Particle sizing of flocculated latex particles by physisorption of nitrogen

Physisorption of nitrogen at one specific pressure is used to determine the specific surface area of a flocculated polystyrene latex by applying BET theory. Assuming that a flocculated sample of Polymer latex is composed of distinct spherical latex particles (i.e., there is no coagulation of particles), the volume–surface-average diameter can be calculated. The resulting diameters are compared to sizes obtained using a disc centrifuge sedimentometer, which fractionizes the particles by sedimentation. The diameters from both techniques were in good agreement, showing that physisorption of nitrogen, which is a simple technique, can be used to determine sizes of flocculated latex particles. This agreement also shows that the flocculation of the polystyrene latex produced separate nonporous spherical particles. When flocculation of a latex is done above its glass transition temperature, coagulation will occur. While other particle sizing techniques can produce particle size distributions, the physisorption of nitrogen only gives the volume–surface-average diameter. However, one advantage of the physisorption of nitrogen is that it covers a broad range of particle sizes compared to most other techniques. © 1994 John Wiley & Sons, Inc.     

Isolation of σ-(L-α-aminoadipyl)-L-cysteinyl-D-valine from culture broths by covalent chromatography

An efficient procedure for the isolation of reduced -(L-α-aminoadipyl)-L-cysteinyl-D-valine (ACV) from culture supernatants of β-lactam antibiotic-producing microorganisms is described. The method utilises covalent chromatography to isolate thiols from culture broths that have been deproteinised and undergone borohydride reduction. 2-Pyridyl disulphide activated thiopropyl Sepharose was employed batchwise to isolate the thiols present in such broths from cultures of the known ACV excreter Cephalosporium acremonium N2 and the penicillin producer Penicillium chrysogenum P2. ACV was separated from these mixtures of thiols by gel permeation chromatograhy. Reversed-phase HPLC analysis showed the ACV to be of a high purity unless isolated from a highly complex culture medium.     

The evolving food and nutrition agenda: policy and research priorities for the coming decade

Enormous progress has been made in the past 100 years in improving diet and nutritional status. However, the job is not done. This paper summarizes some of the current challenges and proposes priorities for future research and policy development. The nutrition agenda is more complex than it was 100 years ago. The world now faces undernutrition side-by-side with dietary excess and related chronic diseases. The complexity of modern nutrition necessitates using a systems approach to identifying effective policies and programs. There is a renewed interest in addressing the new nutrition agenda.     

Flow-through microvial facilitating interface of capillary isoelectric focusing and electrospray ionization mass spectrometry

A capillary electrophoresis mass spectrometry (CE-MS) interface utilizing a flow-through microvial is used to ensure the electric continuity and supply the catholyte and mobilizer solutions during the capillary isoelectric focusing (cIEF) and mobilization process. The flow-through microvial provides a stable chemical environment and helps to improve the ionization efficiency without significantly diluting the analyte. The CE-MS interface facilitates the transfer of the mobilized cIEF effluent to the site of electrospray ionization, and the gaseous ions can be detected directly by a mass spectrometer. It also allows for complete focusing and mobilization processes to be performed automatically in programmed sequences with commercial CE systems. Two different strategies, using either a part of the capillary or the flow-through microvial of the CE-MS interface as the catholyte reservoir for bare fused silica capillaries or neutral coated capillaries, respectively, were developed for automated cIEF-electrospray ionization (ESI)-MS. Reasonable separation efficiency was achieved using proper concentration of carrier ampholytes and suitable strategies of electroosmotic/electrophoretic mobilization.     

Microcavity-integrated graphene photodetector

There is an increasing interest in using graphene (1, 2) for optoelectronic applications. (3-19) However, because graphene is an inherently weak optical absorber (only ≈2.3% absorption), novel concepts need to be developed to increase the absorption and take full advantage of its unique optical properties. We demonstrate that by monolithically integrating graphene with a Fabry-Pérot microcavity, the optical absorption is 26-fold enhanced, reaching values >60%. We present a graphene-based microcavity photodetector with responsivity of 21 mA/W. Our approach can be applied to a variety of other graphene devices, such as electro-absorption modulators, variable optical attenuators, or light emitters, and provides a new route to graphene photonics with the potential for applications in communications, security, sensing and spectroscopy.     

Rheology of short glass fiber-reinforced thermoplastics and its application to injection molding I. Fiber motion and viscosity measurement

A study has been made of the fiber orientation in short glass fiber-filled thermoplastics resulting from convergent, divergent and shear flows. Convergent flow results in high fiber alignment along the flow direction, whereas diverging flow causes the fibers to align at 90° to the major flow direction. Shear flow produces a decrease in alignment parallel to the flow direction and the effect is pronounced at low flow rates. Non-linear Bagley plots have been observed, under some conditions, during rheological measurements. The data are consistent with a pressure dependent viscosity.     

The acylation and phosphorylation pattern of lipid A from Xanthomonas campestris strongly influence its ability to trigger the innate immune response in Arabidopsis

Lipopolysaccharides (LPSs) are major components of the cell surface of Gram-negative bacteria. LPSs comprise a hydrophilic heteropolysaccharide (formed by the core oligosaccharide and the O-specific polysaccharide) that is covalently linked to the glycolipid moiety lipid A, which anchors these macromolecules to the external membrane. LPSs are one of a group of molecules called pathogen-associated molecular patterns (PAMPs) that are indispensable for bacterial growth and viability, and act to trigger innate defense responses in eukaryotes. We have previously shown that LPS from the plant pathogen Xanthomonas campestris pv. campestris (Xcc) can elicit defense responses in the model plant Arabidopsis thaliana. Here we have extended these studies by analysis of the structure and biological activity of LPS from a nonpathogenic Xcc mutant, strain 8530. We show that this Xcc strain is defective in core completion and introduces significant modification in the lipid A region, which involves the degree of acylation and nonstoichiometric substitution of the phosphate groups with phosphoethanolamine. Lipid A that was isolated from Xcc strain 8530 did not have the ability to induce the defense-related gene PR1 in Arabidopsis, or to prevent the hypersensitive response (HR) that is caused by avirulent bacteria as the lipid A from the wild-type could. This suggests that Xcc has the capacity to modify the structure of the lipid A to reduce its activity as a PAMP. We speculate that such effects might occur in wild-type bacteria that are exposed to stresses such as those that might be encountered during plant colonization and disease.     

Full Field Temperature Measurement of Specular Wafers During Rapid Thermal Processing

Many of the processes involved in the creation of semiconductor devices involve high-temperature processing of silicon wafers. The benefits of reduced thermal budget and faster cycle time make rapid thermal processing (RTP) a possible key technology for semiconductor manufacturing. However, the problem of nonuniform wafer temperature has prevented it from further spread among the industry. The first step in developing controls to maintain a uniform wafer temperature is accurate temperature measurement during processing. In this paper, a system was developed to exploit the specular reflectivity of silicon wafers and obtain a measurement of the wafer temperature profile. The spectral reflectivity is determined by measuring the intensity of an incident beam and the beam reflected from the wafer surface. With this measured reflectivity value the spectral-directional wafer emissivity was determined using Kirchhoff's law. The obtained emissivity then was used to calculate the wafer temperature profile from an image obtained with an infrared camera. An experimental study of the transmittance of an undoped silicon calibration wafer at an elevated temperature is also discussed