582 research outputs found

    Spatial and temporal trends of phytoplankton and physiochemical variables in a hypertrophic, monomictic lake

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    Spatial and temporal variations in the physical, chemical and biological composition of Lake Ōkaro were measured over 16 months. Lake Ōkaro is a small (0.32 km2) hypertrophic, monomictic lake located in the Central Volcanic Zone of the North Island, New Zealand. Vertical profiles of temperature, chlorophyll fluorescence, dissolved oxygen concentration (DO), pH, specific conductance, photosynthetically active radiation (PAR) and nutrient species, including ammonium-nitrogen (NH4-N), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N) and phosphate-phosphorus (PO4-P), were collected at up to nine stations at weekly to monthly frequencies. High-frequency variability was assessed during two separate 24-hour monitoring periods, coinciding with an Anabaena spiroides-dominated surface bloom, and a Ceratium hirundinella-dominated deep chlorophyll maximum. Additional data for wind direction and velocity, incident solar irradiance and rainfall was sourced from a meteorological weather station and a lake monitoring buoy at Rotorua, 20 km north of the lake. Spatial variability was more pronounced during summer. Observed vertical gradients in chlorophyll fluorescence, DO, specific conductance and nutrient species were closely linked to thermal stability of the water column. There were large variations in chlorophyll fluorescence amongst stations in summer, which related to displacement of the metalimnion and associated changes in chlorophyll fluorescence. Winter mixing was characterised by relative homogeneity of the water column. Nutrient concentrations were elevated at all depths whereas high concentrations had previously been confined to lower depth strata (the hypolimnion). Temperature profiles in summer displayed clear vertical gradients with a well-defined metalimnion that increased in depth until winter mixing generated isothermal conditions. Chlorophyll fluorescence profiles were characterised by the formation of a DCM that was recurrent over both summer periods, and was strongly statistically related to the depth of the thermocline for the duration of stratification. Dissolved oxygen, specific conductance and pH were relatively uniform horizontally, though pH was consistently lower at a well-sheltered near-shore station. All variables showed strong variations with depth during the stratified period. Dissolved oxygen was negligible or zero below the thermocline for much of the stratified period while specific conductance was lowest above or at the thermocline. There were also strong vertical gradients in nutrient concentrations in summer, with concentrations below the thermocline often an order of magnitude higher than those above. The representativeness of fluorescence at a central station to a whole-lake scale was assessed using a vertical integrated value and the standard error derived from up to eight other stations. Values at the single station frequently deviated from the mean fluorescence of the wider lake, particularly at the DCM which suggests that extrapolating single-station measurements to a whole lake could provide highly exaggerated values of lake fluorescence. High-frequency sampling during the A. spiroides-dominated surface bloom showed diel temperature variations attributed mostly to solar irradiance. There was high light attenuation from the high phytoplankton biomass and consistently elevated pH and DO. Fluorescence profiles suggested that the phytoplankton population was strongly buoyant and did not undergo diel vertical migration. High-frequency sampling during a period when there was a dinoflagellate-dominated DCM showed two coinciding fluorescence peaks had formed at 6-7 and 7-8 m depth and contained morphologically and physiologically distinct taxa. The 6-7 m DCM was predominantly Ceratium hirundinella, while the 7-8 m DCM was composed of C. hirundinella and unidentified colonial picoplankton. Fluorescence profiles suggested diel vertical migration was not taking place, and strong gradients in light, nutrient availability and the relative biomass of the dominants suggested that the 6-7 and 7-8 m DCM populations potentially differed in their modes of nutrition, light history and susceptibility to grazing. This research illustrates the degree of spatial variability that can exist in a small, monomictic hypertrophic lake at a given time, and highlights some of the potential limitations of using single-site monitoring stations to represent the physical, chemical and biological conditions of a whole lake. This information may be used to critically evaluate the reliability of phytoplankton biomass estimates that have been derived from spatially-limited sampling methods. This study further illustrates the role that thermal stratification plays in creating vertical gradients in a number of biological and chemical variables, and demonstrates that parallels exist with regard to DCM formation in oligotrophic and hypertrophic lakes, relating to the interplay between light, chlorophyll fluorescence and thermal stratification. Evidence is also provided showing that diel-scale variations in phytoplankton biomass can differ markedly between a cyanobacteria-dominated surface bloom and a dinoflagellate-dominated DCM, which further highlights the value of high-frequency sampling when seeking to estimate phytoplankton biomass using in situ methods

