bluuebunny/crossref_metadata_2025 huggingface dataset:
African drying oils. III. Component acids of some linoleic‐rich oils. Safflower seed oil
Authors: Barker C. , Hilditch T. P.
Published: July 2007

Like Niger seed oils (Part II) and sunflower seed oils (Part IV), safflower seed oils may vary somewhat widely in their content of Iinoleic acid; oils from Asiatic and some other sources contain 60%, or less, but other seeds grown in America or Australia furnish oils in which linoleic acid forms up to about 77% of the total fatty acids. Such oils contain negligible proportions of linolenic acid, and are excellent non‐yellowing drying oils. Safflower seed grown in Kenya has been examined and found to give oil practically identical with a recently described Australian oil, its component acids being palmitic 6·4, stearic 3·1, arachidic 0·2, oleic 13·4, and linoleic 76·9% by wt.
Studies in acetylene flames. Part II. Formation of carbon monoxide
Authors: Campbell J. R. , Cumming A. P. C. , Horn J. A.
Published: July 2007

The formation of CO from acetylene during combustion was studied by burning vertical acetylene flames in atmospheres consisting of O2 and N2 in known proportions. This has been found to be governed mainly by the percentage oxygen in the inlet gas and its rate of supply to the combustion chamber. Carbon monoxide is produced from a vertical acetylene flame over the whole range of inlet gas compositions containing from 21% O2 downwards to the extinction point. When the percentage O2, in the inlet gas is reduced to a value approaching that of the extinction point, CO is produced in quantities exceeding 0·1. The effect of the addition of CO2 to the inlet gas is to increase the quantity of CO formed.
The electrification of metal dusts
Authors: Boyle A. R. , Llewellyn F. J.
Published: July 2007

The static electrification of a number of metal dusts has been measured in two standard experiments; these results, together with the electrostatic energy required for the ignition of dust clouds of metal powders, provide a basis for the estimation of the electrostatic hazard likely to be encountered in handling quantities of materials.
The alkali refining of oils containing vitamin A
Authors: Hawtman L.
Published: July 2007

Contrary to the previous opinion that alkali refining reduces considerably the vitamin A potency of fish liver oils, it has been found that under usual refining conditions the neutralization with alkalis results in increased potency. The increase is approximately proportional to the free fatty acid content of the original oil. The amount of vitamin A carried away by free fatty acids and “impurities” during the refining process has been determined.
The relative efficiency of “saturant” bitumen as a textile rotproofing agent
Authors: Atkins W. G. , Gupta S. R. Sen , Macmillan W. C.
Published: July 2007

A series of laboratory tests designed to estimate the relative efficiency of bitumen and other materials used as textile rotproofing agents has been carried out, using a new form of testing apparatus for the purpose. Pre‐treatment with cuprammonium followed by bitumen saturation, or a single treatment with a mixture of bitumen and cresylic acid, provides better rot‐protection than bitumen alone.
The synthesis of vinyl chloride from acetylene and hydrogen chloride
Authors: Barton D. H. R. , Mugdan M.
Published: July 2007

The use of solid catalysts in the synthesis of vinyl chloride from hydrogen chloride and acetylene has been investigated. The advantages of employing catalysts in the finely powdered form has been demonstrated, and the value of granular pumice as support indicated. Alumina gel and silica gel have been tried as altematives to active charcoal; alumina gel proved successful.

A brief account of the study of the mechanism of the vinyl chloride reaction, made by the late Dr. Mugdan, has been included.
Oxidation of cerium by potassium chlorate in chloride solution
Authors: Vickery R. C.
Published: July 2007

It is briefly shown that cerium can be oxidized and precipitated from chloride solution by boiling with potassium chlorate. Cerium oxide of high purity may be thus obtained, but only in small yield.
Routine measurement of surface of paint pigments and other fine powders. I
Authors: Carman P. C. , Malherbe P. Le R.
Published: July 2007

The surface of paint pigments can be determined by the air‐permeability method, using a simple technique, which is excellently suited for routine control. Calculation of the surface is not straightforward, owing to the large pan played by slip flow, but such calculations can be simplified for routine work.

Permeability surfaces were found to vary with porosity, and reasons are given for preferring porosities in the range σ = 0.4‐0–0.5. Permeability surfaces are compared with those obtained by low‐temperature nitrogen adsorption; this method is more accurate but is not adapted to routine.
Effect of temperature and presence of hypochlorite on the rate of hydrolysis of cyanogen chloride in alkaline solution
Authors: Eden G. E. , Wheatland A. B.
Published: July 2007

During an investigation on the destruction of cyanide in waste waters by chlorination it was observed that, even in strongly alkaline solution, the first product of the reaction of a cyanide with a hypo‐chlorite is cyanogen chloride; this then undergoes hydrolysis, possibly with formation of a cyanate. The rate of formation of cyanogen chloride is extremely rapid, but hydrolysis, as has been shown by Price et al.,1 proceeds at a measurable rate, given by the equation: magnified image

The value of k1 was estimated by Price to be 600 l./mol. min. at 25°c.

