bluuebunny/crossref_metadata_2025 huggingface dataset:
Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) study of SF6 and SF6–CF4 plasma‐treated low‐density polyethylene films
Authors: Léonard D. , Bertrand P. , Khairallah‐Abdelnour Y. , Arefi‐Khonsari F. , Amouroux J.
Published: December 2004

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) is used to monitor in a semi‐quantitative way the chemical modifications produced at low‐density polyethylene (LDPE) film surfaces by SF6 and SF6–CF4 plasma treatments. The influence of the plasma treatment time (SF6 plasma) and the gas composition (SF6–CF4 plasma) have been investigated. The ToF‐SIMS results are compared with plasma diagnostics (mass spectrometry and optical emission spectroscopy) and with some earlier XPS characterization.

The ToF‐SIMS study of SF6 plasma‐treated LDPE films as a function of the treatment time shows two different structural developments. Beside the expected formation of CxFy structures due to the grafting of F atoms, ToF‐SIMS detects the presence of SFx species at the surface. Their high sensitivity to ablation, due to the plasma ions, was related to two possible interactions of plasma species with the LDPE surface: an adsorption of SFx+/− ions or a dissociative chemisorption of SFx neutral species. In the latter case, the low binding energy of the SC bond can explain the high sensitivity to ablation.

In the case of SF6–CF4 plasma treatment, the incorporation of fluorine, as seen by ToF‐SIMS, is a function of the gas composition. Two maxima are observed when the second gas (either SF6 or CF4) is introduced at low concentration (∼10%). These maxima are confirmed by XPS and actinometric results and are explained with respect to the reciprocal influence of both gases in the plasma discharge.
Ne+ and Ar+ ion bombardment‐induced topography on Si
Authors: Carter G. , Vishnyakov V.
Published: December 2004

The topographic evolution of Si irradiated at room temperature with Ne+ and Ar+ ions in the energy range 5–40 keV at 45° to the substrate normal has been studied. Other than isolated etch pits, no topography results from Ne+ bombardment at all energies and from Ar+ bombardment at 5 and 10 keV. Argon ion bombardment at 20 keV, however, initially produces transverse low‐amplitude waves that transform, with increasing erosion, into larger amplitude, corrugated and faceted, wave‐like structures. The present data do not conform to existing model predictions but do suggest that light low‐energy inert gas ions can be used to inhibit roughening during sputtering erosion.
Electrochemical and thermal oxidation of TiN coatings studied by XPS
Authors: Milošv I. , Strehblow H.‐H. , Navinšek B. , Metikoš‐Huković M.
Published: December 2004

X‐ray photoelectron spectroscopy (XPS) has been used to investigate the electrochemical and thermal oxidation of titanium nitride (TiN) coatings prepared by physical vapour deposition (PVD) at 200°C. Electrochemical oxidation of TiN was carried out at various potentials in phthalate buffer solution (pH 5.0). Evaluation of the XPS Ti 2p and N 1s spectra showed the presence of nitride, oxynitride and oxide species in the layer formed by anodic oxidation. The electrochemical oxidation of TiN to TiO2 proceeds through the formation of a mixed oxynitride/oxide layer, which transforms into oxide (TiO2) at sufficiently positive potentials (E > 1.1 V vs. SHE). The oxidation of TiN to TiO2 is accompanied by the formation of molecular nitrogen (N2). The thickness of the oxide layer reaches ∼7 nm after oxidation at the highest potential (1.9 V). A complete coverage of the TiN surface by TiO2 leads to an anodic peak in the polarization curve. On the basis of angle‐resolved XPS measurements, two types of oxynitride species are identified, which are distributed differently throughout the oxidized layer.

X‐ray photoelectron spectroscopy depth profiles of TiN oxidized at 450°C and 600°C in an oxygen flow reveal that at the lower temperature an oxynitride layer is formed, whereas a thick TiO2 layer appears on top of TiN at the higher temperature. The interface between the nitride and oxide phases is relatively sharp. It is suggested that the mechanism of TiN oxidation proceeds by a progressive replacement of nitrogen by oxygen. The TiN coatings can be used up to 600°C as a protective coating in an oxygen atmosphere.

Valance band spectra of TiN, as well as of electrochemically and thermally oxidized TiN, are presented and discussed.
Evaluation of PVC compound on the Brabender torque rheometer
Authors: Hawkins Tom
Published: December 2004

Increasing the rotor speed during the equilibrium portion of a Brabender torque rheometer test makes the test more sensitive to small changes in critical additives. The improved sensitivity of the instrument can assist processors in selecting the level of an additive for optimum performance and efficiency; in troubleshooting a processing or property problem; and in evaluating the performance of additives, for example, in the laboratory, before production trials.
Recent studies on the use of zinc borate as a flame retardant and smoke suppressant in PVC
Authors: Shen Kelvin K. , Sprague Robert W.
Published: December 2004

