bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas‐Phase Olefin Polymerization in the Presence of Supported and Self‐Supported Ziegler‐Natta Catalysts
Authors: Kanellopoulos Vassileios , Gustafsson Bill , Kiparissides Costas 
Published: April 2008

AbstractThe RPPFM is employed to describe the gas‐phase catalytic polymerization of ethylene in the presence of supported or self‐supported Z‐N catalysts. Numerical simulations are carried out to analyze the effect of the catalyst type on the polymerization rate, particle overheating and the average molecular polymer properties of the polyolefin. It is shown that non‐porous, self‐supported Ziegler‐Natta catalysts exhibit higher particle growth rates and lower particle overheating. The average molecular weight of polyethylene produced by both catalysts is almost identical. Depending on particle size and polymer crystallinity, the average monomer solubility and the effective monomer diffusivity can significantly vary.magnified image
Competitive heavy metal removal by poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid‐co‐itaconic acid)
Authors: Çavuş Selva , Gürdağ Gülten 
Published: April 2008

AbstractThe competitive removal of Pb2+, Cu2+, and Cd2+ ions from aqueous solutions by the copolymer of 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid (AMPS) and itaconic acid (IA), P(AMPS‐co‐IA), was investigated. Homopolymer of AMPS (PAMPS) was also used to remove these ions from their aqueous solution. In the preparation of AMPS–IA copolymer, the molar percentages of AMPS and IA were 80 and 20, respectively. In order to observe the changes in the structures of polymers due to metal adsorption, FTIR spectra by attenuated total reflectancetechnique and scanning electron microscopy (SEM) pictures of the polymers were taken both before and after adsorption experiments. Total metal ion removal capacities of PAMPS and P(AMPS‐co‐IA) were 1.685 and 1.722 mmol Me2+/gpolymer, respectively. Experimental data were evaluated to determine the kinetic characteristics of the adsorption process. Competitive adsorption of Pb2+, Cu2+, and Cd2+ ions onto both PAMPS and P(AMPS‐co‐IA) was found to fit pseudo‐second‐order type kinetics. In addition, the removal orders in the competitive adsorption of these metal ions onto PAMPS and P(AMPS‐co‐IA) were found to be Cd2+ > Pb2+ > Cu2+ and Pb2+ > Cd2+ > Cu2+, respectively. Copyright © 2008 John Wiley & Sons, Ltd.
Flammability properties of intumescent PLA including starch and lignin
Authors: Réti C. , Casetta M. , Duquesne S. , Bourbigot S. , Delobel R. 
Published: April 2008

AbstractThe aim of this study is to evaluate the efficiency of different intumescent formulations to flame retard polylactic acid (PLA). First, the ammonium polyphosphate (APP)/pentaerythritol (PER) system is chosen because it previously demonstrated a good behavior for polyethylenic matrices. The PER is then substituted by bioresources such as lignin and starch. The flame retardant properties of the various formulations are evaluated by limiting oxygen index (LOI), UL‐94, and cone calorimetry. Compared to the PLA/APP/PER composite, the materials containing lignin and starch show lower LOI values but still commercially acceptable (superior to 32%). In contrast, the UL ratings obtained for these formulations are superior to that containing PER (V0 against V2 rating).The cone calorimeter analysis confirms the formation of an intumescent structure for the “green” composites, with a final residue corresponding to 50% of the initial sample mass and also a decrease in the peak of heat release of 50%. Finally, the composition of the formulation is optimized following a mixture design methodology to maximize the quantity of bioresources. A 32% LOI value is obtained for a composite containing 60% PLA, 12% APP, and 28% starch. Copyright © 2008 John Wiley & Sons, Ltd.
Influence of alcohol pre‐infusion on the quality of VARTM composites
Authors: Qiu Jingjing , Li Jing , Zhang Chuck , Liang Richard , Lin Shui‐Shun , Wang Ben , Walsh Shawn 
Published: April 2008

