bluuebunny/crossref_metadata_2025 huggingface dataset:
A CMOS power amplifier with an adaptive bias scheme for mobile radio frequency identification reader applications
Authors: Han Jeonghu , Kim Younsuk , Park Changkun , Lee Dongho , Hong Songcheol
Published: March 2007

A 900‐MHz linear power amplifier with an adaptive bias scheme is fabricated using a 0.25‐μm CMOS technology. The power amplifier operates over the range of 860–960 MHz, which is the ultrahigh‐frequency band for radio frequency identification (RFID). All matching networks and RF chokes are implemented on a chip. The developed power amplifier provides a 1‐dB‐gain‐compression point (P1 dB) of 27 dBm and a power‐added‐efficiency (PAE) of 28% at theP1 dB. The adaptive bias scheme enables the power amplifier to reduce the quiescent power consumption from 280 to 80 mW by adjusting the gate voltage of power transistors as a function of the input power. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1241–1245, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22435
Optical single sideband modulation based on Sagnac interferometer employing in true time delay
Authors: Liu Zhigang , Zheng Xiaoping , Zhang Hanyi , Guo Yili , Zhou Bingkun
Published: March 2007

Polarization maintaining fiber in a Sagnac interferometer is used to generate optical single sideband (OSSB) that can overcome the power penalty brought by optical double sideband modulation in fiber links. This OSSB modulation used in true time delay (TTD) can form digital TTD and overcome the power penalty. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1492–1494, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22436
A band‐pass filter using via‐hole‐wall cavity
Authors: Hwang Ruey Bing , Pan Jun Liang
Published: March 2007

In this paper, we presented a band‐pass filter consisting of a post‐wall cavity resonator. This band‐pass filter was fabricated in a two‐layered printed circuit board, which includes an input and an output substrate integrated waveguides as the feeding structures in the top layer and a cavity in the bottom layer. The interconnection of the signal between different layers is achieved via the apertures etched on the input and output waveguides and cavity. We found the bandwidth of such a class of band‐pass filter could be altered by tuning the length of the coupling apertures. Besides, the pass‐band frequency can be estimated by the resonant frequencies of the cavity. We have fabricated the band‐pass filter on a low‐loss dielectric substrate and measured its S‐parameters, including the return‐ and insertion‐ loss. In addition, the numerical simulation by the CST microwave studio, a full‐wave time‐domain numerical method, was also carried out. A good agreement between the measured and simulation results was obtained. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1456–1459, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22438
Stable narrow linewidth Er‐doped fiber laser at 1550 nm
Authors: Wu Bo , Liu Yongzhi , Dai Zhiyong , Liu Shuang
Published: March 2007

A narrow linewidth fiber laser based on fiber Bragg grating Fabry‐Perot etalon is demonstrated. Spatial hole burning effect is restrained by fiber Faraday rotator. The short fiber Bragg grating Fabry‐Perot etalon as narrow bandwidth filter discriminates and selects laser longitudinal modes efficiently. Stable single frequency 1550 nm laser is acquired. Pumped by 976 nm laser diode, the fiber laser exhibits 11 mW threshold. Output power (50 mW) is obtained upon the 200 mW pump power. Optical‐optical efficiency is 25% and slope efficiency is 27%. The linewidth of laser is less than 10 kHz, measured by the delayed self‐heterodyne method with 10 km single mode fiber. In addition, the lasing linewidth keeps less than 10 kHz over 1 nm tuning range in the temperature tuning experiment. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1453–1456, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22439
THz characterization of high dielectric‐constant materials using double‐layer sample
Authors: Kapilevih B. , Litvak B.
Published: March 2007

A method of measurement of the real and imaginary parts of high dielectric constant materials at THz frequencies is described. The method is based on application of double‐layer sample with variable distance between slabs. The recorded power transmittance inerferogram is employed for reconstructing complex permittivity of a material under test. Reconstructing algorithm and its realization are presented. Example of measurements of the alumina sample in 0.8–1.1 THz has demonstrated a good agreement with independent data obtained from the time‐domain terahertz spectroscopy method. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1388–1391, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22442
Gain equalization methods in erbium‐doped fiber amplifiers
Authors: de Benito Paula , Diaz Silvia , Abad Silvia , Lopez‐Amo Manuel
Published: March 2007

We show experimental performance comparison of different equalization methods in erbium‐doped optical amplifiers based on silica and ZBLAN host materials. Different configurations are analyzed, including the analysis of hybrid silica/ZBLAN configurations, exploring gain, bandwidth, and noise figure performance. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1346–1349, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22445
Novel compact 2.4/5‐GHz dual‐band T‐slot antenna for WLAN operations
Authors: Ren Wang , Shi Zhiguo , Liu Haiwen , Chen Kangsheng
Published: March 2007

This paper proposes a novel compact dual‐band T‐slot antenna for 2.4/5‐GHz wireless applications. The proposed antenna is composed of two orthogonal slots in a 20 mm by 50 mm ground plane. The antenna was fabricated on a FR‐4 substrate (εr = 4.50, tan δ = 0.02) and was measured in a microwave anechoic chamber. The experimental data and the simulation results agree well with each other and show that the proposed antenna can completely cover both 2.4/5‐GHz bands with satisfactory radiation characteristics. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1236–1238, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22451
Double‐layer substrate integrated waveguide structure with variable fractional bandwidth
Authors: Xu Lei , Che Wenquan , Geng Liang , Wang Dapeng
Published: March 2007

