John O'Connell

Association behavior of β-casein

The association behavior of β-casein, a protein with a distinct amphipathic character, was studied. β-Casein exhibits markedly temperaturedependent association behavior; at low temperatures (< 10–15 ◦ C), monomers predominate, but as the temperature is increased, monomers associate, via hydrophobic bonding, into micelles. β-Casein micelles have a hydrodynamic radius of ∼12 nm, a radius of gyration of ∼8. 3n m, and an interaction radius of ∼15 nm. These data are fully consistent with a pervious fluffy particle. The association behavior of β-casein is also strongly affected by concentration and solvent quality. At low concentrations β-casein exhibits a critical micelle concentration (CMC) of approximately 0.05%, w/v, at 40 ◦ C. In the presence of 6 M urea the temperature dependence of β-casein’s association behavior is eliminated, leaving monomers predominantly. Temperature-dependent transformations in micelle morphology can be explained by changes in solvent quality, i.e., the temperature–protein hydrophobicity and temperature–voluminosity profiles of β-casein. The results obtained are consistent with the shell model as developed by Kegeles, in which a distribution of micelle sizes is formed. They contrast with the traditional description of the micellization of β-casein by a two-state model or by the closed-association model, i.e., monomers ⇔ micelles.

Sharing enriched multimedia experiences across heterogeneous network infrastructures

Todays consumers have a wide variety of interactive media and services at their disposal, for instance, through IPTV networks, the Internet, and in-home and mobile networks. A major problem, however, is that media and services do not interoperate across networks because they use different user identities, metadata formats, and signaling protocols, for example. As a result, users cannot easily combine media and services from different network infrastructures and share them in an integrated manner with their family and friends. In addition to limiting peoples media experience, this also hinders the introduction of new services and business models as providers cannot easily develop and operate cross-network services. The goal of our work is to overcome this problem by means of an open and intelligent service platform that allows applications to easily combine media and services from different network infrastructures, and enables consumers to easily share them in an integrated way. The platform includes support for managing multi-user sessions across networks, context-aware recommendations, and cross-network identity management. While there has been prior work on platforms for converged media, our platform is unique in that it provides open, intelligent, and interoperable facilities for sharing media and services across network infrastructures. In addition, our work involves several specific innovations, for instance, pertaining to cross-network session management and synchronization. In this article we discuss the platform, its most important enabling services, and some of the applications we have built on top of it. We also briefly consider the new kinds of business models our platform makes possible.

Effect of β-lactoglobulin and precipitation of calcium phosphate on the thermal coagulation of milk

The effect of beta-lactoglobulin and heat-induced precipitation of calcium phosphate on the pH dependence and mechanism of thermal coagulation of milk throughout the pH range 6.3-7.3 was studied using serum protein-free milk and sodium caseinate as models for micellar and non-micellar milk protein systems respectively. It appears that the specific effect of beta-lactoglobulin at the pH of maximum stability may be related to its ability to chelate calcium. The effect of beta-lactoglobulin at the pH of minimum stability does not appear to be directly related to heat-induced dissociation of K-casein or micellar integrity but may be due to its ability to sensitize casein micelles to heat-induced precipitation of calcium phosphate, by increasing micellar hydrophobicity. The extent of heat-induced precipitation of calcium phosphate, as a function of pH, is an inverse reflection of the pH dependence of heat stability. Micellar integrity appears to play a critical role in the heat stability of milk but for reasons not previously appreciated.

Effects of phenolic compounds on the heat stability of milk and concentrated milk

A methanol extract of green tea was fractionated on Sephadex LH-20. The compounds eluted were identified by thin layer chromatography as catechin–epicatechin, gallocatechin, epigallocatechin, epicatechin gallate and epigallocatechin gallate. When added to milk at 2·0 g/l, these polyphenols, apart from the catechin–epicatechin mixture, increased the heat stability of skim milk, particularly in the region of the minimum (pH 6·8–7·1). When added at 0·4 g/l, green tea polyphenols also increased the heat stability of concentrated milk. The effects of other phenolic compounds on the heat stability of milk were also examined. Chlorogenic acid, guaiacol, thymol, vanillin, butylene hydroxyanisole, propyl gallate and butylene hydroxytoluene did not affect the heat stability of milk or concentrated milk. Quinic acid markedly reduced the heat stability of skim milk. Pyrogallol, catechol, tannic acid, ellagic acid, phloroglucinol and gallate converted a type A heat coagulation time–pH profile to a type B profile. Ferulic acid and vanillic acid increased heat stability in the region of the maximum, with little effect on the minimum, and stability did not recover at pH values on the alkaline side of the minimum. Caffeic acid increased the heat stability of milk while the related non-phenolic compounds 2,5-dimethoxycinnamic acid and 3,4-dimethoxycinnamic acid had no effect.

Organo-arsenic Molecular Layers on Silicon for High-Density Doping

This article describes for the first time the controlled monolayer doping (MLD) of bulk and nanostructured crystalline silicon with As at concentrations approaching 2 × 10(20) atoms cm(-3). Characterization of doped structures after the MLD process confirmed that they remained defect- and damage-free, with no indication of increased roughness or a change in morphology. Electrical characterization of the doped substrates and nanowire test structures allowed determination of resistivity, sheet resistance, and active doping levels. Extremely high As-doped Si substrates and nanowire devices could be obtained and controlled using specific capping and annealing steps. Significantly, the As-doped nanowires exhibited resistances several orders of magnitude lower than the predoped materials.

