Allelochemical regulation of reproduction and seed germination of two BrazilianBaccharis species by phytotoxic trichothecenes

The potent phytotoxic trichothecene roridins and baccharinoids occur naturally in the Brazilian plants,Baccharis coridifolia andB. megapotamica. Biosynthesis of roridins inB. coridifolia appears to be linked to pollination, and the phytotoxins then accumulate in the seed. The roles of the phytotoxins in pollination, seed maturation, and germination of theBaccharis species were investigated. The high production of roridins occurred only in seeds resulting from intraspecific pollination, and the concentration of the toxins in the seeds generally increased with seed maturity. Removal of seed coats from trichothecene-producing BrazilianBaccharis species (B. coridifolia andB. megapotamica) and non-trichothecene-producing AmericanBaccharis species (B. halimifolia andB. glutinosa) resulted in improved seed germination ofB. halimifolia andB. glutinosa but complete inhibition of seed germination ofB. coridifolia andB. megapotamica. Addition of seed coat extracts of the BrazilianBaccharis species of dilute solutions (10^–6g/ml) of roridins or baccharinoids to the decoated seeds ofB. coridifolia andB. megapotamica resulted in germination, while seeds ofB. halimifolia andB. glutinosa were killed by the phytotoxins. Roridins interacted with gibberellic acid, a germination promoter, but not with abscisic acid, a germination inhibitor. The results from this study suggest that macrocyclic trichothecenes have a regulatory role(s) on reproduction and germination of BrazilianBaccharis species in their natural habitat.     

Unconventional Molecular Weight Dependence of Charge Transport in the High Mobility n‐type Semiconducting Polymer P(NDI2OD‐T2)

The charge transport and microstructural properties of five different molecular weight (MW) batches of the naphthalenediimide‐thiophene copolymer P(NDI2OD‐T2) are investigated. In particular, the field‐effect transistor (FET) performance and thin‐film microstructure of samples with MW varying from M_n = 10 to 41 kDa are studied. Unlike conventional semiconducting polymers such as poly(3‐hexylthiophene) where FET mobility dramatically drops with decreasing molecular weight, the FET mobility of P(NDI2OD‐T2)‐based transistors processed from 1,2‐dichlorobenzene is found to increase with decreasing MW. Using a combination of grazing‐incidence wide‐angle X‐ray scattering, near‐edge X‐ray absorption fine‐structure spectroscopy, atomic force microscopy, and resonant soft X‐ray scattering, the increase in FET mobility with decreasing MW is attributed to the pronounced increase in the orientational correlation length (OCL) with decreasing MW. In particular, the OCL is observed to systematically increase from <100 nm for the highest MW samples to ≈1 µm for the lowest MW samples. The improvement in OCL and hence mobility for low MW samples is attributed to the lack of aggregation of low MW chains in solution promoting backbone ordering, with the pre‐aggregation of chains in 1,2‐dichlorobenzene found to suppress longer‐range liquid crystalline order.     

Sliding mode controller design for frequency regulation in an interconnected power system

In this paper, a Sliding mode controller design method for frequency regulation in an interconnected power system is presented. A sliding surface having four parameters has been selected for the load frequency control (LFC) system model. In order to achieve an optimal result, the parameter of the controller is obtained by grey wolf optimization (GWO) and particle swarm optimization (PSO) techniques. The objective function for optimization has been considered as the integral of square of error of deviation in frequency and tie-line power exchange. The method has been validated through simulation of a single area as well as a multi-area power system. The performance of the Sliding mode controller has also been analyzed for parametric variation and random loading patterns. The performance of the proposed method is better than recently reported methods. The performance of the proposed Sliding mode controller via GWO has 88.91% improvement in peak value of frequency deviation over the method of Anwar and Pan in case study 1 and similar improvement has been observed over different case studies taken from the literature.     

Classical and Bayesian inference on progressive‐stress accelerated life testing for the extension of the exponential distribution under progressive type‐II censoring

In this paper, a progressive‐stress accelerated life test under progressive type‐II censoring is considered. The cumulative exposure model is assumed when the lifetime of test units follows an extension of the exponential distribution. The maximum likelihood and Bayes estimates of the model parameters are obtained. The approximate and credible confidence intervals of the estimators are derived. Furthermore, a real lifetime data set is analyzed to illustrate the proposed procedures. Finally, the simulation studies are used to compare between 2 different designs of the progressive‐stress test (simple and multiple ramp‐stress tests).     