The propagation characteristics of double‐layer SIW structures have been investigated in this paper. On the basis of the theory of resonance cavity and SIW, the simple theoretical formulas for the lower and upper frequencies in the passband have been found. The theoretical analyses have indicated that these two frequencies have much dependence on the width of SIW and the length of the coupling slot, the fractional bandwidth of the double‐layer SIW structures can be controllable. Agreement between the simulation data and the calculated results from the formulas can be observed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1459–1463, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22469
Preparation and fluorescent properties of poly(vinyl alcohol) bearing coumarin
Authors: Wang Baoyan , Guan Xiaolin , Hu Yulin , Su Zhixing
Published: April 2007

A novel water‐soluble fluorescent material was prepared via ring‐opening reaction between 4‐methyl‐7‐(2,3‐expoxypropoxy) coumarin (MEC) and poly(vinyl alcohol) (PVA). The fluorescent behaviors of this material (PVA–MEC) in solution, solid and film were studied in detail. The results showed that the fluorescence of PVA–MEC arose from isolated dye molecules and had a good film forming ability. In addition, the effects of acid/base environments on PVA–MEC were studied and the results showed that it was less affected by environment than 7‐HMC. Moreover, relative fluorescence intensity of PVA–MEC had an excellent linear response in the temperature range of 0–60°C. These observations suggest that PVA–MEC is an excellent fluorescent macromolecular material with a convenient method of preparation and had a good water‐soluble ability. Copyright © 2007 John Wiley & Sons, Ltd.
Alumino‐silicate polyacrylic acid and related cements
Authors: Wilson A. D.
Published: March 2007

The composition and setting reaction of cements formed from aluminosilicates and poly(acrylic acid), the ASPA cements, are described. Setting and hardening results from interactions between specially‐formulated, complex, fluorine‐containing calcium aluminosilicate glasses and aqueous solution of poly(acrylic acid) or similar poly(alkenyl carboxylic acids). Protons from the polyacid penetrate the surface of the glass decomposing the negatively charged aluminosilicate network to a siliceous hydrogel and releasing Al3+, Ca2+ and F‐ ions. These ions migrate, probably as complexes, such as AlF2+, AlF2+ and CaF+, into the polyelectrolyte phase where they cross‐link polyanionic chains, by ionic and possibly chelate binding, causing the cement to gel and set. Overall the reaction may be seen as one where flexible hydrogen bonds, in the liquid, are progressively replaced by more rigid ionic ones, leading to gelation.

The set cement is a composite of glass particles sheathed by a silica gel bound by a metal poly anionic matrix. ASPA cements can attain a compressive strength of 200 N/mm2 in 24 h and are adhesive under oral conditions to tooth materials. They find a number of applications in conservative and preventive dentistry.

Certain naturally‐occurring aluminosilicate minerals react with poly(acrylic acid) to form cement but these are much weaker (not exceeding a compressive strength of 30 N/mm2) and are weakened by water.
Production of organometallic polymers via the interfacial technique. reaction variables in the condensation of diamidoximes with cp2ticl2 and partial thermal characterization of the products
Authors: Carraher Charles E. , Frary Ronald
Published: March 2007

Reaction variables of the interfacial condensation of Cp2TiCl2 with diamidoximes is presented. At 1:1 Cp2TiCl2: diamidoxime ratios and less the product is found to contain predominately units of form I. It is tentatively concluded that the disubstituted product, form II, is formed at Cp2TiCl2:diamidoxime ratios > 1. Sodium hydroxide and triethylamine are both found to be adequate added bases for the reaction.

magnified image

High concentrations of Cp2TiCl2 and low concentrations of diamidoxime favour a more rapid reaction.

Thermal degradation of the products in air and nitrogen occur via identical pathways.
Fundamental properties of densified polymeric glasses
Authors: Wetton Raymond E. , Moneypenny Harry G.
Published: March 2007

Glass forming high polymers have been densified by application of high hydrostatic pressure (∼1.5 kbar) in the melt followed by cooling under pressure to ambient. A density increase of about 1% was induced in each of the following polymers: polyvinylchloride, polymethylmethacrylate, polystyrene, poly‐4‐chlorostyrene, poly‐3‐chlorostyrene, poly‐4‐methoxystyrene and poly‐4‐phenoxystyrene. Differential thermal analysis (DSC) and volume relaxation techniques were used to study the reversion of the densified glass to a more normal glass at a temperature ∼Tg – 15 K in general. Enthalpy relaxation (a change from glass I to glass II) in this region gives a peak or diffuse hump on the DSC scan prior to a normal glass transition temperature. It is considered that although the densified glasses may become thermodynamically stable at a sufficiently low temperature they are inherently unstable at ambient. Reversion to a more normal glass is kinetically too slow to measure at ambient in all cases studied except polymethylmethacrylate. Changes of dynamic Young's moduli and dielectric constant with densification are reported in detail for some systems and in summary for others. The densified glasses exhibit moduli higher by ∼6%, dielectric constant higher by ∼2% and depressed secondary mechanical and dielectric relaxation processes. Ultimate property studies are reported for PVC.
Preparation and characterisation of styrene—methyl methacrylate and styrene–methacrylic acid copolymer latices
Authors: Ono Hiroshi , Jidai Eiki , Shibayama Kyōichi
Published: March 2007