In treatment of waste waters containing cyanide the object is to convert the cyanide to relatively non‐toxic substances; cyanogen chloride, which is toxic, is therefore an undesirable intermediate product and it is important to know how quickly it will disappear from solutions undergoing treatment. The rates of hydrolysis of cyanogen chloride at temperatures ranging from 0° to 30° c. were therefore determined in solutions buffered at the pH value of 11, which has been found most suitable for chlorination of waste waters containing cyanide; the effect of the presence of small concentrations of hypochlorite was also investigated, since it had been noted in preliminary experiments that a slight excess of chlorinating agent appeared to accelerate hydrolysis.
The action of boiling distilled water on aluminium
Authors: Bryan J. M.
Published: July 2007

Aluminium and aluminium alloys react initially with boiling water with the evolution of hydrogen, but the action is quickly arrested through the formation of a highly resistant film of alumina monohydrate. Impurities and alloying elements in the metal and emery treatment of the surface have some influence on the reaction, but the most important factor in preventing the corrosion from continuing indefinitely appears to be the presence of a certain minimum quantity of silicon in the metal.
Tachometric titration: A method for the detection of phase changes which are accompanied by changes in viscosity
Authors: Edwards L. J.
Published: July 2007

A method is described whereby viscosity changes in a system may be followed tachometrically. Changes of phase, gelling points and similar phenomena accompanied by sudden large changes in viscosity may be rapidly located. The technique is of wide application, especially in the field of colloid science; although it is empirical in nature, approximate values for absolute viscosities may be obtained, if desired, by calibration against standard liquids.
High‐efficiency laboratory fractionation. V. an automatic laboratory still
Authors: Dixon O. C. , Rosnebeck H. R.
Published: July 2007

It is important that accurate control of operating variables should be maintained throughout a long batch fractionation. This can best be achieved in many distillations by automatic control. In the laboratory still and acccssorics hcrc described, automatic control is provided for the maintcnancc of adiabatic cons in the fractionating column, the adjustment of reflux ratiofto give optimun: fractionation cfficicncy )and the :hourly) changing of rcccivcrs in which distillate is collected! All :hourly)thcsc operations are controllcd by a modified Multclec.' Tempcnture Recorder. This instrument also provides a rccord of the important temperatures and opcntions throughout the distillaiion. An cxamplc is givcn of the use of this still in the fnctionation of a commcrcial iso‐octanc.
Precise laboratory fractionation an automatically controlled column
Authors: Highet H. C. , Godin G. W. , Philpotts A. R. , Twigg G. H.
Published: July 2007

This paper discusses a method of reducing heat losses from laboratory fractionating columns. A differential thermocouple in the lagging detects radial heat flow and controls the current passing through an electrical heater winding in the lagging, by means of a galvanometer, lamp and photocell relay system. Thermal and electrical characteristics are calculated for equipment required to maintain a number of columns adiabatic by intermittent inspection and control. In the second part of the paper construction and operation of a column lagging jacket, controller and inspection unit arc described. Heat losses are reduced to negligible dimensions and up to six jackets have been controlled simultaneously at temperatures up to 265° c. The equipment has been in use for three years with little attention.
The preparation of sodium carboxymethylcellulose
Authors: Brown S. M. , Thomson G. H.
Published: July 2007

A readily soluble sodium carboxymethylcellulose is prepared by a simplified‐technique, using alkali‐cellulose and sodium monochloracetate.
Powder‐size measurement by a combination of the methods of nephelometry and photo‐extinction
Authors: Rose H. E.
Published: July 2007

In the present paper it is shown that a combination of the methods of nephelometry and photo‐extinction offers a means for the determination of the size‐frequency of a fine powder, dependent upon two curves—one of scatter index against particle size as well as the curve of extinction coefficient versus particle size, as required by the conventional photo‐extinction method.

Should these two curves, as appears possible, be more easily defined in terms of the physical characteristics of the powder and suspension fluid than is the curve of extinction coefficient, then the combined technique might prove a more convenient and accurate method of powder size analysis than the photo‐extinction method.

Certain relationships have been derived and, on the basis of a limited number of tests, are shown to be in agreement with experiment.

From the results of scattered‐light tests the extinction‐coefficient/particle‐size relationship has been computed and reproduces in detail a significant feature of the curve as determined by direct measurement.

Although it is not claimed that the present tests, which are largely preliminary to a more detailed investigation, are conclusive, it is felt that they lead to conclusions of such interest as to justify publication in the present form.
The determination of carbon dioxide in coal
Authors: Thomas W. C. , Wilkinson H. C.
Published: July 2007

In the present British Standard method for the determination of carbon dioxide in coals, the carbon dioxide evolved by reaction of the coal with dilute hydrochloric acid or phosphoric acid is absorbed in barium hydroxide, and the excess barium hydroxide is titrated with hydrochloric acid. In Fuel Research Survey Paper No. 44, a method is described in which the carbon dioxide liberated is absorbed in soda‐lime and determined gravimetically. In this paper a third method based on the pressometric principle is described. The amount of carbon dioxide is determined by measuring the pressure developed in an apparatus of constant volume, the pressure and volume relationship having previously been determined using a known amount of sodium carbonate.
Investigations on the passage of light through suspensions
Authors: Andreasen A. H. M. , Krebs K. , Dalsgaard‐Pedersen N. Aa. , Camradt‐Petersen E. , Kjer B.
Published: July 2007

An examination has been made of the manner in which light passing through suspensions of solid materials in water, and the light scattered from such illuminated suspensions, depends upon the particle size of the suspension. The following conceptions are introduced: the specific extinction coefficient of a suspension (ē) and the specific nephelo‐value of a suspension (v̄)

The examination has been made in order to find out how these two quantities vary with the grain size of white as well as of some coloured suspensions. For white suspensions, monodisperse preparations of barium sulphate produced by condensation and fractions of ground barytes produced by elutriation are used; for coloured suspensions, elutriated fractions of chromic oxide and of pyrolusite are used. Special care has been devoted to the production or suspensions with a very high grade of monodispersity.

