This paper deals with the power generation control in variable-speed wind turbines. These systems have two operation regions which depend on wind turbine tip speed ratio. A high-order sliding-mode ...control strategy is then proposed to ensure stability in both operation regions and to impose the ideal feedback control solution in spite of model uncertainties. This control strategy presents attractive features such as robustness to parametric uncertainties of the turbine. The proposed sliding-mode control approach has been validated on a 1.5-MW three-blade wind turbine using the national renewable energy laboratory wind turbine simulator FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code. Validation results show that the proposed control strategy is effective in terms of power regulation. Moreover, the sliding-mode approach is arranged so as to produce no chattering in the generated torque that could lead to increased mechanical stress because of strong torque variations.
•Recyclable composite nanofiber Li+ adsorbents were developed.•H1.6Mn1.6O4 or HMO was used as adsorbent and poly(acrylonitrile) (PAN) as binder.•Highest Li+ adsorption attained at 60wt% HMO/PAN, only ...<4% lower than the HMO.•Minimal deterioration in adsorption performance of composite even after ten cycles.•Adsorption was highly selective towards Li+ as compared to other cations in seawater.
Composite poly(acrylonitrile) (PAN) nanofibers with H1.6Mn1.6O4 (HMO) lithium ion-sieves were prepared, characterized and tested for lithium ion (Li+) recovery. Nanofibers were prepared by electrospinning 10wt% HMO/PAN dope solutions in dimethylformamide with varied HMO loadings. Characterizations performed via XRD, SEM-EDS, capillary flow porometry and mechanical testing revealed highly porous, mechanically and chemically stable composite nanofibers with high water absorption capacity. The similar nanofiber diameters (<300nm) and HMO particle sizes (<100nm) rendered PAN as a binder to have minimal hindrance to the HMOs. Exposure of HMOs on the fiber surface provided good accessibility to the Li+ source, as indicated by the minimal loss of Li+ adsorption capacity of HMOs in PAN as compared to the support-free powdered HMO. All tested adsorbents followed Langmuir-type Li+ adsorption (qm). Increased HMO loadings resulted in improved adsorption performance as more HMOs were exposed on fiber surface and became less affected by the binder; the highest qm=10.3mg/g obtained from 60wt% HMO/PAN was only 4% lower than the support-free HMO. Adsorption loss after ten reuses was minor (<4%), which suggests the long-term stability of HMO/PAN. In seawater desalination retentate, HMO/PAN (60wt%) preferentially adsorbed Li+ over other cations, achieving 99–5312 Li+ separation factors and high Li+ distribution coefficient (KD=770). Li+ was concentrated up to 486 times while interfering cations were enriched only up to <7 times. Overall results demonstrate the potential use and recyclability of the developed HMO/PAN composite nanofiber for Li+ recovery from seawater or other prospective sources.
This paper addresses the problem of controlling power generation in variable-speed wind energy conversion systems (VS-WECS). These systems have two operation regions depending on the wind turbine ...tip-speed ratio. They are distinguished by minimum phase behavior in one of these regions and a nonminimum phase in the other one. A sliding mode control strategy is then proposed to ensure stability in both operation regions and to impose the ideal feedback control solution despite model uncertainties. The proposed sliding mode control strategy presents attractive features such as robustness to parametric uncertainties of the turbine and the generator as well as to electric grid disturbances. The proposed sliding mode control approach has been simulated on a 1.5-MW three-blade wind turbine to evaluate its consistency and performance. The next step was the validation using the National Renewable Energy Laboratory (NREL) wind turbine simulator called the fatigue, aerodynamics, structures, and turbulence code (FAST). Both simulation and validation results show that the proposed control strategy is effective in terms of power regulation. Moreover, the sliding mode approach is arranged so as to produce no chattering in the generated torque that could lead to increased mechanical stress because of strong torque variations.
Electrospun nanofibers of polybenzoxazines (PBzs) were fabricated using an electrospinning process and crosslinked by a sequential thermal treatment. Functionalization by the direct sulfonation ...process followed after the post-electrospinning modification treatment. The first stage of experiment determined the effects of varying the concentration of sulfuric acid as the sulfonating agent in the sulfonation reaction under ordinary conditions. The second stage examined the mechanism and kinetics of the sulfonation reaction using only concentrated H
2
SO
4
at different reaction time periods of 3 h, 6 h, and 24 h. The mechanism of the sulfonation reaction with PBz nanofibers was proposed with only one sulfonic acid (-SO
3
H) group attached to each of the repeating units since only first type substitution in the aromatic structure occurs under this condition. The kinetics of the reaction exhibited a logarithmic correlation where the rate of change in the ion exchange capacity (IEC) with the reaction time increased rapidly and then reached a plateau at the reaction time between 18 h and 24 h. Effective sulfonation was confirmed by electron spectroscopy with a characteristic peak associated with the C-S bond owing to the sulfonate group introduced onto the surface of the nanofibers. ATR-FTIR spectroscopy also confirmed these results for varying reaction times. The SEM images showed that sulfonation has no drastic effects on the morphology and microstructure of the nanofibers but a rougher surface was evident due to the wetted fibers with sulfonate groups attached to the surface. EDX spectra exhibited sulfur peaks where the concentration of sulfonate groups present in the nanofibers is directly proportional to the reaction time. From surface wettability studies, it was found that the nanofibers retained the hydrophobicity after sulfonation but the inherent surface property of PBz nanofibers was observed by changing the pH level of water to basic, which switches its surface properties to hydrophilic. The thermal stability of the sulfonated nanofibers showed almost the same behavior compared to non-sulfonated nanofibers except for the 24 h sulfonation case, which has slightly lower onset temperature of degradation.