Series of styrene‐methyl methacrylate and styrene‐methacrylic acid copolymer latices have been prepared by emulsion polymerisation using polyoxyethylene nonyl phenyl ether as emulsifier and potassium persulphate as initiator. the effects of surfactant concentration and monomer composition on the ultimate particle size and conversion were investigated. The ultimate particle diameters decreased with increasing surfactant concentration, while the conversions were found to be almost independent of surfactant concentration. The ultimate particle diameters were notably decreased by increasing the content of methacrylic acid. Trace carboxyl groups were detected both in polystyrene latex and styrene‐methyl methacrylate copolymer latices. The number of sulphate groups on the polystyrene latex surface was about five times that of carboxyl groups.
Infrared spectra of chlorinated petroleum fractions
Authors: Sosa José M.
Published: March 2007

The infrared spectra of several chlorinated petroleum fractions are reported. Although the spectra of chlorinated branched and linear fractions are different in the 600–800 cm−1 region, it is very difficult to detect less than 15% of the toxic chlorinated kerosene in mixtures with chlorinated n‐paraffin waxes.
Tg/Tm for unsubstituted polymers
Authors: Boyer Raymond F.
Published: April 2007

Polymers under discussion can be represented by [CH2)nR]p where R is CH2, CF2, O, S or CH = CH; and where n can vary from 0 to ∞. The copolymer, P(ethylene‐alt‐TFE) is also included. These polymers tend to be highly crystalline with resultant confusion about their Tg and hence their Tg/Tm values and a clarification scheme is proposed in which it is considered that each such polymer has a double glass transition, Tg(L)/f(χc), Tg(U) = F(χc); and a sub‐glass T<Tg(L) at 0.75 Tg(L), where F(χc) signifies a function of fractional crystallinity, χc. T<Tg(L) and Tg(L) increase linearly with Tm. The ratio, Tg(L)/Tm, is therefore, not a constant but is close to 0.5. T<Tg(L)/Tg(L) is also not a constant but is close to 0.75. Tg(U) lies within a wedge whose top and bottom sides increase with Tm. The premelting, intracrystalline transition temperature, Tαc, is also a linear function of Tm. It is suggested that the scheme outlined above should help to resolve uncertainties in assigning transition temperatures for unsubstituted polymers. The low Tg/Tm values for these polymers is discussed in terms of their small da/dc ratios and small crosssectional areas per chain.
Heat‐resistant resins obtained by polycondensation of aromatic aldehydes with methylpyridines
Authors: Bloch B. , Ropars M.
Published: April 2007

Polycondensation of terephthalic aldehyde with 2,4 — or 2,6‐dimethyl ‐, or 2,4,6 — trimethylpyridine leads to a new kind of heat‐resistant resin with aromatic‐heterocyclic structure.

These resins are mixtures of thermosetting oligomers. A few components have been identified after separation by size‐exclusion chromatography. Although infrared spectroscopy sheds some light on certain aspects of their heat‐curing mechanism, this has not yet been fully elucidated.

Derivatives of trimethylpyridine (symmetrical collidine) appear to be particularly interesting in view of their possible use with reinforcing fibre materials for prepreg fabrication. These derivatives lead to composite materials whose high mechanical properties remain unaffected for several thousand hours at 250°C and a few hours at 350°C.

These products are being developed on an industrial scale under the name of PSP resins.
Effect of substituents in the styrene aromatic ring on water absorption and thermal stability of an unsaturated polyester resin
Authors: Douglas William E. , Pritchard Geoffrey
Published: April 2007

The water absorption at 50°C and dynamic and isothermal thermogravimetric properties were studied for a series of resins made from the same maleic/phthalic anhydride‐based unsaturated polyester cross‐linked with each of styrene, 4‐methyl styrene, 4‐ethyl styrene, 4‐n‐butyl styrene, 4‐isopropyl styrene, tertiary butyl styrene, 4‐chlorostyrene and 3,4‐dichlorostyrene. Chloro substituents and most alkyl groups give rise to a loss of water resistence. However, the tertiary butyl group leads to a decrease in both water absorption and water damage. The thermal stability of the resin is decreased by chloro substituents and increased by n‐alkyl groups, and the results suggest that the main degradation step involves styrene residues, but that the initial decomposition does not do so.
Curing characteristics of anaerobic sealants and adhesives
Authors: Stamper David J.
Published: April 2007

During the past 20 years the usage of anaerobic‐curing sealants and adhesives has grown rapidly from almost nothing to an estimated 1500 tonnes per annum. An annual growth rate in excess of 10% is predicted throughout the present decade.

In this paper, the gradual improvement in the performance characteristics of these systems is traced, from the somewhat uncommercial earliest formulations which required air or oxygen to be bubbled continuously through the system in order to prevent premature gelation, to the present day systems which cure rapidly on most metallic substrates yet possess shelf lives in excess of twelve months.