AbstractIn the vacuum assisted resin transfer molding (VARTM) process, part‐to‐part variations such as the uncertainty in the permeability and race tracking phenomenon make it difficult to achieve consistent mold filling and ensure part quality of composites. Alcohol pre‐infusion was presented in this study as a novel real‐time monitoring and control approach for the flow process in the VARTM process, alcohol test fluid is infused before the actual resin infusion to locate the potential dry spots without using the large quantity of sensors. Then corresponding process control strategy is designed, such as opening the auxiliary gate at specific moment on those predicted dry spot locations to compensate flow defects. Moreover, alcohol can be easily removed by heat without changing the local permeability. The influence of alcohol pre‐infusion on the quality of VARTM composites were investigated in this study. The mechanical tests were conducted to verify that the alcohol pre‐infusion approach has no significant effect on composite properties because alcohol can be removed from fiber by heat and air flow. Specifically, DMA, TGA, and FTIR spectrum proved that negligible difference existed on the resin–fiber interface between the composites with or without alcohol pre‐infusion. Finally, the microscopy results revealed a similar failure path in a resin matrix. TMA results also demonstrated similar dimension stability. This alcohol pre‐infusion approach was effective when compared with computer simulation and could eliminate the occurrence of dry spots and voids without using sensors or data‐acquisition system. The control schemes were shown in a case study to be capable of compensating the flow defects and achieving desired fill patterns in the face of permeability uncertainty. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers
Chronic statin therapy and the risk of colorectal cancer
Authors: Yang Yu‐Xiao , Hennessy Sean , Propert Kathleen , Hwang Wei‐Ting , Sarkar Monika , Lewis James D. 
Published: April 2008

AbstractBackground and AimsEpidemiologic studies on a potential chemopreventive effect of statin therapy have yielded conflicting results. We sought to clarify whether long‐term statin therapy has a chemopreventive effect on the risk of colorectal cancer (CRC) in a large, population‐representative cohort.MethodsA nested case–control study was conducted among patients ≥50 years of age and with ≥5 years of CRC‐free initial follow‐up in the General Practice Research Database (GPRD; 1987–2002). Cases consisted of all patients with incident CRC. Up to 10 controls were matched with each case on practice site and both duration and calendar time of follow‐up prior to the index date. The primary exposure of interest was ≥5 years of cumulative statin use.ResultsWe identified 4432 incident CRC cases and 44 292 controls. The adjusted odds ratio (OR) for ≥5 years of statin exposure was 1.1 (95% confidence interval (CI): 0.5–2.2). Chronic NSAID/aspirin use did not modify this primary association (test for interaction, p = 0.5). Compared to statin non‐users, the adjusted OR for 10 years of statin exposure was 1.3 (95% CI: 0.6–2.7), and the adjusted OR associated with the highest quartile of cumulative statin dose was 1.2 (95% CI: 0.9–1.7). There was a non‐statistically significant trend towards a possible reduction in CRC risk among users of high daily statin dose.ConclusionLong‐term statin therapy at usual doses was not associated with a significantly reduced risk of CRC. A chemopreventive effect at high daily doses cannot be excluded. Copyright © 2008 John Wiley & Sons, Ltd.
Grafting of Paper by Silane Coupling Agents Using Cold‐Plasma Discharges
Authors: Gaiolas Carla , Costa Ana Paula , Nunes Mario , Silva Manuel José Santos , Belgacem Mohamed Naceur 
Published: April 2008

AbstractThe treatment of cellulose with cold plasma in the presence of two silanes is found to be efficient in the grafting of cellulose macromolecules. The occurrence of the grafting is proven by contact angle measurement, ESCA, and SEM. Thus, after plasma treatment the polar component of the surface energy of the treated samples decreases from 23 mJ · m−2 to practically zero. The ESCA spectra showed the appearance of two new peaks at 102 and 150 eV, relative to the presence of Si atoms and a substantial increase in Cl signal, attributed to the enrichment of the surface by CH moieties borne by the silanes. SEM confirms the presence of the silane, both in the bulk and at the surface of the treated samples.magnified image
Resistance monitoring in codling moth: a need for standardization
Authors: Reyes Maritza , Sauphanor Benoît 
Published: April 2008