It is found that ē as well as v̄ for the white suspensions have a distinct maximum at grain sizes of the same order as the wavelength of the transmitted light, whereas ē by the coloured suspensions shows a maximum at grain sizes which are several times smaller than the corresponding grain sizes in the white suspensions.
Design of packed distillation columns. I. Pressure drop through packed distillation columns
Authors: Hands C. H. G. , Whitt F. R. , Gregory K. S.
Published: July 2007

Plots of water‐rate and packing‐shape correction factors for four commonly used sizes of Raschig rings to use with a modified Fanning equation are given. These are for fluid rates commonly associated with distillation, as distinct from absorption.

Experimental evidence is given to show the magnitude of the error involved in applying the results obtained with an air/water system to calculations concerning distillation systems.
The proximate analysis of benzaldehyde mono‐nitration products
Authors: Davey W. , Gwilt J. R.
Published: July 2007

Existing methods for the determination of certain products, individually or in simple mixtures, are reviewed, and a comprehensive scheme of analysis is described for the mono‐nitration products of benzaldehyde.
Manufacture of algal chemicals. U. Production of alginates from brown marine algae
Authors: Bashford L. A. , Thomas R. S. , Woodward F. N.
Published: July 2007

A process for the production from the brown seaweeds Laminaria digitata and Ascophyllum nodosum of calcium alginate of reasonably constant ‘grade’ (50‐100 centistokes) and composition (approx. 95% calcium alginate, 1·3% ‘weed residue’) has been developed on the 25‐1b. wet weed batch scale. Certain aspects of the process have been further examined on the large laboratory scale with particular reference to the initial water‐washing and acid‐leaching stages. Under the best conditions found yields of 85% and upwards have been obtained.
Improved syntheses in the pyrimidine series. 1. The use of pyrimidine‐thiols
Authors: Brown D. J.
Published: July 2007

Syntheses suitable for large laboratory‐scale working, are described for thiocytosine, cytosine, 4‐hydroxypyrimidinc, 4‐amino‐pyrimidine, 2 : 4‐ and 4: 6‐diaminopyrimidincs, uracil, 4‐amino‐6‐hydroxypyrunidine and several of their derivatives. The majority of these syntheses start from thiouracil, which has recently become plentiful; all involve replacement of a thiol‐group by −NH2, ‐OH or‐H.
The solubility of lead in zinc sulphate solutions
Authors: Barker C. W. , Powell J. , Young R. S.
Published: July 2007

The solubility of lead in zinc sulphate solutions was determined over the range of zinc concentration from 75 to 125 g./l., acid concentrations from OT to 75 g./l., and temperatures of 20°‐30° c. In this range of variables normally encountered in electrolytic zinc refineries the lead solubility varied from 4.3 to 6.8 mg./l. It decreased with increase in acid concentration, increased with increase of temperature, and was nearly unaffected by zinc concentration.
The control of foaming. I. The mode of action of chemical anti‐foams
Authors: Pattle R. E.
Published: July 2007

A large number of substances were tested for ability to destroy the foam on four(different foaming aqueous solutions. The ability or inability of the anti‐foams to spread on the foaming liquid was also studied.

It is concluded that anti‐foams act by displacing from the surface the substance causing the foaming (or, in salt solutions, preventing negative adsorption). They may do this either by dissolving in the foam liquid or bespreading over its surface.) The causes of the strong, correlation (found) between foam‐killing and spreading are discussed.
A portable water‐flow gas calorimeter
Authors: Gooderham W. J.
Published: July 2007

A new form of water‐flow gas calorimeter is described in which gas volumes are read with a soap‐film meter, and water volumes on a burete. The calorimeter is a silvered and evacuated resistance‐glass vessel. A new type of pump is used to supply air to the burner. The gross calorific value of a gas can be obtained in to minutes if the rates of flow of air, gas and water arc set correctly. The calorimeter was designed to give results correct to the nearest I3.Th.U. but an accuracy greater than this may he possible.
Noradrenergic regulation in mouse supraoptic nucleus involves a nitric oxide pathway only to regulate arginine‐vasopressin expression and not oxytocin expression
Authors: Maolood Nasren , Grange‐Messent Valérie , Raison Danièle , Hardin‐Pouzet Hélène
Published: July 2007

