Retardation Of Rate Research Articles

Formation of PtSi Schottky barrier MOSFETs using plasma etching

PtSi Schottky barrier (SB) MOSFETs were fabricated and their device performance was characterized. PtSi was selected instead of NiSi to form the p-type SB junction since such a configuration would be easy to fabricate through SF6 based plasma etching. The addition of He-O2 in SF6 decreases the etching rate of PtSi while the etching rate of Pt remains unchanged. The retardation in the etching rate of PtSi in He-O2/SF6 is attributed to the formation of a metal oxide on the etched PtSi surface, as evidenced by the x-ray photoelectron spectroscopy results. Optical emission spectroscopy was conducted to establish the endpoint where the wavelength from the feed gas was traced instead of tracing the etching by-products since the by-products have little association with the plasma reaction. The IDS–VDS curves at various VG–VTH indicate that plasma etching resulted in the successful removal of the Pt on the sidewall region, with negligible damage to the S/D area.

Gelation of a solution of poly(3-hexylthiophene) greatly retards its crystallization rate in the subsequently cast film.

We compared the crystallization rate of poly(3-hexylthiophene) (P3HT) in the film cast from the gel (called "gel-cast film") with that in the film cast from the liquid solution (called "solution-cast film") to understand the effect of solution structure on the structural development in the subsequently cast film of conjugated polymer. P3HT was found to form a homogeneous liquid solution with xylene at elevated temperature. When the freshly prepared semidilute solution was allowed to age at room temperature, the solution transformed into a gel in which a significant amount of nanowhiskers formed. The nanowhiskers in the gel were effectively transferred to the corresponding cast film, while the film cast from the freshly prepared solution only contained a small amount of such a morphological entity. The in situ small-angle X-ray scattering (SAXS) measurement and thermal analysis revealed that both the cold and melt crystallization of P3HT in the gel-cast film were much slower than those in the solution-cast counterpart. The retardation of crystallization rate in the gel-cast film was attributed to the abundance of the nanowhiskers. In this case, the crystallization of P3HT occurred predominantly within the individual nanowhiskers and the mesh regions in the networks of the whiskers, where their limited sizes in at least one dimension imposed a strong spatial constraint to the crystal growth and chain motion for crystallization.

Kinetics study of living microemulsion polymerization mediated by reversible addition-fragmentation chain transfer

Reversible addition-fragmentation chain transfer (RAFT) polymerization is usually carried out in emulsion or miniemulsion, often encounters problems of rate retardation, phase separation, and loss of activity in these systems. Compared with emulsion or miniemulsion, microemulsion remains stable during polymerization because of presence of large amount surfactant that promotes formation of large number of monomer swollen micelles. Therefore, microemulsion typically shows fast polymerization rate and produces latex nanoparticles composed of high molecular weights polymers. Until now, only few RAFT polymerizations have been successfully conducted in microemulsion and related kinetics studies are very limited. Here, kinetics studies on RAFT microemulsion polymerization were carried out and the factors that affected kinetics were detailedly investigated. Kinetic parameters, theoretical molecular weights, chain transfer constant, propagate rate constant, half reaction time and polymerization rate constant were all calculated. Experimental results indicated temperature and concentration of chain transfer agent were important factors which influenced polymerization kinetics. In addition, the chemical structure of chain transfer agent, molecular weights and its distribution, and the morphologies structure of polymers were characterized by 1H NMR, FT-IR, GPC and TEM, respectively.

Keeping those telomeres short! an innovative intratumoral long-term drug delivery system.

