Cooperative shear model for the rheology of glass-forming metallic liquids

A rheological law based on the concept of cooperatively sheared flow zones is presented, in which the effective thermodynamic state variable controlling flow is identified to be the isoconfigurational shear modulus of the liquid. The law captures Newtonian as well as non-Newtonian viscosity data for glass-forming metallic liquids over a broad range of fragility. Acoustic measurements on specimens deformed at a constant strain rate correlate well with the measured steady-state viscosities, hence verifying that viscosity has a unique functional relationship with the isoconfigurational shear modulus.     

Spatial averaging of oceanic rainfall variability using underwater sound: Ionian Sea rainfall experiment 2004

An experiment to evaluate the inherent spatial averaging of the underwater acoustic signal from rainfall was conducted in the winter of 2004 in the Ionian Sea southwest of Greece. A mooring with four passive aquatic listeners (PALs) at 60, 200, 1000, and 2000 m was deployed at 36.85 degrees N, 21.52 degrees E, 17 km west of a dual-polarization X-band coastal radar at Methoni, Greece. The acoustic signal is classified into wind, rain, shipping, and whale categories. It is similar at all depths and rainfall is detected at all depths. A signal that is consistent with the clicking of deep-diving beaked whales is present 2% of the time, although there was no visual confirmation of whale presence. Co-detection of rainfall with the radar verifies that the acoustic detection of rainfall is excellent. Once detection is made, the correlation between acoustic and radar rainfall rates is high. Spatial averaging of the radar rainfall rates in concentric circles over the mooring verifies the larger inherent spatial averaging of the rainfall signal with recording depth. For the PAL at 2000 m, the maximum correlation was at 3-4 km, suggesting a listening area for the acoustic rainfall measurement of roughly 30-50 km(2).     

Non-axisymmetric modes in viscoelastic taylor-couette flow

In this work, the linear stability analysis of the viscoelastic Taylor-Couette flow against non-axisymmetric disturbances is investigated. A pseudospectrally generated, generalized algebraic eigenvalue problem is constructed from the linearized set of the three-dimensional governing equations around the steady-state azimuthal solution. Numerical evaluation of the critical eigenvalues shows that for an upper-convected Maxwell model and for the specific set of geometric and kinematic parameters examined in this work, the azimuthal Couette (base) flow becomes unstable against non-axisymmetric time periodic disturbances before it does so for axisymmetric ones, provided the elasticity number ε (De/Re) is larger than some non-zero but small value (ε 0.01). In addition, as ε increases, different families of eigensolutions become responsible for the onset of instability. In particular, the azimuthal wavenumber of the critical eigensolution has been found to change from 1 to 2 to 3 and then back to 2 as ε increases from 0.01 to infinity (inertialess flow).In an analogous fashion to the axisymmetric viscoelastic Taylor-Couette flow, two possible patterns of time-dependent solutions (limit cycles) can emerge after the onset of instability: ribbons and spirals, corresponding to azimuthal and traveling waves, respectively. These patterns are dictated solely by the symmetry of the primary flow and have already been observed in conjunction with experiments involving Newtonian fluids but with the two cylinders counter-rotatng instead of co-rotating as considered here. Inclusion of a non-zero solvent viscosity (Oldroyd-B model) has been found to affect the results quantitatively but not qualitatively. These theoretical predictions are of particular importance for the interpretation of the experimental data obtained in a Taylor-Couette flow using highly elastic viscoelastic fluids.     

Anelastic to plastic transition in metallic glass-forming liquids

The configurational properties associated with the transition from anelasticity to plasticity in a transiently deforming metallic glass-forming liquid are studied. The data reveal that the underlying transition kinetics for flow can be separated into reversible and irreversible configurational hopping across the liquid energy landscape, identified with beta and alpha relaxation processes, respectively. A critical stress characterizing the transition is recognized as an effective Eshelby "backstress," revealing a link between the apparent anelasticity and the "confinement stress" of the elastic matrix surrounding the plastic core of a shear transformation zone.     

Enhanced aqueous solubilization of tetrachloroethylene by a rhamnolipid biosurfactant

A rhamnolipid biosurfactant produced by Pseudomonas aeruginosa ATCC 9027 was isolated, purified and characterized in terms of its ability to mobilize and solubilize tetrachloroethylene (PCE) for potential use in surfactant-enhanced aquifer remediation (SEAR) applications. Using a drop volume method, the PCE-biosurfactant steady-state interfacial tension was determined and found to be ca. 10 mN/m which is not low enough to cause significant PCE nonaqueous phase liquid (NAPL) mobilization. It was observed that the biosurfactant partitioned significantly into PCE at aqueous concentrations higher than the critical micelle concentration (CMC). After accounting for rhamnolipid partitioning into the PCE phase, a weight solubilization ratio (WSR) of 1.2 g(PCE)/g(rhamnolipid) was determined and through this mechanism the biosurfactant significantly improved the apparent aqueous solubility of PCE.     

