title: Measuring the bulk impedance of brain tissue in vitro

authors: Wilson, Marcus T.

abstract: Theoretical and numerical models of brain activity suggest a link between seizures and electrical connectivity. We have therefore been motivated to measure electrical conductivity in brain tissue. Such measurements in vitro are difficult; it is necessary to use a conductive inorganic salt solution, artificial cerebrospinal fluid (ACSF), to keep the tissue alive. We have attempted to provide a robust method to make such measurements. Mouse brain tissue was sliced (400 μm) using established methods. Half the slices were placed in standard ACSF; half were placed in ACSF devoid of magnesium ions. The latter case promotes seizure activity. Electrical activity was measured with a tungsten electrode at various places on the slices. Sixty-nine samples of cortex (2 mm × 2 mm) were cut with a razor. Their areas were measured with a calibrated microscope. Each sample was placed between two flat Ag/AgCl electrodes in a Perspex sandwich. Excess ACSF was removed with filter paper. The impedance was measured at 25°C from 20 Hz to 2 MHz with an Agilent E4980A four-point impedance meter in a shielded room, using a low current. Between 1 kHz and 100 kHz the conductivity was approximately 0.2 S m⁻¹; outside this range dispersion occurred. Samples prepared in the magnesium-free ACSF had a conductivity about 10% lower. The Cole-Cole model of conductivity was fitted. There were few significant differences between the parameters for the different groups measured.

text: Measuring the bulk impedance of brain tissue in vitro Theoretical and numerical models of brain activity suggest a link between seizures and electrical connectivity. We have therefore been motivated to measure electrical conductivity in brain tissue. Such measurements in vitro are difficult; it is necessary to use a conductive inorganic salt solution, artificial cerebrospinal fluid (ACSF), to keep the tissue alive. We have attempted to provide a robust method to make such measurements. Mouse brain tissue was sliced (400 μm) using established methods. Half the slices were placed in standard ACSF; half were placed in ACSF devoid of magnesium ions. The latter case promotes seizure activity. Electrical activity was measured with a tungsten electrode at various places on the slices. Sixty-nine samples of cortex (2 mm × 2 mm) were cut with a razor. Their areas were measured with a calibrated microscope. Each sample was placed between two flat Ag/AgCl electrodes in a Perspex sandwich. Excess ACSF was removed with filter paper. The impedance was measured at 25°C from 20 Hz to 2 MHz with an Agilent E4980A four-point impedance meter in a shielded room, using a low current. Between 1 kHz and 100 kHz the conductivity was approximately 0.2 S m⁻¹; outside this range dispersion occurred. Samples prepared in the magnesium-free ACSF had a conductivity about 10% lower. The Cole-Cole model of conductivity was fitted. There were few significant differences between the parameters for the different groups measured.

year: 2015

title: An Integrated Alerting Service for Open Digital Libraries: Design and Implementation

authors: Hinze, Annika

subjects: computer science

abstract: Alerting services can provide a valuable support for information seeking in Digital Libraries (DL). Several systems have been proposed. Most of them have serious drawbacks, such as limited expressiveness, limited coverage, and poor support of federated and distributed collections. 
In this paper, we present the detailed design and implementation for a comprehensive alerting service for digital libraries. We demonstrate typical user interactions with the system. Our alerting service is open to other event sources, supports a rich variety of event types, and works on distributed as well as on federated DL collections.

text: An Integrated Alerting Service for Open Digital Libraries: Design and Implementation Alerting services can provide a valuable support for information seeking in Digital Libraries (DL). Several systems have been proposed. Most of them have serious drawbacks, such as limited expressiveness, limited coverage, and poor support of federated and distributed collections. 
In this paper, we present the detailed design and implementation for a comprehensive alerting service for digital libraries. We demonstrate typical user interactions with the system. Our alerting service is open to other event sources, supports a rich variety of event types, and works on distributed as well as on federated DL collections.

year: 2005

title: Mining at Te Aroha before the murder in February 1881

authors: Hart, Philip

abstract: Mining was slow to restart after the Christmas holidays on a goldfield whose value was still unknown. Some miners did not return, but other men, mostly with mining experience, replaced them. As was pointed out, more testing was required to justify the cautious optimism, and more explorations did not discover any payable ore or a reef of any sort. More capital was needed to fund adequate development, and the lack of a battery held back the field.
Some searched the nearby countryside, fruitlessly, but at Tui the mostly Maori miners working there seemed to be having better results. Unskilled miners who drove incompetent and even dangerous adits wasted their efforts, while others were accused of shepherding their ground. Two companies formed during January attracted many small investors, but experienced miners started leaving for newer finds, and non-miners abandoned their attempts at mining after discovering that gold was not easy to find. But others remained hopeful, and waited for the erection of a local battery to prove the value of what they had found.

text: Mining at Te Aroha before the murder in February 1881 Mining was slow to restart after the Christmas holidays on a goldfield whose value was still unknown. Some miners did not return, but other men, mostly with mining experience, replaced them. As was pointed out, more testing was required to justify the cautious optimism, and more explorations did not discover any payable ore or a reef of any sort. More capital was needed to fund adequate development, and the lack of a battery held back the field.
Some searched the nearby countryside, fruitlessly, but at Tui the mostly Maori miners working there seemed to be having better results. Unskilled miners who drove incompetent and even dangerous adits wasted their efforts, while others were accused of shepherding their ground. Two companies formed during January attracted many small investors, but experienced miners started leaving for newer finds, and non-miners abandoned their attempts at mining after discovering that gold was not easy to find. But others remained hopeful, and waited for the erection of a local battery to prove the value of what they had found.

year: 2016