Reaction mechanisms are postulated for the ever‐more efficient curing systems being developed and also for the extremely delicate balance between high reactivity and extended storage stability in commercially available products.
Positron annihilation measurements and their application to thermosets
Authors: Coleman Clifford F. , Smith Frederick A. , Hughes Anthony E.
Published: April 2007

Positrons which annihilate with electrons in solids usually give rise to two gamma rays, each with an energy close to 0.511 MeV, which are emitted in almost exactly opposite directions. The spread of the energies about the nominal value, which amounts to a few keV, is a Doppler effect reflecting the velocities along the direction of gamma emission of the electrons with which the positrons happen to annihilate. Thus the shape of the annihilation line gives a weighted measure of the electron momentum distrubution, emphasising the conduction electrons and the loosely bound localised electrons. The Positron Annihilation Techniques (PAT) allow this distribution to be determined non‐destructively, and lend themselves to comparative measurements. If some of the positrons are trapped at negatively charged sites within a solid the annihilation radiation will reflect both the changed momentum distribution of the electrons seen at the trapping sites and the relative number of positrons which are trapped at the time of annihilation. To be effective the traps must have a mean spacing < 100 nm, but the sensitivity of PAT to atomic scale traps such as vacancies can nevertheless be very high. Finally, in materials containing few free electrons, information can be extracted from the formation of the positron analogue of the hydrogen atom, positronium.

With standard positron sources probing depths in plastics can be a few millimetres. The PAT techniques have already proved their worth in investigations of electron momentum distributions in ordered solids, and in investigations of phase changes and of mechanical and fatigue damage in metals and alloys. Their out‐of‐the‐way combination of characteristics makes them well worth consideration in other materials applications when conventional techniques run into difficulties.
The application of ultra‐violet microscopy to thermosetting polymers
Authors: Billingham Norman C. , Calvert Paul D. , Ghaemy Mosa G.
Published: April 2007

Optical microscopy with ultra‐violet illumination has been used to monitor the curing reactions and final structure of an amine‐cured epoxy resin system. When low concentrations of u.v. absorbing additive are added to the resin before curing, the additive is usually completely uniformly distributed in the cured product. No density variations on a scale resolvable in optical microscopy are visible. Similarly when a u.v. absorbing eragent is allowed to diffuse into the cured resin its diffusion profile is normal and shows no detectable density fluctuations in the resin. Reaction of cured resins with a reagent which couples with amino groups to give u.v. absorbing adducts shows that conventional hand mixing techniques do not produce complete mixing of the resin components and spatially non‐uniform concentrations of unreacted amines are found. This effect can only be removed by unusually thorough mixing techniques. Use of a water soluble u.v. absorber allows penetration of the epoxy by water to be followed. In particular, the penetration of fibre‐matrix interfaces by water can be visualised.
Rubber‐Toughened Polyester Resins
Authors: Alexander I. J.
Published: April 2007

Blending elastomers into plastics to produce polymer composites with improved properties, particularly toughness, is a well known technique exemplified by such products as high‐impact polystyrene (HIPS), ABS and rubber‐toughened epoxies. In this present work a wide range of elastomers has been studied to find polyester resin‐rubber compositions which are storage‐stable, have acceptable rheology and cure characteristics, and, when cured, provide materials with significantly improved toughness.

It has now been shown that commercially available liquid rubbers, when suitably modified, will remain dissolved in the resin without separation, and that the cured polyester‐rubber composition has a complex polyphase morphology which resembles, for example, that found in HIPS. The fracture energy of these materials has been shown to be many times that of conventional polyester resins.

In further work methods have been developed which make possible the incorporation of much higher molecular weight rubbers into polyester resins to produce impact resistant products.
Some aspects of the effects of fillers on the behaviour of PVC in fires
Authors: Matthews George , Plemper George S.
Published: April 2007

The effects of particle size and concentration of calcium carbonate fillers on the critical oxygen index and the evolution of hydrogen chloride during pyrolysis of unplasticised PVC has been shown to parallel the effects in plasticised PVC but to differ from them in two respects. Coarser varieties of calcium carbonate (i.e. appreciably greater than 0.1 micron) react with pyrolysis hydrogen chloride more efficiently in UPVC than in plasticised PVC.

Plots of critical oxygen index against concentration of calcium carbonate in UPVC show two inflexions, maxima at low concentrations (i.e. < 30 PHR) and minima at high concentration (i.e. > 40 PHR). Similar inflexions are also shown with alumina trihydrate and silica. In both plasticised and unplasticised PVC, calcium oxide produces a steady fall in critical oxygen index with increasing concentration, more marked than with calcium carbonate at equal hydrogen chloride retentions.

