Flux and rejection in the ultrafiltration of colloids

Charge on colloidal particles is shown to affect the filtration process in two ways. The effect of changing the charge of the particles, such as by varying pH, is to alter the observable flux which goes through a minimum as the charge is increased. At fixed charge the flux first decreases with particle size and then increases. Charge also influences the mechanism of particle rejection. If primary particles are stable colloids, smaller than the surface pores, they may penetrate the membrane but not necessarily pass all the way through. When particle charge is low enough for flocculation to be significant, rejection will most likely occur at the membrane surface as flocculation results in particles growing to become large enough to be rejected.     

Epoxy‐amine networks with varying epoxy polydispersity

Solid, high molecular weight DGEBA‐based epoxies were blended with high purity liquid DGEBA to create several resins with equivalent epoxy equivalent weights, but with polydispersity indices (PDIs) ranging from 3 to over 10. The resins were cured with a stoichiometric amount of polyetheramine and compared to a nonblended epoxy with PDI of 1.8. Modulus, glass transition temperatures, and molecular weight between cross‐links were measured using dynamic mechanical analysis. Coefficients of thermal expansion (CTE) were measured and used to extend room temperature density measurements as a function of temperature. Fracture properties were also measured. Overall, the increased polydispersity has almost negligible effect, with the main difference occurring in the slope of the glassy CTE, with more polydisperse epoxies having a slower increase in CTE. In comparison to previous work where bimodal amines were blended with DGEBA, we conclude that epoxy resins are far more sensitive to distributions in the flexible portion, rather than the more rigid one. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41503.     

Structure, cell wall elasticity and polysaccharide properties of living yeast cells, as probed by AFM

Although the chemical composition of yeast cell walls is known, the organization, assembly, and interactions of the various macromolecules remain poorly understood. Here, we used in situ atomic force microscopy (AFM) in three different modes to probe the ultrastructure, cell wall elasticity and polymer properties of two brewing yeast strains, i.e. Saccharomyces carlsbergensis and S. cerevisiae. Topographic images of the two strains revealed smooth and homogeneous cell surfaces, and the presence of circular bud scars on dividing cells. Nanomechanical measurements demonstrated that the cell wall elasticity of S. carlsbergensis is homogeneous. By contrast, the bud scar of S. cerevisiae was found to be stiffer than the cell wall, presumably due to the accumulation of chitin. Notably, single molecule force spectroscopy with lectin-modified tips revealed major differences in polysaccharide properties of the two strains. Polysaccharides were clearly more extended on S. cerevisiae, suggesting that not only oligosaccharides, but also polypeptide chains of the mannoproteins were stretched. Consistent with earlier cell surface analyses, these findings may explain the very different aggregation properties of the two organisms. This study demonstrates the power of using multiple complementary AFM modalities for probing the organization and interactions of the various macromolecules of microbial cell walls.     

Active site-directed inhibitors of Rhodococcus 20 S proteasome. Kinetics and mechanism

We have studied the mechanism of inhibition of the recombinant Rhodococcus proteasome by four different chemical classes of active site-directed small molecule inhibitors. Clasto-lactacystin beta-lactone is a time-dependent inhibitor of the Rhodococcus proteasome's ability to hydrolyze Suc-Leu-Leu-Val-Tyr-AMC, a substrate for this proteasome's single type of active site, and proceeds with a kinact/[I] of 1,700 M-1 s-1. Using peptide mapping of tryptic digests, LC/MS, and amino acid sequence analysis, we have established that the Ogamma of the hydroxyl group on the N-terminal threonine of the beta-subunit is the sole modification made by the beta-lactone. Active site titrations of the Rhodococcus proteasome with reversible peptide aldehydes show the expected stoichiometry of one inhibitor molecule per beta-subunit. Prior modification with beta-lactone completely abrogates the binding of peptidyl boronic acid inhibitors, suggesting that these inhibitors also inactivate the enzyme by reacting with the Ogamma moiety on Thr1. High performance liquid chromatography analysis of peptidyl vinyl sulfone-modified intact Rhodococcus proteasome beta-subunit and its tryptic peptides suggests that the peptidyl vinyl sulfone modifies a residue in the N-terminal 20 amino acids. This modification is also blocked by prior treatment with beta-lactone.     