By the Oxygen Index test, zinc borate alone is an effective flame retardant in rigid PVC. In flexible PVC formulations containing 50 phr of dioctyl phthalate as the plasticizer, zinc borate in combination with antimony oxide displays a synergistic effect at a total loading of more than 10 phr (1‐to‐1 ratio). In the presence of 30 phr of alumina trihydrate, this synergism increases significantly at a total loading as low as 5 phr. Zinc borate also shows strong synergism with alumina trihydrate. Zinc borate acts as a smoke suppressant in plasticized PVC. With alumina trihydrate, a strong smoke‐reducing synergism is created. Zinc borate in a flexible PVC formulation markedly increases the amount of char formed, whereas the addition of antimony oxide, a vapor phase flame retardant, has little effect on char formation. Zinc borate is a good afterglow suppressant. Volatilized zinc derived from the zinc borate probably contributes to flame retardancy but not to smoke suppression. Zinc compounds can alter the pyrolysis chemistry by catalyzing dehydrohalogenation and promoting crosslinking, resulting in increased char formation and a decrease in both smoke production and flaming combustion.
The measurement of PVC primary particle breakdown
Authors: Rosenthal Jay
Published: December 2004

The breakdown of primary particle structure in PVC is intimately related to the mechanical properties of the material. This article addresses the measurement of primary particle breakdown through microscopic observation, torque bowl rheometry, penetration impact, yield stress determinations, and zero length capillary rheometry. It is found that each method gives information which identifies certain stages in the breakdown process and complements information obtained from the other methods. Characterization via penetration impact identifies the melt conditions at which both the onset of a continuous network on the microscopic scale and primary particle breakdown occurs. Yield stress determined as a function of melt temperature identifies the completion of primary particle breakdown. The onset of primary particle breakdown, as well as the breakdown of other structural units, such as grains, are readily determined by torque bowl rheometry. However, the results from zero‐length capillary rheometry cannot, as yet, be readily generalized in terms of the particulate breakdown process.
Precipitated calcium carbonates as weathering enhancers and impact modifiers for rigid PVC siding and profiles
Authors: Mathur K. K. , Tapper M.
Published: December 2004

A study conducted to determine the suitability of calcium carbonate (CaCO3) fillers in exterior PVC applications revealed that the surface‐treated precipitated CaCO3s of average particle sizes 0.5 micron and 0.07 micron, in fact, minimized the initial yellowing of PVC seen on weathering. It is hypothesized that these particle‐size CaCO3s, being optimum for light scattering, provide greater UV protection. Further, the high surface areas of these CaCO3s increase the capacity to neutralize the HCl responsible for yellowing of the PVC. The optimum filler level is 5 to 10 phr. At this loading level, long‐term impact strength is also retained.
The diffusion of chloroform and carbon tetrachloride from rigid PVC pipe and rigid CPVC pipe into water
Authors: Desrosiers Donald G. , Dunnigan Paula C.
Published: December 2004

The objective ofthis study was to determine whether or not chloroform (CHCl3) and carbon tetrachloride (CCl4) diffuse from poly(vinyl chloride) (PVC) or chlorinated poly(vinyl chloride) (CPVC) pipe into water in the absence of solvent cement. Milli Q water (water which has been deionized, demineralized, and purified of residual organic matter) and tap water were permitted to stand in specimens of recently extruded pipe for 14 days in an attempt to simulate a condition of prolonged stagnation. The CHCl3 and CCl4 in the water were then measured utilizing an analytical method sensitive to 0.01 μg/1 (ppb).

CHCl3 and CCl4 do not diffuse from Geon PVC or TempRite CPVC pipe or fitting compounds in significant quantities under these test conditions. Where sporadic positive responses were noted, these were in the low or fractional μg/1 (ppb) ranges and are far lower than levels commonly found in chlorinated tap water. The low, sporadic values obtained for CHCl3 and CCl4 in both Milli Q and tap water do not permit the calculation of meaningful diffusion constants.
Controlling static electricity in PVC packaging
Authors: Rogers Jay L.
Published: December 2004

The importance of establishing a more sophisticated approach for the control of static electricity in PVC packaging has been underscored by the microelectronics industry and its need for protecting products from electrostatic discharge. Four basic classifications; conductive, static dissipative, antistatic, and insulative, as well as a series of acceptable definitions are now available. Insulative PVC is made conductive by the inclusion of conductive carbon blacks. Antistatic PVC is prepared by the incorporation of an antistatic additive in the compound or by topical application of an antistat from solution. There are no static dissipative additives as such. A more sophisticated approach, such as lamination of different materials is required to prepare a static dissipative product.
Residence time effects during capillary flow of a rigid PVC formulation
Authors: Rangel‐Nafaile C. , García‐Rejón A. , León A. García
Published: December 2004

A typical rigid PVC formulation was rheologically characterized using capillary and parallel plate rheometers within regular processing temperatures and deformations. At 190°C and in an intermediate range of shear rates (10 to 100 l/s) the stress response was a function of the flowing time in the capillary. This behavior was not observed at other temperatures (170 and 210°C). Small amplitude oscillary shear experiments for the same compound but with various thermomechanical histories showed a different behavior as compared to the results of the capillary flow. The specific results of the capillary experiments are consistent with the hypothesis of particulate flow of PVC and also point out the influence of the stabilizers and lubricants in the flow behavior of the compound. The time dependent effect is analyzed in terms of the coupling of thermal and mechanical stresses with the unmelted particles present in the flow field.
Pigments for PVC applications
Authors: Lele Subhash S.
Published: December 2004

