Length Of Critical Period Research Articles

Phonon thermal conductivity reduction in silicene nanotubes with isotope substitution.

We used molecular dynamics simulations to study the isotopic doping effects on phonon thermal conductivity in armchair silicene nanotubes (SNTs). The phonon thermal conductivity of armchair SNTs can be effectively tuned with isotope substitution. Randomly and superlattice-structured isotopic doping can significantly reduce thermal conductivity. By analyzing the phonon vibrational spectrum, we reveal the underlying physical insights into the relationship between randomly isotopic doping concentration and thermal conductivity. Given the same doping concentration, the superlattice-structured doping method can reduce thermal conductivity more significantly than the disordered doping. For the isotopic superlattice doping method, the completion between the phonon interfacial scattering and phonon tunneling may cause minimum thermal conductivity at the critical period length. This study provides a possible means to effectively reduce the thermal conductivity of thermoelectric SNTs through isotopic doping engineering.

Impact of water deficit on critical period of pigweed (amaranthus retroflexus l.) in sunflower

ABSTRACT-The critical period of weed control is a part of crop life cycle during which weeds must be kept weed-free to avoid yield losses due to competition. In order to evaluate the effect of deficit irrigation on critical period of redroot pigweed (Amaranthus retroflexus L.) in sunflower (Helianthus annuus L.), an experiment was carried out as split plot based on randomized complete block design with three replications at the experimental farm of College of Agriculture, Shiraz University, during 2010 and 2011 growing seasons. Factors were water deficit at three levels (100%, 75% and 50% of field capacity) as main plots and weed interference periods in weedy and weed-free plots at five sunflower growth stages (8-leaf, 12-leaf, head emergence, flowering and maturity) as subplots. Results showed that water deficit decreased grain yield and grain yield components in both years. Critical period of redroot pigweed in normal irrigation with accepting 5% yield loss in sunflower was 35-86 DAP (days after planting) in the first year and 49-94 DAP in the second year. By decreasing irrigation water to 75%FC and 50%FC, the length of critical period increased to 34-100 and 32-105 DAP in the first year and 50-101 DAP and 44-98 DAP in the second year of the study, respectively. Generally, our results showed water deficit extended the length of critical period of redroot pigweed in sunflower. Nomenclature: Redroot pigweed, Amaranthus retroflexus L.; Sunflower, Helianthus annuus L.

Phonon thermal transport in semi-disordered isotopic-superlattice graphene nanoribbons

ABSTRACTThe thermal conductance of isotopic-superlattice graphene nanoribbons randomly mixed with isotope defects is investigated by atomistic Green’s function method. The isotopic-superlattice structure reduces the thermal conductance, which changes non-monotonically as the superlattice period length decreases, and there exists a minimum thermal conductance at the critical period length. About 20% defects just further increase the reduction and shorten the critical period length. As the defect concentration in superlattice increases, the thermal conductance decreases monotonically in the zigzag nanoribbon, but in armchair nanoribbon the thermal conductance first decreases to its minimum value and then increases. The isotopic doping effect is particularly evident for large isotope mass, in armchair nanoribbons and for out-of-plane phonon modes. Isotope defects lead to additional phonon scattering in the superlattice structure, which is explained by analyzing the phonon transmittance.

Multi-criteria approach in solar urban water supply systems

An innovative method for sizing solar photovoltaic (PV) pumping systems in urban water supply systems (UWSSs) is presented. The methodology is based on various critical period approaches (the critical period method). A multi-criteria analysis was carried out to evaluate the effects of the critical period duration on the system characteristics. It was found that the critical period length is a design variable that significantly affects the economic, environmental and social aspects of the solution, with a lengthening of the critical period resulting in improvement of the overall sustainability of the solution. The results obtained indicate that a solar PV system is a promising solution to the energy sustainability of UWSSs. This form of energy supply does not emit greenhouse gases and furthermore the ‘social cost’ of carbon dioxide estimates decrease. The concept of a stand-alone PV energy system is a particularly promising sustainable energy solution.

EphB2 signaling regulates lesion-induced axon sprouting but not critical period length in the postnatal auditory brainstem

BackgroundStudies of developmental plasticity may provide insight into plasticity during adulthood, when neural circuitry is less responsive to losses or changes in input. In the mammalian auditory brainstem, globular bushy cell axons of the ventral cochlear nucleus (VCN) innervate the contralateral medial nucleus of the trapezoid body (MNTB) principal neurons. VCN axonal terminations in MNTB, known as calyces of Held, are very large and specialized for high-fidelity transmission of auditory information. Following unilateral deafferentation during postnatal development, VCN axons from the intact side form connections with novel targets, including the ipsilateral MNTB. EphB signaling has been shown to play a role in this process during the first postnatal week, but mechanisms involved in this reorganization during later developmental periods remain unknown.ResultsWe found that EphB2 signaling reduces the number of induced ipsilateral projections to the MNTB after unilateral VCN removal at postnatal day seven (P7), but not after removal of the VCN on one side at P10, after the closure of the critical period for lesion-induced innervation of the ipsilateral MNTB.ConclusionsResults from this study indicate that molecular mechanisms involved in the development of circuitry may also play a part in rewiring after deafferentation during development, but do not appear to regulate the length of critical periods for plasticity.

