495 research outputs found
Photosynthesis Under Field Conditions. VIII. Analysis of Windspeed Fluctuation Data to Evaluate Turbulent Exchange Within a Corn Crop
Turbulent transfer within a crop of corn was characterized
by an aerodynamic approach. The distributions
of windspeed within an immature and a mature crop
were measured using both cup and heated thermocouple
anemometers. A combination of the statistical and mixing-length
theories was employed to analyze the wind
data for transfer coefficients.
Eulerian time scales of turbulence were calculated from
the windspeed fluctuations of selected 30-second periods
of semi-steady wind. Momentum transfer coefficients were
determined from the scale of turbulence by equating it to
the mixing length and assuming isotropy. The resulting
values were as large as 8,000 cm2 sec-1. The shearing
stress profiles calculated with these values had unrealistically
sharp maximums just below the top of the crop.
This anomaly was considered an artifact of the method
resulting from extreme anisotropy in the turbulent shear
flow.
The K values obtained by the statistical mixing length
method were approximately ten times larger than those
determined by logarithmic profile analysis. The latter
values were considered more nearly correct and were used
as a basis for correcting the other values.
The results showed that the magnitude of turbulent
transfer is several orders of magnitude greater than
molecular diffusion even at levels deep within the crop.
The transfer coefficient showed a marked attenuation
with depth below the top of the corn but remained a
function of windspeed at all heights
Photosynthesis Under Field Conditions. XA. Assessing Sources and Sinks of Carbon Dioxide in a Corn (Zea mays L.) Crop Using Momentum Balance Approach
In a previous communication we described a meteorological
method of assessing the vertical distribution of photosynthesis
and respiration activity in a corn crop. The
method, however, is tedious. Here we describe a much
simpler method. Results indicate that all the leaves of
a corn crop appear to follow the same near-linear light
response curve, at least above the compensation point.
Below the compensation point, all leaves evidently respire
very little
Photosynthesis Under Field Conditions. IX. Vertical Distribution of Photosynthesis Within a Corn Crop
The vertical distribution of the photosynthetic fixation
of carbon dioxide within a crop of corn was calculated
from carbon dioxide profile data and transfer coefficients
obtained by analysis of windspeed measurements. Infrared
analyzers were used to measure the carbon dioxide
concentration at several heights within and above the
crop. The calculated total fixation for the day was approximately
60 g CO? m-? (equivalent to 470 pounds of sugar
per acre per day). The results demonstrated the importance
of the upper leaves in the fixation of carbon dioxide
and showed the increased fixation by the lower leaves
during periods of high light penetration. There was some
indication that a coupling existed between the level of
windspeed and fixation under conditions of high light
and relatively low windspeed. With refinement in technique
the method could be used to obtain more quantitative
estimates of the distribution of photosynthesis in
other crops
The Energy Budget at the Earth's Surface: Assessing Sources and Sinks of Carbon Dioxide in a Corn Crop Using a Momentum Balance Approach
In two previous communications (Wright and Lemon 1966a, 1966b) an
aerodynamic method was described for evaluating the source and sink
distribution of carbon dioxide in plant communities. Some data were
presented for a corn crop, giving quantitative information about
photosynthetic fixation and respiration release of carbon dioxide, layer
by layer, within the crop.
In the method, CO2 concentration profiles and windspeed measurements of
the bulk air were made within and above the crop. The analysis of the
windspeed measurements to calculate diffusivity coefficients required
tedious analysis of windspeed fluctuations and the application of
complicated statistical and mixing length theories. It is our purpose
to present here a simpler method, requiring vertical profiles of mean
windspeed, vertical profiles of mean carbon dioxide concentration and
representative vertical profiles of the foliage surface area density of
the plant community
Photosynthesis Under Field Conditions. XB. Origins of Short-Time CO2 Fluctuations in a Cornfield
Studies of the vertical distributions of CO? fluctuation
in a cornfield were made in the 4-to 0.25-cycle/min frequency
range. Amplitude of fluctuations decreased with
height above the ground. Frequency in this range appeared
rather constant, however. Sources and sinks for
CO? within the cornfield contribute to the fluctuations;
however, eddy structure originating inside and/or outside
the cornfield plays an important role too
In situ high pressure powder diffraction study of proton conductors based on metal phosphonates
Soft Porous Metal Organic frameworks (MOFs) are referred to as a class of coordination polymers that exhibit structural flexibility in response to guest interactions or physical stimuli [1]. By combining softness and regularity, the responsive crystalline frameworks show, for instance, unique mechanisms of separation and storage of gases.