Skillful selection and evaluation of pigments for use in PVC compositions demands careful recognition and interpretation of side effects. These include possible interfering effects due to additives such as lubricants, heat and light stabilizers, U.V. screeners, etc. In addition, it has been observed that pigments can chemically react with polymers (PVC included) initiating degradative processes or catalyzing oxidation of PVC or its additives. Other changes affecting pigment performance in PVC include its solvation by the polymer at high processing temperatures and particle size reduction by abrasion during high intensive premixing. Also, in applications where amount of heat build‐up of dark vinyls due to light absorption is important, inorganic pigments are shown to be superior to their organic counterparts. However, care in controlling processing temperatures to preclude polymer‐pigment reactions needs to be exercised when inorganic pigments such as iron oxide, cadmium yellow pigments, and any other mixed metal oxides are evaluated, for use in PVC compounds.
An investigation of calcium stearate dispersion in dryblends
Authors: Clark Dane , Woodley Tom
Published: December 2004

Flowable grades of calcium stearate have coarser particle sizes in order to reduce dusting and improve bulk handling properties. This study shows that in many cases, some flowable grades of calcium stearate will disperse as homogeneously as a powdered grade and under these conditions the two grades of calcium stearate could be used interchangeably. Under some conditions, however, some flowable grades of calcium stearate will not completely disperse and so the use of flowable grades of calcium stearate must be considered on a case by case basis.
Microstructure of PVC primary particles
Authors: Noel Oscar F. , Bauer Jon F.
Published: December 2004

The microstructure of suspension PVC primary particles has been revealed by scanning electron microscopy. The primary particles are composed of agglutinated domains which resemble linked sausage and in some cases are branched. Use of highly polished thin sections and special ion etching techniques appears responsible for revealing these microstructural features not previously reported by other investigators.
The powder properties of poly(vinyl chloride) resins
Authors: Schwaegerle Paul R.
Published: December 2004

The properties of powders depend mainly upon the characteristics of the individual particles and their interactions. In the case of PVC resins, particle characteristics vary broadly depending upon the manufacturing process used or variables within a given process. In this paper, the effects of grain size, size distribution, grain shape, degree of compaction and static on the bulk density and flow properties of PVC resins are studied. Results indicate that grain shape mainly affects bulk density while grain size and distribution mainly affect powder flow. The degree of compaction and the amount of static on the resin grains are variables which can overwhelm other powder properties.
A second generation high performance screw for low extrusion temperature rigid PVC profile compounds
Authors: Kim H. T.
Published: December 2004

The melting and extrusion behavior of low shear rigid PVC profile compounds such as Geon 8700A were investigated in order to answer the fundamental question as to why the output rate of this type of compound is relatively low compared to other types of PVC compound. Typically, the extrusion rate of Geon 8700A is less than half those achieveable on other PVC compounds. A part of the reason is that the extrusion melt temperature of Geon 8700A has to be kept below 360°F in order to preserve primary PVC particles in extrudates and to maintain smooth extrudate surfaces.

The study showed that Geon 8700A follows an entirely different melting mechanism in extrusion—quite opposite to the one previously accepted. Geon 8700A undergoes the melting mechanism observed by Menges, et al. due mainly to its nonwetting characteristic on the barrel surface while most other PVC compounds follow the mechanism described by Tadmor. The difference between the two mechanisms lies in the location of the melt pool formation—the Tadmor model in the pushing side of the screw flight and the Menges in the opposite leading side of the screw flight. Extruding Geon 8700A on screws—notably 2‐channel screws—optimized for the different Tadmor model is one of the major reasons for such a poor performance with this compound.

A new dual pitch deep channel screw has been developed. It is optimized for the melting mechanism of Geon 8700A, resulting in a dramatic improvement in both output rates and extrudate quality. Rates of 350 pounds/hour at 350°F and 400 pounds/hour at 363°F have been achieved on the 3–1/2 inch extruder, whereas 150 to 200 pounds/hour at 350°F is common with the standard screws. This new screw technology, with its high output rate and superior extrudate quality capability, makes the extrusion of cube compounds on single screw extruders competitive with powder extrusion on multi‐screw extruders.
PVC in communications cable
Authors: Kaufman Stanley
Published: December 2004

PVC has a balance of properties that makes it the predominant material used in cable and wire for building applications. The primary reason PVC is used is to satisfy the need for fire resistance. Its electrical properties are adequate for nearly all communications applications in buildings.
Rheology of PVC; part IV: Particulate flow
Authors: Utracki L. A.
Published: December 2004

The behavior of polyvinyl chloride, (PVC), formulation changes drastically with the temperature and the method of sample preparation. In the steady state shear mode, upon a decrease of the rate of deformation, the data may show either a steady increase of the shear viscosity or leveling off to a Newtonian plateau. In the dynamic test mode, the storage modulus, G′, shows a viscoelastic behavior, whereas the loss modulus, G″, shows the yield. Only at temperatures above 210°C are normal flow curves for polymer melts obtained. Rigid PVC wire coating formulation was examined at 140 to 220°C using serrated parallel plates, 2.5 cm in diameter. The data at frequencies ω = 10−2 to 102 rads/s were recorded. The results were analyzed in terms of the relation, derived for polymeric composites, in which the yield stress was explicitly incorporated. It was found that G″ (but not G*) could be easily understood in terms of the model, provided that the yield stress was allowed to vary with the temperature. Three distinct flow zones were observed with the two border‐temperatures at about 180 and 210°C, assigned respectively as due to gel and crystalline melting. These findings were supported by earlier results of the dielectric measurements. In conclusion, treating PVC as a composite provides a simple and effective means of data interpretation.
Effects of postchlorination on key product and processing properties of PVC
Authors: Neuman Richard C.
Published: December 2004