AbstractBACKGROUND: A wide range of methods has been used for monitoring resistance in Cydia pomonella L. However, the results from specific tests are not always concordant and they generate doubts over the extent to which the data represent the field situation. Therefore, the variability in the expression of resistance mechanisms and in resistance ratios between developmental stages and their reliability in a field situation were studied.RESULTS: Neonate larvae showed the highest insecticide resistance, except to spinosad. Resistance ratios were from 2 to 9.5, depending on the insecticide and the strain tested, when compared with the susceptible strain. Spinosad exhibited the highest resistance ratio for diapausing larvae (4.4, 12.2 and 4.4 for Raz, Rdfb and RΔ strains, respectively). Enzymatic ratios were higher in adults than in neonates or diapausing larvae, and the highest enzymatic ratios were observed for mixed‐function oxidases (7.3–36.7 for adults of resistant strains).CONCLUSIONS: The sensitivity of different instars depends on the insecticides used, and there is a differential expression of resistance mechanisms between stages. For the population considered in this study, tests on neonates provided the most consistent results to the field situation, but adult response to chlorpyrifos‐ethyl and azinphos‐methyl in the laboratory was also consistent with the field results. Copyright © 2008 Society of Chemical Industry
Using alternative data sources to study rural migration: examples from Illinois
Authors: Foulkes Matthew , Newbold K. Bruce 
Published: April 2008

AbstractOne of the problems frequently faced by migration researchers is the paucity of national census migration data for small rural areas. Drawing upon a larger, multi‐level research project that focused upon rural poverty migration within Illinois, this article illustrates the opportunities and challenges associated with using community‐based data sources to measure mobility in small rural communities. Use of alternative migration data sources can present opportunities to circumvent common problems with census‐based data sources, including addressing temporal shortfalls, providing custom geographies, and capturing the movement of difficult‐to‐enumerate subpopulations. Alternative data‐sets may also allow researchers to formulate new questions that are more oriented to society's pressing problems. Yet, users of non‐traditional data‐sets also face issues of indirect measurement, data quality, comparability, replication, costs, and moral and ethical concerns. As use of non‐traditional migration data sources increases, researchers will need to become familiar with both the benefits and pitfalls of these data‐sets. Copyright © 2008 John Wiley & Sons, Ltd.
X‐ray diffraction studies of selective area grown InGaN/GaN multiple quantum wells on multi‐facet GaN ridges
Authors: O'Malley S. M. , Bonanno P. L. , Wunderer T. , Brückner P. , Neubert B. , Scholz F. , Kazimirov A. , Sirenko A. A. 
Published: April 2008

AbstractThe structural properties of InGaN/GaN multiple quantum wells (MQW) were studied using synchrotron based high resolution x‐ray diffraction (HRXRD). MQW structures were grown on the top and sidewall facets of triangular and trapezoidal shaped GaN ridges by metalorganic vapour phase epitaxy (MOVPE) in the regime of selective area growth (SAG). Period and strain variations as a function of oxide mask width were determined for both the sidewall and the top facet growth. Oxide mask widths ranged between 2 and 20 µm with openings between adjacent masks of 4 and 6 µm. Analysis of the x‐ray diffraction curves revealed a sidewall / vertical growth rate ratio of ∼0.3 through a comparison of the top to sidewall facet MQW periods. Masks orientated along the 〈11‐20〉 crystallographic direction showed stronger growth enhancement along with large global strain for MQW growth on the top (0001) plane. Interpreting our results within the framework of vapour phase diffusion revealed that inter‐facet migration of group‐III species needs to be taken into account. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enhancement of external quantum efficiency in GaN‐based light emitting diodes using a suspended geometry
Authors: Fellows Natalie , Masui Hisashi , Sato Hitoshi , Asamizu Hirokuni , Iza Michael , Zhong Hong , Nakamura Shuji , DenBaars Steven P. 
Published: April 2008