The complex behaviour is attributed to the number of factors contributing to overall burning behaviour. Of these, char formation, in particular, is not readily assessed numerically, and consequently it has not been possible to quantify the contributions of the individual effects.
Upper and lower critical solution temperatures in 1‐octanol solutions of polyethylene
Authors: Muraoka Yoichiro , Inagaki Hiroshi , Suzuki Hidematsu
Published: April 2007

Cloud points of 1‐octanol solutions of four linear polyethylene samples having different molecular weights were measured visually in both regions of the upper and lower critical solution temperatures (UCST and LCST). From the (temperature, polymer weight fraction) phase diagrams drawn, the UCST and LCST were determined. These data were plotted according to Shultz and Flory, to yield the results of ΘU = 444 K and ψ1,U = 1.16 for the UCSTS and ΘL = 621 K and ψ1,L = −5.4 for the LCSTs. Here, Θ is the Flory theta temperature, ψ1 is the entropy of dilution parameter, and the subscripts U and L refer to the UCST and LCST respectively. The interaction parameter χ1 of the present solutions over the temperature range from ΘU to ΘL was first estimated according to the Eichinger version of the classical lattice theory. Secondly, the Flory and the Patterson polymer solution theories were applied in order to obtain the information on each contribution of cohesive energy and free volume to χ1(T) separately. It was found that the final results significantly depend upon the reference temperature at which the equation‐of‐state parameters are determined. This finding suggests that the temperature reduction in the Foory theory is inadequate.
Ultrasonic attenuation and adiabatic compressibility of polyethyleneoxide‐water mixtures
Authors: Pethrick Richard A. , Poh B. T.
Published: April 2007

Ultrasonic attenuation and velocity measurements are reported at 2MHz over a temperature range from 293 to 353K for mixtures of polyethylene oxide and water for concentrations from 0 to 100%. The ultrasonic attenuation in the mixtures was observed to be lower than that in the ideal solution. This implies that the structural distribution in the system is changing with concentration. Studies of the compressibility of water indicate the existence of a minimum at approximately 343K. Introduction of polyethylene oxide leads to a shift of the minimum to lower temperature. These data are interpreted in terms of changes in the structure of water and the interaction of the polymer with water.
Dielectric and physico‐mechanical properties of butyl rubber loaded with some white fillers
Authors: Hanna Faika F. , Yehia Abbas A. , Hakim Itedal K. , Bishai Augenie M. , Saad Azima L. G.
Published: April 2007

A systematic dielectric study over the frequency region from 0.06 to 300kHz has been carried out on butyl rubber loaded with one of six white fillers namely talc, calcium carbonate, dolomite, barytes, kaolin and silica in increasing quantities at room temperature. A low frequency loss term whose maximum lies around 104Hz for all samples is noticed and is attributed to Maxwell‐Wagner losses arising from the interfacial polarisation due to the presence of the ingredients added stepwise to raw rubber. These losses are found to increase by the addition of filler and the cause of this increase is interpreted.
Soluble synthetic polymers as targetable agents for intracellular drug release
Authors: Lloyd John B. , Duncan Ruth , Pratten Margaret K.
Published: April 2007

Soluble synthetic polymers have potential as targetable drug delivery and release agents. Copolymers of 2‐hydroxypropylmethacrylamide with oligopeptide side‐chains have been used to demonstrate the attachment of drug analogues by covalent linkages susceptible to hydrolysis by lysosomal enzymes but stable in plasma. Targeting of polymers to particular sites has been illustrated by making use of the substrate specificity of adsorptive pinocytosis.
Release of ergotamine from poly (2‐hydroxyethyl Methacrylate)
Authors: Huglin Malcolm B. , Sloan David J.
Published: April 2007

The release of the alkaloid ergotamine from thin discs of poly(2‐hydroxyethyl methacrylate) [PHEMA] into an aqueous buffered medium has been effected under sink conditions and monitored by fluorescence spectroscopy. The process was found to be diffusion controlled, the fraction of available drug released being linear in (time)1/2 during the initial stages. The influences of disc thickness, drug load and temperature were investigated and yielded 2.0 (± 1.0) × 10−13 m2 s−1 for the diffusion coefficient of ergotamine through the swollen gel at 310K and a value of 69 ± 5 kJ mol−1 for the activation energy of diffusion. For the uptake of aqueous buffer alone into PHEMA the corresponding values were ca 100 times greater and three times smaller respectively.
The automation of a torsional braid analyser, interfaced with an apple microcomputer
Authors: Cowie John M. G. , Ferguson Roderick
Published: April 2007

The automation of a torsional braid analyser by interfacing with an Apple II microcomputer is described. The use of an analogue to digital convertor is discussed together with appropriate mathematical procedures for carrying out the subsequent on‐line data processing. Finally, the advantages of this automated system for obtaining thermomechanical spectra of polymeric materials, as compared with the previous method of data collection and analysis, are discussed.
Recent trends in the stabilisation of polymers
Authors: Scott Gerald
Published: April 2007

Polymers are subject to oxidation during processing due to the application of mechanical stress (shear) which leads to the scission of the polymer backbone and the formation of initiating macroalkyl radicals. Under the conditions of low oxygen concentration in commercial mixing operations, a catalytic redox antioxidant mechanism can operate which involves the alternating oxidation of alkyl radicals and reduction of alkylperoxyl radicals.