The behavior of PVC resins has been shown to change dramatically when postchlorinated from 57 to 70 percent chlorine. Many of these changes are beneficial: heat resistance, thermoformability, and combustion properties are improved to an extent that opens new market opportunities for properly formulated chlorinated PVC (CPVC) materials. Sharply increasing melt viscosity also results from increasing chlorine content, creating the need for compounding and processing expertise differing from that for rigid PVC. The fact that such expertise has been developed, and is constantly being improved, is expanding the use of CPVC.
Monitoring process conditions of plastisols using a dielectrometer
Authors: Lin Shiow‐Ching
Published: December 2004

Traditionally, an instrument such as an Instron rheometer or thermal analysis is used to characterize the processing conditions of a plastisol. The Instron rheometer is useful only when the material begins to build up mechanical strength. A rheometer such as a Plasti‐corder suffers from the requirement of large sample and low sensitivity toward rheology change caused by phase variation. Thermal analysis only responds to the heat capacity and enthalpy changes at transitions occurring during plasticization. The plasticization involves only weak thermal change and is difficult to detect by thermal analysis. However, the more sensitive method of dielectrometric analysis, which needs only a small sample, was used to detect any rheological change of a plastisol during plasticization. Because the information obtained is from molecular motion, the results are accurate and the speed of characterization is rapid.
Rheology of dispersions of poly(vinyl chloride) with liquid rubbers
Authors: Drag Jiří , Šimoník Josef
Published: December 2004

The effect of polybutadiene and butadiene‐acrylonitrile rubbers on the rheological properties of PVC plastisols was studied. The results obtained show that the flow properties of these blends can be described by the Ostwald‐de Weale equation. Parameters of this equation depend on the amount of rubber in the blend and its solubility parameter which can be derived from the rubber structure.
Regulation of inorganic pigments used in plastics
Authors: Balmer Demetra
Published: December 2004

Review of the government regulations of the major inorganic pigments used in plastics particularly of the metals involved in formation of color.
Functional acrylic monomers as modifiers for PVC plastisol formulations
Authors: Weaver David L.
Published: December 2004

Functional acrylic monomers are used as coagents with polyvinyl chloride plastisols to improve abrasion resistance, tensile strength, chemical resistance, permanent set, hardness, and adhesion. The emphasis of this paper is on the enhancement of physical properties which can be achieved through addition of a variety of different functional acrylic monomers (mono‐, di‐, and tri‐functional) to a PVC plastisol formulation. Collected test data will be given to show the effect these monomers have on the plastisol's physical properties.
Dynamic mechanical analysis of poly(vinyl chloride) compounds and blends
Authors: Rohn Charles L.
Published: December 2004

PVC is one of the most versatile and cost effective commercial polymers. A main limitation of PVC is optimizing its fabrication characteristics and end use properties with minimum adverse effect on either. PVC compounding technology is supersensitive due to effect of subtle variations in formulations causing “inspec” products during one production run and “out‐of‐spec” products in another. Large variations in properties are frequently due to improper mixing. Dynamic mechanical analyses provides a method of monitoring variations in mixing and their affect on morphological structure deviations which can lead to poor processing and end use properties.
Effect of morphology and refractive index on toughness and clarity balance of MBS modified vinyl bottles
Authors: Dunkelberger D. L. , Dougherty E. P.
Published: December 2004

Impact modifiers are used to enhance the toughness of rigid vinyl by providing a dispersed rubbery phase to absorb impact energy and prevent fracture of the otherwise brittle matrix. MBS impact modifiers are complex core//shell polymer structures based on specially prepared butadiene/styrene rubber latices with multiple stages of acrylic and other polymers grafted to them. In addition to providing a rubbery dispersed phase to improve to improve the toughness of vinyl, these structures also maintain clarity by matching the refractive index of the rubber particles with that of the vinyl matrix. Data will be present showing the effect of the rubber morphology, particle size and refractive index on the balance of impact strength and clarity of MBS modified vinyl packaging formulations.
PVC/plasticizer compatibility: Evaluation and its relation to processing
Authors: Ramos‐Devalle Luis , Gilbert Marianne
Published: December 2004

The compatibility of suspension poly(vinylchloride) [PVC] with twelve different plasticizers was determined using calculated compatibility predictors, as well as actual measurements of compatibility. Solubility parameters were capable of classifying plasticizers of a given family in terms of their compatibility with PVC, but were not useful for comparing plasticizers from different families. A polarity parameter, the product of the molar mass of the plasticizer and its polarity ratio, was found to be a useful predictor of activity for monomeric plasticizers.
Use of organotin stabilizers—risk assessment analysis
Authors: Mesch Keith A. , Kugele Thomas G.
Published: December 2004