AbstractUsing a transparent and mirror‐less chip mounting technique we have increased the total external efficiency by 26%. This increase in the external quantum efficiency for a light‐emitting diode (LED) was based on c ‐plane (0001) bulk GaN employing a suspended geometry. A small size LED (200 x 550 μm2) affixed to a Ag header is compared to an LED die lifted off the header. The output power for the LED in the suspended geometry was 30.4 mW, a 13% increase over the conventional placement and the EQE increased from 49% to 56% at a forward current of 20 mA under pulsed conditions. The suspended die was then placed into a cone optic and its output power and EQE improved to 34 mW and 62%, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High quality, high efficiency and ultrahigh In‐content InGaN QWs – the problem of thermal stability
Authors: Fuhrmann D. , Jönen H. , Hoffmann L. , Bremers H. , Rossow U. , Hangleiter A. 
Published: April 2008

AbstractInxGa1‐xN/GaN quantum well (QW) structures with Indium concentrations above 30% suited for light emitters in the green and beyond have been investigated. The structures were optimized for homogeneous Indium distributions and abrupt interfaces. We obtained very high internal quantum efficiencies (IQE) of 80% and 70% for 460 nm and 510 nm emission wavelength, respectively. However, for high In concentrations the heterostructures are thermally less stable. This is evident from systematic studies including varied GaN cap temperatures and different post annealing procedures. For elevated temperatures we observe a reduction of the PL intensity, a broadening and a shift to higher energies of the PL lines without indication of phase separation. The reason is the soft indium‐nitrogen bond, the degradation likely occurs by In interdiffusion or outdiffusion via defects in the structures. The critical temperatures are well below those typical for p‐GaN contact layer growth and thus need to be considered in device applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
GaN growth on silane exposed AlN seed layers
Authors: Ruiz‐Zepeda F. , Contreras O. , Dadgar A. , Krost A. 
Published: April 2008

AbstractThe microstructure and surface morphology of GaN films grown on AlN seed layers exposed to silane flow has been studied by TEM and AFM. The epilayers were grown on silicon (111) substrates by MOCVD. The AlN seed layer surface was treated at different SiH4 exposure times prior to the growth of the GaN film. A reduction in the density of threading dislocations is observed in the GaN films and their surface roughness is minimized for an optimal SiH4 exposure time between 75‐90 sec. At this optimal condition a step‐flow growth mode of GaN film is predominant. The improvement of the surface and structure quality of the epilayers is observed to be related to an annihilation process of threading dislocations done by SiNx masking. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of Mg‐doped AlInN grown by metalorganic vapor phase epitaxy
Authors: Cheng A. T. , Su Y. K. , Lai W. C. 
Published: April 2008

AbstractWe report on the growth of undoped and Mg‐doped AlInN by metalorganic vapor phase epitaxy (MOVPE). The indium content and the full width at half maximum (FWHM) of undoped AlInN layer were 20.9% and 219.6 arcsec, respectively, from HRXRD measurement. It was also observed that an additional satellite peak was formed near the AlInN peak after introducing the Mg dopant. The sheet hole concentration of 4.73×1012 cm–2 was achieved after performing the thermal annealing. As the flow rate of Cp2Mg source was increased, we found that both the satellite peak and the AlInN peak shifted toward higher angles. However, higher Cp2Mg flow rate would not only decrease the conductivity of AlInN layer due to the higher Al content shown in HRXRD spectrum but increase the surface roughness. Therefore, these results suggest that p‐type AlInN cladding layer nearly lattice‐matched to GaN will be realized with lower Cp2Mg flow rate for optical device applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
MOVPE growth and photoluminescence properties of InAsN QDs
Authors: Kuboya S. , Takahashi S. , Thieu Q. T. , Nakajima F. , Katayama R. , Onabe K. 
Published: April 2008

AbstractThe self‐assembled InAsN quantum dots (QDs) were grown on the GaAs (001) substrates by MOVPE using 1,1‐dimethylhydrazine (DMHy) as the N precursor, and their photoluminescence (PL) properties were investigated. The N incorporation leads to a decrease in the QDs size for an equivalent amount of source supply due to the increase in the wetting layer thickness. It also leads to an increase in the QDs density which is interpreted by the reduced surface migration length. The PL from the electron ground state of the InAsN QDs clearly shows the red‐shift to 1159 nm by the N incorporation, indicating that the effect of the huge bandgap bowing is dominant over the quantum size effect in the InAsN QDs. The thermal activation energy of the QDs derived from the temperature dependence of the integrated PL intensity decreases from 176 meV to 140 meV by the DMHy supply, which is explained by the lowering of the electron quantum state of the thicker wetting layer caused by the N incorporation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Increase in the growth rate of GaN single crystals grown by gallium hydride vapor phase epitaxy method
Authors: Imade Mamoru , Yamada Norihide , Kitano Yoshihiro , Kawamura Fumio , Yoshimura Masashi , Kitaoka Yasuo , Mori Yusuke , Sasaki Takatomo 
Published: April 2008