Telomerase activation and an alternative lengthening of telomeres (ALT) mechanism are two telomere-lengthening cancer cell survival mechanisms elicited by both chemo- and/or radiotherapy. Telomere lengthening interferes with cell lethality and results in the immortalization of cancer cells. To counteract these mechanisms, we developed a drug delivery system (DDS) consisting of a polymeric implant that is inserted directly into tumors. The DDS releases, continuously and gradually, a cationic porphyrin (PdTMPyP4) for >30 days after a single application, and inhibits telomerase activation. The PdTMPyP4 porphyrin is incorporated into a poly(co-glycolic lactic)acid (PLGA) polymer, solidified and cut into small rods. PdTMPyP4 release from the rods was measured spectrophotometrically over time. Uptake of Pd in the DNA of in L428 Hodgkins lymphoma cells was measured by ICP-MS, and telomerase activation by the TRAP assay. The rods were placed into the growth medium of cells whose growth rate was measured for 11 and 19 days. The cylinders were also inserted directly into KHJJ murine mammary tumors borne on the thighs of BALB/c mice and the tumor growth rate measured. In vitro, >10(9)Pd atoms were measured in the DNA of each L428 cell and telomerase activity was reduced by ~15% within 24 h. A one-time application of the rod in the cell medium induced a factor of >5 greater lethality compared to a blank rod or untreated controls. In vivo, a one-time insertion of the rod into tumors resulted in the retardation of the growth rate by factors of 3-5 compared to untreated controls. Systemic uptake after intratumoral insertion of the rod was negligible. The results suggest that the direct intratumoral insertion of a PdTMPyP4-containing polymeric rod would be of benefit as an adjuvant treatment for patients undergoing chemo- or radiotherapy. By preventing the lengthening of telomeres and therefore the unrestricted growth of cancer cells, our DDS will provide a significant therapeutic advantage to these treatments without affecting normal tissues.

Dissecting the effect of chemical additives on the enzymatic hydrolysis of pretreated wheat straw

Chemical additives were examined for ability to increase the enzymatic hydrolysis of thermo-acidically pretreated wheat straw by Trichoderma reesei cellulase at 50°C. Semi-empirical descriptors derived from the hydrolysis time courses were applied to compare influence of these additives on lignocellulose bioconversion on a kinetic level, presenting a novel view on their mechanism of action. Focus was on rate retardation during hydrolysis, substrate conversion and enzyme adsorption. PEG 8000 enabled a reduction of enzyme loading by 50% while retaining the same conversion of 67% after 24h. For the first time, a beneficial effect of urea is reported, increasing the final substrate conversion after 48h by 16%. The cationic surfactant cetyl-trimethylammonium bromide (CTAB) enhanced the hydrolysis rate at extended reaction time (rlim) by 34% and reduced reaction time by 28%. A combination of PEG 8000 and urea increased sugar release more than additives used individually.

Solvothermal synthesis of Sm-doped BiOBr/RGO composite as an efficient photocatalytic material for methyl orange degradation

A novel Sm-doped BiOBr/reduced graphene oxide (RGO) composite photocatalyst was synthesized by the solvothermal method using methanol as solvent. The crystallanity, morphology, and chemical compositions were examined using XRD, TEM and SEM-EDAX. The photocatalytic ability of prepared sample was investigated using methyl orange (MO). The results show that Sm-BiOBr/RGO is an excellent photocatalytic material better than pure BiOBr and BiOBr/RGO composite. The enhancement might be ascribed to the higher adsorption of dyes, effective charge separation efficiency and retardation of recombination rate due to Sm doping and RGO incorporation.

Detection of Fusarium langsethiae on wheat in Belgium

In 2010, the populations of Fusarium sp. and Microdochium sp. were monitored in Belgium and 16 strains were identified as Fusarium langsethiae on wheat in Belgium. The other species identified from the sampling were F. poae, F. tritinctum, F. graminearum, F. avenaceum and Microdochium nivale. The pathogenicity potential of the F. langsethiae strains was assessed via an in vitro coleoptile growth rate test on wheat seedlings and compared with strains of F. poae, F. tritinctum, F. graminearum and F. avenaceum known to cause Fusarium head blight. The results showed the ability of F. langsethiae to cause retardation in the wheat coleoptile growth rate, but at a lower rate than F. graminearum, F. avenaceum, F. poae and F. tricinctum. A test for mycotoxin production in vitro showed the ability of the four strains tested to produce T-2 and HT-2 toxins at a rate of up to 290 mg kg−1. This is the first report on the potential pathogenicity of F. langsethiae on wheat in Belgium, a species known to produce T-2 and HT-2 toxins, which are highly toxic for humans and animals.

