186 research outputs found
Near Time-Optimal Transient Response in DC-DC Buck Converters Taking into Account the Inductor Current Limit
No full textThis paper analyzes the general problem of
inductor current limitation in the time-optimal load transient
response of a DC-DC buck converter. The concept of currentlimited,
time-optimal control (CL-TOC) is introduced and
compared to the previously reported unconstrained timeoptimal
solutions. A fundamental tradeoff between maximum
allowed current overshoot and voltage recovery time is
recognized, and a set of design equations is developed which
provide the engineer with the necessary analytical tools for the
controller design. Furthermore, the minimum number of
switching actions required to handle a generic current-limited
TOC is determined, leading to the formulation of a minimumswitch
CL-TOC concept. Two distinct approaches for minimumswitch
digital CL-TOC are then introduced. The first method,
which is an extension of a charge-balance approach, has the
advantage of achieving the time-optimal switching sequence
without the need for a prior knowledge of the output filter LC
parameters. The second approach implements a near CL-TOC
employing the switching surface concept and defining the
current limitation in the state-space. Simulation and
experimental results are provided to demonstrate the
effectiveness of the approaches
Variation in pathogenicity in the Fusarium verticillioides populations isolated from maize during the growing season
No full textIn Northern Italy the main etiological agent of Fusarium ear rot in maize is Fusarium verticillioides, the major producer of fumonisins. The role of F. verticillioides population variability, on disease incidence variation has not yet elucidated, and seems to be important for resistance breeding, evolutionary risk of the pathogen, and efficacy of the agricultural management practices. One hundred eighty one F. verticillioides strains were randomly selected among F. verticillioides populations associated with maize samples collected during different maize growth stages in three fields located in Lombardia region. Pathogenicity assays of the selected F. verticillioides strains was assessed on maize by evaluating seed germination percentages and calculating the percentage infection index (I%I) concerning seed colonization, radicle decay, and coleoptile rot. Seed germination occurred still when F. verticillioides colonized the entire kernel.To investigate variation in pathogenicity within the populations, cluster and principal component (PC) analyses were computed using I%Is obtained. Observed I%Is were very variable with significant correlations between seed colonization and both radicle decay and coleoptile rot. Cluster analysis showed that isolates were grouped in three main clusters. Bi-plot of PCA revealed that F. verticillioides strains isolated at seed and at maturity stages were gathered, while strains isolated from maize debris and at seedling and pre-silking stages showed a scattered distribution. F. verticillioides pathogenicity seemed to vary according to the maize growing stages, particularly when seedborne population and strains isolated at pre-silking stages are taken into account. Information gained from the combination of clustering method and PC analysis inferred that F. verticillioides pathogenicity showed very high intraspecific variability
Assessing pigmented pericarp of maize kernels as possible source of resistance to fusarium ear rot, Fusarium spp. infection and fumonisin accumulation
No full textOne of the purposes of maize genetic improvement is the research of genotypes resistant to fusarium ear rot (FER) and fumonisin accumulation. Flavonoids in the pericarp of the kernels are considered particularly able to reduce the fumonisin accumulation (FUM). The aim of this field study was to assess the effect of flavonoids, associated with anti-insect protection and Fusarium verticillioides inoculation, on FER symptoms and fumonisin contamination in maize kernels. Two isogenic hybrids, one having pigmentation in the pericarp (P1-rr) and the other without it (P1-wr), were compared. P1-rr showed lower values of FER symptoms and FUM contamination than P1-wr only if the anti-insect protection and the F. verticillioides inoculations were applied in combination. Fusarium spp. kernel infection was not influenced by the presence of flavonoids in the pericarp. Artificial F. verticillioides inoculation was more effective than anti-insect protection in enhancing the inhibition activity of flavonoids toward FUM contamination. The interactions between FUM contamination levels and FER ratings were better modeled in the pigmented hybrid than in the unpigmented one. The variable role that the pigment played in kernel defense against FER and FUM indicates that flavonoids alone may not be completely effective in the resistance of fumonisin contamination in maize
