717 research outputs found
Stomatal control of leaf fluxes of carbonyl sulfide and CO<sub>2</sub> in a <i>Typha</i> freshwater marsh
Carbonyl sulfide (COS) is an emerging tracer to constrain land photosynthesis at canopy to global scales, because leaf COS and CO2 uptake processes are linked through stomatal diffusion. The COS tracer approach requires knowledge of the concentration normalized ratio of COS uptake to photosynthesis, commonly known as the leaf relative uptake (LRU). LRU is known to increase under low light, but the environmental controls over LRU variability in the field are poorly understood due to scant leaf scale observations.Here we present the first direct observations of LRU responses to environmental variables in the field. We measured leaf COS and CO2 fluxes at a freshwater marsh in summer 2013. Daytime leaf COS and CO2 uptake showed similar peaks in the mid-morning and late afternoon separated by a prolonged midday depression, highlighting the common stomatal control on diffusion. At night, in contrast to CO2, COS uptake continued, indicating partially open stomata. LRU ratios showed a clear relationship with photosynthetically active radiation (PAR), converging to 1.0 at high PAR, while increasing sharply at low PAR. Daytime integrated LRU (calculated from daytime mean COS and CO2 uptake) ranged from 1 to 1.5, with a mean of 1.2 across the campaign, significantly lower than the previously reported laboratory mean value (∼ 1.6). Our results indicate two major determinants of LRU – light and vapor deficit. Light is the primary driver of LRU because CO2 assimilation capacity increases with light, while COS consumption capacity does not. Superimposed upon the light response is a secondary effect that high vapor deficit further reduces LRU, causing LRU minima to occur in the afternoon, not at noon. The partial stomatal closure induced by high vapor deficit suppresses COS uptake more strongly than CO2 uptake because stomatal resistance is a more dominant component in the total resistance of COS. Using stomatal conductance estimates, we show that LRU variability can be explained in terms of different patterns of stomatal vs. internal limitations on COS and CO2 uptake. Our findings illustrate the stomata-driven coupling of COS and CO2 uptake during the most photosynthetically active period in the field and provide an in situ characterization of LRU – a key parameter required for the use of COS as a photosynthetic tracer
Mesenchymal stem cells for kidney transplantation
Published online: July 24, 2014The long term consequence of immunosuppressive therapy in kidney transplantation has prompted investigation of alternative means to modify the immune response to the allograft. Cell based therapies are potentially attractive as they may provide a long lasting immunomodulatory effect, may repair tissues and reduce the necessity to take immunosuppressive drug therapy. Of the current cell therapies, mesenchymal stem cells have now been trialled in small numbers of human kidney transplantation with apparent safety and potential efficacy. Many issues however need to be resolved before these cells will become mainstays of transplant immunosuppression including ex vivo modification to enhance immunomodulatory properties, cell number, route and frequency of administration as well as cellular source of origin.Bron Lett, Kisha N Sivanathan, P Toby Coate
All-optical generation and photoassociative probing of sodium Bose-Einstein condensates
We demonsatrate an all optical technique to evaporatively produce sodium
Bose-Einstein condensates (BEC). We use a crossed-dipole trap formed from light
near 1060 nm, and a simple ramp of the intensity to force evaporation. In
addition, we introduce photoassociation as diagnostic of the trap loading
process, and show that it can be used to detect the onset of Bose-Einstein
condensation. Finally, we demonstrate the straightforward production of
multiple traps with condensates using this technique, and that some control
over the spinor state of the BEC is achieved by positioning the trap as well.Comment: 8 pages, 10 figure
Sub-Natural-Linewidth Quantum Interference Features Observed in Photoassociation of a Thermal Gas
By driving photoassociation transitions we form electronically excited
molecules (Na) from ultra-cold (50-300 K) Na atoms. Using a second
laser to drive transitions from the excited state to a level in the molecular
ground state, we are able to split the photoassociation line and observe
features with a width smaller than the natural linewidth of the excited
molecular state. The quantum interference which gives rise to this effect is
analogous to that which leads to electromagnetically induced transparency in
three level atomic systems, but here one of the ground states is a
pair of free atoms while the other is a bound molecule. The linewidth is
limited primarily by the finite temperature of the atoms.Comment: 4 pages, 5 figure
Piloting an Educational Response to Violence in Uganda: Prospects for a New Curriculum