Use of X-ray diffraction in assessing the aging pattern of asphalt fractions

The X-ray diffraction (XRD) method was employed to investigate and compare some of the crystallite parameters and aromaticity of asphaltenes obtained from fresh and aged Arabian asphalts, procured from Ras Tanura (RT) and Kuwait (KW) refineries. A few crystallite parameters in the polar aromatics, naphthene aromatics and saturate fractions of these Arabian asphalts were also determined. The results obtained by XRD method for both the types of asphaltenes and other fractions were evaluated and compared. Significant differences were observed between the structure and the aging patterns of fresh and aged asphaltenes of RT and KW asphalt. The results indicate that the source and chemistry of asphalt are responsible for the aging behavior of its components. The rolling thin-film oven and the pressurized aging vessel tests were used to simulate asphalt aging in this research.     

A frequency domain design of PID controller for an AVR system

We propose a new proportional-integral-derivative （PID） controller design method for an automatic voltage regula- tion （AVR） system based on approximate model matching in the frequency domain. The parameters of the PID controller are obtained by approximate frequency response matching between the closed-loop control system and a reference model with the desired specifications. Two low frequency points are required for matching the frequency response, and the design method yields linear algebraic equations, solution of which gives the controller parameters. The effectiveness of the proposed method is demonstrated through examples taken from the literature and comparison with some popular methods.     

Preparation of poly(lactic acid) fiber by dry‐jet‐wet‐spinning. I. Influence of draw ratio on fiber properties

Poly(lactic acid) fiber was prepared by dry‐jet‐wet spinning of the polymer from chloroform solution and with methanol as the precipitating medium. The as‐spun fiber was subsequently made into high strength fiber by two‐step process of drawing at a temperature of 90°C and subsequent heat setting in the temperature range of 120°C. The draw ratio had significant influence on the crystallinity and the tensile strength of the fiber. The fiber with the tenacity of 0.6 GPa and modulus of 8.2 GPa was achieved at a draw ratio of 8. The differential scanning calorimetry revealed an increase in the glass‐transition temperature with the increase in the draw ratio, which suggests the orientation of chains during the drawing process. The surface morphology of the filament as revealed by scanning electron microscopy shows that fibers are porous in nature, but a significant reduction in the porosity and pore size of the fiber was observed with the increase in the draw ratio. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1239–1246, 2006     

Characterization of polyurethane foams prepared from liquefied sawdust by crude glycerol and polyethylene glycol

The aim of this study was to investigate polyurethane foams (PUF) properties obtained from crude glycerol (CG) and polyethylene glycol (PEG) based liquefaction of sawdust. The four types of foam were prepared by producing polyols from different weight loadings of PEG to CG as the liquefaction solvent. The produced polyurethane foams showed densities from 0.042 to 0.08 g/cm³ and compressive strengths from 200 to 311 kPa. The foams obtained from CG/PEG based liquefaction, had more uniform and regular cell structure than foams derived from liquefaction by CG. Also with the increasing percentage of PEG to CG in liquefaction, closed cell content of the synthesized foams increased and the size of cells decreased. The thermal conductivity of the produced foams was between 0.031 and 0.040 W/m K. Foams produced from liquefaction by binary solvent had lower thermal conductivity. However all foams showed approximately similar thermal degradation curves; maximum thermal decomposition temperature was seen for the foam produced from higher weight ratio of PEG to CG in liquefaction. PU foams produced from PEG/CG based liquefaction process had improved properties over from foams derived from sawdust liquefaction by CG.     

Development of membranes by radiation grafting of acrylamide into polyethylene films: Influence of synthesis conditions

SYNOPSIS: The graft copolymerization of acrylamide monomer into polyethylene films was carried out by the preirradiation method. The influence of synthesis conditions, such as monomer concentration, preirradiation dose, reaction temperature, Mohr's salt, and pregrafting storage was investigated. The order of dependence of the rate of grafting on preirradiation dose and monomer concentration was found to be 0.87 and 1.86, respectively. An activation energy of 22.9 kJ/mol for the grafting reaction was obtained. The storage of preirradiated polyethylene film at −4°C prior to the reaction showed a decrease in the degree of grafting up to 10 days, beyond which the degree of grafting remained constant. The addition of FeSO₄ in the grafting medium not only inhibits the homopolymerization of the monomer but also decreases the degree of grafting. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1331–1337, 2000