The influence of flavonoids in maize pericarp on fusarium ear rot symptoms and fumonisin accumulation under field conditions
No full textBreeding efforts have been undertaken to increase resistance of maize to fusarium ear rot (FER) and to fumonisin accumulation. Flavonoids in the pericarp of the kernels are considered particularly able to reduce the fumonisin accumulation. The aim of this 2-year field study was to assess the effect of flavonoids on FER symptoms and fumonisin contamination in maize kernels using two isogenic hybrids, one providing pigmentation in the pericarp (P1-rr) and the other without it (P1-wr). FER incidence (FERi), FER severity (FERs), the incidence of infections caused by Fusarium spp. in symptomless kernels (FF) and fumonisin contamination (FUM) were assessed in both hybrids. Significant differences between the two hybrids were detected mainly in 2012 trials where P1-rr showed lower FERi (P<001), FF (P<005) and FUM (P<01) than P1-wr. Site, characterized by local temperature and precipitation, played a relevant role in modelling all the measured variables, as its effect was highly significant in both years, whether they were considered individually or altogether. The interaction of hybrid with location was a significant (P<0001) source of variation only for FF. FF, together with FERi, was also significantly (P<0001) influenced by the interaction of hybrid with year. In general, FUM was more influenced by year and location parameters, such as temperatures during late ripening, than by flavonoid presence in kernel pericarp. The results indicate that flavonoid pigments alone may not be an important component in the resistance of maize to fumonisin accumulation
Ultra-sensitive measurement of transverse displacements with linear photonic gears
No full textAccurately measuring mechanical displacements is essential for a vast portion of current technologies. Several optical techniques accomplish this task, allowing for non-contact sensing even below the diffraction limit. Here we introduce an optical encoding technique, dubbed “linear photonic gears”, that enables ultra-sensitive measurements of a transverse displacement by mapping it into the polarization rotation of a laser beam. In ordinary ambient conditions, we measure the relative shift between two objects with a resolution of 400 pm. We argue that a resolution of 50 pm should be achievable with existing state-of-the-art technologies. Our single-optical-path scheme is intrinsically stable and it could be implemented as a compact sensor, using cost effective integrated optics. We anticipate it may have a strong impact on both research and industry
Calculating transition dipole moments of phosphorescent emitters for efficient organic light-emitting diodes
No full textThe out-coupling of light from an organic light-emitting diode, and thus its efficiency, strongly depends on the orientation of the transition dipole moment (TDM) of the emitting molecules with respect to the substrate surface. Despite the importance of this quantity, theoretical investigations of the direction of the TDM of phosphorescent emitters based on iridium(iii) complexes remain limited. One challenge is to find an appropriate level of theory able to accurately predict the direction of the TDM. Here, we report relativistic time-dependent density functional theory (TDDFT) calculations of the TDM, emission energies and lifetimes for both the ground-state (S0) and triplet (T1) excited-state geometries of fac-tris(2-phenylpyridyl)iridium(iii) (Ir(ppy)3), using the two-component zero-order regular approximation (ZORA) or including spin-orbit coupling (SOC) perturbatively using the simpler one-component (scalar) formulation. We show that the one- and two-component approaches give similar emission energies and overall radiative lifetimes for each individual geometry. Use of the S0 geometry leads to two of the excited triplet substates being degenerate, with the degeneracy lifted for the T1 geometry, with the latter matching experiment. Two-component calculations using the T1 geometry give results for the direction of the TDM more consistent with experiment than calculations using the S0 geometry. Finally, we show that adding a dielectric medium does not affect the direction of TDM significantly, but leads to better agreement with the experimentally measured radiative lifetime.Mohammad Babazadeh, Paul L. Burn and David M. Huan
Effetto del genotipo e del trattamento antipiralide sulla contaminazione da specie afferenti al clade Gibberella fujikuroi in mais coltivato in Lombardia
