Thick-film 3-stage m.i.c. IMPATT diode-amplifier on ferrite

A 3-stage hybrid m.i.c. gallium-arsenide IMPATT-diode amplifier is described with an output of 1.05 W at 9.2 GHz, a large-signal gain of 21 dB and a bandwidth to ?3 dB greater than 1 GHz; the amplifier is stable at all input levels. The concept of an effective radius, first proposed to explain the properties of disc capacitors, has been used successfully in the circulator design. Close attention has been paid to screening the unencapsulated diodes to prevent r.f. radiation and to incorporating resistive-loading circuits to suppress spurious out-of-band oscillations.     

Silicon IMPATT cascaded amplifier: 6 W (c.w.) at 9.6 GHz

A compact silicon IMPATT 4-stage coaxial amplifier has given 6.3 W (c.w.) with a power gain of 28 dB and an instantaneous bandwidth (?1 dB) of 200 MHz centred at 9.6 GHz. A gain ripple of less than 0.2 dB and phase deviation from linearity of ±3° across a 30 MHz bandwidth slot was obtained at the full rated output power. The overall efficiency was 4.5%. Commercial devices and circulators were used throughout the unit and the power in the final stage was obtained by combining the available powers from four separate devices. Particular attention was paid to the circuits to reduce the onset of spurious oscillations under large-signal conditions.     

Filter efficiency as a function of nanoparticle velocity and shape

The filtration efficiency of a conventional fibrous filter was investigated with particular emphasis on the removal of particles with different shapes. A previous study has shown that particles of spherical shape are removed from the gas carrier with efficiencies which are higher when compared to cubic particles of the same aerodynamic size. In this project, to challenge our previously made explanation, spherical PSL and cubic MgO particles were tested along with particles of sodium chloride (NaCl) of intermediate shape (cubic particles with rounded edges) at a range of filtration velocities from 5 to 20 cm/s. It was found that particles of NaCl are removed with efficiencies lower then those for PSL particles but higher than the efficiencies for cubic particles of MgO, at the lowest filtration velocity when inertial effects are negligible. The rounded NaCl particles, depending on the geometry of the contact, could either land on the rounded corner and hence roll, land on a sharp edge and hence tumble, or slide. This range of options alters the probability of detachment of the particle. The difference between the filter efficiencies for cubic MgO particles and intermediate shaped NaCl particles is decreasing with the increase in velocity. With increasing velocity, the filtration efficiency of the cubic MgO particles, exceeds the filtration efficiency for the intermediate shaped NaCl particles, due to the dominating inertial effects of the denser, and hence heavier, MgO particles. This paper shows the results of these experiments and, we hope, will ignite the interest of the aerosol community towards further theoretical analysis of the phenomenon.     

Comparison of Fixed and Fluidized Activated Carbon Beds for Removal of Organic Vapors

Activated carbons are commonly used for removal of organic vapors from exhaust air streams. Two configurations, including fixed and fluidized carbon beds are usually employed in industry to meet various requirements of the industrial process which is being used. This paper investigates the performance of such configurations and provides a comparative analysis. It was found that for thin carbon layers, the fixed bed performs more efficiently with the difference exceeding 15 % for the layers with the thickness less than 15 mm. This difference is decreasing with increase of the layer thickness and becomes less than 5 % for the beds thicker than 100 mm. Considering various advantages of the fluidized beds over fixed beds, including lower resistance to the gas flow, excellent gas distribution and minimal possibility of clogging in case of existence of alien particles in the gas, they are recommended for use with the minimal thickness of the layer to be larger than 100 mm.     

Attrition due to mixing of hot and cold FCC catalyst particles

The formation of fines in a fluidized catalytic cracker unit (FCCU) due to catalyst attrition and fracture is a major source of catalyst loss. In addition to the generation of fine particles, a significant amount of aerosols have been identified in the stack emission of FCCUs. To determine the source of these aerosols, samples of fresh and equilibrium (e-cat) type catalysts were heated up to 600 °C and mixed with cold samples, simulating the thermal shock and particle fracture, which occurs inside an FCCU when catalyst is added. The thermal shock in the experiments produced fine particles and aerosols, which were captured on filters and analyzed using scanning electron microscopy (SEM) imaging and atomic absorption tests. It was found that significant quantities of metal rich aerosols were generated by the thermal shock. This production of fine particles and aerosols is a new phenomenon that can help explain excessive catalyst emissions from operating FCCUs.     

