Vc Max Research Articles

Parameter optimization of BEPS model based on the flux data of the temperate deciduous broad-leaved forest in Northeast China.

Keeping other parameters as empirical constants, different numerical combinations of the main photosynthetic parameters Vc max and Jmax were conducted to estimate daily GPP by using the iteration method in this paper. To optimize Vc max and Jmax in BEPSHourly model at hourly time steps, simulated daily GPP using different numerical combinations of the parameters were compared with the flux tower data obtained from the temperate deciduous broad-leaved forest of the Maoershan Forest Farm in Northeast China. Comparing the simulated daily GPP with the observed flux data in 2011, the results showed that optimal Vc max and Jmax for the deciduous broad-leaved forest in Northeast China were 41.1 μmol·m-2·s-1 and 82.8 μmol·m-2·s-1 respectively with the minimal RMSE and the maximum R2 of 1.10 g C·m-2·d-1 and 0.95. After Vc max and Jmax optimization, BEPSHourly model simulated the seasonal variation of GPP better.

Evaluation of the performance of three elastomers for non-lethal projectile applications

Less lethal kinetic ammunitions with soft noses such as eXact iMpact 1006, National Sports Spartan and B&T have been commonly used by military and law enforcement officers in the situations where lethal force is not warranted. In order to explore new materials to be used as nose in such ammunitions, a scholastic study using finite element simulations has been carried out to evaluate the effectiveness of two rubber like elastomers and a polyolefinic foam (low density, highly compressible, stiff and closed cell type of thermos plastic elastomer). State-of-the art thorax surrogate MTHOTA has been employed for the evaluation of blunt thoracic trauma. Force-rigid wall method was employed for the evaluation of head damage curves for each material. XM 1006 has been used as the benchmark projectile for the purpose of comparison. Both blunt thoracic trauma and head damage criterion point of view, both rubbers (R1 and R2) have yielded high values of VC max and peak impact force. Polyolefinic foam (F1) considered in the study has yielded very promising VC max values and very less peak impact force when compared with those of bench mark projectile XM 1006.

Improving Hybrid III Injury Assessment in Steering Wheel Rim to Chest Impacts Using Responses from Finite Element Hybrid III and Human Body Model

Objective: The main aim of this study was to improve the quality of injury risk assessments in steering wheel rim to chest impacts when using the Hybrid III crash test dummy in frontal heavy goods vehicle (HGV) collision tests. Correction factors for chest injury criteria were calculated as the model chest injury parameter ratios between finite element (FE) Hybrid III, evaluated in relevant load cases, and the Total Human Model for Safety (THUMS). This is proposed to be used to compensate Hybrid III measurements in crash tests where steering wheel rim to chest impacts occur. Methods: The study was conducted in an FE environment using an FE-Hybrid III model and the THUMS. Two impactor shapes were used, a circular hub and a long, thin horizontal bar. Chest impacts at velocities ranging from 3.0 to 6.0 m/s were simulated at 3 impact height levels. A ratio between FE-Hybrid III and THUMS chest injury parameters, maximum chest compression C max, and maximum viscous criterion VC max, were calculated for the different chest impact conditions to form a set of correction factors. The definition of the correction factor is based on the assumption that the response from a circular hub impact to the middle of the chest is well characterized and that injury risk measures are independent of impact height. The current limits for these chest injury criteria were used as a basis to develop correction factors that compensate for the limitations in biofidelity of the Hybrid III in steering wheel rim to chest impacts. Results: The hub and bar impactors produced considerably higher C max and VC max responses in the THUMS compared to the FE-Hybrid III. The correction factor for the responses of the FE-Hybrid III showed that the criteria responses for the bar impactor were consistently overestimated. Ratios based on Hybrid III and THUMS responses provided correction factors for the Hybrid III responses ranging from 0.84 to 0.93. These factors can be used to estimate C max and VC max values when the Hybrid III is used in crash tests for which steering wheel rim to chest interaction occurs. Conclusions: For the FE-Hybrid III, bar impacts caused higher chest deflection compared to hub impacts, although the contrary results were obtained with the more humanlike THUMS. Correction factors were developed that can be used to correct the Hybrid III chest responses. Higher injury criteria capping limits for steering wheel impacts are acceptable. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Early impact of smoking on lung function, health, and well‐being in adolescents