    γδ T cell response to prolonged heavy endurance exercise

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    The focus of this study was to assess exercise-induced alterations in circulating γδ T cell subpopulations and memory phenotypes after a prolonged heavy-intensity exercise bout. Ten highly-trained endurance cyclists (mean ± SEM: age 24.0 ± 1.3 years; height 1.81 ± 0.02 m; body mass 73.3 ± 1.8 kg; peak oxygen uptake 60.7 ± 1.5 mL.kg-1.min-1) performed 2 h of cycling exercise at 90% of the second ventilatory threshold. Blood samples were collected before exercise, immediately post-exercise, 1 h, 2 h, 4 h, and 6 h post-exercise. Flow cytometry was used to examine γδ T cell subsets, memory phenotypes and receptor expression. A significant decrease in cell concentration was observed in total γδ T cells and the δ2 subset from pre-exercise to 1 h, 2 h, and 4 h post-exercise. Further analysis of the δ2 subset revealed a significant decrease from pre-exercise to 1 h, 2 h, and 4 h post-exercise in naive δ2 cells, and a significant decrease from pre-exercise to 1 h and 2 h post-exercise in central memory δ2 cells. A significant decrease was observed in γδ T cells expressing CD11ahigh, CD62Lhigh and CD94+ from pre-exercise to 1 h, 2 h, and 4 h post-exercise. Furthermore, a significant decrease was observed from pre-exercise to 1 h post-exercise in CD62Llow and CD94- γδ T cells. These results suggest an exercise-stress-induced redistribution of γδ T cells from the circulation with greater propensity for antigen stimulation, tissue and lymph node homing potential for a duration of 4 h after the cessation of exercise

    Temporally and genetically discrete periods of wheat sensitivity to high temperature

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    Successive single day transfers of pot-grown wheat to high temperature (35/30oC day/night) replicated controlled environments, from the second node detectable to the milky-ripe growth stages, provides the strongest available evidence that the fertility of wheat can be highly vulnerable to heat stress during two discrete peak periods of susceptibility: early booting (decimal growth stage (GS) 41-45) and early anthesis (GS 61-65). A double Gaussian fitted simultaneously to grain number and weight data from two contrasting elite lines (Renesansa, listed in Serbia, Ppd-D1a, Rht8; Savannah, listed in UK, Ppd-D1b, Rht-D1b) identified peak periods of main stem susceptibility centred on 3 (s.e.= 0.82) and 18 (s.e. = 0.55) days (mean daily temperature = 14.3oC) pre-GS 65 for both cultivars. Severity of effect depended on genotype, growth stage and their interaction: grain set relative to that achieved at 20/15oC dropped below 80% for Savannah at booting and Renesansa at anthesis. Savannah was relatively tolerant to heat stress at anthesis. A further experiment including 62 lines of the mapping, doubled-haploid progeny of Renesansa x Savannah found tolerance at anthesis to be associated with Ppd-D1b, Rht-D1b, and a QTL from Renesansa on chromosome 2A. None of the relevant markers were associated with tolerance during booting. Rht8 was never associated with heat stress tolerance, a lack of effect confirmed in a further experiment where Rht8 was included in a comparison of near isogenic lines in a cv. Paragon background. Some compensatory increases in mean grain weight were observed, but only when stress was applied during booting and only where Ppd-D1a was absent

    Accountability synopticism: How a think tank and the media developed a quasimarket for school choice in British Columbia