‘Stable’ free radicals (A) notably phenoxyl and nitroxyl radicals and inorganic radicals such as I are very effective melt stabilisers for polyolefins because of their ability to undergo reversible oxidation and reduction. magnified image

A similar mechaism has been shown to operate during the mechano‐oxidation of rubbers in service (fatigue) and during the photo‐oxidation of polyolefins.
The structures of polydienes prepared anionically in tetrahydrofuran in the presence of sterically hindered lewis acids II ‐ polyisoprene and trimesityl boron
Authors: Bres Philippe , Richards David H. , Stewart Malcolm J. , Viguier Michele
Published: April 2007

The presence of the sterically hindered Lewis acid, trimesityl boron, during the anionic polymerisation of isoprene is shown to affect the structure of the resulting polymer only marginally. This behaviour contrasts with its effect when the monomer is butadiene. The principal change is an increase in 1,4‐content at the expense of 1,2‐structure, with the proportion of 3,4‐structure remaining unaffected. These results are explained in terms of the isomeric forms of the propagating anion.
Positron annihilation and X‐ray diffraction studies of cellulose and some derivatives
Authors: Doyle Stephen , Malhotra Bansi D. , Peacock Norman , Pethrick Richard A.
Published: April 2007

Positron lifetime measurements are reported over a temperature range from 290 to 380K on cellulose and certain of its derivatives. The lifetime spectra were resolved into three components each attributed to a different mode of positron annihilation in the polymer. The longest lifetime component is associated with the decay of ortho‐positronium and is a function of the average cavity distribution in the sample. It is observed that significant differences exist in the lifetimes of positrons in cellulose and its derivatives which can be interpreted as evidence for changes in the free volume distribution in these materials. Comparison of positron decay in samples of cellulose acetate prepared at both room temperature and elevated temperature indicate that the phenomena of gelation in this material is accompanied by a reduction of free volume. The correlation of such observations with the dynamic properties of these polymers is discussed.
The isolation and characterisation of grafts from glass surfaces and their immiscibility with homopolymer
Authors: Eastmond Geoffrey C. , Mucciariello Gennaro
Published: April 2007

A procedure for photochemically detaching, isolating and characterising grafts (produced by a method developed previously by the authors) from glass surfaces is described. Preliminary results indicate that the molecular weights and molecular weight distributions can be varied through control of the kinetics of graft formation; our previous studies are seen to have produced a high surface coverage of grafts of high molecular weight. A thermodynamic argument is developed to explain the immiscibility of grafts with free homopolymer for high surface coverage by grafts from which it is seen that the immiscibility is entropy‐driven. Comparisons are drawn between our previous studies and relevant studies by other workers and apparent anomolies are explained.
Electron beam lithography — influence of molecular characteristics on the performance of positive resists
Authors: Sharma Varinder K. , Affrossman Stanley , Pethrick Richard A.
Published: April 2007

Polymers are widely used as resists in electron beam lithography. This paper is concerned with theoretical modelling of the electron beam lithographic process and establishing criteria which need to be satisfied for a polymer to behave as a good positive resist. The effects of molecular weight, tacticity, solvent selection and sequence structure are discussed. Criteria are presented upon which the design of a new resist material may be based.
Spacial arrangement of poly(vinylacetate) synthesised by matrix polymerisation
Authors: Bezdadea Mariana , Leanca Mihai
Published: April 2007

The tactic structure of PVAc synthesised by matrix polymerisation was reported. At temperatures below 0°C, for a ratio, matrix to monomer, equal to 3, a higher packing degree of the macromolecular chains was obtained. The third peak of the X‐ray diffraction spectra of matrix samples suggests the existence of isotactic polymer.
Mechanochemically initiated polymerisations. 12. Spectral and thermal characterisation of some products obtained by vibratory milling of benzene and pyridine
Authors: Oprea Cleopatra Vasiliu , Popa Marcel , Cascaval Constantin N.
Published: April 2007

Vibratory milling is used to open the aromatic ring of compounds such as benzene and pyridine and this is followed by concatenation of the structural units. The products obtained form both the soluble fractions in methanol, i.e. dimethylformamide and the insoluble fraction, the latter being found in the prevalent amount. Analysis of the soluble fractions by infrared spectroscopy (i.r.) and pyrolysis‐gas chromatography (p.‐g.c.) conforms their linear structure of the polyenic type with some short crosslinkings and a great sensitivity to the action of atmospheric oxygen.
Properties of (BA)n‐B type block copolymers of butadiene and dimethyl itaconate prepared using macroazonitrile initiators
Authors: Cowie John M. G. , Yazdani‐Pedrarn Mehrdad
Published: April 2007

Multi‐block copolymers of the (BA)n‐B type, where A is poly(dimethyl itaconate) and B is polybutadiene, were synthesised using a macroazonitrile initiator. This was prepared by the reaction of 4, 4′ azobis (4‐cyanopentanoyl chloride) with hydroxyl terminated polybutadienes. and subsequent decomposition of the azo group in the presence of dimethyl itaconate monomer yielded the block copolymer. Measurement of their glass transition temperatures revealed that the copolymers formed two phases. The dynamic thermomechanical properties were measured and this demonstrated that in the temperature range 290–400K, the glassy poly(dimethyl itaconate) blocks acted as crosslinking sites for the elastomeric polybutadiene blocks and that the materials behaved like typical elastoplastic block copolymers. Property variation was obtained when the ratio of polybutadiene to poly(dimethyl itaconate) in the copolymers was altered.
Molecular weight averages and distributions of unsaturated polyesters: Their effect on the properties of styrene‐crosslinked networks
Authors: Douglas William E. , Ghotra Joginder S. , Ho Dawn , Pritchard Geoffrey
Published: April 2007