Smoking is the single most important risk factor for the development of chronic obstructive pulmonary disease, and more than 80% of adult smokers started smoking before the age of 20. The aim of our study was to evaluate the early impact of smoking on lung function, health, and well-being in adolescents. Twenty-four non-smokers (10 male, 14 female, mean age 17.6 years) and 24 smokers (mean of 3.5 pack-years; 15 male, 9 female, mean age 17.8 years) were compared in terms of lung function, bronchial hyperreactivity (BHR), levels of exhaled carbon monoxide (eCO), exhaled nitric oxide (eNO), and blood counts. A questionnaire containing items from the ISAAC study was used to detect differences in health and well-being. There were no significant differences in lung function values between non-smokers and smokers (VC 95% vs. 103%, FEV(1) 106% vs. 116%, FEV(1) %/VC MAX 94.6% vs. 95.2%), whereas BHR significantly differed (P < 0.05). Furthermore, significant differences were found for eCO, eNO, Hb, leukocytes, and neutrophils. Health and well-being in terms of sleep and physical activity were significantly worse in smokers. Our results suggest an early impact of smoking on health after as few as 3.5 pack-years. Early signs of smoking are an increase in BHR, changes in blood count and a decrease of eNO even before changes in lung function become apparent.

The use of pupillometry in the assessment of cardiac autonomic function in elite different type trained athletes

The aim of the present study was to evaluate cardiac autonomic function by pupillometry in male athletes. Fifteen elite endurance- (END) and eleven power-trained (POWER) athletes and fifteen sedentary individuals (CONTROL) were studied. All subjects underwent three pupillometric measurements: at rest, peak exercise testing and recovery phase. The pupillometric indices studied were: baseline pupil radius (R1), minimum pupil radius (R2), maximum constriction velocity (VC(max)), maximum constriction acceleration (AC(max)), amplitude (AMP, R1-R2), constriction ratio (AMP%). During exercise, RR intervals were obtained for each subject with a Polar S810i for time and frequency domain heart rate variability (HRV) analysis. The following parameters of HRV were measured: standard deviation of all NN intervals (SDNN), the mean square successive differences (rMSSD), percent of NN intervals differing >50 ms from the preceding NN (pNN50), low (LF)- and high (HF)- frequency components of the autoregressive power spectrum of the NN intervals and their ratio (LF/HF). At rest and recovery, END showed significantly increased VC(max) and AC(max) compared to POWER and CONTROL. AMP% was significantly greater in END at rest, peak exercise and recovery compared to POWER and CONTROL. END and POWER had significantly greater AMP at rest and recovery compared to CONTROL. Moreover, all HRV indices were significantly increased in END compared to POWER and CONTROL. However, POWER showed significantly increased rMSSD and LF compared to CONTROL. HRV parameters were significantly correlated with pupillometric parameters during exercise. Our results indicated that any kind of exercise training and mainly endurance one affects autonomic regulation of pupillary light reflex.

Photosynthetic down-regulation under elevated CO 2 exposure can be prevented by nitrogen supply in nodulated alfalfa

Increasing atmospheric CO 2 concentrations are expected to enhance plant photosynthesis and yield. Nevertheless, after long-term exposure, plants acclimate and show a reduction in photosynthetic activity (called down-regulation), which may cause a reduction in potential yield. Some authors suggest that down-regulation is related to nutrient availability, and more specifically, to an insufficient plant C sink strength caused by limited N supply. In this paper, we tested whether or not N availability prevents down-regulation of photosynthesis in nodulated alfalfa plants ( Medicago sativa L.). To do so, we examined the effect of the addition of different levels of NH 4NO 3 (0, 10, and 15 mM) to 30-day-old nodulated alfalfa plants exposed to ambient (approximately 400 μmol mol −1) or elevated CO 2 (700 μmol mol −1) during a period of 1 month in growth chambers. After 2 weeks of exposure to elevated CO 2, no significant differences were observed in plant growth or photosynthesis rates. After 4 weeks of treatment, exclusively N 2 fixing alfalfa plants (0 mM NH 4NO 3) showed significant decreases in photosynthesis and Vc max . Photosynthetic down-regulation of these plants was caused by the C/N imbalance as reflected by the carbohydrate and N data. On the other hand, plants supplied with 15 mM NH 4NO 3 grown under elevated CO 2 maintained high photosynthetic rates owing to their superior C/N adjustment. The intermediate N treatment, 10 mM NH 4NO 3, also showed photosynthetic down-regulation, but to a lesser degree than with 0 mM treatment. The present study clearly shows that external N supply can reduce or even avoid acclimation of photosynthesis to elevated CO 2 as a consequence of the increase in C sink strength associated with N availability.