Modelling Fatigue Crack Growth Rates in Aluminium Plates Reinforced by Bonded Fibre-Metal Laminates for Fatigue Life Extension

Aircraft structural design and manufacture is moving towards lighter structures that have extended lives and improved damage tolerance. Hybrid structures are a possible solution to improve damage tolerance. They are a combination of metallic structure locally reinforced with adhesively bonded damage tolerant straps. In the present study a 3D finite element model has been developed with a bond line delamination growing under a fatigue law. A series of fatigue delamination tests on bonded aluminium were performed to provide input data. An iterative model for crack and debonding growth was developed to describe how debonding influence crack stress intensity and crack profile, which in turn influence debonding. The model predicts decrease in stress intensity on the bonded face and an overall retardation of fatigue crack growth rates. The stress intensity factor was predicted to vary through the thickness of the substrate due to the phenomenon of secondary bending and also the bridging effect caused by the presence of the reinforcing strap.

Numerical Simulation of Fatigue Crack Growth Rate and Crack Retardation due to an Overload Using a Cohesive Zone Model

In this work, a numerical method is pursued based on a cohesive zone model (CZM). The method is aimed at simulating fatigue crack growth as well as crack growth retardation due to an overload. In this cohesive zone model, the degradation of the material strength is represented by a variation of the cohesive traction with respect to separation of the cohesive surfaces. Simulation of crack propagation under cyclic loads is implemented by introducing a damage mechanism into the cohesive zone. Crack propagation is represented in the process zone (cohesive zone in front of crack-tip) by deterioration of the cohesive strength due to damage development in the cohesive element. Damage accumulation during loading is based on the displacements in the cohesive zone. A finite element model of a compact tension (CT) specimen subjected to a constant amplitude loading with an overload is developed. The cohesive elements are placed in front of the crack-tip along a pre-defined crack path. The simulation is performed in the finite element code Abaqus. The cohesive elements behavior is described using the user element subroutine UEL. The new damage evolution function used in this work provides a good agreement between simulation results and experimental data.

Mixing effects of biogas and dimethyl ether (DME) on combustion and emission characteristics of DME fueled high-speed diesel engine

The purpose of this investigation is to study the effect of biogas mixing on the combustion and emission characteristics of DME fueled diesel engine. Combustion performance was assessed in terms of combustion pressure, rate of heat release (ROHR), ignition delay, and an indicated mean effective pressure (IMEP). NOx, soot, HC and CO emissions were also analyzed using an emission analyzer.Increase in biogas mixing ratio caused a decrease in peak combustion pressure, ignition retardation and reduction in rate of combustion pressure increase. Increase in biogas also induced a decrease in the peak value and gradient of ROHR. Injection and ignition timings showed a linear correlation regardless of biogas mixing ratio when DME was injected toward the piston bowl. At the same injection timing, the increase of biogas caused a decrease in IMEP when DME was injected into the piston bowl. When DME was injected toward the crevice and squish region, IMEP increased as the biogas mixing ratio increased, and IMEP showed a linear correlation with SOI. ISNOx emissions decreased with the increase in biogas. The soot emissions level was close to zero in all test conditions. However, ISHC and ISCO emissions showed an increasing trend with increasing biogas mixing ratio.