Unsaturated polyesters have been synthesised and modified to determine the effect of number‐average molecular weight (M̄n) and molecular weight distribution (MWD) on the following properties of the polyesters after crosslinking with styrene: (i) water absorption, (ii) initial mechanical properties and (iii) property retention after immersion The most important factor was found to be the very low molecular weight ‘tail’ which adversely affected behaviour in several respects. Above a certain M̄n, initial mechanical properties were insensitive to the variables mentioned, but mechanical property retention after immersion closely reflected the water absorption behaviour by its dependence on the average chain length and the low molecular weight constituents. The importance of removing such constituents is apparent.
Reform in statistical education
Authors: Huck Schuyler W.
Published: April 2007

Two questions are considered in this article: (a) What should professionals in school psychology do in an effort to stay current with developments in applied statistics? (b) What should they do with their existing knowledge to move from surface understanding of statistics to deep understanding? Written for school psychologists who have completed their formal education, this article examines the way in which four kinds of relatively new technological tools—Java applets, electronic discussion groups, blogs, and online books, tutors, and courses—can help professionals increase their knowledge and understanding of statistical concepts and procedures. Because new statistical procedures, over time, enter the arsenal of applied researchers, and given that the National Association of School Psychologists explicitly states that continuing professional development in research is an expectation, the information presented here shows school psychologists that there are useful and efficient ways for them to “keep current” with advances in applied statistics. © 2007 Wiley Periodicals, Inc. Psychol Schs 44: 527–533, 2007.
NF‐kappaB in the lungs of premature rabbits during mechanical ventilation—comparison between conventional mechanical ventilation (CMV) and high‐frequency oscillation (HFO)
Authors: Oba Kunihiro , Yamashita Hiroko , Waragai Aki , Kawano Toshio
Published: March 2007

The purpose of this study is to compare pulmonary nuclear factor‐kappaB (NF‐kappaB) activity of conventional mechanical ventilation (CMV) with that of high‐frequency oscillation (HFO) in premature rabbit lungs. For surfactant‐depleted model, we used premature rabbits in order to exclude the effect of lung lavage on the activation of NF‐kappaB. The premature rabbits were delivered at a gestational age of 27 days by hysterotomy. Both modes of the ventilator were set at the same MAP and FiO2. We used animals that had PCO2 levels of approximately 50‐mmHg. Animals were sacrificed after 1‐hr ventilation with CMV or HFO. Then activity of pulmonary NF‐kappaB was assessed. We observed that NF‐kappaB activity was higher in the lungs of CMV compared with those of HFO, as measured by Western blot analysis. The activity level of NF‐kappaB in the lungs measured by ELISA was significantly higher in CMV group than in HFO group. We conclude that a higher level of NF‐kappaB activation was associated with CMV when compared to HFO. Pediatr Pulmonol. 2007; 42:446–451. © 2007 Wiley‐Liss, Inc.
A model of restriction endonuclease MvaI in complex with DNA: A template for interpretation of experimental data and a guide for specificity engineering
Authors: Kosinski Jan , Kubareva Elena , Bujnicki Janusz M.
Published: April 2007

R.MvaI is a Type II restriction enzyme (REase), which specifically recognizes the pentanucleotide DNA sequence 5′‐CCWGG‐3′ (W indicates A or T). It belongs to a family of enzymes, which recognize related sequences, including 5′‐CCSGG‐3′ (S indicates G or C) in the case of R.BcnI, or 5′‐CCNGG‐3′ (where N indicates any nucleoside) in the case of R.ScrFI. REases from this family hydrolyze the phosphodiester bond in the DNA between the 2nd and 3rd base in both strands, thereby generating a double strand break with 5′‐protruding single nucleotides. So far, no crystal structures of REases with similar cleavage patterns have been solved. Characterization of sequence‐structure‐function relationships in this family would facilitate understanding of evolution of sequence specificity among REases and could aid in engineering of enzymes with new specificities. However, sequences of R.MvaI or its homologs show no significant similarity to any proteins with known structures, thus precluding straightforward comparative modeling. We used a fold recognition approach to identify a remote relationship between R.MvaI and the structure of DNA repair enzyme MutH, which belongs to the PD‐(D/E)XK superfamily together with many other REases. We constructed a homology model of R.MvaI and used it to predict functionally important amino acid residues and the mode of interaction with the DNA. In particular, we predict that only one active site of R.MvaI interacts with the DNA target at a time, and the cleavage of both strands (5′‐CCAGG‐3′ and 5′‐CCTGG‐3′) is achieved by two independent catalytic events. The model is in good agreement with the available experimental data and will serve as a template for further analyses of R.MvaI, R.BcnI, R.ScrFI and other related enzymes. Proteins 2007. © 2007 Wiley‐Liss, Inc.
“Chemistry for all, instead of chemistry just for the elite”: Lessons learned from detracked chemistry classrooms
Authors: Watanabe Maika , Nunes Nicole , Mebane Sheryl , Scalise Kathleen , Claesgens Jennifer
Published: March 2007