Noradrenalin (NA) regulates the expression of arginine‐vasopressin (AVP) and oxytocin (OT) by magnocellular neurons in the supraoptic nucleus (SON) of the hypothamalus. Nitric oxide (NO) may be one of the factors involved in the NA signaling pathway regulating AVP and OT expression. To test this possibility, we used an ex vivo experimental model of mouse hypothalamus slices. Increases in AVP and OT levels in the SON were detected by immunohistochemistry and immunoenzyme assays after 1 hr and 4 hr incubations with NA (10−4 M). There was also an increase in the expression and activity of neuronal NOS and inducible NOS in the SON as assessed by immunohistochemical and histoenzymological analysis of NADPH‐diaphorase, whereas endothelial NOS was undetectable. To specify the role of NO, the slices were treated with NA and L‐arginine methyl ester (L‐NAME, an NOS inhibitor; 3 μM). This treatment for 1 hr abolished the NA‐induced increase in AVP. Treatment with sodium nitroprusside (SNP, an NO donor; 0.1 mM) increased AVP levels, confirming that NO regulates AVP expression. Addition of 1 mM EGTA during the incubation with NA reduced the AVP increase by half, indicating that both nNOS and iNOS activities are involved in the regulation. A 1‐hr treatment with L‐NAME did not prevent the increase in OT induced by NA; similarly, treatment with SNP had no effect. These findings show that NO is involved in the regulation of AVP expression by NA and that NA control of OT expression is independent of NO. © 2007 Wiley‐Liss, Inc.
Dual effect of adenovirus‐mediated transfer of BMP7 in mixed neuron‐glial cultures: Neuroprotection and cellular differentiation
Authors: Tsai May‐Jywan , Weng Ching‐Feng , Shyue Song‐Kun , Liou Dann‐Ying , Chen Chien‐Hung , Chiu Chuan‐Wen , Yang Tzu‐Hsuan , Pan Hsu‐An , Liao Roanna I‐Hsin , Kuo Huai‐Sheng , Huang Ming‐Chao , Huang Wen‐Cheng , Hoffer Barry J. , Cheng Henrich
Published: July 2007

Bone morphogenetic proteins (BMPs), members of the TGF‐β superfamily, have been implicated in nervous system development and in response to injury. Previous studies have shown that recombinant BMP7 can enhance dendritic growth and protect cultured neurons from oxidative stress. Because of the presence of extracellular BMP antagonists, BMP7 seems to act locally. Therefore, the present study uses BMP7 overexpression using adenovirus (Ad)‐mediated gene transfer to examine its effect in mixed neuronal cultures. Enhanced BMP7 expression selectively induces neuronal CGRP expression in a time‐dependent manner. BMP7 overexpression not only significantly protects cultures from H2O2 toxicity but reduces lipopolysaccharide (LPS) stimulation. Concurrently, it profoundly reduces microglial numbers, but increases oligodendroglial and endothelial cells. Together, low‐dose and continuously expressed BMP7 is both neuroprotective and differentiation‐inductive. © 2007 Wiley‐Liss, Inc.
Aging attenuates dynactin–dynein interaction: Down‐regulation of dynein causes accumulation of endogenous tau and amyloid precursor protein in human neuroblastoma cells
Authors: Kimura Nobuyuki , Imamura Osamu , Ono Fumiko , Terao Keiji
Published: July 2007

Impaired axonal transport may promote pathogenesis in neurodegenerative disorders, such as Alzheimer's disease (AD). We previously showed that tau, amyloid precursor protein (APP), and intracellular amyloid β‐protein (Aβ) accumulate in the nerve‐ending fraction of aged monkey brains, perhaps because of impaired axonal transport. In the present study, we assessed age‐related changes of axonal transport motor proteins in aged monkey brains. Western blotting showed that kinesin, dynein, and dynactin (DYN) localizations dramatically changed with aging, and dynein level in nerve‐ending fractions increased significantly. Coimmunoprecipitation analyses showed that DYN–dynein intermediate chain (DIC) interactions decreased, suggesting that age‐related attenuation of this interaction may cause the impairment of dynein function. Moreover, RNAi‐induced down‐regulation of DIC in human neuroblastoma cells caused endogenous tau and APP to accumulate, and their subcellular localizations were also affected. Our findings suggest that aging attenuates DYN–DIC interaction, representing one of the risk factors for age‐related impaired dynein function and even for accumulation of disease proteins. © 2007 Wiley‐Liss, Inc.
Molecular chaperone‐mediated tau protein metabolism counteracts the formation of granular tau oligomers in human brain
Authors: Sahara N. , Maeda S. , Yoshiike Y. , Mizoroki T. , Yamashita S. , Murayama M. , Park J.‐M. , Saito Y. , Murayama S. , Takashima A.
Published: July 2007

Intracellular accumulation of filamentous tau proteins is a defining feature of neurodegenerative diseases termed tauopathies. The pathogenesis of tauopathies remains largely unknown. Molecular chaperones such as heat shock proteins (HSPs), however, have been implicated in tauopathies as well as in other neurodegenerative diseases characterized by the accumulation of insoluble protein aggregates. To search for in vivo evidence of chaperone‐related tau protein metabolism, we analyzed human brains with varying degrees of neurofibrillary tangle (NFT) pathology, as defined by Braak NFT staging. Quantitative analysis of soluble protein levels revealed significant positive correlations between tau and Hsp90, Hsp40, Hsp27, α‐crystallin, and CHIP. An inverse correlation was observed between the levels of HSPs in each specimen and the levels of granular tau oligomers, the latter of which were isolated from brain as intermediates of tau filaments. We speculate that HSPs function as regulators of soluble tau protein levels, and, once the capacity of this chaperone system is saturated, granular tau oligomers form virtually unabated. This is expressed pathologically as an early sign of NFT formation. The molecular basis of chaperone‐mediated protection against neurodegeneration might lead to the development of therapeutics for tauopathies. © 2007 Wiley‐Liss, Inc.
Determination of gastrodin and vanillyl alcohol in Gastrodia elata Blume by pressurized liquid extraction at room temperature
Authors: Ong Eng Shi , Heng Ming Yuan , Tan Swee Ngin , Hong Yong Jean Wan , Koh Huijing , Teo Chin Chye , Hew Choy Sin
Published: July 2007