An enhanced surface passivation effect in InGaN/GaN disk-in-nanowire light emitting diodes for mitigating Shockley–Read–Hall recombination

We present a detailed study of the effects of dangling bond passivation and the comparison of different sulfide passivation processes on the properties of InGaN/GaN quantum-disk (Qdisk)-in-nanowire based light emitting diodes (NW-LEDs). Our results demonstrated the first organic sulfide passivation process for nitride nanowires (NWs). The results from Raman spectroscopy, photoluminescence (PL) measurements, and X-ray photoelectron spectroscopy (XPS) showed that octadecylthiol (ODT) effectively passivated the surface states, and altered the surface dynamic charge, and thereby recovered the band-edge emission. The effectiveness of the process with passivation duration was also studied. Moreover, we also compared the electro-optical performance of NW-LEDs emitting at green wavelength before and after ODT passivation. We have shown that the Shockley-Read-Hall (SRH) non-radiative recombination of NW-LEDs can be greatly reduced after passivation by ODT, which led to a much faster increasing trend of quantum efficiency and higher peak efficiency. Our results highlighted the possibility of employing this technique to further design and produce high performance NW-LEDs and NW-lasers.

Optimizing vanadium pentoxide thin films and multilayers from dip-coated nanofluid precursors.

Using an alkoxide-based precursor, a strategy for producing highly uniform thin films and multilayers of V2O5 is demonstrated using dip coating. Defect-free and smooth films of V2O5 on different surfaces can be deposited from liquid precursors. We show how pinholes are formed due to heterogeneous nucleation during hydrolysis as the precursor forms a nanofluid. Using knowledge of instability formation often found in composite nanofluid films and the influence of cluster formation on the stability of these films, we show how polymer-precursor mixtures provide optimum uniformity and very low surface roughness in amorphous V2O5 and also orthorhombic V2O5 after crystallization by heating. Pinhole and roughness instability formation during the liquid stage of the nanofluid on gold and ITO substrates is suppressed giving a uniform coating. Practically, understanding evolution pathways that involve dewetting processes, nucleation, decomposition, or hydrolysis in complex nanofluids provides a route for improved uniformity of thin films. The method could be extended to improve the consistency in sequential or iterative multilayer deposits of a range of liquid precursors for functional materials and coatings.

A Session Model for Cross-Domain Interactive Multi-User IPTV

This work proposes a session model for crossdomain interactive multi-user IPTV. The model has been designed to Support the creation and consumption of multi-user multimedia sessions that span multiple technology domains like managed IPTV, mobile network, home network and the Internet. These sessions can combine content and services from various domains and the model enables shared experiences between users at different locations, connected across diverse technology domains. This paper describes the session model, gives an overview of the general architecture and presents the results of an implementation that spans home, internet and mobile networks. This session model has been and first application demonstrators have been realized.

Influence of ethanol on the rennet-induced coagulation of milk.

The influence of ethanol on the rennet-induced coagulation of milk was studied to investigate potential synergistic effects of these two mechanisms of destabilisation on the casein micelles. Addition of 5% (v/v) ethanol reduced the rennet coagulation time (RCT) of milk, whereas higher levels of ethanol (10-20%, v/v) progressively increased RCT. The temperature at which milk was coagulable by rennet decreased with increasing ethanol content of the milk. The primary stage of rennet coagulation, i.e., the enzymatic hydrolysis of kappa-casein, was progressively slowed with increasing ethanol content (5-20%, v/v), possibly due to ethanol-induced conformational changes in the enzyme molecule. The secondary stage of rennet coagulation, i.e., the aggregation of kappa-casein-depleted micelles, was enhanced in the presence of 5-15% ethanol, the effect being largest at 5% ethanol. Enhanced aggregation of micelles is probably due to an ethanol-induced decrease in inter-micellar steric repulsion. These results indicate an interrelationship between the effects of ethanol and chymosin on the casein micelles in milk, which may have interesting implications for properties of dairy products.

Chemical approaches for doping nanodevice architectures

Advanced doping technologies are key for the continued scaling of semiconductor devices and the maintenance of device performance beyond the 14 nm technology node. Due to limitations of conventional ion-beam implantation with thin body and 3D device geometries, techniques which allow precise control over dopant diffusion and concentration, in addition to excellent conformality on 3D device surfaces, are required. Spin-on doping has shown promise as a conventional technique for doping new materials, particularly through application with other dopant methods, but may not be suitable for conformal doping of nanostructures. Additionally, residues remain after most spin-on-doping processes which are often difficult to remove. In situ doping of nanostructures is especially common for bottom-up grown nanostructures but problems associated with concentration gradients and morphology changes are commonly experienced. Monolayer doping has been shown to satisfy the requirements for extended defect-free, conformal and controllable doping on many materials ranging from traditional silicon and germanium devices to emerging replacement materials such as III-V compounds but challenges still remain, especially with regard to metrology and surface chemistry at such small feature sizes. This article summarises and critically assesses developments over the last number of years regarding the application of gas and solution phase techniques to dope silicon-, germanium- and III-V-based materials and nanostructures to obtain shallow diffusion depths coupled with high carrier concentrations and abrupt junctions.