A wideband RF amplifier for satellite tuners

This paper presents the design and measured performance of a wideband amplifier for a direct conversion satellite tuner.It is composed of a wideband low noise amplifier(LNA) and a two-stage RF variable gain amplifier(VGA) with linear gain in dB and temperature compensation schemes.To meet the system linearity requirement, an improved distortion compensation technique and a bypass mode are applied on the LNA to deal with the large input signal.Wideband matching is achieved by resistive feedback and an off-chip LC-ladder matching network.A large gain control range(over 80 dB) is achieved by the VGA with process voltage and temperature compensation and dB linearization.In total,the amplifier consumes up to 26 mA current from a 3.3 V power supply. It is fabricated in a 0.35-μm SiGe BiCMOS technology and occupies a silicon area of 0.25 mm~2.     

一种片上变压器为负载的用于0.13 μm CMOS工艺2.4GHz WLAN的接收机射频前端电路

A 2.4 GHz radio frequency receiver front end with an on-chip transformer compliant with IEEE 802.11b/g standards is presented. Based on zero-IF receiver architecture, the front end comprises a variable gain common-source low noise amplifier with an on-chip transformer as its load and a high linear quadrature folded Gilbert mixer. As the load of the LNA, the on-chip transformer is optimized for lowest resistive loss and highest power gain. The whole front end draws 21 mA from 1.2 V supply, and the measured results show a double side band noise figure of 3.75 dB, -31 dBm IIP3 with 44 dB conversion gain at maximum gain setting. Implemented in 0.13 μ m CMOS technology, it occupies a 0.612 mm² die size.     

Insecticidal activity of monoterpenes against Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst)

Secondary metabolites play an important role in plant resistance to insects. The monocyclic monoterpenes 1,8-cineole (eucalyptol) and R-(+)-limonene have been considered economically important in this context. Cineole is a component of different species of Eucalyptus spp. and limonene is a constituent of Citrus spp. essential oils. These substances were bioassayed to determine possible fumigant, contact, and ingestion activity against Rhyzopertha dominica (F.), lesser grain borer, and Tribolium castaneum (Herbst), red flour beetle, which are important pests of stored grain. It was possible to show that both compounds are insecticidal against the two insects, mainly in the contact and/or ingestion action.     

The effect of quaternary ammonium on discharge characteristic of a non-aqueous electrolyte Li/O2 battery

The effect of quaternary ammonium on discharge characteristic of Li/O₂ cells was studied by using Super-P carbon as air cathode, a 0.2 mol kg⁻¹ LiSO₃CF₃ 1:3 (wt.) PC/DME solution as baseline electrolyte, and tetrabutylammonium triflate (NBu₄SO₃CF₃) as an electrolyte additive or a co-salt. Results show that Li/O₂ cells can run normally in an electrolyte with NBu₄SO₃CF₃ as the sole conductive salt. However, such cells suffer lower voltage and capacity as compared with those using the lithium ionic baseline electrolyte. This is due to the larger molar volume of quaternary ammonium cation, which results in less deposition of oxygen reduction products on the surface of carbon. When used as an electrolyte additive or a co-salt, the ammonium is shown to increase capacity of Li/O₂ cells. The plot of differential capacity versus cell voltage shows that the Li/O₂ cell with ammonium added has broad and scatted differential capacity peaks between the voltages of two reactions of “2Li + O₂ → Li₂O₂” and “2Li + Li₂O₂ → 2Li₂O”. This phenomenon can be attributed to the phase transfer catalysis (PTC) property of quaternary ammonium on the second reaction. Due to inverse effects of the cation geometric volume and the PTC property of ammonium ions on the discharge capacity, there is an optimum range for the concentration of ammonium. It is shown that the addition of NBu₄SO₃CF₃ increases discharge capacity of Li/O₂ cell only when its concentration is in a range from 5 mol% to 50 mol% vs. the total of Li/ammonium mixed salt, and that the optimum concentration is about 5 mol%. In this work we show that the addition of 5 mol% NBu₄SO₃CF₃ into the baseline electrolyte can increase discharge capacity of a Li/O₂ cell from 732 mAh g⁻¹ to 1068 mAh g⁻¹ (in reference to the weight of Super-P carbon) when the cell is discharged at 0.2 mA cm⁻².     