Pressurized liquid extraction (PLE) at room temperature with a laboratory‐assembled system was applied for the extraction of gastrodin (GA) and vanillyl alcohol (VA) in Gastrodia elata Blume. The proposed system setup for this current work was simpler as no heating and backpressure regulator was required. Extraction with PLE was carried out dynamically at a flow rate of 1.5 mL/min, at room temperature, under an applied pressure of 10–20 bars with an extraction time of 40–50 min. The extraction efficiencies of the proposed method using 20% aqueous ethanol were compared with heating under reflux using organic solvents such as methanol and ethanol/water (20:80) for different batches of medicinal plant materials. For the determination of GA and VA in G. elata Blume, the extraction efficiencies of PLE at room temperature were observed to be comparable with heating under reflux. The method precision was found to vary from 1.6 to 8.6% (RSD, n = 6) on different days. The marker compounds present in the various medicinal plant extracts were determined by gradient elution HPLC and HPLC/MS/MS. Our work demonstrated the possibility of implementation of PLE at room temperature and the advantages of minimizing the use of organic solvents in the extraction process.
The fractal calibration method applied to the characterization of polymers in solvent mixtures and in mixed gel packings by SEC
Authors: Porcar Iolanda , García‐Lopera Rosa , Abad Concepción , Campos Agustín
Published: July 2007

The size‐exclusion chromatographic (SEC) behaviour of different solvent/polymer systems in three packing sets has been analysed from fractal considerations. The three‐column sets studied are specifically formed by: (i) ‘pure’ μ‐styragel, (ii) ‘mixed’ TSK Gel HHR + XL + HR and (iii) mixed TSK Gel HXL + HR + XL. The experimental data reveals that in most of the systems assayed the classical universal calibration (UC) is not fulfilled, denoting the existence of secondary effects accompanying the main SEC mechanism. In order to obtain an accurate characterization of different polymers eluted in solvent mixtures and/or mixed packings, the use of a reliable and trusted calibration curve is required. In this sense, two alternative procedures have been analysed: the specific (SC) and the fractal (FC) calibrations. The results have evidenced that the use of the FC instead of the classical universal method diminishes up to nine times (in the case of the μ‐styragel set) the mean deviation on the calculated molar mass with respect to the value given by the supplier. In the case of TSK Gel‐based sets, the mean deviation is reduced to the half. The SC curve made with standards of the sample under study also reduces the mean deviation values but needs a broad set of narrow standards, whereas the fractal approach only needs one polymeric sample to build up the calibration curve.
Characteristics of a cylindrical disk‐loaded slow‐wave structure found by theoretical, experimental, and computational techniques
Authors: Wallett Thomas M. , Qureshi A. Haq
Published: July 2007

The dispersion characteristics and interaction impedances of a disk‐loaded cylindrical waveguide structure were investigated using theoretical, computer, and experimental techniques. Satisfactory agreement has been demonstrated between the experimentally determined values, the results obtained theoretically, and the computer‐generated values using the ARGUS and SOS computer codes. © 1994 John Wiley & Sons, Inc.
Full‐wave convergence analysis of microstrip transmission parameters
Authors: Carroll James Mason , Chang Kai
Published: July 2007

Full‐wave electromagnetic simulators have enabled microwave designers to simulate complex geometries which sometimes cannot be done by conventional computer‐aided design (CAD) nodal simulators. However, designers should pay close attention to how the numerical implementation of the full‐wave analysis can affect the results of the electromagnetic simulation. This study uses various modeling parameters to determine the convergence of a GaAs microstrip's simulated transmission line characteristics. A commercially available program, Sonnet's “EM,” was used for the analysis but the results can be generalized for any full‐wave analysis. This article explores the limits of Sonnet as well as showing that a designer must use a convergence analysis to prove the validity of an electromagnetic simulation. © 1994 John Wiley & Sons. Inc.
A GaAsFET spice model for active filter tuning purposes
Authors: Richard William D. , Gregory Robert O.
Published: July 2007

Modeling GaAsFETs in MMIC active filter circuits at microwave frequencies is hampered by the complex dependence of the small‐signal model elements on bias voltages, bias currents, and frequency. Several authors have attempted an improved GaAsFET model by starting with the Curtice model of the device. This article takes a different path in developing a model for SPICE usage: a Curtice model GaAsFET is used to set the DC bias conditions; based upon these bias conditions, values for each small‐signal element are calculated. This model has been found to be especially useful for tuning studies of MMIC active filters. Results are presented for an MMIC active bandpass filter based on a twin‐tee notch filter. © 1994 John Wiley & Sons, Inc.
Itrative design‐oriented analysis method for class‐ab high‐efficiency microwave power amplifiers
Authors: Giannini Franco , Leuzzi Giorgio , Limiti Ernesto , Scucchia Lucio
Published: July 2007

Optimum choice of bias point, load and drive level for solid‐state power amplifiers is performed via a design methodology based on a novel iterative analysis method. The effectiveness of the proposed methodology and the corresponding level of accuracy is demonstrated through a comparison with the results of a more elaborate commercial CAD software and with experimental data, © 1994 John Wiley & Sons, Inc.
An expansion function suited for fast full‐wave spectral domain analysis of microstrip discontinuities
Authors: Cicchetti Renato , Faraone Antonio
Published: July 2007