A Spoken Dialogue System for Navigation in Non-Immersive Virtual Environments

Navigation is the process by which people control their movement in virtual environments and is a corefunctional requirement for all virtual environment (VE) applications. Users require the ability to move, controllingorientation, direction of movement and speed, in order to achieve a particular goal within a VE. Navigation israrely the end point in itself (which is typically interaction with the visual representations of data) but applicationsoften place a high demand on navigation skills, which in turn means that a high level of support for navigationis required from the application. On desktop systems navigation in non‐immersive systems is usually supportedthrough the usual hardware devices of mouse and keyboard. Previous work by the authors shows that many usersexperience frustration when trying to perform even simple navigation tasks — users complain about getting lost,becoming disorientated and finding the interface `difficult to use'. In this paper we report on work in progressin exploiting natural language processing (NLP) technology to support navigation in non‐immersive virtualenvironments. A multi‐modal system has been developed which supports a range of high‐level (spoken) navigationcommands and indications are that spoken dialogue interaction is an effective alternative to mouse and keyboardinteraction for many tasks. We conclude that multi‐modal interaction, combining technologies such as NLP withmouse and keyboard may offer the most effective interaction with VEs and identify a number of areas where furtherwork is necessary. ACM CSS: I.3.6 Computer Graphics Methodology and Techniques—Interaction and Techniques, I.3.7 Three‐DimensionalGraphics and Realism—Virtual Reality, I.2.7 Natural Language Processing—Speech Recognitionand Synthesis     

Interval Relations in Lexical Semantics of Verbs

Numerous temporal relations of verbal actions have been analysed in terms of various grammatical means of expressing verbal temporalisation such as tense, aspect, duration and iteration. Here the temporal relations within verb semantics, particularly ordered pairs of verb entailment, are studied using Allen's interval-based temporal formalism. Their application to the compositional visual definitions in our intelligent storytelling system, CONFUCIUS, is presented, including the representation of procedural events, achievement events and lexical causatives. In applying these methods we consider both language modalities and visual modalities since CONFUCIUS is a multimodal system.     

Effect of temperature on InGaAsP alloy composition

The influence of growth temperature on the composition of InGaAsP films grown by low pressure metalorganic vapor phase epitaxy (MOVPE) is reported for quaternary (Q) alloys having bandgap wavelengths of λ_g = 1.1, 1.3, and 1.5 μn. Films with these different Q-compositions were deposited lattice matched to InP at a growth temperature of 675°C. Subsequent growth experiments were then performed for each Q-composition in which the input gas flow rates were kept the same and only the temperature changed in 25°C decrements down to 600°C. Photoluminescence (PL) and lattice mismatch (LMM) measurements of the resulting films were used to determine the effect of growth temperature on film composition. The PL data indicate a temperature shift in the PL wavelength of −1.8 nm/ °C for the 1.5Q composition, −2.9 nm/°C for 1.3Q, and −4.3 nm/°C for 1.1Q. Negative shifts were also observed in LMM of −80 ppm/°C for 1.5Q, −150 ppm/°C for 1.3Q, and −250 ppm/°C for 1.1Q. The Ga/In and P/As ratios of the Q-filmswere measured by secondary ion mass spectroscopy and correlated with full-wafer maps of the PL wavelength and lattice mismatch to gain insight into the processes responsible for wafer nonuniformity in MOVPE.     

Very compact external cavity diffraction-coupled tapered laser diodes

To maintain the same beam quality as that of a single emitter and to be close to diffraction limit, we have combined a phase corrected array, emitting at lambda = 975 nm, coherently using the Talbot effect. First, to improve the beam quality of the array, a phase correcting system was added. The FWHM divergences of the array (which is approximately the same as that of the single emitter since the emitters within the array are not optically coupled to each other) were reduced from 34 degrees to 0.17 degrees in the fast axis and from 3.5 degrees to 0.7 degrees in the slow axis at 6 A. Then, to be close to the diffraction limit, we have combined this corrected array coherently using the Talbot effect. We have obtained a quasi-monolobe slow axis far field profile for the in-phase mode with a central peak divergence of only 0.27 degrees at 1.5 A, 315 mW under cw operation, and of only 0.20 degrees at 2.5 A, 787 mW under pulsed operation. To our knowledge, this is the first demonstration of coherent coupling of a corrected tapered laser diode array in an external Talbot cavity.     

Analytic three-dimensional response function of a double-shielded magnetoresistive or giant magnetoresistive perpendicular head

Using the Fourier method, we have derived a three-dimensional, fully analytic model of a shielded magnetoresistive or giant magnetoresistive head for perpendicular replay. The head may include side shields. The field and the spectral response function are expressed in closed form. Here, we use the model to show the effect of varying the sensor-shield spacings and the air-bearing-surface-underlayer separation on the field and response of the sensor at high areal density.