Aluminum agglomeration reduction in a composite propellant using tailored Al/PTFE particles

In solid propellants, aluminum is widely used to improve performance, yet theoretical specific impulse is still not achieved largely because of two-phase flow losses. Losses could be reduced if aluminum particles quickly ignited, more gaseous products were produced and if upon combustion, aluminum particle breakup occurred. To explore this, tailored, fuel-rich, mechanically activated composite particles (aluminum/polytetrafluoroethylene, Al/PTFE 90/10 and 70/30 wt.%) are considered as replacements for reference aluminum powders (spherical, flake, or nanoscale) in a composite solid propellant. The effects on burning rate, pressure dependence, and aluminum ignition, combustion, and agglomeration are quantified. Using microscopic imaging, it is observed that tailored particles promptly ignite at the burning surface and appear to breakup into smaller particles, which can increase the heat feedback to the burning surface. Replacement of spherical aluminum with Al/PTFE 90/10 wt.% does not significantly affect propellant burning rate. However, Al/PTFE 70/30 wt.% increases the pressure exponent from 0.36 to 0.58, which results in a 50% increase in propellant burning rate at 13.8 MPa. This increased pressure sensitivity is consistent with more kinetically controlled combustion that occurs from smaller burning metal particles near the surface. Combustion products were quench collected using a new, liquid-free technique at 2.1 and 6.9 MPa and were measured. Both Al/PTFE 90/10 and 70/30 wt.% composite particles reduce the coarse product fraction and diameter. The most significant reduction occurs from 70/30 wt.% particle use, where average coarse product diameter is 25 μm, which is smaller than the original, average particle size and is also smaller than the 76 μm products collected from reference spherical aluminized propellant. This is a 66% decrease in agglomerate diameter or a 96% decrease in volume compared to agglomerates formed from reference spherical aluminum. Smaller diameter condensed phase products and more gaseous products will likely decrease two-phase flow loss and reduce slag accumulation.     

Adhesive Bonding to Galvanized Steel: I. Lap Shear Strengths and Environmental Durability

Initial (i.e., unaged) adhesion, as well as adhesion after seven day, 60°C water immersion and six week scab corrosion accelerated environmental exposures, has been assessed for five different one and two-part epoxy adhesives, bonded to three different types of galvanized steel substrates. We have shown that adhesion, as measured by lap shear strength, is specific to the galvanized substrate type. In general, for a given adhesive, adhesion to “hot-dipped” galvanized substrates is harder to achieve and maintain under accelerated environmental exposure than is adhesion to “electroplated” galvanized. Also, for a given type of galvanized steel, the one-part epoxies evaluated generally showed higher initial strengths, as well as better strength retention under environmental exposure than did the two-part epoxies.     

The effect of fluorosurfactant,copolymer latex,and cross-linker on the surface properties of floor polishes: An investigation using AFM with adhesion mapping

The performances of three fluorosurfactants of different perfluoroalkyl chain lengths in styrene-butadiene (SB) and styrene-acrylic (SA) latex formulations having different virtual cross-linkers were investigated with atomic force microscopy (AFM). Topographic mapping provided no conclusive relationship with macroscopic observations of floor polish performance (with “performance” being judged by absence of haze and uniformity of flow and leveling.) Adhesion mapping of the film surfaces revealed mesoscale lateral phase separation for the zinc cross-linked SB latex formulations with specific fluorosurfactants, but not for the SA latex formulations with either calcium or zinc cross-linking. FT-IR spectroscopy analysis supports the contention that lateral phase separation occurred due to the formation of a complex between the fluorosurfactant and the zinc cross-linking agent when used in the SB formulations. All three fluorosurfactants successfully flowed and leveled the SA formulation, using either calcium or zinc cross-linking, without the formation of a complex. These experiments present high resolution adhesion maps of latex films that link mesoscopic properties to macroscopic performance of the dried floor polish films.     

THE POTENTIAL FOR METHANOL PRODUCTION FROM NATURAL GAS BY DIRECT CATALYTIC PARTIAL OXIDATION

ABSTRACT

An evaluation of methanol production from natural gas by the conventional synthesis process shows that gas feedstock and capital charges are the dominant components of the methanol cost. Small but significant reductions In product cost can be made by increasing the conversion per pass and heat recovery from the synthesis reactor. However, the overall performance of the process is limited by the high cost and thermal Inefficiencies associated with the steam reforming step used to produce the synthesis gas. Catalytic partial oxidation (CPO) of methane directly to methanol has a potential advantage over the conventional process in that it eliminates the need for steam reforming. However, although considerable research has been conducted on CPO, no commercially viable process has yet been developed. An economic evaluation of a conceptual process for methanol production by CPO has been carried out assuming pure oxygen is used as oxidant. Results show that CPO has potential for reducing the coat of methanol provided the total oxidation of methane to CO₂ and water Is minimised. On the criteria used In this evaluation, CPO is cheaper than synthesis when less than 23% of the methane is completely oxidised. Further research on CPO is warranted and should concentrate on maximising the selectivity of the reaction towards methanol formation.     

PARTITIONING OF ALKYLPYRIDINES BETWEEN SHALE-DERIVED MIDDLE DISTILLATE FUEL AND WATER

ABSTRACT

A nitrogen-rich shale-derived middle distillate fuel was selected for the study of the partitioning of alkyl pyridines with water of pH 5. This particular middle distillate fuel, was found to contain acid extractable compounds composed mainly, about 90%, of alkyl substituted pyridines. The pyridine content of the extracts was determined by combined capillary column GC/HS. The partitioning was observed to be acid dependent.