Organotin compounds have long been known in the PVC industry for their excellent performance properties in almost every application. Over the past several years, a wide variety of health and environmental studies have been conducted which demonstrate the safe use of these performance chemicals as PVC heat stabilizers. This paper introduces the “risk equation” and then applies this equation to the foreseeable exposure risks involved with the use of organotin stabilizers during PVC processing. Further, migration of organotin species from PVC end‐use articles is discussed with comparison to established long‐term no‐effect levels for these chemicals. The environmental fate of organotin compounds and their effects on some species of microorganisms is also addressed. The risk equation is used to fully evaluate all potential hazards to provide a fully informed risk assessment for the use of organotin stabilizers in PVC.
Melt filtration: The final step in the purification of PVC bottles for recycling
Authors: Sadowski Gary M. , Shaw Lane G.
Published: December 2004

The final step in the purification of PVC bottles for recycling is melt filtration. However, this common practice increases in complexity when dealing with a clear, thermally sensitive material such as PVC. This paper will explore both conventional and new techniques for melt filtration. This paper also describes various types of contamination found in the form of other polymers and foreign material, as well as experimental data on acceptable levels and processing conditions to purge them from the vinyl melt stream.
Factors affecting the abrasiveness of filled rigid PVC dry blends
Authors: Augustyn E. J. , Leonard J.
Published: December 2004

Abrasion due to the high speed mixing of rigid PVC dry blends filled with CaCO3 was found to be a function of both the mixing conditions and type and level of CaCO3 used. Laboratory scale tests showed that abrasion is a function of mix time, mix speed, and mixer blade geometry. These variables were standardized to develop a laboratory abrasion test using a Hockmeyer mixer equipped with a soft 3‐in diameter aluminum mixing blade. This procedure was used to investigate the effect of CaCO3 property variables on abrasion during rigid PVC dry blending. Multiple linear regression analysis at 30 phr CaCO3 showed that abrasion increased with filler top cut, mean, acid insolubles, and MgCO3 content, but diminished with an increase in percent less than 1 micron fraction. A more generalized abrasion predictor model was developed by considering surface area to be a linear function of top cut, mean, and percent less than 1 micron properties. Abrasion was greatly minimized by using finer particle size, higher surface area CaCO3 with low acid insoluble and magnesium carbonate levels. These criteria also aid in reducing the abrasive effects of TiO2 during dry blending through a CaCO3/TiO2 interaction.
Primary structure of the nuclear forms of phospholipid hydroperoxide glutathione peroxidase (PHGPx) in rat spermatozoa
Authors: Maiorino Matilde , Mauri PierLuigi , Roveri Antonella , Benazzi Louise , Toppo Stefano , Bosello Valentina , Ursini Fulvio
Published: December 2004

Phospholipid hydroperoxide glutathione peroxidase is a monomeric Se‐peroxidase highly expressed in mammalian male germ cells. Its nuclear form, sperm nuclei glutathione peroxidase (snGPx), has been originally identified in maturating spermatozoa as a transcription product containing an alternative exon within the phospholipid hydroperoxide glutathione peroxidase gene. In this paper, we show that this form is inconstantly detectable in rat spermatozoa where a 20.0 and 25.9 kDa major forms are detected instead. These have been conclusively characterized. The N‐terminus sequence of the 20.0 kDa form confirmed that the protein is identical to cytosolic form, suggesting diffusion into the nucleus. The 25.9 kDa protein represented a truncated form of the previously described nuclear snGPx, lacking the basic nuclear localization signal. This protein is present in two forms differing from each other by the presence of an N‐terminal methionine. The presence of traces of the larger snGPx form suggests that exhaustive proteolytic processing of the precursor produces the 25.9 kDa enzyme, although the alternate use of a downstream ATG, at least in rodents, could not be unequivocally ruled out.
Use of misoprostol on an outpatient basis for postdate pregnancy
Authors: Kipikasa J.H. , Adair C.D. , Williamson J. , Breen J.M. , Medford L.K. , Sanchez‐Ramos L.
Published: December 2004

Objective

Within the obstetric community, several studies suggest that cervical ripening and labor induction after 40 weeks' gestation leads to improved maternal and neonatal outcomes. The most effective drug regimen to safely promote labor has not been determined.

Method

Forty‐nine subjects followed in an outpatient obstetrical clinic with pregnancies of at least 40 weeks' gestation, and an unfavorable Bishop score were assigned randomly to receive oral misoprostol 50 or 25 μg every 3 days for a maximum of three doses.

Results

Twenty‐three subjects received misoprostol 25 μg and 26 received 50 μg. The mean interval (±standard deviation) from start of cervical ripening to delivery was 2.4 days ±0.3 vs. 3.9 days ±0.7 for the 50 and 25 μg groups (P<0.05). No adverse events were noted. However, due to small sample size, less frequent adverse events may be missed. Type II errors cannot be excluded.