Cloud Stabilization of Orange Juice by High Pressure Processing

High pressure processing (HPP) was investigated as a means to preserve cloud in freshly squeezed orange juice. Cloud loss is a major quality defect in orange juice, and methods of preserving cloud without the extreme temperatures used in commercial pasteurization are desirable. Pressures from 500 to 900 MPa were investigated at dwell times of 1 sec, 1 min and 10 min. Higher pressures and longer processing times were more effective at preserving cloud, while all treatments yielded a microbially stable product. A 90-day shelf life under refrigeration conditions could be achieved using pressures of 700 MPa and higher combined with treatment times of 1 min.     

Filtration of nanosized particles with different shape on oil coated fibres

In our previous work it has been shown that perfectly spherical polystyrene latex (PSL) particles have higher filtration efficiency compared to cubic magnesium oxide (MgO) particles of the same electrical mobility as PSL particles. This disparity was ascribed to the different nature of motion of the spherical and cubic particles along the fibre surface, following the initial collision. After touching the fibre surface and before coming to rest, the spherical particles could either slide or roll compared to the cubic ones, which could slide or tumble. During tumbling, the area of contact between the particle and the fibre changes significantly, thus affecting the bounce probability, whilst for the spheres, the area of contact remains the same for any point of particle trajectory. In this project, the polypropylene filter was coated with a thin layer of mineral oil that was used to absorb the energy and, respectively, to minimize particle motion along the fibre after collision. The filtration efficiency of spherical PSL, and cubic MgO particles was measured in the size range of 50–300 nm, for filtration velocity of 10 and 20 cm/s. It was found that, regardless of shape, both particle types have very similar filtration efficiency. The theoretical predictions are in good agreement with our experimental results. Therefore, the conclusion can be drawn that the oil coating minimizes the amount of particle motion along the fibre after initial collision, making results for all particle shapes similar.     

Structure-function relationships in side chain lactam cross-linked peptide models of a conserved N-terminal domain of apolipoprotein E

Bioactive peptides have multiple conformations in solution but adopt well-defined conformations at lipid surfaces and in interactions with receptors. We have used side chain lactam cross-links to stabilize secondary structures in the following peptide models of a conserved N-terminal domain of apolipoprotein E (cross-link periodicity in parentheses): I, H2N-GQTLSEQVQEELLSSQVTQELRAG-COOH (none); III, [sequence; see text] (i to i + 3); IV,[sequence; see text] (i to i + 4); IVa, [sequence, see text] (i to i + 4) (lactams above the sequence, potential salt bridges below the sequence). We previously demonstrated [Luo et al. (1994) Biochemistry 33, 12367-12377; Braddock et al. (1996) Biochemistry 35, 13975-13984] that peptide III, containing lactam cross-links between the i and i + 3 side chains, enhances specific binding of LDL via a receptor other than the LDL-receptor. Peptide III in solution consists of two short alpha helices connected by a non alpha helical segment. Here we examine the hypothesis that the domain modeled by peptide III is one antipode of a conformational switch. To model another antipode of the switch, we introduced two strategic modifications into peptide III to examine structure-function relationships in this domain: (1) the spacing of the lactam cross-links was changed (i to i + 4 in peptides IV and IVa) and (2) peptides IV and IVa contain the two alternative sequences at a site of a possible end-capping interaction in peptide III. The structure of peptide IV, determined by 2D-NMR, is alpha helical across its entire length. Despite the remarkable degree of structural order, peptide IV is biologically inactive. In contrast, peptides III and possibly IVa contain a central interruption of the alpha helix, which appears necessary for biological activity. These and other studies support the hypothesis that this domain is a conformational switch which, to the extent that it models apolipoprotein E itself, may modulate interactions between apo E and its various receptors.     

Cardiovascular risk factor levels in adults with mental retardation

Cardiovascular risk factors in a population of adults with mental retardation were examined. The subjects resided in three types of settings (16+ bed facility, group home, and natural family) and were measured on the following parameters: blood lipids, obesity, and smoking. The data were compared to a nonretarded population and to the guidelines established by the National Cholesterol Education Program. Results indicated that adults with mental retardation had cardiovascular risk profiles similar to those of individuals without mental retardation in the Framingham Offspring Study and that to the extent that cardiovascular health is a concern to the general population, it must also be a concern for individuals with mental retardation.