A representation of the surface current density particularly suited for the electrodynamic characterization of arbitrarily shaped discontinuities in monolithic microwave and millimeter‐wave integrated circuits (MMICs) is presented. The spectral domain approach (SDA) is adopted to carry out the analysis. Some numerical results, obtained using the proposed current representation, are compared with those available in the literature. A fast and excellent numerical convergence for the scattering parameters is achieved.
Algorithms for the computer‐aided design of nonsynchronous, noncommensurate transmission‐line impedance transformers
Authors: Rosloniec Stanislaw
Published: July 2007

The new algorithms for design of nonsynchronous noncommensurate transmission‐line impedance transformers are presented. These algorithms make it possible to design the two‐, four‐, and six‐section transformers with the equal ripple insertion loss functions. The transformers designed in this way are significantly shorter in comparison to the corresponding well‐known quarter‐wave Chebyshev ones (synchronous commensurate). It is also shown that transformers of this type can be easily used as new prototype circuits for designing some other microwave devices. The 3‐dB three‐port power divider is described as an example of a device designed in this manner.
A rigorous design of millimeter‐waveguide devices using the 3d finite element method
Authors: Courivaud Nadine , Verdeyme Serge , Aubourg Michel , Guillon Pierre
Published: July 2007

A rigorous filter design using the finite element method and an optimization process is described. To show the validity of this method, it is here applied to a millimeter‐wavelength metal insert filter. The influence of higher order mode interactions and of metallic losses is also described. © 1994 John Wiley & Sons, Inc.
Low‐noise gaas MESFET optimization using an orthogonal array approach
Authors: Miller Dain C. , Sadler Robert A. , Bahl Inder J.
Published: July 2007

This article presents an experimental optimization of the noise figure of small‐signal self‐aligned FETs. An L18orthogonal array has been used to find the main effects of specific device parameters on noise performance at 18 GHz. This knowledge has been used to find an alternative device which shows a ∼0.7‐dB improvement in noise measure without requiring major process changes. Hybrid low‐noise amplifiers built with the improved FETs confirm the noise performance and show record power performance for high dynamic range applications. © 1994 John Wiley & Sons, Inc.
Analysis of propagation on open microstrip lines using mixed‐order covariant projection vector finite elements
Authors: Crain Bruce R. , Peterson Andrew F.
Published: July 2007

Many different procedures have been proposed for the finite element analysis of dielectric‐loaded waveguiding structures. However, most of these approaches are unreliable because of the appearance of spurious modes. Mixed‐order covariant projection finite elements have been shown to eliminate difficulties with spurious modes in vector waveguide formulations. The authors have developed a method to analyze open region dielectric‐loaded waveguiding problems using mixed‐order covariant projection finite elements. Details of the construction of the eigenvalue equation are presented. The treatment of open geometries using local absorbing boundary conditions is discussed. An efficient sparse eigensolver, based on iterative methods, that can solve the resulting nonlinear eigenvalue problem, is described. Analysis results are presented that demonstrate the ability of the formulation to solve for the propagating modes of open microstrip lines without the appearance of spurious modes.
Multipole‐accelerated capacitance computation for 3‐D structures in a stratified dielectric medium using a closed‐form Green's function
Authors: Jandhyala Vikram , Michielssen Eric , Mittra Raj
Published: July 2007

In this article, the capacitance matrices of three‐dimensional conducting structures embedded in a stratified dielectric medium are computed by using the fast muitipole method in conjunction with a closed‐form approximation of the appropriate Green's function. Image charges that result from the employment of this Green's function are incorporated into the fast multipole method. This technique is used to accelerate the iterative generalized minimal residual‐based solution of the system of equations generated by the method of moments. This yields the charge distributions on the conductors and thereby the required capacitance matrix. It is shown that the use of this technique typically results in a speedup of more than an order of magnitude over iterative and direct methods without a compromise of the numerical accuracy.
Specific applications of different modeling techniques for microwave package and structures design
Authors: Vilcot Anne , Ndagijimana Fabien , Cabon Béatrice
Published: July 2007

Different simulation methods for analyzing microwave interconnects are presented. Dynamic and static as well as two‐dimensional (2D) or three‐dimensional (3D) methods are investigated, such as the method of moments (MoM), the SDM, and TLM method, in their specific domains of predilection. Results are finally compared together with those obtained from a commercial software product based on the FEM method. © 1995 John Wiley & Sons, Inc.
An electrothermal functional model of the microwave FET suitable for nonlinear simulation
Authors: Rizzoli Vittorio , Costanzo Alessandra , Lipparini Alessandro , Mastri Franco , Muzzarelli Giulio
Published: July 2007

This article introduces a CAD‐oriented functional model of the microwave FET depending on temperature as an additional state variable in addition to the usual gate and drain voltages. The model is fully conservative and non‐quasistatic, and thus considerably more advanced than other currently available empirical models. A novel parameter extraction strategy allows the simultaneous determination of the voltage and temperature dependence of the constitutive relations, making use of a set of DC measurements and bias‐dependent scattering matrices obtained at a single ambient temperature. The model can be coupled to a harmonic‐balance algorithm for the efficient electrothermal simulation of temperature‐dependent nonlinear microwave circuits, which the authors discussed in a previous article.
Nonlinear simulations in time domain methods
Authors: Mueller Ulf , Beyer Adalbert
Published: July 2007