No full textFusarium ear rot (FER) of maize is caused by Fusarium species belonging to Gibberella fujikuroi species complex (GFC) well known as fumonisin (FUM) producers. European corn borer (ECB), the most common maize pest in northern Italy, favors the infection of maize by GFC strains. Since ECB control is not completely effective in lowering fumonisin contamination, additional preventive means, such as increased maize resistance, are required in order to assure a more effective protection. Flavonoids in maize pericarp seem to be able to reduce the fumonisin accumulation. The goal of this study was to assess the effect of flavonoids associated with insecticides on ECB and FER rating under field conditions in Lombardy. Two maize hybrids were sown in 2011 and 2012, one hybrid characterized by the presence of flavonoids in pericarp and the other without pigmentation. The ECB damage incidence, frequency and severity of FER, together with the incidence of GFC strains and FUM in kernels, were assessed in each genotype. In 2012, the ECB control associated with flavonoids presence reduced all the measured parameters except FUM contamination. FUM contamination seemed to be more influenced by the local GFC population and the environment rather than pesticides and pericarp pigmentation
Growth, photosynthesis and production of safflower (Carthamus tinctorius L.) in response to different levels of salinity and drought
No full textIn order to investigate the effects of salinity and drought stress on the photosynthesis, growth and production responses of safflower, two experiments were performed in Isfahan, Iran using four different levels of saline water, four different levels of irrigation water, and their combinations which were applied at three different growth stages (stem elongation, heading, and flowering) in 2016 and 2017. A split-plot experiment based on complete block design was performed with three replicates. The plant height, leaf area index, relative water content, number of heads per plant, number of seeds per head, 1000-seeds weight, seed yield, oil content, net photosynthetic rate, stomatal conductance and transpiration rate decrease under salinity, drought, and simultaneous stresses. The reduction in seed yield caused by the 10 dS m-1 and 40% of irrigation treatment was higher at the heading stage (92.6%) when compared with the stem elongation (71.04%) and flowering (89.9%) stages. In general, the reduction in seed yield caused by salinity-drought stress was higher at the heading stage as compared with stem elongation and the flowering stages.Full Tex
Colorimetric detection of chromium(VI) ions in water using unfolded-fullerene carbon nanoparticles
No full textWater pollution caused by hexavalent chromium (Cr(VI)) ions represents a serious hazard for human health due to the high systemic toxicity and carcinogenic nature of this metal species. The optical sensing of Cr(VI) through specifically engineered nanomaterials has recently emerged as a versatile strategy for the application to easy-to-use and cheap monitoring devices. In this study, a one-pot oxidative method was developed for the cage opening of C60 fullerene and the synthesis of stable suspensions of N-doped carbon dots in water–THF solutions (N-CDs-W-THF). The N-CDs-W-THF selectively showed variations of optical absorbance in the presence of Cr(VI) ions in water through the arising of a distinct absorption band peaking at 550 nm, i.e., in the transparency region of pristine material. Absorbance increased linearly, with the ion concentration in the range 1–100 μM, thus enabling visual and ratiometric determination with a limit of detection (LOD) of 300 nM. Selectivity and possible interference effects were tested over the 11 other most common heavy metal ions. The sensing process occurred without the need for any other reactant or treatment at neutral pH and within 1 min after the addition of chromium ions, both in deionized and in real water sam-ples
A WEAP-MODFLOW surface water-groundwater model for the irrigated Miyandoab plain, Urmia lake basin, Iran: Multi-objective calibration and quantification of historical drought impacts
No full textThis study develops and applies the first coupled surface water-groundwater (SW-GW) flow model for the irrigated Miyandoab plain located in the Urmia basin, in the northwest of Iran. The model is implemented using a dynamic coupling between MODFLOW and WEAP and consists of spatially distributed monthly water balances for the aquifer, root-zone, rivers, canals, and reservoirs. Multi-objective calibration of the model using river discharge and GW level data yields accurate simulation of historical conditions, and results in better constrained parameters compared to using either data source alone. Model simulations show that crop water demand cannot be met during droughts due to limited GW pumping capacity, and that increased GW pumping has a relatively strong impact on GW levels due to the small specific yield of the aquifer. The SW-GW model provides a unique tool for exploring management options that sustain agricultural production and downstream flow to the shrinking Urmia Lake.Accepted author manuscriptWater Resource
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