Effects of intracanopy lighting on photosynthetic characteristics in cucumber

Plants of cucumber ( Cucumis sativus L. cv. Euphorbia) were grown in a traditional high-wire cultivation system to investigate the effects of three lighting regimes on photosynthetic characteristics, leaf area and yield. The lighting regimes included overhead lighting (OH), where all the lamps were mounted above the canopy and overhead + intracanopy lighting (OH + IC) which comprised 65% of overhead lamps and 35% of lamps mounted vertically along the plant rows. All overhead lighting was provided for 20 h day −1 and intracanopy lighting was provided for either 20 h or 24 h day −1 lighting period. Intracanopy lighting improved the light distribution in the canopy. Gas exchange measurements showed that intracanopy lighting increased net photosynthesis ( P N) and photosynthetic capacity ( P max). Parameters calculated from CO 2 response ( A/ C i ) curves showed that in vivo estimate of the maximum rate of Rubisco carboxylation (Vc max) and the maximum rate of electron transport ( J max) were affected by light regime. Intracanopy light increased yield by 11% compared to traditional overhead light.

Diurnal changes in photosynthetic parameters of Populus tremuloides, modulated by elevated concentrations of CO 2 and/or O 3 and daily climatic variation

The diurnal changes in light-saturated photosynthesis (Pn) under elevated CO 2 and/or O 3 in relation to stomatal conductance ( g s), water potential, intercellular [CO 2], leaf temperature and vapour-pressure difference between leaf and air (VPD L) were studied at the Aspen FACE site. Two aspen ( Populus tremuloides Michx.) clones differing in their sensitivity to ozone were measured. The depression in Pn was found after 10:00 h. The midday decline in Pn corresponded with both decreased g s and decreased Rubisco carboxylation efficiency, Vc max. As a result of increasing VPD L, g s decreased. Elevated [CO 2] resulted in more pronounced midday decline in Pn compared to ambient concentrations. Moreover, this decline was more pronounced under combined treatment compared to elevated CO 2 treatment. The positive impact of CO 2 on Pn was relatively more pronounced in days with environmental stress but relatively less pronounced during midday depression. The negative impact of ozone tended to decrease in both cases.

Optimizing the statistical estimation of the parameters of the Farquhar–von Caemmerer–Berry model of photosynthesis

The model of Farquhar, von Caemmerer and Berry is the standard in relating photosynthetic carbon assimilation and concentration of intercellular CO(2). The techniques used in collecting the data from which its parameters are estimated have been the object of extensive optimization, but the statistical aspects of estimation have not received the same attention. The model segments assimilation into three regions, each modeled by a distinct function. Three parameters of the model, namely the maximum rate of Rubisco carboxylation (V(c max)), the rate of electron transport (J), and nonphotorespiratory CO(2) evolution (R(d)), are customarily estimated from gas exchange data through separate fitting of the component functions corresponding to the first two segments. This disjunct approach is problematic in requiring preliminary arbitrary subsetting of data into sets believed to correspond to each region. It is shown how multiple segments can be estimated simultaneously, using the entire data set, without predetermination of transitions by the investigator. Investigation of the number of parameters that can be estimated in the two-segment model suggests that, under some conditions, it is possible to estimate four or even five parameters, but that only V(c max), J, and R(d), have good statistical properties. Practical difficulties and their solutions are reviewed, and software programs are provided.

