910 research outputs found
A dynamic hydro-mechanical and biochemical model of stomatal conductance for C4 photosynthesis
C4 plants are major grain (maize, sorghum), sugar (sugarcane) and biofuel (Miscanthus) producers,
and contribute ~20% to global productivity. Plants lose water through stomatal pores in order to
acquire CO2 (assimilation, A), and control their carbon-for-water balance by regulating stomatal
conductance (gS). The ability to mechanistically predict gS and A in response to atmospheric CO2,
water availability and time is critical for simulating stomatal control of plant-atmospheric carbon
and water exchange under current, past or future environmental conditions. Yet, dynamic
mechanistic models for gS are lacking, especially for C4 photosynthesis. We developed and coupled
a hydro-mechanical model of stomatal behaviour with a biochemical model of C4 photosynthesis,
calibrated using gas exchange measurements in maize, and extended the coupled model with time-
explicit functions to predict dynamic responses. We demonstrated the wider applicability of the
model with three additional C4 grass species in which interspecific differences in stomatal
behaviour could be accounted for by fitting a single parameter. The model accurately predicted
steady-state responses of gS to light, atmospheric CO2 and O2, soil drying and evaporative demand,
as well as dynamic responses to light intensity. Further analyses suggest the effect of variable leaf
hydraulic conductance is negligible. Based on the model, we derived a set of equations suitable for
incorporation in land surface models. Our model illuminates the processes underpinning stomatal
control in C4 plants and suggests the hydraulic benefits associated with fast stomatal responses of
C4 grasses may have supported the evolution of C4 photosynthesis
Variation in the quality of meat from Irish steers at the time of slaughter.
End of Project ReportThere is no information on the variation in quality, in particular
tenderness, that exists in Irish Beef nor is there information on the
variation that would remain if optimum practices were imposed at
all stages of the beef production chain. Evaluation of the success of
measures to improve beef consistency requires information on
existing variation and the minimum variation achievable.The objectives
of this project were (i) to establish the variation that exists in
the quality of meat from Irish cattle, (ii) to quantify the minimum
variation in meat quality that can be achieved in a practical beef production
system, (iii) to determine the effects and mechanisms of
additional sources of variation.
The conclusions from this project are:
• The M. longissimus dorsi (loin) was found to be more variable
than the M. semimembranosus (topside) for most quality
attributes examined (tenderness, sarcomere length and pH).
The scale of variation within the loin was similar to that
reported by the other research groups within the EU and US.
Heifers were more variable than steers for most attributes,
while there was no consistent classification effect on the
variability of meat quality attributes.
• Tenderness was equally variable in meat from genetically similar
steers, managed similarly, compared to commercial steers
randomly selected from a factory lairage but matched for
weight and grade.This was likely a result of both groups being
crossbred beef cattle of similar age, fat score, carcass weight
and managed identically post-mortem. However, variation in
tenderness of both groups was less than that observed in
a survey of commercial throughput (experiment 1). This
decrease is attributed to better pre-and-post-slaughter handling
practices.
• The data suggest that selection of sires (within a breed) with
better than average conformation has no deleterious effect on the eating quality of beef of their progeny.A more comprehensive
comparison of sires within a breed and between
breeds is required to confirm the generality of this conclusion.
• In a comparison of genotypes, gender and slaughter weights,
there was no evidence that variation around the mean value
for tenderness differed between breeds or liveweights after
14 days ageing. Bulls were more variable than steers for some
quality traits but the variation in tenderness was similar for
bulls and steers after 14 days ageing.
• While optimising the management of animals during the pre
and post-slaughter period reduced variation in tenderness,
some residual variation remained. A large percentage of the
residual variation in tenderness (Warner Bratzler shear force)
after 2 and 7 days post-mortem was explained by proteolysis
(breakdown of myofibrillar proteins).Variation in tenderness
(Warner Bratzler shear force) after 2 days post-mortem was
largely explained by phosphates (energy) and proteolysis,
while sensory tenderness was largely explained by phosphates
and glycolytic potential.
• Further work is required to reduce residual variation in Irish
beef and to determine the causes of this variation
Studies on Pre-slaughter Handling of Pigs and its Relationship to Meat Quality
End of Project ReportsTwo quality defects of pork which are affected by preslaughter
handling are PSE (Pale Soft Exudative) and DFD (Dark
Firm Dry) meat.
The incidence of PSE pork is mainly a function of the breed of
pig but short-term stressful handling before slaughter and feeding
too close to slaughter are also involved. DFD meat is a result of
prolonged stressful handling. PSE meat is pale and uneven in
colour and exudes fluid making it unattractive in the retail display
while dark meat appears stale and is prone to bacterial spoilage.
After slaughter muscle metabolism continues and muscle glycogen
is converted to lactic acid reducing meat pH. Prolonged stress
results in glycogen depletion, pre-slaughter feeding results in
elevated levels. Colour may be assessed subjectively by eye or
objectively by a meter colour but pH of the meat is closely related
to colour and measurement of pH at 45 minutes post-slaughter is
frequently used to predict ultimate colour and pH.
