1000 resultados para Microclimatic conditions


Relevância:

20.00% 20.00%

Publicador:

Resumo:

The aim of this study was to characterize gas exchange responses of young cashew plants to varying photosynthetic photon flux density (PPFD), temperature, vapor-pressure deficit (VPD), and intercellular CO2 concentration (Ci), under controlled conditions. Daily courses of gas exchange and chlorophyll a fluorescence parameters were measured under natural conditions. Maximum CO2 assimilation rates, under optimal controlled conditions, were about 13 mmol m-2 s-1 , with light saturation around 1,000 mmol m-2 s-1. Leaf temperatures between 25ºC and 35ºC were optimal for photosynthesis. Stomata showed sensitivity to CO2, and a closing response with increasing Ci. Increasing VPD had a small effect on CO2 assimilation rates, with a small decrease above 2.5 kPa. Stomata, however, were strongly affected by VPD, exhibiting gradual closure above 1.5 kPa. The reduced stomatal conductances at high VPD were efficient in restricting water losses by transpiration, demonstrating the species adaptability to dry environments. Under natural irradiance, CO2 assimilation rates were saturated in early morning, following thereafter the PPFD changes. Transient Fv/Fm decreases were registered around 11h, indicating the occurrence of photoinhibition. Decreases of excitation capture efficiency, decreases of effective quantum yield of photosystem II, and increases in non-photochemical quenching were consistent with the occurrence of photoprotection under excessive irradiance levels.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Here we present a 30 000 years low-resolution climate record reconstructed from groundwater data. The investigated site is located in the Bohemian Cretaceous Basin, in the corridor between the Scandinavian ice sheet and the Alpine ice field. Noble gas temperatures (NGT), obtained from groundwater data, preserved multicentennial temperature variability and indicated a cooling of at least 5-7 °C during the last glacial maximum (LGM). This is further confirmed by the depleted δ18O and δ2H values at the LGM. High excess air (ΔNe) at the end of the Pleistocene is possibly related to abrupt changes in recharge dynamics due to progression and retreat of ice covers and permafrost. These results agree with the fact that during the LGM permafrost and small glaciers developed in the inner valleys of the Giant Mountains (located in the watershed of the aquifers). A temporal decrease of deuterium excess from the pre-industrial Holocene to present days is linked to an increase of the air temperatures, and probably also to an increase of water pressure at the source region of precipitation over the past few hundred years

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Blowing and drifting of snow is a major concern for transportation efficiency and road safety in regions where their development is common. One common way to mitigate snow drift on roadways is to install plastic snow fences. Correct design of snow fences is critical for road safety and maintaining the roads open during winter in the US Midwest and other states affected by large snow events during the winter season and to maintain costs related to accumulation of snow on the roads and repair of roads to minimum levels. Of critical importance for road safety is the protection against snow drifting in regions with narrow rights of way, where standard fences cannot be deployed at the recommended distance from the road. Designing snow fences requires sound engineering judgment and a thorough evaluation of the potential for snow blowing and drifting at the construction site. The evaluation includes site-specific design parameters typically obtained with semi-empirical relations characterizing the local transport conditions. Among the critical parameters involved in fence design and assessment of their post-construction efficiency is the quantification of the snow accumulation at fence sites. The present study proposes a joint experimental and numerical approach to monitor snow deposits around snow fences, quantitatively estimate snow deposits in the field, asses the efficiency and improve the design of snow fences. Snow deposit profiles were mapped using GPS based real-time kinematic surveys (RTK) conducted at the monitored field site during and after snow storms. The monitored site allowed testing different snow fence designs under close to identical conditions over four winter seasons. The study also discusses the detailed monitoring system and analysis of weather forecast and meteorological conditions at the monitored sites. A main goal of the present study was to assess the performance of lightweight plastic snow fences with a lower porosity than the typical 50% porosity used in standard designs of such fences. The field data collected during the first winter was used to identify the best design for snow fences with a porosity of 50%. Flow fields obtained from numerical simulations showed that the fence design that worked the best during the first winter induced the formation of an elongated area of small velocity magnitude close to the ground. This information was used to identify other candidates for optimum design of fences with a lower porosity. Two of the designs with a fence porosity of 30% that were found to perform well based on results of numerical simulations were tested in the field during the second winter along with the best performing design for fences with a porosity of 50%. Field data showed that the length of the snow deposit away from the fence was reduced by about 30% for the two proposed lower-porosity (30%) fence designs compared to the best design identified for fences with a porosity of 50%. Moreover, one of the lower-porosity designs tested in the field showed no significant snow deposition within the bottom gap region beneath the fence. Thus, a major outcome of this study is to recommend using plastic snow fences with a porosity of 30%. It is expected that this lower-porosity design will continue to work well for even more severe snow events or for successive snow events occurring during the same winter. The approach advocated in the present study allowed making general recommendations for optimizing the design of lower-porosity plastic snow fences. This approach can be extended to improve the design of other types of snow fences. Some preliminary work for living snow fences is also discussed. Another major contribution of this study is to propose, develop protocols and test a novel technique based on close range photogrammetry (CRP) to quantify the snow deposits trapped snow fences. As image data can be acquired continuously, the time evolution of the volume of snow retained by a snow fence during a storm or during a whole winter season can, in principle, be obtained. Moreover, CRP is a non-intrusive method that eliminates the need to perform man-made measurements during the storms, which are difficult and sometimes dangerous to perform. Presently, there is lots of empiricism in the design of snow fences due to lack of data on fence storage capacity on how snow deposits change with the fence design and snow storm characteristics and in the estimation of the main parameters used by the state DOTs to design snow fences at a given site. The availability of such information from CRP measurements should provide critical data for the evaluation of the performance of a certain snow fence design that is tested by the IDOT. As part of the present study, the novel CRP method is tested at several sites. The present study also discusses some attempts and preliminary work to determine the snow relocation coefficient which is one of the main variables that has to be estimated by IDOT engineers when using the standard snow fence design software (Snow Drift Profiler, Tabler, 2006). Our analysis showed that standard empirical formulas did not produce reasonable values when applied at the Iowa test sites monitored as part of the present study and that simple methods to estimate this variable are not reliable. The present study makes recommendations for the development of a new methodology based on Large Scale Particle Image Velocimetry that can directly measure the snow drift fluxes and the amount of snow relocated by the fence.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