Temperature acclimation of photosynthesis: mechanisms involved in the changes in temperature dependence of photosynthetic rate

Growth temperature alters temperature dependence of the photosynthetic rate (temperature acclimation). In many species, the optimal temperature that maximizes the photosynthetic rate increases with increasing growth temperature. In this minireview, mechanisms involved in changes in the photosynthesis-temperature curve are discussed. Based on the biochemical model of photosynthesis, change in the photosynthesis-temperature curve is attributable to four factors: intercellular CO2 concentration, activation energy of the maximum rate of RuBP (ribulose-1,5-bisphosphate) carboxylation (Vc max), activation energy of the rate of RuBP regeneration (Jmax), and the ratio of Jmax to Vc max. In the survey, every species increased the activation energy of Vc max with increasing growth temperature. Other factors changed with growth temperature, but their responses were different among species. Among these factors, activation energy of Vc max may be the most important for the shift of optimal temperature of photosynthesis at ambient CO2 concentrations. Physiological and biochemical causes for the change in these parameters are discussed.

Photosynthetic and stomatal responses of potatoes grown under elevated CO 2 and/or O 3—results from the European CHIP-programme

The physiological effects of elevated CO 2 and/or O 3 on Solanum tuberosum cv. Bintje were examined in Open-Top Chambers during 1998 and 1999 at experimental sites across Europe as part of the EU ‘Changing Climate and Potential Impacts on Potato Yield and Quality’ programme (CHIP). At tuber initiation (≈20 days after emergence, DAE) elevated CO 2 (680 μl l −1) induced a 40% increase in the light saturated photosynthetic rate ( A sat) of fully expanded leaves in the upper canopy. This was 16% less than expected from short-term exposures of plants grown under ambient CO 2 (360 μl l −1) to elevated CO 2, indicating that photosynthetic acclimation began at an early stage of crop growth. This effect resulted from a combination of a 12% reduction in stomatal conductance ( g s) and a decline in photosynthetic capacity, as indicated by the significant reductions in the maximum carboxylation rate of Rubisco ( Vc max) and light-saturated rate of electron transport ( J max) under elevated CO 2. The seasonal decline in the promotion of photosynthesis by elevated CO 2 reflected the concurrent decrease in g s. Vc max and J max were both reduced in plants grown under elevated CO 2 until shortly after maximum leaf area (MLA) was attained. Although non-photorespiratory mitochondrial respiration in the light ( R d) increased during the later stages of the season, net photosynthesis was consistently increased by elevated CO 2 during the main part of the season. Photosynthetic rate declined more rapidly in response to elevated O 3 under ambient CO 2, and the detrimental impact of O 3 was most obvious after MLA was attained (DAE 40–50). Several exposure indices were compared, with the objective of determining the critical ozone level required to induce physiological effects. The critical O 3 exposure above which a 5% reduction in light saturated photosynthetic rate may be expected (expressed in terms of cumulative exposure above 0 nl l −1 O 3 between emergence and specific dates during the season (AOT0-cum)) was 11 μl l −1 h; however this value should only be extrapolated beyond the CHIP dataset with caution. The interaction between O 3 and stomatal behaviour was more complex, as it was influenced by both long-term and daily exposure levels. Elevated CO 2 counteracted the adverse effect of O 3 on photosynthesis, perhaps because the observed reduction in stomatal conductance decreased O 3 fluxes into the leaves. The results are discussed in the context of nitrogen deficiency, carbohydrate accumulation and yield.

Will rising CO2 protect plants from the midday sun? A study of photoinhibition of Quercus myrtifolia in a scrub‐oak community in two seasons