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    This paper describes how a locally developed school ranking systemaffected student enrolment patterns in British Columbia over time.In developing an annual school ‘report card’ that was published innewspapers and online, the Vancouver-based Fraser Institute createda marketplace for school choice by devising an accountability schemethat highlighted and concealed visibility asymmetries between schools.Against the backdrop of a shifting political landscape, report cardshelped focus the public’s attention on school achievement scores thatidentified low-, mid-, and high-performing schools. A quasi-market foreducation emerged in the non-place of language and discourse whenschool ranking results became the basis by which parents made decisionsabout where to send their children to school. When student achievementdata is used to identify British Columbia’s ‘best’ and ‘worst’ performingsecondary schools in this way, standardized assessment practices may beconsidered high-stakes

    Measurement crosstalk between two phase qubits coupled by a coplanar waveguide

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    We analyze the measurement crosstalk between two flux-biased phase qubits coupled by a resonant coplanar waveguide cavity. After the first qubit is measured, the superconducting phase can undergo damped oscillations resulting in an a.c. voltage that produces a frequency chirped noise signal whose frequency crosses that of the cavity. We show experimentally that the coplanar waveguide cavity acts as a bandpass filter that can significantly reduce the crosstalk signal seen by the second qubit when its frequency is far from the cavity's resonant frequency. We present a simple classical description of the qubit behavior that agrees well with the experimental data. These results suggest that measurement crosstalk between superconducting phase qubits can be reduced by use of linear or possibly nonlinear resonant cavities as coupling elements.Comment: 4 pages, 3 figure

    Vacuum-Gap Capacitors for Low-Loss Superconducting Resonant Circuits

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    Low-loss microwave components are used in many superconducting resonant circuits from multiplexed readouts of low-temperature detector arrays to quantum bits. Two-level system defects in amorphous dielectric materials cause excess energy loss. In an effort to improve capacitor components, we have used optical lithography and micromachining techniques to develop superconducting parallel-plate capacitors in which lossy dielectrics are replaced by vacuum gaps. Resonance measurements at 50 mK on lumped LC circuits that incorporate these vacuum-gap capacitors (VGCs) reveal loss tangents at low powers as low as 4x10^{-5}, significantly lower than with capacitors using amorphous dielectrics. VGCs are structurally robust, small, and easily scaled to capacitance values above 100 pF.Comment: 5 pages, 6 figures, .docx forma

    Physical properties of blood are altered in young and lean women with polycystic ovary syndrome

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    Classic features of polycystic ovary syndrome (PCOS) include derangement of metabolic and cardiovascular health, and vascular dysfunction is commonly reported. These comorbidities indicate impaired blood flow; however, other than limited reports of increased plasma viscosity, surprisingly little is known regarding the physical properties of blood in PCOS. We aimed to investigate whether haemorheology was impaired in women with PCOS. We thus measured a comprehensive haemorheological profile, in a case-control design, of lean women with PCOS and age-matched healthy controls. A clinical examination determined similar cardiovascular risk for the two groups. Whole blood and plasma viscosity was measured using a cone-plate viscometer. The magnitude and rate of red blood cell (RBC) aggregation was determined using a light-transmission aggregometer, and the degree of RBC deformability was measured via laser-diffraction ektacytometry. Plasma viscosity was significantly increased in women with PCOS. Blood viscosity was also increased for PCOS at lower-to-moderate shear rates in both native and standardised haematocrit samples. The magnitude of RBC aggregation–a primary determinant of low-shear blood viscosity–was significantly increased in PCOS at native and 0.4 L·L(-1) haematocrit. No difference was detected between PCOS and CON groups for RBC deformability measurements. A novel measure indicating the effectiveness of oxygen transport by RBC (i.e., the haematocrit-to-viscosity ratio; HVR) was decreased at all shear rates in women with PCOS. In a group of young and lean women with PCOS with an unremarkable cardiovascular risk profile based on clinical data, significant haemorheological impairment was observed. The degree of haemorheological derangement observed in the present study reflects that of overt chronic disease, and provides an avenue for future therapeutic intervention in PCOS
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