Experimental Method to Discriminate RAFT Models between Intermediate Termination and Slow Fragmentation via Comparison of Rates of Miniemulsion and Bulk Polymerization

A simple model discrimination method for RAFT polymerization mechanism, proposed on a theoretical basis, is applied to the polystyryl dithiobenzoate‐mediated styrene polymerization. It is confirmed that the intermediate termination (IT) is the major reason for the rate retardation. The method utilizes the theoretical finding that the IT model shows a significantly larger polymerization rate in miniemulsion compared with the corresponding bulk polymerization, while the slow fragmentation model does not change the polymerization rate. The miniemulsion polymerization rate increases as the droplet size is made smaller, which agrees reasonably well with the theoretical prediction. The present model discrimination method is easy to apply, and would provide great insight into both basic and applied research in RAFT polymerization.

Fatigue Crack Growth Life Prediction around Cold Expanded Hole Using Finite Element Method

Cold expansion process is widely used to enhance fatigue life of fastener holes in aircraft industry. The benefit derived from cold expansion treatment is attributed to residual stresses induced around hole. This work is aimed at establishing a simple procedure for predicting Fatigue Crack Growth (FCG) life around cold expanded holes. Cold expansion process is simulated for uncracked and cracked holes using Finite Element method. The effect of residual stresses is accounted to predict FCG life using Willenborg's model. As a result of cold expansion, significant retardation in FCG rate and life improvement is achieved.

Fabrication of large diameter TiO<SUB align="right">2 nanotube for bone morphogenetic protein-2 delivery

A localised and release-controlled carrier is essential to enhance the effectiveness of bone morphogenetic protein in bone regeneration and repair. In this work, TiO2 nanotubes with diameter larger than 350 nm were successfully fabricated for the first time by electrochemical method using diethylene glycol electrolyte. The diameter of the nanotubes reaches 550 nm and 680 nm at 90 V and 100 V, respectively. Their influences for bone morphogenetic protein-2 (BMP-2) delivery were investigated. In the study of protein release, fabricated TiO2 nanotubes have shown superhydrophilic properties that induce tight interaction with BMP-2. The release profile of the TiO2 nanotubes demonstrated a larger retention of protein, a more significant suppression of the initial burst and a better retardation of the release rate. Elution profile was also found to be dependent greatly on the density and the diameter of the nanotubes. Results have shown that the initial burst was larger for nanotubes with lower density and more proteins were released from nanotubes with larger diameter for the whole elution process.

The Influence of RAFT on the Microstructure and the Mechanical Properties of Photopolymerized Poly(butyl acrylate) Networks

Statistical networks of butyl acrylate and 1,4‐butanediol diacrylate are photopolymerized in bulk, both in the presence and absence of the RAFT agent EPHT. The amounts of crosslinker and RAFT agent are varied. The Young's moduli of the RAFT networks are always lower than those of conventionally obtained networks. With increasing amounts of RAFT agent, the Young's modulus decreases and the strain at break values increase, respectively. The network density, the apparent molar mass of the network chains and the swelling show significant differences between RAFT‐ and conventionally obtained networks. The degree of swelling and the amount of extractable polymer increase largely with the amount of RAFT agent. Kinetic DSC measurements show that the gel point is delayed with increasing amounts of RAFT agent. In addition, a rate retardation effect with increasing RAFT agent concentration is observed. image

Fatigue modelling of aluminium plates reinforced with bonded fibre metal laminates

Purpose – This paper aims to present the implementation of a finite element (FE) model used to establish crack and delamination development in a Glare reinforced aluminium plate under fatigue loading. This model predicts the behaviour of bonded GLARE straps used as crack retarders for life extension of aircraft structures. In particular, it takes into account the interaction that exists between the substrate crack and the delamination crack at the interface with the reinforcement. Design/methodology/approach – In this work, a 3D FE model with three-layer continuum shell elements has been developed to calculate changes in substrate stress intensity and in fatigue crack growth (FCG) rate produced by bonded strap reinforcement. Both circular and elliptical strap delamination geometries were incorporated into the model. Calculated stress intensity factors (SIFs) were used together with measured FCG data for substrate material to predict FCG rates for the strapped condition. Findings – The model predicted a decrease in the SIF and a retardation of FCG rates. The SIF was predicted to vary through the thickness of the substrate due to the phenomenon of secondary bending and also the bridging effect caused by the presence of the strap. The influence of delamination shape and size on substrate crack stress intensity and delamination strain energy release rate has been calculated. Originality/value – This research aims at developing modelling techniques that could be used when studying larger reinforced structures found in aircraft.