AbstractA dependence of Gallium hydride (GaHx: x = 1, 2, 3) production on the growth rate of GaN crystals grown by the gallium hydride vapor phase epitaxy (GaH‐VPE) method was investigated. By this method, GaN crystals are synthesized in a reaction between GaHx and NH3. The growth rate of GaN crystals has been as low as 20 μm/h at a maximum because the poor reactivity of H2 gas with Ga metal limits the production of GaHx. In this study, the interfacial area between Ga metal and H2 gas was enlarged to increase the GaHx synthesis, which thereby enabled an increase in the growth rate to 68 μm/h. We showed clearly that the growth rate of GaN by the GaH‐VPE method is limited by the efficiency of the reaction between the Ga metal and H2 gas. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
V‐defect analysis in green and deep green light emitting diode structures
Authors: Zhu M. , Detchprohm T. , You S. , Wang Y. , Xia Y. , Zhao W. , Li Y. , Senawiratne J. , Zhang Z. , Wetzel C. 
Published: April 2008

AbstractIn 535‐565 nm green and deep green LED dies on c‐plane sapphire, we correlate the structural morphology with photoluminescence performance. Two classes of material with active region roughness of 4 nm and 0.4 nm (RMS) are analyzed in transmission electron microscopy. In the rough material, a high density of edge‐type dislocations is identified that originates within the quantum wells (QWs). They initiate V‐defects that exhibit {10$ \bar 1 $1} growth facets with a second set of narrow QWs and barriers. As V‐defects widen with progressive growth, the width of QW and barriers on the c‐plane increases. In the smooth material, however, no V‐defects can be found. QWs and barriers are highly uniform and homogenous throughout the structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ultra‐incompressible and hard technetium carbide and rhenium carbide: First‐principles prediction
Authors: Wang Yuan Xu 
Published: April 2008

AbstractUsing density functional theory, the author predicts that the compounds ReC and TcC with the hexagonal WC‐like structure are ultra‐incompressible and hard materials. This is concluded from the very large bulk and shear moduli. The phonon dispersion reveals no soft modes indicating the stability of the two materials. The calculated density of states shows that ReC and TcC are metallic. The structural and elastic properties of OsC, IrC, and PtC with hexagonal and cubic structure are also investigated for comparison. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The effect of temperature and humidity fluctuations on the liquid water path of non‐precipitating closed‐cell stratocumulus clouds
Authors: de Roode Stephan R. , Los Alexander 
Published: April 2008

AbstractThe spatial variability of the liquid water path (LWP) is analyzed from a large‐eddy simulation of the diurnal cycle of stratocumulus clouds as observed during FIRE I. In stratocumulus clouds, the temperature and the total specific humidity cannot fluctuate independently, but are tightly connected to fluctuations in the liquid water potential temperature. If the latter are relatively small, a strong positive correlation between the temperature and the total specific humidity can be expected. The effect of temperature fluctuations on the magnitude of liquid water fluctuations must be considered to properly compute the LWP distribution in stratocumulus clouds.The simulated stratocumulus cloud fields are used to compute the albedo inhomogeneity factor χ according to the effective thickness approach. During the day, the mean LWP decreases due to short‐wave radiative warming. Also, the probability density function for the LWP becomes positively skewed due to cumuli that have their base well below the mean stratocumulus cloud‐base height. For this situation, the inhomogeneity factor χ displays a minimum value of about 0.85. For solid (unbroken) cloud with an assumed Gaussian distribution for the optical depth, we find that the minimum inhomogeneity factor will be about 0.8. This minimum value for the inhomogeneity factor, and that from the LES results, are larger than reported from FIRE I observations. Copyright © 2008 Royal Meteorological Society