Functionalization of PBz by electrospinning of nanofibers then thermal crosslinking followed by direct sulfonation process.
Hyptis colombiana (Lamiaceae family), a species also treated as Cantinoa colombiana in a recently segregated genus from Hyptis, is a perennial herb or subshrub native to the Andes of northern South ...America. H. colombiana leaves are commonly used in traditional medicine to treat respiratory and digestive illnesses. In this study, H. colombiana plants at different phenological stages (vegetative, flowering, and post-flowering) were harvested to obtain essential oils (EOs) and extracts (from fresh plant materials or post-distillation waste) whose chemical compositions and antioxidant activities were determined. H. colombiana EOs distilled by microwave-assisted hydrodistillation were analyzed by GC/MS/FID, and hydroalcoholic extracts obtained from fresh plant materials or post-distillation waste were analyzed by UHPLC-ESI+/−-Orbitrap-MS. The antioxidant activity was evaluated by the ABTS+• and ORAC assays. The principal compounds found in EOs were sesquiterpene hydrocarbons (65%); specifically, (E)-β-caryophyllene and germacrene D. Pyranone, rosmarinic acid, rutin, and p-hydroxybenzoic acid were the main constituents in H. colombiana extracts. After analyzing the chemical composition and antioxidant activity (ORAC) of EOs and hydroethanolic extracts from flowering H. colombiana plants, minimal variations were found. It is advisable to harvest H. colombiana plants during their flowering stage to acquire EOs and extracts that can be utilized in the agro-industry of EOs and their natural derivatives.
The safety of thiopurines and anti-tumor necrosis factor-α (TNF-α) drugs during pregnancy remains controversial, as the experience with these drugs in this situation is limited. Our aim is to assess ...the safety of thiopurines and anti-TNF-α drugs for the treatment of inflammatory bowel disease (IBD) during pregnancy.
Retrospective, multicenter study in IBD patients. Pregnancies were classified according to the therapeutic regimens during pregnancy or during the 3 months before the conception: non-exposed group, pregnancies exposed to thiopurines alone (group A), and pregnancies exposed to anti-TNF-α drugs (group B). An unfavorable Global Pregnancy Outcome (GPO) was considered if pregnancy developed with obstetric complications in the mother and in the newborn.
A total of 187 pregnancies in the group A, 66 pregnancies in the group B, and 318 pregnancies in the non-exposed group were included. The rate of unfavorable GPO was different among the three groups (31.8% in non-exposed group, 21.9% in group A, and 34.8% in group B), being lower in pregnancies under thiopurines than among non-exposed (P = 0.01). The rate of pregnancy complications was similar among the three groups (27.7% in non-exposed, 20.9% in group A, and 30.3% in group B). The rate of neonatal complications was different among the three groups (23.3% in non-exposed group, 13.9% in group A, and 21.2% in group B), being lower in pregnancies under thiopurines than among non-exposed (P = 0.01). In the multivariate analysis, the treatment with thiopurines (odds ratio = 0.6; 95% confidence interval = 0.4-0.9, P = 0.02) was the only predictor of favorable GPO, whereas maternal age >35 years at conception was the only predictor of unfavorable GPO. The treatment with anti-TNF-α drugs was not associated with an unfavorable GPO.
The treatment with thiopurines and anti-TNF-α drugs does not seem to increase the risk of complications during pregnancy and does seem to be safe for the newborn.
The study aimed to investigate physiological and psychological states prior to competition and prior to training in three different demanding activities. Eighteen canoe athletes, 18 street runners ...and 18 jiu-jitsu fighters were included in this study (n=54). The Competitive State Anxiety Inventory-2 (CSAI-2), salivary cortisol and heart rate variability (HRV) were measured at two time points (pre-training and pre-competition). Somatic anxiety (F
= 15.29, p = 0.0003), HRV (F
= 23.24, p < 0.0001) and salivary cortisol (F
= 22.96, p < 0.0001) were significantly greater at the pre-competition measurement point than at the pre-training point, but without a main effect of the type of athlete on these variables. A main effect of the type of athlete was found on somatic anxiety (F
= 6.58, p = 0.0033), cognitive anxiety (F
= 10.69, p = 0.0002) and self-confidence (F
= 5.42, p = 0.0080). Correlations between most CSAI-2 and physiological parameters were not significant (p > 0.05). In conclusion, the results indicated that both emotional indices and psychophysiological indices of stress are higher before competition than before training, with differences between emotional states between these sports. Although correlations between emotional states and psycho-physiological states before competition and before training were largely non-significant, these findings reinforce the importance of psychological monitoring of athletes in association with traditional physiological markers such as cortisol and HRV in sportive training programmes as complementary resources to improve both competition performance and the training routine.
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•Methodology based on Eurocodes and analysis of discontinuous MEF model is presented.•Eurocodes reliability criterion and classical limit analysis approach are combined.•Methodology ...allows checking all the ultimate limit states in any design situation.•Ultimate limit states of SEQ, with sliding between blocks, STR and SBC are analyzed.•Collapse progress can be predicted in case that the structure loses the stability.
This work proposes a methodology, based on finite element simulation, for analyzing masonry historical structures, according to Eurocodes, that has been applied for the assessment of the Saint Sebastian church, located in Piedratajada (Zaragoza, Spain). Settlement pathologies were detected and the aim of the work is to verify the current safety level and to propose reinforcement solutions if necessary. Results confirm the effect of soil settlement and allow establish the maximum admissible value. If that value is reached, a couple of reinforcement solutions, installing sheets of steel or carbon fiber composite, are proposed and analyzed.
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