Conclusion

In the prevention of postdate pregnancy, outpatients use of oral misoprostol 50 μg appears to result in earlier delivery, as compared to 25 μg.
Periodic finite element/boundary element modeling of capacitive micromachined ultrasonic transducers
Authors: Ballandras S. , Wilm M. , Daniau W. , Reinhardt A. , Laude V. , Armati R.
Published: December 2004

The possibility to excite and detect acoustic waves in fluids using capacitive transducers built on silicon using surface micromachining offers attractive opportunities in the manufacturing of high quality low cost imaging probes. As in the case of standard probe transducers, simulation codes are required to accurately design such devices. The periodic structures extensively used for these capacitive transducers has to be accounted for. In this work, a two-dimensional finite element analysis of capacitive micromachined ultrasonic transducers (cMUT) is proposed, taking into account periodicity and radiation in fluids. The convergence of the calculation is verified using different computation approaches. It is then shown that the periodic computations provide a rapid and precise analysis of the cMUT compared to non periodic calculations. The mutual displacements are deduced from the periodic harmonic calculation, providing an efficient estimation of cross-talk phenomena arising for cMUT radiating in water. The capability of cMUT operating under such conditions to generate a low velocity wave guided at the fluid/silicon interface is theoretically pointed out.
An Examination of Radiation Hormesis Mechanisms Using a Multistage Carcinogenesis Model
Authors: Schöllnberger H. , Stewart R. D. , Mitchel R. E. J. , Hofmann W.
Published: December 2004

A multistage cancer model that describes the putative rate-limiting steps in carcinogenesis is developed and used to investigate the potential impact on cumulative lung cancer incidence of the hormesis mechanisms suggested by Feinendegen and Pollycove. In the model, radiation and endogenous processes damage the DNA of target cells in the lung. Some fraction of the misrepaired or unrepaired DNA damage induces genomic instability and, ultimately, leads to the accumulation of malignant cells. The model explicitly accounts for cell birth and death processes, the clonal expansion of initiated cells, malignant conversion, and a lag period for tumor formation. Radioprotective mechanisms are incorporated into the model by postulating dose and dose-rate-dependent radical scavenging. The accuracy of DNA damage repair also depends on dose and dose rate. As currently formulated, the model is most applicable to low-linear-energy-transfer (LET) radiation delivered at low dose rates. Sensitivity studies are conducted to identify critical model inputs and to help define the shapes of the cumulative lung cancer incidence curves that may arise when dose and dose-rate-dependent cellular defense mechanisms are incorporated into a multistage cancer model. For lung cancer, both linear no-threshold (LNT-), and non-LNT-shaped responses can be obtained. If experiments demonstrate that the effects of DNA damage repair and radical scavenging are enhanced at least three-fold under low-dose conditions, our studies would support the existence of U-shaped responses. The overall fidelity of the DNA damage repair process may have a large impact on the cumulative incidence of lung cancer. The reported studies also highlight the need to know whether or not (or to what extent) multiply damaged DNA sites are formed by endogenous processes. Model inputs that give rise to U-shaped responses are consistent with an effective cumulative lung cancer incidence threshold that may be as high as 300 mGy (4 mGy per year for 75 years) for low-LET radiation.
Enhancement of Cognitive and Electrophysiological Measures of Hippocampal Functioning in Rats by a Low, but Not High, Dose of Dehydroepiandrosterone Sulfate (DHEAS)
Authors: Diamond David M.
Published: December 2004

Dehydroepiandrosterone sulfate (DHEAS) is a steroid hornone that is synthesized, de novo, in the brain. Endogenous DHEAS levels correlate with the quality of mental and physical health, where the highest levels of DHEAS occur in healthy young adults and reduced levels of DHEAS are found with advanced age, disease, or extreme stress. DHEAS supplementation, therefore, may serve as a therapeutic agent against a broad range of maladies. This paper summarizes laboratory findings on dose-response relationships between DHEAS and cognitive and electrophysiological measures of hippocampal functioning. It was found that a low, but not a high, dose of DHEAS enhanced hippocampal primed burst potentiation (a physiological model of memory) as well as spatial (hippocampal-dependent) memory in rats. This complex dose-response function of DHEAS effects on the brain and memory may contribute toward the inconsistent findings that have been obtained by other investigators in studies on DHEAS administration in people.
FEATURE DECOMPOSITION ARCHITECTURES FOR NEURAL NETWORKS: ALGORITHMS, ERROR BOUNDS, AND APPLICATIONS
Authors: WANG HAIYING , MUKHOPADHYAY SNEHASIS , FANG SHIAOFEN
Published: December 2004

In recent years, systems consisting of multiple modular neural networks have attracted substantial interest in the neural networks community because of various advantages they offer over a single large monolithic network. In this paper, we propose two basic feature decomposition models (namely, parallel model and tandem model) in which each of the neural network modules processes a disjoint subset of the input features. A novel feature decomposition algorithm is introduced to partition the input space into disjoint subsets solely based on the available training data. Under certain assumptions, the approximation error due to decomposition can be proved to be bounded by any desired small value over a compact set. Finally, the performance of feature decomposition networks is compared with that of a monolithic network in real-world bench-mark pattern recognition and modeling problems.
EFFECTS OF DILATION AND TRANSLATION ON A PERCEPTRON-TYPE LEARNING RULE FOR HIGHER ORDER HOPFIELD NEURAL NETWORKS
Authors: LENZE BURKHARD , RADDATZ JÖRG
Published: December 2004

In this paper, we will take a further look at a generalized perceptron-like learning rule which uses dilation and translation parameters in order to enhance the recall performance of higher order Hopfield neural networks without significantly increasing their complexity. We will practically study the influence of these parameters on the perceptron learning and recall process, using a generalized version of the Hebbian learning rule for initialization. Our analysis will be based on a pattern recognition problem with random patterns. We will see that in case of a highly correlated set of patterns, there can be gained some improvements concerning the learning and recall performance. On the other hand, we will show that the dilation and translation parameters have to be chosen carefully for a positive result.
A CONJUGATE GRADIENT-NEURAL NETWORK TECHNIQUE FOR ULTRASOUND INVERSE IMAGING
Authors: ZHANG XIAODONG , BROSCHAT SHIRA L. , FLYNN PATRICK J.
Published: December 2004