The objective of this study was to examine pre-slaughter handling
practices and their relationship with meat quality (pH, colour).
In the first trial, a survey of the amounts of stomach contents in
pigs at slaughter in two factories found similar amounts to
comparable surveys in France and the UK. It was concluded that
most pigs had been fasted for an adequate time before delivery.
The relationship between the amount of stomach contents and
meat quality in this survey was poor.
In the second trial, pigs from the Moorepark herd fed by either a
computerised wet feeding system or an ad libitum dry feed system
were slaughtered after overnight fasting or with feed available up
to loading for transport to the factory, two to three hours before
slaughter. There was no difference between feeding systems in
meat colour or pH but fasted pigs, on both feeding systems, had
darker meat and meat of a higher pH.
In the third and fourth trials a survey of transport vehicles was
carried out and meat quality of pigs delivered in modern and old-type vehicles was compared. Most trucks examined (78%) were
four years old or more. Few had modern hydraulic lifting gear for
the top decks. Space allowances during transportation were
generally adequate but delays in unloading could, in warm weather,
cause stress on pigs. There was little evidence for an effect of
vehicle on meat quality parameters but day to day variation in
carcass temperature and pH suggested a need for further research
on factory influences on meat quality.
Feeding of Magneium Aspartate to pigs for the last 5 days prior
to slaughter has been shown, in Australia, to have a beneficial
effect on meat colour and drip loss. In the final trial in this study
Mg Asp had no effect on meat quality parameters.European Union Structural Funds (EAGGF
A geological model of the chalk of East Kent
This report describes the geological modelling of the Chalk in the North Downs of East Kent,
within the catchment of River Great Stour and eastwards to the coast, including the Isle of
Thanet. This work was funded by the Environment Agency to support investigations of the local
hydrogeology and thereby to enhance catchment management.
The whole area is underlain by the Upper Cretaceous Chalk Group, with the Palaeogene
succession of the Thanet Sand Formation, the Lambeth Group and the Thames Group overlying
it in the northern and central eastern parts.
The project included a desk study revision of the Chalk of the North Downs, using the new
Chalk lithostratigraphy. The revisions to the geology are shown on the 1:50 000 scale geological
map which accompanies this report. Together with evidence from boreholes and from seismic
surveys, the new outcrop patterns have been incorporated into a geological model, using both
computer software (EarthVision) and manual methods.
The introduction describes the background to the project. The second chapter describes the
sources for the data used in the model: published and unpublished geological maps, borehole
records (both lithological and geophysical), seismic surveys, biostratigraphic records, digital
topographic information, and the published literature.
Each Chalk formation present in the area is then briefly described in the third chapter, noting its
relationship to the older lithostratigraphic divisions, and to biostratigraphic zones. The local
Chalk succession extends from the base of the Chalk Group to the Newhaven Chalk Formation,
here represented by the Margate Chalk Member. Evidence for the thickness of each formation is
reviewed.
The early Palaeogene formations (the Thanet Sand, Upnor, Harwich and London Clay
formations) are also briefly described (Chapter 4) and the local superficial deposits mentioned,
with references to detailed descriptions (Chapter 5). Apart from minor adjustments to the outcrop
of the basal Palaeogene surface, no revision of these formations was done for this study
Correlated variability of Mkn 421 at X-ray and TeV wavelengths on timescales of hours
Mkn 421 was observed for about two days with BeppoSAX, prior to and partly
overlapping the start of a 1 week continuous exposure with ASCA in April 1998,
as part of a world-wide multiwavelength campaign. A pronounced, well defined,
flare observed in X-rays was also observed simultaneously at TeV energies by
the Whipple Observatory's 10 m gamma-ray telescope. These data provide the
first evidence that the X-ray and TeV intensities are well correlated on
time-scales of hours.Comment: 4 pages, 1 figure, presented at the VERITAS Workshop on the TeV
Astrophysics of Extragalactic Object
Quantum field dynamics of the slow rollover in the linear delta expansion
We show how the linear delta expansion, as applied to the slow-roll
transition in quantum mechanics, can be recast in the closed time-path
formalism. This results in simpler, explicit expressions than were obtained in
the Schr\"odinger formulation and allows for a straightforward generalization
to higher dimensions. Motivated by the success of the method in the
quantum-mechanical problem, where it has been shown to give more accurate
results for longer than existing alternatives, we apply the linear delta
expansion to four-dimensional field theory.
At small times all methods agree. At later times, the first-order linear
delta expansion is consistently higher that Hartree-Fock, but does not show any
sign of a turnover. A turnover emerges in second-order of the method, but the
value of at the
turnover. In subsequent applications of the method we hope to implement the
calculation in the context of an expanding universe, following the line of
earlier calculations by Boyanovsky {\sl et al.}, who used the Hartree-Fock and
large-N methods. It seems clear, however, that the method will become
unreliable as the system enters the reheating stage.Comment: 17 pages, 9 figures, revised version with extra section 4.2 including
second order calculatio
Are markers of inflammation more strongly associated with risk for fatal than for nonfatal vascular events?