This pilot study assessed Mato-Oput5 (hereafter the curriculum), a new peace education curriculum, for indications of beneficial efficacy, specifically the capacity to reduce negative attitudes towards conflict and violence, and injury and violence rates. A cluster randomisedcontrol design was used. Three of the six purposively selected schools were exposed to the curriculum. Mato-Oput5 is a value-based, formalised curriculum taught by specifically trainedteachers. Its learning areas include conflict, conscience, violence, non-violence, impulse control, anger management, kindness, forgiveness, empathy and reconciliation. The results showed the baseline and post-intervention bio-demographic characteristics of the treatment arms to be comparable, thus suggesting baseline group equivalence and randomisation success. The follow-up loss was 9%. The mean pre- and post-intervention intentional incidentrates of the intervention and control groups were 270/1000 and 370/1000, and 190/1000 and 350/1000, respectively: these differences were not significant. The intervention had no effect onpost-intervention intentional incident rates. There were indications of beneficial efficacy in the curriculum, especially its ability to cause attitude shifts in support of non-violence. Statisticallysignificant behavioural effects were not detected although a downward rate trend was seen in the intervention group
A soil diffusion–reaction model for surface COS flux: COSSM v1
Soil exchange of carbonyl sulfide (COS) is the second largest COS flux in terrestrial ecosystems. A novel application of COS is the separation of gross primary productivity (GPP) from concomitant respiration. This method requires that soil COS exchange is relatively small and can be well quantified. Existing models for soil COS flux have incorporated empirical temperature and moisture functions derived from laboratory experiments but not explicitly resolved diffusion in the soil column. We developed a mechanistic diffusion–reaction model for soil COS exchange that accounts for COS uptake and production, relates source–sink terms to environmental variables, and has an option to enable surface litter layers. We evaluated the model with field data from a wheat field (Southern Great Plains (SGP), OK, USA) and an oak woodland (Stunt Ranch Reserve, CA, USA). The model was able to reproduce all observed features of soil COS exchange such as diurnal variations and sink–source transitions. We found that soil COS uptake is strongly diffusion controlled and limited by low COS concentrations in the soil if there is COS uptake in the litter layer. The model provides novel insights into the balance between soil COS uptake and production: a higher COS production capacity was required despite lower COS emissions during the growing season compared to the post-senescence period at SGP, and unchanged COS uptake capacity despite the dominant role of COS emissions after senescence. Once there is a database of soil COS parameters for key biomes, we expect the model will also be useful to simulate soil COS exchange at regional to global scales
Piloting an Educational Response to Violence in Uganda: Prospects for a New Curriculum
This pilot study assessed Mato-Oput5 (hereafter the curriculum), a new peace education curriculum, for indications of beneficial efficacy, specifically the capacity to reduce negative attitudes towards conflict and violence, and injury and violence rates. A cluster randomised control design was used. Three of the six purposively selected schools were exposed to the curriculum. Mato-Oput5 is a value-based, formalised curriculum taught by specifically trained teachers. Its learning areas include conflict, conscience, violence, non-violence, impulse control, anger management, kindness, forgiveness, empathy and reconciliation. The results showed the baseline and post-intervention bio-demographic characteristics of the treatment arms to be comparable, thus suggesting baseline group equivalence and randomisation success. The follow-up loss was 9%. The mean pre- and post-intervention intentional incident rates of the intervention and control groups were 270/1000 and 370/1000, and 190/1000 and 350/1000, respectively: these differences were not significant. The intervention had no effect on post-intervention intentional incident rates. There were indications of beneficial efficacy in the curriculum, especially its ability to cause attitude shifts in support of non-violence. Statistically significant behavioural effects were not detected although a downward rate trend was seen in the intervention group
Spinor dynamics in an antiferromagnetic spin-1 thermal Bose gas
We present experimental observations of coherent spin-population oscillations
in a cold thermal, Bose gas of spin-1 sodium-23 atoms. The population
oscillations in a multi-spatial-mode thermal gas have the same behavior as
those observed in a single-spatial-mode antiferromagnetic spinor Bose Einstein
condensate. We demonstrate this by showing that the two situations are
described by the same dynamical equations, with a factor of two change in the
spin-dependent interaction coefficient, which results from the change to
particles with distinguishable momentum states in the thermal gas. We compare
this theory to the measured spin population evolution after times up to a few
hundreds of ms, finding quantitative agreement with the amplitude and period.
We also measure the damping time of the oscillations as a function of magnetic
field.Comment: 5 pages, 3 figure
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