AbstractOver a large part of the photoperiod, light energy absorbed by upper canopy leaves saturates photosynthesis and exceeds the energetic requirements for light‐saturated linear electron flow through photosystem II (JPSII), so that photoinhibition results. From a theoretical consideration of the response of light‐saturated photosynthesis to elevated atmospheric CO2 partial pressure (pCO2) it may be predicted that, where light‐saturated photosynthesis is Rubisco‐limited, an increase in pCO2 will stimulate JPSII. Therefore, the proportion of absorbed quanta dissipated photochemically will increase and the potential for photoinhibition of photosynthesis will decrease. This was tested by measuring modulated chlorophyll a fluorescence from Quercus myrtifolia Willd. growing in the field in open‐top chambers, at either current ambient or elevated (ambient + 35 Pa) pCO2 on Merritt Island, Florida, USA. During spring and summer, light‐saturated photosynthesis at current ambient pCO2 was Rubisco‐limited. Consistent with theoretical prediction, JPSII was increased and photoinhibition decreased by elevated pCO2 in spring. In the summer, when growth had largely ceased, an acclimatory decrease in the maximum Ribulose 1,5 bisphosphate saturated carboxylation capacity (Vc max) removed the stimulation of JPSII seen in the spring, and photoinhibition was increased in elevated pCO2. It is concluded that, for Q. myrtifolia growing in the field, the effects of elevated pCO2 on JPSII and photoinhibition will reflect seasonal differences in photosynthetic acclimation to elevated pCO2 in a predictable manner.

Modeling CO2 and water vapor turbulent flux distributions within a forest canopy

One‐dimensional multilayer biosphere‐atmosphere models (e.g., CANVEG) describe ecosystem carbon dioxide (CO2) and water vapor (H2O) fluxes well when cold temperatures or the hydrologic state of the ecosystem do not induce stomatal closure. To investigate the CANVEG model framework under such conditions, CO2, H2O, and sensible heat fluxes were measured with eddy‐covariance methods together with xylem sap flux and leaf‐level gas exchange in a 16‐year‐old (in 1999) southeastern loblolly pine forest. Leaf‐level gas exchange measurements, collected over a 3‐year period, provided all the necessary biochemical and physiological parameters for the CANVEG model. Using temperature‐induced reductions of the biochemical kinetic rate constants, the CANVEG approach closely captures the diurnal patterns of the CO2 and H2O fluxes for two different formulations of the maximum Rubisco catalytic capacity (Vc max) ‐ temperature function, suggesting that the CANVEG approach is not sensitive to Vc max variations for low temperatures. A soil moisture correction (wr) to the Ball‐Berry leaf‐conductance approach was also proposed and tested. The wr magnitude is consistent with values predicted by a root‐xylem hydraulic approach and with leaf‐level measurements. The wr correction significantly improves the model's ability to capture diurnal patterns of H2O fluxes for drought conditions. The modeled bulk canopy conductance (Gm) for pine foliage estimated from the CANVEG‐modeled multilevel resistance values agreed well with canopy conductance (Gc) independently estimated from pine sap flux measurements. Detailed sensitivity analysis suggests that the leaf‐level physiological parameters used in CANVEG are not static. The dynamic property of the conductance parameter, inferred from such sensitivity analysis, was further supported using 3 years of porometry measurements. The CANVEG model also reproduced basic biochemical processes as demonstrated by the agreement between modeled and leaf‐level measured Ci/Ca, where Ci and Ca are the intercellular and atmospheric CO2 concentration, respectively. The model estimated that vapor pressure deficit does not vary significantly within the canopy but that Ci/Ca varied by more than 15%. The broader implication of this variation is that “big‐leaf” approaches that compress physiological and biochemical parameters into bulk canopy stomatal properties may be suitable for estimating water vapor flux but biased for CO2 ecosystem fluxes.

Assessing the influence of exogenous ethylene on electron transport and fluorescence quenching in leaves of Glycine max

We conducted a series of modeling exercises designed to re-evaluate the light-response and CO 2-response curves of Taylor and Gunderson ( Pl. Physiol. 86, 85–92, 1988) and to examine further their conclusion that ethylene-induced inhibition of electron transport may contribute to reduced CO 2 assimilation in leaves of Glycine max. By partitioning the response of CO 2 assimilation to either electron transport-limited or Rubisco-limited rates of carboxylation, we calculated that the electron transport capacity ( J max) of ethylene-treated leaves decreased by over 30% following a 4-hr exposure to 10 μl/l ethylene and noted that ethylene-induced reductions in CO 2 assimilation could be explained without a decrease in Rubisco activity ( Vc max). Measurements of in vivo Chl fluorescence supported these observations and indicated that the efficiency by which excitation energy was captured in PSII (i.e. ( F m − F o/ F m) was reduced from 0.80 to 0.73 after a 4-hr exposure to 10 μl/l ethylene. This reduction was also accompanied by a 12% decrease in steady-state photochemical quenching ( q p), indicating that a lower proportion of open or oxidized PSII reaction centers were participating in light-dependent processes. Effects of ethylene on Chl fluorescence were amplified at increased irradiance, suggesting that photoinhibition may play a role in the ethylene-induced inhibition of CO 2 assimilation.

