title: Anesthesia-induced state transitions in neuronal populations

authors: Sleigh, James W.

subjects: General anesthesia

abstract: It is a simple observation that the function of the central nervous system changes abruptly at certain critical brain concentrations of the anesthetic drug. This can be viewed as analogous to “state transitions” in systems of interacting particles, which have been extensively studied in the physical sciences. Theoretical models of the electroencephalogram (EEG) are in semi-quantitative agreement with experimental data and show some features suggestive of anesthetic-induced state transitions (critical slowing, the biphasic effect, increase in spatial correlations, and entropy changes). However, the EEG is only an indirect marker of the (unknown) networks of cortical connectivity that are required for the formation of consciousness. It is plausible that anesthetic-induced alteration in cortical and corticothalamic network topology prevents the formation of a giant component in the neuronal population network, and hence induces unconsciousness.

text: Anesthesia-induced state transitions in neuronal populations It is a simple observation that the function of the central nervous system changes abruptly at certain critical brain concentrations of the anesthetic drug. This can be viewed as analogous to “state transitions” in systems of interacting particles, which have been extensively studied in the physical sciences. Theoretical models of the electroencephalogram (EEG) are in semi-quantitative agreement with experimental data and show some features suggestive of anesthetic-induced state transitions (critical slowing, the biphasic effect, increase in spatial correlations, and entropy changes). However, the EEG is only an indirect marker of the (unknown) networks of cortical connectivity that are required for the formation of consciousness. It is plausible that anesthetic-induced alteration in cortical and corticothalamic network topology prevents the formation of a giant component in the neuronal population network, and hence induces unconsciousness.

year: 2010

title: The potential for an independent source of Younger Dryas tree-ring radiocarbon data from the Lake Ontario region, North America, and its palaeoenvironmental context

authors: Griggs, Carol

abstract: Tree rings are the gold standard for the calibration of radiocarbon dates into calendar years with limited error due to their annual record of radiocarbon content in the atmosphere. Currently, the tree-ring 14C data used in the International Radiocarbon Calibration curve (IntCal13) are from multiple sources back to ~ 10 ka cal BP for the northern hemisphere. However, the source for tree-ring calibration data prior to ~10 ka cal BP, including the Younger Dryas (YD) and most of the Early Holocene (EH) chronozones, is limited to central Europe. Substantial quantities of logs found in the lowlands of Lake Ontario in North America, dating from 12.1 to 11.2 ka cal BP, have great potential for providing unique YD-EH tree-ring 14C data from a new, previously unrepresented, geographic location and for adding a new perspective to ongoing debates such as the timing of the YD/EH transition in continental North America. Preliminary fieldwork yielded over 43 logs, predominantly spruce (Picea spp.), found buried in alluvial strata over 0.2 hectares of the floodplain at Bell Creek near Fulton, NY. Dendrochronological analysis of 32 spruce logs from this collection has produced several chronologies, one 183 years in length and a second of 147 years with a possible crossdate yielding a chronology of 260 years. Ongoing survey of the site suggests that there is high preservation potential in the same stratigraphic units in an additional ~2 hectares of floodplain, and sample collection with subsequent analysis will increase the chronology’s sample depth, extend its length, and potentially provide a robust, independent Younger Dryas – Early Holocene 14C record. Initial assessments of climatic, hydrological, environmental, and isostatic variations and events over time from the tree rings and their stable isotopes, as well as pollen, macrofossil, and sediment analyses and isostatic modeling indicate substantial changes in the Bell Creek Valley and surrounding lowlands both during the YD and into the mid-Holocene. These changes include significant alterations in the rate, volume, and direction of stream flow, and transition from a boreal riparian environment on a low-order river to a wetlands, then back to a riparian environment with much less streamflow and occasional flooding, similar to the Bell Creek Valley today.