The Role of Titanium Dioxide on the Hydration of Portland Cement: A Combined NMR and Ultrasonic Study

Titanium dioxide (TiO₂) is an excellent photocatalytic material that imparts biocidal, self-cleaning and smog-abating functionalities when added to cement-based materials. The presence of TiO₂ influences the hydration process of cement and the development of its internal structure. In this article, the hydration process and development of a pore network of cement pastes containing different ratios of TiO₂ were studied using two noninvasive techniques (ultrasonic and NMR). Ultrasonic results show that the addition of TiO₂ enhances the mechanical properties of cement paste during early-age hydration, while an opposite behavior is observed at later hydration stages. Calorimetry and NMR spin–lattice relaxation time T₁ results indicated an enhancement of the early hydration reaction. Two pore size distributions were identified to evolve separately from each other during hydration: small gel pores exhibiting short T₁ values and large capillary pores with long T₁ values. During early hydration times, TiO₂ is shown to accelerate the formation of cement gel and reduce capillary porosity. At late hydration times, TiO₂ appears to hamper hydration, presumably by hindering the transfer of water molecules to access unhydrated cement grains. The percolation thresholds were calculated from both NMR and ultrasonic data with a good agreement between both results.     

Retention of structurally diverse drugs in human serum albumin chromatography and its potential to simulate plasma protein binding

The retention behavior of 39 structurally diverse neutral, basic and acidic drugs was investigated on an HSA stationary phase using PBS buffer (pH 7.0) and acetonitrile or 2-propanol as organic modifiers. Extrapolated or directly measured log k_w values as well as isocratic retention factors were correlated with plasma protein binding data taken from the literature. Retention factors determined in the presence of 10% acetonitrile led to high quality 1:1 correlation with apparent log K_HSA values. The derived reference equation was successfully validated using a secondary set of 24 drugs. Further analysis of HSA retention into more fundamental properties revealed the involvement of anionic species in solute-stationary phase interactions, expressed by the negatively charged fraction, besides the partitioning mechanism which was reflected by lipophilicity. Protonation of basic drugs, although less important, may also influence retention, leading to reduced partitioning into the HSA surface as a net effect, while it seems to have no effect on HSA binding. The above results were further confirmed by linear solvation energy relationships (LSER).     

Cross-linguistic studies of children's and adults' vowel spaces

This study examines cross-linguistic variation in the location of shared vowels in the vowel space across five languages (Cantonese, American English, Greek, Japanese, and Korean) and three age groups (2-year-olds, 5-year-olds, and adults). The vowels /a/, /i/, and /u/ were elicited in familiar words using a word repetition task. The productions of target words were recorded and transcribed by native speakers of each language. For correctly produced vowels, first and second formant frequencies were measured. In order to remove the effect of vocal tract size on these measurements, a normalization approach that calculates distance and angular displacement from the speaker centroid was adopted. Language-specific differences in the location of shared vowels in the formant values as well as the shape of the vowel spaces were observed for both adults and children.     

Effects of temperature,pH, and ionic strength on the adsorption of nanoparticles at liquid–liquid interfaces

The effects of temperature, pH and sodium chloride (NaCl) concentration on the equilibrium and dynamic interfacial tension (IFT) of 4.4-nm gold nanoparticles capped with n-dodecanethiol at hydrocarbon–water interfaces was studied. The pendant drop technique was used to study the adsorption properties of these nanoparticles at the hexane–water and nonane–water interfaces. The physical size of the gold nanoparticles was determined by TEM image analysis. The interfacial properties of mixtures of these nanoparticles, having different sizes and capping agents, were then studied. The addition of NaCl was found to cause a decrease of the equilibrium and dynamic IFT greater than that which accompanies the adsorption of nanoparticles at the interface in the absence of NaCl. Although IFT values for acidic and neutral conditions were found to be similar, a noticeable decrease in the IFT was found for more basic conditions. Increasing the temperature of the system was found to cause an increase in both dynamic and equilibrium IFT values. These findings have implications for the self-assembly of functionalized gold nanoparticles at liquid–liquid interfaces.     

Sesquiterpenes from Chrysoma Pauciflosculosa

Abstract

The aerial parts of Chrysoma pauciflosculosa (syn. Solidago pauciflosculosa) gave two new sesquiterpenes, (+)-β-turmerone and a bisabolane endoperoxide, together with the known (-)-α-trans-bergamotene and (+)-β-sesquiphellandrene. When exposed to air and light, (+)-β-turmerone and (+)-β-sesquiphellandrene gave oxidative degradation products, involving hydroperoxide intermediates. Photosensitized singlet oxygen reactions of (+)-β-turmerone provided a series of bisabolane-type endoperoxides. The structures of the natural compounds as well as those of the degradation products and derivatives were elucidated by chemical and spectroscopic methods, mainly NMR and MS. Aqueous solutions of (+)-β-turmerone,(+)-β-sesquiphellandrene and (-)-α-trans-bergamotene were tested for their effects on the germination and radicle growth of three Florida sandhill species, Rudbeckia hirta, Schizachyrium scoparium, Leptochloa dubia, as well as Lactuca sativa. (+)-β-Turmerone significantly inhibited germination of L. sativa, stimulated radicle growth of L. sativa and S. scoparium at the 10^?4 M level, and mildly inhibited radicle growth of R. hirta, as did (+)-β-sesquiphellandrene. (-)-α-trans-Bergamotene stimulated germination of S. scoparium and L. sativa and significantly enhanced radicle growth of S. scoparium.