Since computer capabilities steadily increased during the past decades, time domain methods for the simulation of electromagnetic field behavior became more and more efficient in analyzing microwave and millimeter‐wave structures. They even enable the modeling of linear and nonlinear lumped devices embedded into a linear, passive, waveguiding environment. In this article, the principles of nonlinear modeling in the time domain using field simulation methods will be summarized and the applicability will be demonstrated for the TLM method.
Modeling of dispersive microwave FET devices using a quasi‐static approach
Authors: Kompa Günter
Published: July 2007

In the design of active microwave circuits nonlinear device models are of great importance to allow one to predict the reliability of circuit performance. This article reflects our experimental approach in nonlinear FET modeling. Consistent bias‐dependent model elements of the FET small‐signal equivalent circuit are obtained by a recently developed unique multibias extraction procedure which permits the reduction of the nonlinear analysis to the inner part of a FET device. A dispersive nonlinear FET model with current and charge sources being integral functions of the bias‐dependent small‐signal model parameters is proposed. A bias‐dependent difference transconductance and difference channel conductance are introduced as relevant dispersion parameters. The proposed nonlinear FET model is verified on the basis of our signal waveform measurement technique using combined frequency‐ and time‐domain signal detection.
Steady state analysis of free or forced oscillators by harmonic balance and stability investigation of periodic and quasi‐periodic regimes
Authors: Ngoya Edouard , Suárez Almudena , Sommet Raphaël , Quéré Raymond
Published: July 2007

This article presents a practical and effective method to analyze the steady state regimes, periodic or quasi‐periodic, and the stability of free and forced oscillators, based on the use of voltage and current probes. The efficiency of this method comes from the fact that it converts the analysis of an autonomous circuit into the analysis of a series of closely related nonautonomous circuits, which in turn relies on the power of the harmonic balance equation for these kinds of systems. The effectiveness of the method is shown by full analysis of a practical example.
Steady‐state analysis of nonlinear forced and autonomous microwave circuits using the compression approach
Authors: Kunisch Jürgen , Wolff Ingo
Published: July 2007

This article discusses techniques for the analysis of nonlinear microwave circuits that contain lumped nonlinear elements. Emphasis is put on specific harmonic balance‐based technique which allows us to retain the field theoretical accuracy in cases where lumped nonlinear elements are embedded closely within complex metallization structures. © 1995 John Wiley & Sons, Inc.
The effects of finite dielectric layers in multilevel microstrip interconnects
Authors: Engel Andrew G. , Katehi Linda P. B.
Published: July 2007

Microstrip with finite‐width substrate and ground plane and coupled multilevel microstrip with a finite‐width intermediate dielectric layer are examined with an integral equation‐mode matching method. The effects of varying the distance of a microstrip from the edge of a finite‐width substrate and ground plane are studied in the frequency and time domains. Coupled multilevel microstrip with a finite‐width and homogeneous intermediate layer are also characterized in the frequency and time domains, and the coupling between the two lines is found to be much greater when the intermediate layer is finite. © 1995 John Wiley & Sons. Inc.
Efficient use of commercial electromagnetic simulators for microwave and millimeter‐wave circuits
Authors: Jain Nitin , Onno Peter
Published: July 2007

Efficient use of electromagnetic simulators is accomplished by classification of EM problems into three categories—characterization of circuit elements, optimization of circuit elements, and creation of circuit element libraries. Real circuit examples in each of the three categories are given to demonstrate the practical aspects of efficient EM simulations and the computer resources required. © 1995 John Wiley & Sons, Inc.
Electromagnetic design of high‐temperature superconducting microwave filters
Authors: Bandler John W. , Biernacki Radoslaw M. , Chen Shao Hua , Getsinger William J. , Grobelny Piotr A. , Moskowitz Charles , Talisa Salvador H.
Published: July 2007

We present novel approaches to electromagnetic design of high‐temperature superconducting (HTS) quarter‐wave parallel coupled‐line microstrip filters. The desired narrow bandwidths (less than 2%) coupled with the large dielectric constant of substrate materials used in the HTS technology (εr≈ 24) make the design problems difficult to treat accurately for many traditional microwave circuit design software packages with analytical/empirical models. We have successfully performed an HTS filter design with accurate electromagnetic field simulations. We discuss problems related to electromagnetic design of such filters. We describe a look‐up table method and a powerful space mapping optimization technique, which dramatically reduce the CPU time needed in the design process. Finally, we address the issue of improved modeling of the HTS filter using analytical/empirical models. © 1995 John Wiley & Sons, Inc.
Glucuronidation of curcuminoids by human microsomal and recombinant UDP‐glucuronosyltransferases
Authors: Hoehle Simone I. , Pfeiffer Erika , Metzler Manfred
Published: July 2007