<p><b>Background:</b> Circulating inflammatory markers may more strongly relate to risk of fatal versus nonfatal cardiovascular disease (CVD) events, but robust prospective evidence is lacking. We tested whether interleukin (IL)-6, C-reactive protein (CRP), and fibrinogen more strongly associate with fatal compared to nonfatal myocardial infarction (MI) and stroke.</p>
<p><b>Methods and Findings:</b> In the Prospective Study of Pravastatin in the Elderly at Risk (PROSPER), baseline inflammatory markers in up to 5,680 men and women aged 70-82 y were related to risk for endpoints; nonfatal CVD (i.e., nonfatal MI and nonfatal stroke [n = 672]), fatal CVD (n = 190), death from other CV causes (n = 38), and non-CVD mortality (n = 300), over 3.2-y follow-up. Elevations in baseline IL-6 levels were significantly (p = 0.0009; competing risks model analysis) more strongly associated with fatal CVD (hazard ratio [HR] for 1 log unit increase in IL-6 1.75, 95% confidence interval [CI] 1.44-2.12) than with risk of nonfatal CVD (1.17, 95% CI 1.04-1.31), in analyses adjusted for treatment allocation. The findings were consistent in a fully adjusted model. These broad trends were similar for CRP and, to a lesser extent, for fibrinogen. The results were also similar in placebo and statin recipients (i.e., no interaction). The C-statistic for fatal CVD using traditional risk factors was significantly (+0.017; p<0.0001) improved by inclusion of IL-6 but not so for nonfatal CVD events (p = 0.20).</p>
<p><b>Conclusions:</b> In PROSPER, inflammatory markers, in particular IL-6 and CRP, are more strongly associated with risk of fatal vascular events than nonfatal vascular events. These novel observations may have important implications for better understanding aetiology of CVD mortality, and have potential clinical relevance.</p>
Association of visit-to-visit variability in blood pressure with cognitive function in old age: prospective cohort study
<p>Objective To investigate the association between visit-to-visit variability in blood pressure and cognitive function in old age (>70 years).</p>
<p>Design Prospective cohort study.</p>
<p>etting PROSPER (PROspective Study of Pravastatin in the Elderly at Risk) study, a collaboration between centres in Ireland, Scotland, and the Netherlands.</p>
<p>Participants 5461 participants, mean age 75.3 years, who were at risk of cardiovascular disease. Blood pressure was measured every three months during an average of 3.2 years. Visit-to-visit variability in blood pressure was defined as the standard deviation of blood pressure measurements between visits.</p>
<p>Main outcome measures Four domains of cognitive function, testing selective attention, processing speed, and immediate and delayed memory. In a magnetic resonance imaging substudy of 553 participants, structural brain volumes, cerebral microbleeds, infarcts, and white matter hyperintensities were measured.</p>
<p>Results Participants with higher visit-to-visit variability in systolic blood pressure had worse performance on all cognitive tests: attention (mean difference high versus low thirds) 3.08 seconds (95% confidence interval 0.85 to 5.31), processing speed −1.16 digits coded (95% confidence interval −1.69 to −0.63), immediate memory −0.27 pictures remembered (95% confidence interval −0.41 to −0.13), and delayed memory −0.30 pictures remembered (95% confidence interval −0.49 to −0.11). Furthermore, higher variability in both systolic and diastolic blood pressure was associated with lower hippocampal volume and cortical infarcts, and higher variability in diastolic blood pressure was associated with cerebral microbleeds (all P<0.05). All associations were adjusted for average blood pressure and cardiovascular risk factors.</p>
Conclusion Higher visit-to-visit variability in blood pressure independent of average blood pressure was associated with impaired cognitive function in old age
Higher Order Evaluation of the Critical Temperature for Interacting Homogeneous Dilute Bose Gases
We use the nonperturbative linear \delta expansion method to evaluate
analytically the coefficients c_1 and c_2^{\prime \prime} which appear in the
expansion for the transition temperature for a dilute, homogeneous, three
dimensional Bose gas given by T_c= T_0 \{1 + c_1 a n^{1/3} + [ c_2^{\prime}
\ln(a n^{1/3}) +c_2^{\prime \prime} ] a^2 n^{2/3} + {\cal O} (a^3 n)\}, where
T_0 is the result for an ideal gas, a is the s-wave scattering length and n is
the number density. In a previous work the same method has been used to
evaluate c_1 to order-\delta^2 with the result c_1= 3.06. Here, we push the
calculation to the next two orders obtaining c_1=2.45 at order-\delta^3 and
c_1=1.48 at order-\delta^4. Analysing the topology of the graphs involved we
discuss how our results relate to other nonperturbative analytical methods such
as the self-consistent resummation and the 1/N approximations. At the same
orders we obtain c_2^{\prime\prime}=101.4, c_2^{\prime \prime}=98.2 and
c_2^{\prime \prime}=82.9. Our analytical results seem to support the recent
Monte Carlo estimates c_1=1.32 \pm 0.02 and c_2^{\prime \prime}= 75.7 \pm 0.4.Comment: 29 pages, 3 eps figures. Minor changes, one reference added. Version
in press Physical Review A (2002
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