Dynamics of desorption with lateral diffusion

The dynamics of desorption from a submonolayer of adsorbed atoms or ions are significantly influenced by the absence or presence of lateral diffusion of the adsorbed particles. When diffusion is present, the adsorbate configuration is simultaneously changed by two distinct processes, proceeding in parallel: adsorption/desorption, which changes the total adsorbate coverage, and lateral diffusion, which is coverage conserving. Inspired by experimental results, we here study the effects of these competing processes by kinetic Monte Carlo simulations of a simple lattice-gas model. In order to untangle the various effects, we perform large-scale simulations, in which we monitor coverage, correlation length, and cluster-size distributions, as well as the behavior of representative individual clusters, during desorption. For each initial adsorbate configuration, we perform multiple, independent simulations, without and with diffusion, respectively. We find that, compared to desorption without diffusion, the coverage-conserving diffusion process produces two competing effects: a retardation of the desorption rate, which is associated with a coarsening of the adsorbate configuration, and an acceleration due to desorption of monomers "evaporated" from the cluster perimeters. The balance between these two effects is governed by the structure of the adsorbate layer at the beginning of the desorption process. Deceleration and coarsening are predominant for configurations dominated by monomers and small clusters, while acceleration is predominant for configurations dominated by large clusters.

Exposure to cadmium causes declines in growth and photosynthesis in the endangered aquatic fern (Ceratopteris pteridoides)

With rapid development of agriculture and urbanization, aquatic systems and aquatic plants in China face a great threat of heavy metal pollution where toxic contaminant cadmium (Cd) concentrations were reported up to 4500μgl−1 in some heavy metal polluted waters. Our objectives were to assess the biological causes of heavy metal Cd in aquatic systems associated with the population decline of an endangered aquatic species Ceratopteris pteridoides. The effects of cadmium (Cd) toxicity on the photosynthetic performance, leaf chlorophyll content, antioxidant enzyme activities and nitrogen metabolism in C. pteridoides were investigated under greenhouse conditions. Seedlings were exposed to various Cd concentrations (0, 5, 10, 20, and 40μM) for 7 days. The accumulation of Cd ions in plant tissues inhibited the relative growth rate of C. pteridoides through net assimilation rate retardation and leaf area ratio reduction. A significant reduction in biomass was observed in C. pteridoides at 20 and 40μM Cd concentrations. Exposure to Cd severely restricted plant net photosynthetic rates. Factors limiting photosynthesis in Cd-treated plants were more related to non-stomatal constraints than to stomatal limitation. Cd reduced chlorophyll content of the treated plants and affected also plant ribulose-1,5-bisphosphate (RuBP) activity and regeneration capacity. Decreased leaf photosynthesis showed that a significant amount of Rubisco was not active in photosynthesis under Cd stress. The Cd treatments reduced significantly the relative quantum efficiency of PSII, electron transport rate and photochemical efficiency of PSII reaction centers, which corresponded to the reduction in Rubisco activity. Increased Cd concentrations showed similar effects on the superoxide dismutase, catalase, and peroxidase activities in the leaves and roots. Also, Cd retention caused cell membrane damage shown by increased malondialdehyde content. Cd toxicity may have interfered with plant nutritional assimilation because there was a deficiency in nitrogen uptake and translocation, shown by the reduced nitrate reductase and glutamine synthetase activities. We conclude that physiological disturbances in Cd-stressed plants are congruent with the observed plant growth inhibition. Plant Cd stress inhibited both nitrogen absorption and photosynthesis in C. pteridoides, thus enhancing its mortality risk. An efficient strategy to restore environmental quality for this endangered fern implies the reduction of Cd pollution in the environment.