Glucuronidation is an important pathway in the metabolism of curcumin, but the isoforms of uridine‐5′‐diphosphoglucuronosyltransferase (UGT) involved are not known. Here, we report on the glucuronidation of the three natural curcuminoids and their major phase I metabolites with microsomes from human liver and intestine as well as with human recombinant UGTs. Microsomes from human liver generated predominantly the phenolic and small amounts of the alcoholic glucuronide of each curcuminoid, whereas intestinal microsomes formed only the phenolic conjugates but with higher activities. The phenolic glucuronidation of the curcuminoids was predominantly catalyzed by hepatic UGT1A1 and intestinal UGT1A8 and 1A10, whereas UGT1A9, 2B7, and 1A8 exhibited high activities for hexahydro‐curcuminoids. UGT1A9 was able to form the alcoholic glucuronide of each curcuminoid in addition to the phenolic conjugate. These data suggest that the gastrointestinal tract contributes substantially to the glucuronidation of curcuminoids in humans, which may have important implications for their pharmacokinetic fatein vivo.
White‐marker imaging—Separating magnetic susceptibility effects from partial volume effects
Authors: Seppenwoolde Jan‐Henry , Vincken Koen L. , Bakker Chris J.G.
Published: July 2007

By applying dephasing gradients, local magnetic field inhomogeneitiescan selectively visualized with positive contrast, such as those created by magnetically labeled cells. This is known as “white‐marker imaging.” In white‐marker imaging, subvoxel signal variations are also visualized as a result of partial volume (PV) effects and may compromise the identification of magnetic structures (e.g., magnetically‐labeled cells). This study presents the theory and proof‐of‐principle experiments of a strategy to eliminate PV effects during white‐marker imaging. The strategy employs the asymmetry of the signal response curves for non‐PV effects as a function of externally applied gradients. In the case of PV effects, subtraction of the symmetrical signal responses eliminates their contribution. In vitro experimental images were made using a spherical phantom with cylindrical elements. In vivo images of the brain were obtained at a location that included air cavities (susceptibility effects) and the circle of Willis (PV effect). The results show that PV effects were eliminated in the in vitro experiments and were virtually absent under in vivo conditions. Magn Reson Med, 2007. © 2007 Wiley‐Liss, Inc.
Absolute quantification of phosphorus metabolite concentrations in human muscle in vivo by 31P MRS: a quantitative review
Authors: Kemp Graham J. , Meyerspeer Martin , Moser Ewald
Published: July 2007

31P MRS offers a unique view of muscle metabolism in vivo, but correct quantification is important. Inter‐study correlation of estimates of [Pi] and [phosphocreatine (PCr)] in a number of published studies suggest that the main technical problem in calibrated 31P MRS studies is the measurement of PCr and Pi signal intensities, rather than absolute quantification of [ATP]. For comparison, we discuss the few published biopsy studies of calf muscle and a selection of the many studies of quadriceps muscle. The ATP concentration is close to the value that we obtained in calf muscle in our own study, presented here, on four healthy subjects, by localised 31P MRS using a surface coil incorporating an internal reference and calibrated using an external phantom. However, the freeze‐clamp biopsy PCr concentration is ∼20% lower than the value obtained by 31P MRS, consistent with PCr breakdown by creatine kinase during freezing. Finally, we illustrate some consequences of uncertainty in resting [PCr] for analysis of mitochondrial function from PCr kinetics using a published 31P MRS study of exercise and recovery: the lower the assumed resting [PCr], the lower the absolute rate of oxidative ATP synthesis estimated from the PCr resynthesis rate; in addition, the lower the assumed resting [PCr], or the higher the assumed [total creatine], the higher the apparent resting [ADP], and therefore the more sigmoid the relationship between the rate of oxidative ATP synthesis and [ADP]. Correct quantification of resting metabolite concentrations is crucially important for this sort of analysis. Our own results ([PCr] = 33 ± 2 mM, [Pi] = 4.5 ± 0.2 mM, and [ATP] = 8.2 ± 0.4 mM; mean ± SEM) are close to the overall mean values of the 10 published studies on calf muscle by ‘calibrated’ 31P MRS (as in the present work), and of [PCr] and [Pi] in a representative selection of ‘uncalibrated’ 31P MRS studies (i.e. from measured PCr/ATP and Pi/ATP ratios, assuming a literature value for [ATP]). Copyright © 2007 John Wiley & Sons, Ltd.
FDDI: Understanding the fibre distribute data interface
Authors: Jones Kotherine
Published: July 2007

This is the first of three articles focusing on FDDI. The definition and the applicable standards are covered herein; the hardware will be discussed in the following article, and the network management of FDDI will be discussed in the third.
How Bandwidth‐on‐demand Technologies Bring New Efficiencies to Enterprise Networking
Authors: Luczak Mark
Published: July 2007

Cell relay switching, used in conjunction with other wide area network technologies such as frame relay multiplexing, is an important new tool network managers can use to take existing T1 backbone networks into the next decade.
The Management Aspects of Frame Relay
Authors: Muller Nathan J.
Published: July 2007

If the marketing hype is to be believed, frame relay offers benefits that are too compelling to ignore. But when the layers of hype are peeled away, what remains are several unresolved issues in such critical areas as standards compliance, congestion control and network management.
The growth of international VSAT: Satellite‐based solutions for data, voice and video
Authors: Henner Lucy
Published: July 2007

Emerging countries are installing digital satellite transmission systems that eliminate the cost and geographic problems of traditional telecommunication systems and give them the switching and connectivity capabilities of more advanced countries.
Optimizing Router Performance in TCP/IP Networks
Authors: Danrich Joe , Henderson Frank
Published: July 2007

This article reviews the steps necessary to configure and implement a complex router internetwork. This article will specifically concentrate on Cisco routers, and since they support Transmission Control Protocol/Internet Protocol (TCP/IP) natively, it will concentrate on a backbone network employing that protocol.