to occur in all three peaks of the spectrum.
Finally, we address the practical problem of producing an effective coupling between an atom and a realistic three-dimensional squeezed field of modest angular spread. We show that this can be achieved, in principle, inside a microscopic plane mirror cavity, provided the injected squeezed field is suitably mode-matched to the cavity.

text: Two-state systems with non-Markovian thermal and squeezed quantum noise inputs The effect of quantum noise on the two-state system is studied in the context of (i) coherent quantum tunnelling in a double-well system subject to low temperature quantum noise, and (ii) the two-level atom subject to finite bandwidth squeezed noise. Our approach to these problems is based on the adjoint equation, which describes the evolution of a quantum stochastic density operator. This equation is amenable to solution by ordinary stochastic methods, of which numerical simulation plays the most significant role in our calculations.
The dissipative double-well system is relevant to the search for macroscopic quantum coherence in superconducting quantum interference devices, and previous work, starting from a two-state model and using path integral methods, has established the so-called “noninteracting-blip approximation” as a central result. The adjoint equation, applied to this problem in the weak coupling limit, is shown to closely reproduce this result. The noninteracting-blip approximation entails a Markovian-type assumption about the noise, and, by means of stochastic simulation, we are able to check, and confirm, the validity of this assumption, even for the case of a zero-temperature bath.
Squeezed light, which has reduced quantum fluctuations in one quadrature phase, has been produced experimentally, and possible applications are under active consideration. Analyses of the effect of squeezed light on fundamental radiative processes in simple atoms have revealed interesting possibilities, most notably line-narrowing in the fluorescence spectrum. The original analyses in this field of research have been based on the assumption of broad bandwidth squeezing, and we review the primary results found in this limit. Also in this limit, we study in more detail the phenomenon of squeezed-light-induced photon echoes.
For broad bandwidth squeezing, line-narrowing in resonance fluorescence is restricted to the central fluorescence peak, while the Rabi sidebands exhibit broadening. We examine strongly driven resonance fluorescence for the case in which squeezing is confined to relatively small regions of frequency space about individual fluorescence peaks. It is shown that the noisy component associated with the unsqueezed quadrature phase can be effectively decoupled from the atomic dynamics, which allows narrowing to occur in all three peaks of the spectrum.
Finally, we address the practical problem of producing an effective coupling between an atom and a realistic three-dimensional squeezed field of modest angular spread. We show that this can be achieved, in principle, inside a microscopic plane mirror cavity, provided the injected squeezed field is suitably mode-matched to the cavity.

year: 1990

title: A case study of Pipiri Ki A Papatūānuku

authors: Tamoko-o-te-rangi, Ormsby

subjects: environmental initiatives

abstract: This thesis is an examination and analysis of the environmental initiative Pipiri Ki A Papatūānuku, co-founded by Waimirirangi Ormsby (née Koopu-Stone) and myself, Tamoko Ormsby. The primary aim of this research was to achieve an understanding of the PKP initiative at the individual level and to inform future collective action at the community level. As such, my primary research question is:

How can Pipiri Ki A Papatūānuku inform community-scale action that contributes to our more-than-human relationship with Papatūānuku within our current capitalist settler-colonial context?

The study is part-autoethnographic in that it is informed by my personal reflections and experiences as a co-founder, operator, and participant of the initiative. In addition, the study explores the number of participants who signed up yearly for each action and employs a brief descriptive analysis of the initiative.

The literature review explores how common Western notions of environmentalism are devoid of the spiritual, cultural, and relational aspects present within indigenous and Māori knowledge systems. It touches on the histories of capitalism and colonialism and how these have led to the consumptogenic society we are in. It aims to illustrate the nexus between the Māori and Western Eurocentric worlds.

He Whatu is the framework that has emerged from this case study as the means to respond to the primary research question. The framework was developed by analyzing the key themes of PKP over the years 2017 to 2021. He Whatu has five key elements: Identity, Language, Distance, Practicality, and Influence; each with three subcategories. It is activated through provoking key conversations to inform future community action.

text: A case study of Pipiri Ki A Papatūānuku This thesis is an examination and analysis of the environmental initiative Pipiri Ki A Papatūānuku, co-founded by Waimirirangi Ormsby (née Koopu-Stone) and myself, Tamoko Ormsby. The primary aim of this research was to achieve an understanding of the PKP initiative at the individual level and to inform future collective action at the community level. As such, my primary research question is:

How can Pipiri Ki A Papatūānuku inform community-scale action that contributes to our more-than-human relationship with Papatūānuku within our current capitalist settler-colonial context?

The study is part-autoethnographic in that it is informed by my personal reflections and experiences as a co-founder, operator, and participant of the initiative. In addition, the study explores the number of participants who signed up yearly for each action and employs a brief descriptive analysis of the initiative.

The literature review explores how common Western notions of environmentalism are devoid of the spiritual, cultural, and relational aspects present within indigenous and Māori knowledge systems. It touches on the histories of capitalism and colonialism and how these have led to the consumptogenic society we are in. It aims to illustrate the nexus between the Māori and Western Eurocentric worlds.

He Whatu is the framework that has emerged from this case study as the means to respond to the primary research question. The framework was developed by analyzing the key themes of PKP over the years 2017 to 2021. He Whatu has five key elements: Identity, Language, Distance, Practicality, and Influence; each with three subcategories. It is activated through provoking key conversations to inform future community action.

year: 2023