Kinetics of Dithiobenzoate‐Mediated Methyl Methacrylate Polymerization

AbstractThe equilibrium constant, Keq, of the reversible addition–fragmentation chain transfer (RAFT) model system methyl methacryl dithiobenzoate (MMADB) and of methyl methacrylate (MMA) polymerization mediated by MMADB is studied via electron paramagnetic resonance (EPR) spectroscopy in the range 70 to 110 °C and at −40 °C, respectively. The measured difference in activation energy of the addition and fragmentation steps is: Ea(kad) – Ea(kfrag) ≈ −36.6 kJ mol−1. Significant amounts of “missing step” products from reaction of the cross‐termination product with a methyl methacrylyl radical are found. The fast “missing step” reaction and low Keq, due to slow kad, are responsible for rate retardation being absent in dithiobenzoate‐mediated MMA polymerization.magnified image

Negative Priming Effect on Organic Matter Mineralisation in NE Atlantic Slope Sediments

The priming effect (PE) is a complex phenomenon which describes a modification (acceleration or retardation) in the mineralisation rate of refractory organic matter (OM) following inputs of labile material. PEs are well-studied in terrestrial ecosystems owing to their potential importance in the evolution of soil carbon stocks but have been largely ignored in aquatic systems despite the fact that the prerequisite for their occurrence, i.e. the co-existence of labile and refractory OM, is also true for sediments. We conducted stable isotope tracer experiments in continental margin sediments from the NE Atlantic (550–950 m) to study PE occurrence and intensity in relation to labile OM input. Sediment slurries were treated with increasing quantities of the 13C-labelled diatom Thalassiosira rotula and PE was quantified after 7, 14 and 21 days. There was a stepwise effect of diatom quantity on its mineralisation although mineralisation efficiency dropped with increasing substrate amounts. The addition of diatomaceous OM yielded a negative PE (i.e. retardation of existing sediment OM mineralisation) at the end of the experiment regardless of diatom quantity. Negative PE is often the result of preferential utilisation of the newly deposited labile material by the microbial community (“preferential substrate utilization”, PSU) which is usually observed at excessive substrate additions. The fact that PSU and the associated negative PE occurred even at low substrate levels in this study could be attributed to limited amounts of OM subject to priming in our study area (∼0.2% organic carbon [OC]) which seems to be an exception among continental slopes (typically >0.5%OC). We postulate that PEs will normally be positive in continental slope sediments and that their intensity will be a direct function of sediment OC content. More experiments with varying supply of substrate targeting C-poor vs. C-rich sediments are needed to confirm these hypotheses.

Experimental and Analytical Studies on the Effect of Excessive Loading on Fatigue Crack Propagation in Piping Materials

The seismic design review guide in Japan was revised in September 2006 to address the occurrence of a large earthquake beyond the design basis. In addition, Japanese nuclear power plants (NPPs) experienced multiple large earthquakes, such as Niigata-ken Chuetsu-Oki Earthquake in 2007 and the Great East Japan Earthquake in 2011. Therefore, it is very important to assess the structural integrity of reactor piping under such a large earthquake when a crack exists in the piping. In this work, crack growth behavior after excessive loading during the large-scale earthquake were experimentally and analytically evaluated for carbon steel and austenitic stainless steel. Some cyclic loading patterns with increasing and decreasing load amplitudes and maximum loads were applied to fatigue crack growth test specimens. From the results, the retardation of crack growth rate was clearly observed after excessive loading. In addition, the applicability to the retardation effect of the modified Wheeler model was confirmed. It is also concluded that the retardation effect has little influence on the failure probability due to seismic loading using probabilistic fracture mechanics (PFM) analyses with the modified Wheeler model.