In this paper, a new technique for solving the two-dimensional inverse scattering problem for ultrasound inverse imaging is presented. Reconstruction of a two-dimensional object is accomplished using an iterative algorithm which combines the conjugate gradient (CG) method and a neural network (NN) approach. The neural network technique is used to exploit knowledge of the statistical characteristics of the object to enhance the performance of the conjugate gradient method. The results for simulations show that the CGNN algorithm is more accurate than the CG method and, in addition, convergence occurs more rapidly. For the CGNN algorithm, approximately 50% fewer iterations are needed to obtain the inverse solution for a signal-to-noise ratio (SNR) of 50 dB. For a smaller SNR of 35 dB, the CGNN method is not as accurate, but it still gives reasonable results.
A NUMERICAL STUDY OF CONJUGATE GRADIENT DIRECTIONS FOR AN ULTRASOUND INVERSE PROBLEM
Authors: ZHANG XIAODONG , BROSCHAT SHIRA L. , FLYNN PATRICK J.
Published: December 2004

In ultrasound inverse problems, the integral equation can be nonlinear, ill-posed, and computationally expensive. One approach to solving such problems is the conjugate gradient (CG) method. A key parameter in the CG method is the conjugate gradient direction. In this paper, we investigate the CG directions proposed by Polyak et al. (PPR), Hestenes and Stiefel (HS), Fletcher and Reeves (FR), Dai and Yuan (YD), and the two-parameter family generalization proposed by Nazareth (TPF). Each direction is applied to three test cases with different contrasts and phase shifts. Test case 1 has low contrast with a phase shift of 0.2π. Reconstruction of the object is obtained for all directions. The performances of the PPR, HS, YD, and TPF directions are comparable, while the FR direction gives the poorest performance. Test case 2 has medium contrast with a phase shift of 0.75π. Reconstruction is obtained for all but the FR direction. The PPR, HS, YD, and TPF directions have similar mean square error; the YD direction takes the least amount of CPU time. Test case 3 has the highest contrast with a phase shift of 1.003π. Only the YD direction gives reasonably accurate results.
ABSORPTION EFFECTS ON SECOND-HARMONIC GENERATION AND CASCADED WAVELENGTH CONVERSION IN NONLINEAR OPTICAL POLYMERS
Authors: KIM MIN-SU , JU JUNG JIN , PARK SEUNG KOO , DO JUNG YUN , LEE MYUNG-HYUN
Published: December 2004

Although nonlinear optical (NLO) polymers often exhibit very high optical nonlinearities, they have barely been applied to tentative NLO devices. The main reason lies in their high absorption losses, and this fundamental trade-off between optical nonlinearity and absorption, stems further advancement. Our theoretical analyses inform us that absorption effect is much less critical in cascaded wavelength conversion (CWC) than in second-harmonic generation (SHG), especially when absorption loss is very high at a given second-harmonic wavelength. Based on this result, we propose CWC as a more practical application of NLO polymers than SHG.
DOUBLY RESONANT TWO-PHOTON ABSORPTION CROSS-SECTIONS: IT DOES NOT GET ANY BIGGER THAN THIS
Authors: KUZYK MARK G.
Published: December 2004

Ever since researchers first probed materials with light, a natural question they have asked pertains to the strength of this interaction. Can materials be made to more strongly absorb light at certain wavelengths, thereby yielding vibrant colors? Can the nonlinear interaction between two beams be used to make an optical switching device? How efficiently can we convert the frequency of light through a nonlinear interaction? All of these questions, in effect, are the same. Equivalently, the question can be phrased as, "how large can we make the linear or the nonlinear susceptibility?" In this paper, we apply sum rules to calculate the maximum limit of the doubly resonant two-photon absorption cross-section. We find that even for a single electron system, the cross-section can exceed δ=105 GM .
PASSIVE MODE LOCKING OF A Nd3+:YAG LASER WITH A SATURABLE ABSORBER IN THE FORM OF THIN FILMS OF J-AGGREGATES
Authors: PLEKHANOV A. I. , KUCH'YANOV A. S. , MARKOV R. V. , SIMANCHUK A. E. , AVDEEVA V. I. , SHAPIRO B. I. , SHELKOVNIKOV V. V.
Published: December 2004

A novel type of a saturable absorber for passive mode locking was proposed. As the novel saturable absorber, we studied the thin solid films of the molecular J-aggregates of polymethyn dyes. The films of the J-aggregates were prepared using different polymethyn dyes. Linear and nonlinear optical properties of these films were investigated. Passive mode locking using these films as the saturable absorber was performed in a Nd 3+: YAG laser. Stable generation of short pulses (pulse duration 13 ps) was achieved.
ALL-POLYMER BASED FLEXIBLE FIELD EFFECT TRANSISTOR USING POLY(3,4-ETHYLENEDIOXYTHIOPHENE) (PEDOT) AND POLYPYRROLE (PPY)
Authors: KANG H. S. , KANG H.-S. , LEE J. K. , JOO J. , LEE M. S. , KIM M. S. , LEE J. Y.
Published: December 2004

