Variability in Flavonoid Compounds of Four Tribulus Species: Does it Play a Role in Their Identification by Desert Locust Schistocerca gregaria?

We examined how variability in phenolic metabolism of four closely related Tribulus taxa might affect palatability to Schistocerca gregaria. Plants were collected in the Mauritanian breeding areas of the locust. Eighteen flavonoids (caffeoyl derivatives, quercetin glycosides, including rutin, and kaempferol glycosides) were detected with high-performance liquid chromatography in leaf extracts. Principal component analysis (PCA) differentiated relative abundance of flavonoids of Tribulus terrestris from T. longipetalus, T. ochroleucus, and T. bimucronatus. Flavonoid content of T. terrestris leaves varied between northern and southern Mauritanian sites. Dual choice tests with plants whose flavonoid profiles had been determined previously were analyzed by multiple regression. The data suggest that the desert locust prefers T. terrestris plants rich in quercetin glycosides.     

Sol–Gel Combustion Synthesis of Nanocrystalline YAG Powder from Metal-Organic Precursors

Yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) nanocrystalline powders were synthesized by a novel sol–gel combustion process. Yttrium acetate and aluminum sec-butoxide were used as the precursors and triethanolamine was used as the chelating agent and fuel. Thermal and crystallization behaviors of the YAG precursor powders were investigated by thermal gravimetric differential thermal analysis (DTA), Fourier transform infrared spectrum, and X-ray diffraction. The combustion-synthesized powders are amorphous and transform to a pure YAG crystalline phase at 900°C. The crystallization activation energy of amorphous YAG precursor was investigated by variable heating rate DTA. The calculated activation energy is 58.9 KJ/mol. The average crystalline size of heat-treated YAG powders at 900°C is ∼20 nm.     

First-principles modeling of lattice defects: advancing our insight into the structure-properties relationship of ice

We discuss a number of examples that demonstrate the value of computational modeling as a complementary approach in the physics and chemistry of ice I _h , where real-life experiments often do not give direct access to the desired information or whose interpretation typically requires uncontrollable assumptions. Specifically, we discuss two cases in which, guided by experimental insight, density-functional-theory-based first-principles methods are applied to study the properties of lattice defects and their relationship to ice I _h s macroscopic behavior. First, we address a question involving molecular point defects, examining the energetics of formation of the molecular vacancy and a number of different molecular interstitial configurations. The results indicate that, as suggested by earlier experiments, a configuration involving bonding to the surrounding hydrogen-bond network is the preferred interstitial structure in ice I _h . The second example involves the application of modeling to elucidate on the microscopic origin of the experimental observation that a specific type of ice defect is effectively immobile while others are not. Inspired by previous suggestions that this defect type may be held trapped at other defect sites and our finding that the bound configuration is the preferred interstitial configuration in ice I _h , we use first-principles modeling to examine the binding energetics of the specific ice defect to the molecular vacancy and interstitial. The results suggest a preferential binding of the immobile defect to the molecular interstitial, possibly explaining its experimentally observed inactivity.     

CALCULATION OF DENSITY AND OPTICAL CONSTANTS OF A GLASS FROM ITS COMPOSITION IN WEIGHT PERCENTAGE*

Relationships previously deduced and tested by the authors for the calculation of the density, refractive index, and. dispersion of a glass from its composition, expressed in terms of the “atomic fractions” of the components, are transformed into equivalent equations for the calculation of these quantities from the weight percentages or weight fractions. The necessary constants for use with these equations are tabulated.     

Analytical comparison of nine PCR primer sets designed to detect the presence of Escherichia coli/Shigella in water samples

The analytical performance of 9 different PCR primer sets designed to detect Escherichia coli and Shigella in water has been evaluated in terms of ubiquity, specificity, and analytical detection limit. Of the 9 PCR primer sets tested, only 3 of the 5 primer sets targeting uidA gene and the primer set targeting tuf gene amplified DNA from all E. coli strains tested. However, of those 4 primer sets, only the primer set targeting the tuf gene also amplified DNA from all Shigella strains tested. For the specificity, only the primer sets targeting the uidA gene were 100% specific although the primer sets targeting 16S rRNA, phoE, and tuf genes only amplified Escherichia fergusonii as non-specific target. Finally, the primer set targeting the 16S-ITS-23S gene region, was not specific as it amplified DNA from many other Enterobacteriaceae species. In summary, only the assay targeting the tuf gene detected all E. coli/Shigella strains tested in this study. However, if it becomes important to discriminate between E. coli and E. fergusonii, assays targeting the uidA gene would represent a good choice although none of them were totally ubiquitous to detect of the presence of Shigella strains.     

Effect of Platinum on the Growth Rate of the Oxide Scale Formed on Cast Nickel Aluminide Intermetallic Alloys

Thermo-Gravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM) data of the initial stages of oxidation of Ni₅₀Al₅₀ and Ni₄₀Pt₁₀Al₅₀ alloys of low and high sulfur content at 900°C and 1100°C are reported. The results show that the addition of Pt promotes the growth of the transient θ-Al₂O₃ oxide scale. This effect is particularly sensitive in the initial stages of oxidation at 1100°C where Pt considerably increases the total mass gain. It is attenuated in the presence of a high sulfur content in the alloy, indicating a competitive effect of Pt and S on the segregation of Al. The slower θ-to-α transition observed in the presence of Pt leads to an extended lifetime of the θ phase layer, which is proposed to be beneficial to the relaxation of the stresses created by the growth of α-Al₂O₃.     

Dense TiO2 Coating Using the Solution Precursor Plasma Spray Process

A dense titania (TiO₂) coating was deposited from an ethanol solution containing titanium isopropoxide using the solution precursor plasma spray process. Thermal and crystallization behaviors of the solution precursor were investigated by thermal gravimetric analysis–differential thermal analysis, Fourier-transform infrared spectrum, and X-ray diffraction (XRD). XRD and Raman spectrum analyses confirmed that the coating is exclusively composed of rutile TiO₂. Scanning electron micrographs show the as-sprayed coating is dense with uniform thickness and there are no coarse splat boundaries. The individual ultrafine splats (1–5 μm diameter) are composed of columnar grains. X-ray photoelectron spectroscopy analysis indicates that some Ti–OH groups exist in the as-sprayed coating surface. Deposition mechanisms are described based on model experiments.     

Methods for designing efficient parallel‐recursive filter structures for computing discrete transforms

Analytical and numerical approaches are presented for the design of first‐order and second‐order recursive digital filter banks for computing linear, discrete transforms. This subject has been studied extensively for the case of trigonometric transforms. The focus of this paper is on discrete polynomial transforms, and Clenshaw's recurrence formulae are used to design the second‐order filters. The efficiency of the implementation for a specific transform is dependent upon the characteristics of recurrence relations for the transform basis vectors. Efficient implementations are derived for the discrete cosine transform and the inverse discrete Legendre transform from analytical expressions for basis vector recurrence relations. A numerical procedure is presented to search for the existence and parameters of an efficient implementation when analytical expressions for the basis vector recurrence relations are unknown. This revised version was published online in June 2006 with corrections to the Cover Date.     

Estimates for Polynomial Roots

Given a complex polynomial, we obtain lower bounds for the moduli of the roots outside the unit circle. Our main tool is the method of Dandelin–Graeffe, which can be used directly for polynomials with distinct absolute values of the roots. In the general case the arguments of the powers of the roots must be controlled, and we achieve this by two methods: a theorem of Dirichlet, and an argument using linear recurrent sequences. Received: July 11, 2000; revised version: August 6, 2001