Here we report the effects of high pressures of CO2 on the frameworks of two types of coordination polymers based on multifunctional metal phosphonates, which exhibit proton conductivity at high relative humidity in addition to porous properties. The first one, Ni2(H2O)2(O3PCH2N(C4H8)NCH2PO3)⋅8H2O (Ni-STA-12) is a well-known MOF material structural featured by 1D channels build from MO5N octahedra linked by the piperazinyl moieties [2]. The second solid, Mg[(HO3PCH2)2NHCH2C6H4CH2NH-(CH2PO3H)2]·2H2O, (MgHDTMP·2H2O), is a pillared layer metal phosphonate containing flexible alkyldiaminetetraphosphonate as linker of the inorganic layers. For both solids, in situ synchrotron powder diffraction data were collected on BL04-MSPD under different pressures of CO2 (up to ~10 bar) and temperatures at ALBA (Barcelona, Spain). The resulting structural changes observed on their frameworks as well as their proton conductivities will be discussed.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. Junta de Andalucía,Proyecto de Excelencia P12-FQM-1656 MINECO: MAT2013-41836-R
Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells
A microscopic theory for the generation and propagation of coherent LA
phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum
well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is
driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump
laser and is treated theoretically using the density matrix formalism. We use
realistic wurzite bandstructures taking valence-band mixing and strain-induced
piezo- electric fields into account. In addition, the many-body Coulomb
ineraction is treated in the screened time-dependent Hartree-Fock
approximation. We find that under typical experimental conditions, our
microscopic theory can be simplified and mapped onto a loaded string problem
which can be easily solved.Comment: 20 pages, 17 figure
Neurology
Contains reports on six research projects.U. S. Public Health Service (B-3055-4, B-3090-4, MH-06175-02)U. S. Air Force (AF49(638)-1313)U.S. Navy. Office of Naval Research (Nonr-1841(70)
Cost and Outcome of Behavioural Activation versus Cognitive Behavioural Therapy for Depression (COBRA): a randomised, controlled, non-inferiority trial
Background Depression is a common, debilitating, and costly disorder. Many patients request psychological therapy, but the best-evidenced therapy—cognitive behavioural therapy (CBT)—is complex and costly. A simpler therapy—behavioural activation (BA)—might be as effective and cheaper than is CBT. We aimed to establish the clinical efficacy and cost-effectiveness of BA compared with CBT for adults with depression. Methods In this randomised, controlled, non-inferiority trial, we recruited adults aged 18 years or older meeting Diagnostic and Statistical Manual of Mental Disorders IV criteria for major depressive disorder from primary care and psychological therapy services in Devon, Durham, and Leeds (UK). We excluded people who were receiving psychological therapy, were alcohol or drug dependent, were acutely suicidal or had attempted suicide in the previous 2 months, or were cognitively impaired, or who had bipolar disorder or psychosis or psychotic symptoms. We randomly assigned participants (1:1) remotely using computer-generated allocation (minimisation used; stratified by depression severity [Patient Health Questionnaire 9 (PHQ-9) score of <19 vs ≥19], antidepressant use, and recruitment site) to BA from junior mental health workers or CBT from psychological therapists. Randomisation done at the Peninsula Clinical Trials Unit was concealed from investigators. Treatment was given open label, but outcome assessors were masked. The primary outcome was depression symptoms according to the PHQ-9 at 12 months. We analysed all those who were randomly allocated and had complete data (modified intention to treat [mITT]) and also all those who were randomly allocated, had complete data, and received at least eight treatment sessions (per protocol [PP]). We analysed safety in the mITT population. The non-inferiority margin was 1·9 PHQ-9 points. This trial is registered with the ISCRTN registry, number ISRCTN27473954. Findings Between Sept 26, 2012, and April 3, 2014, we randomly allocated 221 (50%) participants to BA and 219 (50%) to CBT. 175 (79%) participants were assessable for the primary outcome in the mITT population in the BA group compared with 189 (86%) in the CBT group, whereas 135 (61%) were assessable in the PP population in the BA group compared with 151 (69%) in the CBT group. BA was non-inferior to CBT (mITT: CBT 8·4 PHQ-9 points [SD 7·5], BA 8·4 PHQ-9 points [7·0], mean difference 0·1 PHQ-9 points [95% CI −1·3 to 1·5], p=0·89; PP: CBT 7·9 PHQ-9 points [7·3]; BA 7·8 [6·5], mean difference 0·0 PHQ-9 points [–1·5 to 1·6], p=0·99). Two (1%) non-trial-related deaths (one [1%] multidrug toxicity in the BA group and one [1%] cancer in the CBT group) and 15 depression-related, but not treatment-related, serious adverse events (three in the BA group and 12 in the CBT group) occurred in three [2%] participants in the BA group (two [1%] patients who overdosed and one [1%] who self-harmed) and eight (4%) participants in the CBT group (seven [4%] who overdosed and one [1%] who self-harmed). Interpretation We found that BA, a simpler psychological treatment than CBT, can be delivered by junior mental health workers with less intensive and costly training, with no lesser effect than CBT. Effective psychological therapy for depression can be delivered without the need for costly and highly trained professionals. Funding National Institute for Health Research
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