We face the problem of characterizing the periodic cases in parametric families of (real or complex) rational diffeomorphisms having a fixed point. Our approach relies on the Normal Form Theory, to obtain necessary conditions for the existence of a formal linearization of the map, and on the introduction of a suitable rational parametrization of the parameters of the family. Using these tools we can find a finite set of values p for which the map can be p-periodic, reducing the problem of finding the parameters for which the periodic cases appear to simple computations. We apply our results to several two and three dimensional classes of polynomial or rational maps. In particular we find the global periodic cases for several Lyness type recurrences

Relevância:

20.00% 20.00%

Publicador:

Resumo:

When colonizing a new habitat, populations must adapt their sexual behaviour to new ecological constraints. Because caves display drastically different conditions from surface habitats and cave animals are deprived from visual information, hypogean populations are expected to have modified their mate preference and signalling behaviour after cave colonization. Here, we experimentally examined the female preference and the sexual behaviour of brook newts Calotriton asper from different cave and river populations, either in light or in darkness. Our results suggest that females prefer large individuals in both hypogean and epigean populations, but that this preference is only expressed in the light conditions of their native habitat. Hence, some mate choice criteria would be maintained across genetically divergent populations and throughout dissimilar habitats. However, this sexual behaviour is likely to be expressed via a different sensory pathway in the different habitats, suggesting that a sensory shift has occurred in cave populations, enabling animals to communicate through a non-visual channel.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Active personal dosemeters (APD) have been found to be very efficient tools to reduce occupational doses in many applications of ionizing radiation. In order to be used in interventional radiology and cardiology (IR/IC), APDs should be able to measure low energy photons and pulsed radiation with relatively high instantaneous personal dose equivalent rates. A study concerning the optimization of the use of APDs in IR/IC was performed in the framework of the ORAMED project, a Collaborative Project (2008-2011) supported by the European Commission within its 7th Framework Program. In particular, eight commercial APDs were tested in continuous and pulsed X-ray fields delivered by calibration laboratories in order to evaluate their performances. Most of APDs provide a response in pulsed mode more or less affected by the personal dose equivalent rate, which means they could be used in routine monitoring provided that correction factors are introduced. These results emphasize the importance of adding tests in pulsed mode in type-test procedures for APDs. Some general recommendations are proposed in the end of this paper for the selection and use of APDs at IR/IC workplaces.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Introduction: Therapeutic drug monitoring (TDM) of imatinib has been increasingly proposed for chronic myeloid leukaemia (CML) patients, as several studies have found a correlation between trough concentrations (Cmin) >=1000ng/ml and improved response. The pharmacological monitoring project of EUTOS (European Treatment and Outcome Study) was launched to increase the availability of imatinib TDM, standardize labs, and validate proposed Cmin thresholds. Using the collected data, the objective of this analysis was to characterize imatinib Population pharmacokinetics (Pop-PK) in a large cohort of European patients, to quantify its variability and the influence of demographic factors and comedications, and to derive individual exposure variables suitable for further concentration-effect analyses.¦Methods: 4095 PK samples from 2478 adult patients were analyzed between 2006 and 2010 by LC-MS-MS and considered for Pop-PK analysis by NONMEM®. Model building used data from 973 patients with >=2 samples available (2590 samples). A sensitivity analysis was performed using all data. Available comedications (27%) were classified into inducers or inhibitors of P-glycoprotein, CYP3A4/5 and organic-cation-transporter-1 (hOCT-1).¦Results: A one-compartment model with linear elimination, zero-order absorption fitted the data best. Estimated Pop-PK parameters (interindividual variability, IIV %CV) for a 40-year old male patient were: clearance CL = 17.3 L/h (37.7%), volume V = 429L (51.1%), duration of absorption D1 = 3.2h. Outliers, reflecting potential compliance and time recording errors, were taken into account by estimating an IIV on the residual error (35.4%). Intra-individual residuals were 29.1% (proportional) plus ± 84.6 ng/mL (additive). Female patients had a 15.2% lower CL (14.6 L/h). A piece-wise linear effect of age estimated a CL of 18.7 L/h at 20 years, 17.3 L/h at 40 and 13.8 L/h at 60 years. These covariates explained 2% (CL) and 4.5% (V) of IIV variability. No effect of comedication was found. The sensitivity analysis expectedly estimated increased IIV, but similar fixed effect parameters.¦Conclusion: Imatinib PK was well described in a large cohort of CML patients under field conditions and results were concordant with previous studies. Patient characteristics explain only little IIV, confirming limited utility of prior dosage adjustment. As intra-variability is smaller than inter-patient variability, dose adjustment guided by TDM could however be beneficial in order to bring Cmin into a given therapeutic target.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