We fabricated all-polymer based flexible field effect transistors (FETs) using poly (3,4-ethylenedioxythiophene) (PEDOT) or polypyrrole (PPy) as the active layer and gate electrode. Polyvinyle cinnamate (PVCN) and epoxy were used for a dielectric layer. The PEDOT and PPy as the active layer and electrode were patterned through simple photo-lithography, and PVCN and epoxy as insulating layers were coated by using a spin-coater. We estimated the threshold voltage and trans-conductance through measuring the drain-source current (I ds ) as a function of gate bias (V g ). We suggest that ionic motion in the active layer plays an important role for electrical properties.
LIGHT-EMITTING PROPERTIES OF FLUORENE-BASED COPOLYMERS
Authors: HWANG DO-HOON , LEE JONG-DON , PARK MOO-JIN , LEE JI-HOON , LEE CHANG-HEE
Published: December 2004

A series of random copolymers of 2,7-dibromo-9,9-bis(4′-n-octyloxyphenyl) fluorene (BOPF) and 2,7-dibromo-N-(2′-ethylhexyl)carbazole (EHC) were synthesized through Ni (0)-mediated polymerization. Carbazole comonomer was introduced to improve the hole-transporting properties of PBOPF. The synthesized poly(BOPF-co-EHC)s showed similar UV-visible absorption and PL emission to PBOPF. EL devices were fabricated in an ITO/PEDOT/polymer/Ca/Al configuration. EL devices which used copolymers showed improved device performance over devices which used PBOPF homopolymers due to a more balanced charge transport.
THEORETICAL INVESTIGATION ON ENERGY GAP OF FLUORENE-THIOPHENE COPOLYMER
Authors: POOLMEE P. , HANNONGBUA S.
Published: December 2004

In this work, HOMO-LUMO energy gap and the lowest excitation energy of poly [2,7-(9,9-dihexylfluorene)-co-alt-2,5-(decylthiophene) were performed by different methods. The obtained results indicate that TDDFT(B3LYP/6-31G*)//B3LYP/6-31G* calculations can be useful to provide reliable energetic and structural results of this polymer. The HOMO-LUMO predictions were not accurately obtained as compared to the experimental results. The inverse chain length approximation by using TDDFT(B3LYP/6-31G*)//B3LYP/6-31G* calculations provides energy gap of 2.50 eV, which is in an excellent agreement with the experimental data. However, it was found that the HOMO-LUMO energy gaps obtained from B3LYP calculations were still far from the experimental data.
ON THE MULTIDIMENSIONALITY OF INTRAMOLECULAR HYDROGEN BOND DYNAMICS: HYDROGEN TRANSFER AND IVR IN 3,7-DICHLOROTROPOLONE
Authors: GIESE KAI , LAHAV DORON , KÜHN OLIVER
Published: December 2004

In this work, we investigate the intramolecular vibrational energy redistribution associated with the hydrogen transfer in a derivative of tropolone, namely 3,7-dichlorotropolone. Our quantum simulation is based on the Cartesian reaction surface Hamiltonian together with the multi-configurational time-dependent Hartree approach for the wave-packet propagation. We compare results for two model systems with 6 and 14 dimensions, respectively. The 6D model accounts for the most strongly coupled modes, whereas the 14D model includes further modes with significantly weaker couplings. The linear absorption spectrum of both models shows the development of an OH-stretching band. Furthermore the results show that despite the fact, that the additional modes in the 14D system couple significantly weaker, there are qualitative differences in the decay behavior of an OH-stretching excitation. Limitations of the present reaction surface approach are also discussed.
Lipopolysaccharide induces 5-lipoxygenase-activating protein gene expression in THP-1 cells via a NF-κB and C/EBP-mediated mechanism
Authors: Serio Kenneth J. , Reddy K. Veera , Bigby Timothy D.
Published: December 2004

We examined induced expression of the 5-lipoxygenase-activating protein (FLAP), which is critical for leukotriene synthesis in mononuclear phagocytes. Prolonged exposure to the bacterial component, lipopolysaccharide (LPS), increased FLAP gene transcription, mRNA expression, and protein expression in the human monocyte-like THP-1 cell line. Activation and inhibition of the NF-κB pathway modulated LPS induction of FLAP gene expression. An NF-κB-mediated mechanism of action was supported by overexpression of dominant-negative IκBα and p50/p65 proteins. EMSA/supershift and DNase I footprint analyses revealed that p50 binds to an NF-κB site located in the proximal FLAP promoter, while chromatin immunoprecipitation assays demonstrated that LPS induced binding of p50 but not of p65. Moreover, EMSA/supershift analyses demonstrated that LPS induced time-dependent binding of THP-1 nuclear extracts (containing p50) to this promoter region. Mutation of the NF-κB site decreased basal promoter activity and abolished the p50- and p65-associated induction. EMSA/supershift analyses also demonstrated that LPS induced binding of THP-1 nuclear extracts [containing CCAAT/enhancer binding protein (C/EBP)-α, -δ, and -ε] to a C/EBP site located adjacent to the NF-κB site in the FLAP promoter. We conclude that LPS enhances FLAP gene expression via both NF-κB- and C/EBP-mediated transcriptional mechanisms in mononuclear phagocytes.