Within the already limited literature on instructional practices in detracked classrooms, there are even fewer research‐based studies of detracked science classrooms. This article attempts to address this gap in the research literature, delving into the unique challenges and instructional responses to teaching detracked science. The authors report on a case study of two chemistry teachers' heterogeneous classrooms at a racially diverse, public high school in California, where all students have been required to take chemistry since the school's founding in 1994. The authors highlight the following four beliefs and instructional practices that were instrumental in teachers' successful efforts to teach detracked chemistry classes: (1) teachers' true belief in a developmental conception of ability and intelligence; (2) a focus on an inquiry‐based pedagogical approach to chemistry foregrounding real‐world contexts; (3) a focus on teaching students study skills; and (4) a strong sense of community in the classroom, where students are held responsible for their own and each other's learning. To illustrate each of these findings, the authors select vivid examples from fieldnotes of classroom observations as well as interviews of teachers and students that make clear how teachers enacted and students experienced these elements in chemistry classrooms. © 2007 Wiley Periodicals, Inc.Sci Ed91:683–709, 2007
Statistical tests with accurate size and power for balanced linear mixed models
Authors: Muller Keith E. , Edwards Lloyd J. , Simpson Sean L. , Taylor Douglas J.
Published: March 2007

The convenience of linear mixed models for Gaussian data has led to their widespread use. Unfortunately, standard mixed model tests often have greatly inflated test size in small samples. Many applications with correlated outcomes in medical imaging and other fields have simple properties which do not require the generality of a mixed model. Alternately, stating the special cases as a general linear multivariate model allows analysing them with either the univariate or multivariate approach to repeated measures (UNIREP, MULTIREP). Even in small samples, an appropriate UNIREP or MULTIREP test always controls test size and has a good power approximation, in sharp contrast to mixed model tests. Hence, mixed model tests should never be used when one of the UNIREP tests (uncorrected, Huynh–Feldt, Geisser–Greenhouse, Box conservative) or MULTIREP tests (Wilks, Hotelling–Lawley, Roy's, Pillai–Bartlett) apply. Convenient methods give exact power for the uncorrected and Box conservative tests. Simulations demonstrate that new power approximations for all four UNIREP tests eliminate most inaccuracy in existing methods. In turn, free software implements the approximations to give a better choice of sample size. Two repeated measures power analyses illustrate the methods. The examples highlight the advantages of examining the entire response surface of power as a function of sample size, mean differences, and variability. Copyright © 2007 John Wiley & Sons, Ltd.
Renaissance in chiroptical spectroscopic methods for molecular structure determination
Authors: Polavarapu Prasad L.
Published: March 2007

Two of the chiroptical spectroscopic methods, namely optical rotatory dispersion (ORD) and electronic circular dichroism (ECD), have been around for several decades. But their use in determining the absolute configuration and predominant conformation is gaining renewed interest with the availability of quantum mechanical methods for predicting ORD and ECD. Two other methods, namely vibrational circular dichroism (VCD) and vibrational Raman optical activity (VROA), are relatively new and offer convenient approaches for deducing the structural information in chiral molecules. With the availability of quantum mechanical programs for predicting VCD and VROA, these methods have attracted numerous new researchers to this area. This review summarizes the latest developments in these four areas and provides examples where more than one method has been used to confirm the information obtained from individual methods. © 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 7: 125–136; 2007: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20117
1992: State of play
Authors: Goodman Brian
Published: April 2007

Now past the halfway point for establishing a single market by 1992, the 12 member states of the European Economic Community are pausing to review the progress. What has been accomplished so far? And what remains to be done? The answers to these questions are outlined, providing background to the most important question: How will your organization be affected?
Obtaining U.S. Government backing for your export transactions
Authors: Krahmer Elizabeth M.
Published: April 2007

A guarantee or insurance from a U.S. government may be what you need to get bank financing for your export transactions.
Streamlining international transportation costs
Authors: Ramsdale Phil , Harvey Steve
Published: April 2007

International transportation costs are one of the most overlooked segments of a multinational's operating expenses. Waste abounds. Here's what companies can do to better control this cost area.
Using “Rapid Response” as a competitive tool
Authors: Simon Donald R. , Alvarez Suzanne G.
Published: April 2007

New technology allows companies to respond quickly to customer demands that differ from country to country. In the international arena, time and flexibility are competitive weapons.
Understanding India's attitude toward foreign investment
Authors: Ganguly Sumit
Published: April 2007

India's leadership of the developing world is long standing, and understanding why it has reservations about a complete commitment to free trade and opening its economy to foreign investment–India has once again been listed under the Super 301 clause of the 1988 Trade Act–can provide insights into the thinking of other developing countries.
The meaning of German unification
Authors: Geipel Gary L.
Published: April 2007

Like most experiments, the merger of Germany will likely be messy. But in time, a united Germany will emerge that is an industrial and technological powerhouse like nothing Europe has seen before.
4. Management of the infertile couple in tertiary care, part 1
Authors: Mcclure Neil
Published: March 2007

As well as all the investigations and services offered by secondary care, the tertiary care unit provides advanced fertility surgery and, in particular, assisted reproductive technologies (ARTs). In the first part of this article, Professor McClure discusses ovarian hyperstimulation and subsequent oocyte retrieval, which are the cornerstone of therapy for couples undergoing ARTs. He also outlines how sperm is collected and prepared for use in assisted conception techniques. For those couples who are unable to produce their own gametes, most ART units offer donor sperm and donor oocytes. Copyright © 2007 Wiley Interface Ltd