The objectives of this work were to evaluate two greenhouse screening methods for sudden death syndrome (SDS) and to determine which one is best correlated with field resistance of soybean genotypes. The evaluations were done with three sets of genotypes that were classified as partially resistant, intermediate, and susceptible to SDS based on previous field evaluations. These three sets were independently evaluated for greenhouse SDS reactions using cone and tray inoculation methods. Plants were infected using grains of white sorghum [Sorghum bicolor (L.) Moench] infested with Fusarium solani f. sp. glycines. Foliar symptom severity was rated 21 days after emergence. The cone and field SDS ratings were significantly correlated and ranged from 0.69 for set 1 to 0.51 for set 3. Correlations of SDS ratings of genotypes between field and greenhouse tray ratings were significant for set 1 and not significant for set 2. The cone method showed the highest correlation with field results and is recommended to screen soybean genotypes for SDS resistance.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Interferon-gamma release assays for the diagnosis of tuberculosis (TB) can give indeterminate results. The prevalence of indeterminate test results (ITRs) among T-SPOT.TB tests was assessed. A retrospective analysis of samples processed in 2005 was performed. ITRs were assessed by age, sex, immunosuppression, distance to the laboratory and season. A subgroup of tests performed for specific indications (contact tracing, migrants with positive tuberculin skin test, TB suspects and immunosuppression) were analysed separately. Of a total of 1,429 tests, 49 (3.4%) were indeterminate. ITRs were significantly associated with old age (>75 versus 5-75 yrs; odds ratio (OR) 7.97, 95% confidence interval (CI) 3.968-15.438) and the season during which samples were transported (autumn and winter versus spring and summer; OR 3.47, 95% CI 1.753-7.514). The incidence of ITR was 302 (2.0%) among TB contacts, 75 (1.6%) among immigrants, 156 (3.0%) in TB suspects and 32 (3.0%) among immunosuppressed patients. Sex, young age and distance to the laboratory were not associated with the rate of ITR. Of the 13 tests with ITR that were repeated, 10 gave a clear positive or negative result. Indeterminate test results with T-SPOT.TB under routine conditions were infrequent and more common in individuals aged >75 yrs than in children and younger adults. The incidence of indeterminate test results was low and similar among healthy tuberculosis contacts, immigrants with a positive tuberculin skin test, tuberculosis suspects and the immunosuppressed. The conditions of transportation may influence the incidence of indeterminate test results.

Relevância:

20.00% 20.00%

Publicador:

Resumo:

Hysteresis cycles are very important features of energy conversion and harvesting devices, such as batteries. The efficiency of these may be strongly affected by the physical size of the system. Here, we show that in systems which are small enough, the existence of physical boundaries which produce nonhomogeneities of the interaction potential gives rise to inflections and barriers in the associated free energy. This in turn brings on irreversible processes which can be triggered under suitable external conditions imposed by a heat bath. As an example, by controlling the temperature, the state of a small system may be impelled to oscillate between two different structural configurations or aggregation states avoiding equilibrium coexistence and therefore dissipating energy. This cyclical behavior associated with a hysteresis cycle may be prototypical of energy conversion, storage, or generating nanodevices, as exemplified by Li-ion insertion batteries.