text: The potential for an independent source of Younger Dryas tree-ring radiocarbon data from the Lake Ontario region, North America, and its palaeoenvironmental context Tree rings are the gold standard for the calibration of radiocarbon dates into calendar years with limited error due to their annual record of radiocarbon content in the atmosphere. Currently, the tree-ring 14C data used in the International Radiocarbon Calibration curve (IntCal13) are from multiple sources back to ~ 10 ka cal BP for the northern hemisphere. However, the source for tree-ring calibration data prior to ~10 ka cal BP, including the Younger Dryas (YD) and most of the Early Holocene (EH) chronozones, is limited to central Europe. Substantial quantities of logs found in the lowlands of Lake Ontario in North America, dating from 12.1 to 11.2 ka cal BP, have great potential for providing unique YD-EH tree-ring 14C data from a new, previously unrepresented, geographic location and for adding a new perspective to ongoing debates such as the timing of the YD/EH transition in continental North America. Preliminary fieldwork yielded over 43 logs, predominantly spruce (Picea spp.), found buried in alluvial strata over 0.2 hectares of the floodplain at Bell Creek near Fulton, NY. Dendrochronological analysis of 32 spruce logs from this collection has produced several chronologies, one 183 years in length and a second of 147 years with a possible crossdate yielding a chronology of 260 years. Ongoing survey of the site suggests that there is high preservation potential in the same stratigraphic units in an additional ~2 hectares of floodplain, and sample collection with subsequent analysis will increase the chronology’s sample depth, extend its length, and potentially provide a robust, independent Younger Dryas – Early Holocene 14C record. Initial assessments of climatic, hydrological, environmental, and isostatic variations and events over time from the tree rings and their stable isotopes, as well as pollen, macrofossil, and sediment analyses and isostatic modeling indicate substantial changes in the Bell Creek Valley and surrounding lowlands both during the YD and into the mid-Holocene. These changes include significant alterations in the rate, volume, and direction of stream flow, and transition from a boreal riparian environment on a low-order river to a wetlands, then back to a riparian environment with much less streamflow and occasional flooding, similar to the Bell Creek Valley today.

year: 2015

title: Recognising the negative impacts of aquatic weed management: Okawa Bay, Lake Rotoiti case study

authors: Scholes, Paul

abstract: The Te Arawa Rotorua Lakes Programme continues to implement measures to maintain and restore lake water quality in line with trophic level indices (TLI’s) for respective lakes. In Lakes Rotorua and Rotoiti this has also meant not only reducing nutrients to and in the lakes but also managing periodic cyano-bacterial (blue-green) algal blooms.
Restoration measures in the Rotorua and Rotoiti catchments have included land use management efforts to arrest nutrient inputs; diversion of Lake Rotorua waters from entering Rotoiti; sewage reticulation of lakeside communities; and treatment of inflows
with aluminium sulphate (alum). While restoration efforts have produced water quality gains in both lakes, in recent years, cyano-bacterial blooms have occurred in the shallow embayment of Lake Rotoiti, known as Okawa Bay.
These water quality gains have not come without a cost. Submerged aquatic weeds such as Hornwort are an increasing problem in the Rotorua Te Arawa Lakes and significant resources are needed to manage infestations primarily for aesthetic and recreational
amenity. Control of exotic aquatic weed is mostly with application of herbicide. Herbicide treatment leaves a decomposing biomass in the waterbody, potentially increasing the nutrient status.
We examine the impact aquatic weed decomposition has had on Okawa Bay’s nutrient status and the cyano-bacterial blooms over recent summers, and Bay of Plenty Regional Council’s response to reduce localised bloom development.

text: Recognising the negative impacts of aquatic weed management: Okawa Bay, Lake Rotoiti case study The Te Arawa Rotorua Lakes Programme continues to implement measures to maintain and restore lake water quality in line with trophic level indices (TLI’s) for respective lakes. In Lakes Rotorua and Rotoiti this has also meant not only reducing nutrients to and in the lakes but also managing periodic cyano-bacterial (blue-green) algal blooms.
Restoration measures in the Rotorua and Rotoiti catchments have included land use management efforts to arrest nutrient inputs; diversion of Lake Rotorua waters from entering Rotoiti; sewage reticulation of lakeside communities; and treatment of inflows
with aluminium sulphate (alum). While restoration efforts have produced water quality gains in both lakes, in recent years, cyano-bacterial blooms have occurred in the shallow embayment of Lake Rotoiti, known as Okawa Bay.
These water quality gains have not come without a cost. Submerged aquatic weeds such as Hornwort are an increasing problem in the Rotorua Te Arawa Lakes and significant resources are needed to manage infestations primarily for aesthetic and recreational
amenity. Control of exotic aquatic weed is mostly with application of herbicide. Herbicide treatment leaves a decomposing biomass in the waterbody, potentially increasing the nutrient status.
We examine the impact aquatic weed decomposition has had on Okawa Bay’s nutrient status and the cyano-bacterial blooms over recent summers, and Bay of Plenty Regional Council’s response to reduce localised bloom development.

year: 2015