Examination of meteorology-based predictions of Fusarium head blight of wheat grown at two locations in the southern Pampas region of Argentina

In Argentina, head blight or scab is a highly risky disease (caused by Fusarium graminearum) of wheat, although its occurrence is sporadic depending on prevalent environmental variables. These traits stimulated the development of predictive models of head blight epidemics, which would help growers in the selection of control strategies. Regression models for predicting head blight incidence were developed at Pergamino (33°56S, 60°30W), associating temperature and moisture variables with mean disease data (empirical approach). Recently a new fundamental-empirical approach for estimating Fusarium index (incidence%×severity%/100) was developed using data from Pergamino and Marcos Juarez (32°41′S, 62°07′W). Validation studies of both empirical and fundamental-empirical approaches were carried out at northern and southern locations showing good results after making a few changes. The objective of this work was to examine the goodness of fit of the predicted values from both approaches (original and including some of the changes derived from previous validation studies) in comparison with median disease data in two southern locations of the Pampas region: Balcarce (37°45′S, 58°18′W) and Barrow (38°19′S, 60°15′W), for the 2002, 2003 and 2004 wheat seasons. Partial and mean deviation values between observed and predicted data were calculated. In accordance with previous validation studies, successful Fusarium index estimations were achieved decreasing the heat accumulation defining the length of the wheat critical period for infection to 450 degree days [base mean daily temperature (Td)=10°C]. Reducing the critical period length [450 degree days (base Td=0°C) instead of 530] and increasing maximum and minimum temperature thresholds (30° instead of 26°C and 11°C instead of 9°C) of the empirical equation thermal variable led to satisfactory Fusarium incidence predictions. This study showed that both approaches developed at northern locations of the Pampas region can be portable and useful for predicting disease intensity at more southern locations, making only a few changes. Differences in wheat cultivar behaviour regarding the disease were observed in the analysed data but this effect was not considered in this study.

Optimal upgrading of forest road networks: Scenario analysis vs. stochastic modelling

A two-stage stochastic model with binary choice in the first stage has been developed to optimise the upgrading of a real-world forest road network, geographically located in the middle of Sweden. We have compared the model with solutions to the same problem from deterministic scenario analysis. Upgrade policies can be achieved swiftly using both approaches, since the road network is of moderate size. However, a deterministic approach is considerably faster when larger problems are involved. The study here, furthermore, indicates that deterministic scenario analysis provides us with quick, near-optimal solutions to the stochastic model, which are of reasonable good quality. We conclude that the model used here is rather insensitive to uncertainty in critical period length, such as the length of spring thaw, at least when applied to the medium-sized problem presented here. Nevertheless, we strongly recommend the use of the stochastic model whenever possible, since the stochastic and deterministic solutions differ, due to the hedging effect in the stochastic solution.

Meteorological-Based Predictions of Wheat Head Blight Epidemic in the Southern Argentinean Pampas Region

In Argentina, head blight is a highly risky disease (caused by Fusarium graminearum), although its occurrence is sporadic depending on prevalent environmental variables. These traits stimulated the development of predictive models of head blight occurrence which would help growers in the selection of control strategies. Empirical equations for predicting head blight incidence were developed at Pergamino (33° 56′ S, 60° 30′ W) associating temperature and moisture variables with mean disease data. Recently a new fundamental-empirical approach for estimating Fusarium index (incidence% x severity%/100) was developed using data of Pergamino and Marcos Juarez (32° 41′ S, 62°07′ W). In this study our objective was to validate both approaches at three more southern locations: La Dulce (38° 10′ S, 58° 00′ W), Miramar (38° 00′ S, 57° 33′ W) and Balcarce (37° 45′ S, 58° 18W), for the 2001 crop season. Examining partial and mean deviation values between observed and predicted incidence data, an underestimation especially at La Dulce was assessed. A clear improvement of incidence goodness of fit estimations was obtained decreasing the heat accumulation defining the length of the wheat critical period for infection. Employing this last critical period length for the fundamental-empirical approach led to satisfactory Fusarium index predictions. This study showed that both approaches developed at northern locations of the Pampas region can be portable and useful for predicting disease intensity at more southern locations, making only a few changes.

Statistical properties of the critical period

The probability distribution of the length of the critical period, defined as the time interval during which an initially full reservoir is completely emptied, can be determined using the storage theory when the inflows are considered as discrete variables. For continuous inflows, which is the case in practice, the problem should be solved by simulation. In this study the probability density function (pdf) and parameters of the critical period length are determined for normally and lognormally distributed annual flows for various levels of regulation and a range of reservoir sizes.