Lusitropic effect and modifications of contraction-relaxation coupling induced by α-adrenergic stimulation in rat left ventricular papillary muscle

Phenylephrine (PE) and metaraminol (MR) were studied alone at 2 × 10 −5 m and at 4 × 10 −5 m respectively. These drugs were also used both in the presence of either propranolol (PR) at 4 × 10 −7 m ( PE PR and MR PR groups) or prazosin (PZ) at 2 × 10 −7 m ( PE PZ and MR PZ groups). Specific α-adrenergic stimulation (AS) was induced in the PE PR and MR PR groups. These AS were evaluated in isotonic and isometric conditions on rat left ventricular papillary muscle. Peak shortening velocity ( Vc max) and peak lengthening velocity ( Vr max) were calculated from the twitch with preload only. Positive ( + dF dt max ) and negative ( − dF dt max ) peak derivative forces were calculated from the isometric twitch. Two coefficients R 1 and R 2 were used to measure the coupling between contraction and relaxation at low and heavy load, respectively: R 1 = V r max V r max and R 2 = ( + dF dt max ) ( − dF dt max ) . In all groups, there was a significant positive inotropic effect. As compared to control values before AS, R 1 significantly decreased in all groups, ( PE PR : −15%; MR PR : −18%; PE PZ : −8%; MR PZ : −23%; PE: −19%; MR: −32%). On the other hand, R 2 significantly decreased only in three groups ( PE PZ : −5.4%; MR PZ : −16.5%; MR: −12.0%) whereas it did not significantly change in the three other groups ( PE PR ; MR PR ; PE). In all groups, and at low load, Vr max increased more than Vc max (positive relaxant effect i.e. R 1 decreased). At heavy load, despite the positive inotropic effect, there was no significant relaxant effect after predominent α-AS. These results indicate that α-AS modified the coupling between contraction and relaxation differently, depending on the level of load.

A viscous tolerance criterion for soft tissue injury assessment

Experiments in our laboratory have documented that high-speed impact can cause severe injury to internal organs before either of the currently accepted chest injury criteria, which are based on spinal acceleration or chest compression, approach their tolerance limit. Those studies demonstrate an interdependence between the velocity of deformation and compression of the body on injury risk. A tolerable level of chest compression at a low velocity can prove to be fatal at higher velocities of deformation. The observation of a rate-sensitive tolerable compression led to the introduction of the Viscous criterion, VC max , which accounts for the importance of both parameters. VC max is the maximum of the product of velocity of deformation ( V) and compression ( C), and is derivable from the chest deflection response. This paper presents the empirical evidence and theoretical basis supporting the Viscous criterion, and shows it to be an indicator of the energy dissipated by soft tissue deformation. The Viscous criterion accurately predicts the risk of vital organ and soft tissue injury when other criteria fail.

Diurnal variations in renal excretion of electrolytes, uric acid and total amino nitrogen in various renal diseases and in essential hypertension

Results of earlier investigations and observations from clinical practice indicate that diurnal variations in renal excretion of different urinary constituents diminish when kidney is damaged. Consequently the diagnostic value of the so-called “clearance indices” ( C x ) has been studied. Performed as 24-h tests, C x was estimated every 3 h taking into account the maximum oscillations of C x ( VC max ). The tests were performed in 63 patients who were classified into the following groups: ( I) acute glomerulonephritis (9); ( 2) chronic glomcrulonephritis (13); ( 3) pyelonephritis (8); ( 4) nephrosis (5); ( 5) other renal diseases (low nephron syndrome, polycystic degeneration of the kidney, post-nephrectomy states, etc.) (9); ( 6) essential hypertension (19); ( 7) controls (healthy medical students) (10). The following conclusions were drawn: ( 1) Kidney functional disturbances in most cases are characterised by decrease in C x and VC x max. (2) In the healthy controls low water intake causes a decrease of C x and VC x max.