C1 C3 Research Articles

Anticancer activity and DNA-binding properties of novel cationic Pt(II) complexes

In this study, three structurally related cationic Pt complexes, [Pt(ppy)(dppe)]CF3CO2: C1, [Pt(bhq)(dppe)]CF3CO2: C2, and [Pt(bhq)(dppf)]CF3CO2: C3, in which ppy=deprotonated 2-phenylpyridine, bhq=deprotonated benzo[h]quinoline, dppe=bis(diphenylphosphino)ethane and dppf=1,1′-bis(diphenylphosphino)ferrocene, were used for the assessment of their anticancer activities against Jurkat and MCF-7 cancer cell lines. The Pt complexes (C1–C3) demonstrated significant level of anticancer properties, as measured using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay. Moreover, the changes in nuclear morphology with Acridine Orange (AO) staining reveal that these complexes are capable to induce apoptosis, and only C1 stimulates activity of Caspase-3 in Jurkat cancer cells. To get a better insight into the nature of binding between these cationic Pt complexes and DNA, different spectroscopic techniques and gel electrophoresis were applied. On the basis of the results of UV/vis absorption spectroscopy, CD experiment and fluorescence quenching of ethidium bromide (EB)–DNA, the interaction between DNA and the Pt complexes is likely to occur through a mixed-binding mode. Overall, the present work suggests that a controlled modification could result in new potentially antitumor complexes which can survive the repair mechanism and induce facile apoptosis.

Origin and carbon isotope fractionation of CO2 in marine sour gas reservoirs in the Eastern Sichuan Basin

According to gas chemical and carbon isotopic compositions for 75 gas samples from the Eastern Sichuan Basin, C1–C3 gaseous hydrocarbons are dominant with high dryness coefficient (C1/C1–3=0.99–1.0). Despite the presence of various contents of H2S and CO2, a reasonably good positive correlation is exhibited when both contents are>5%. The carbon dioxide in the natural gas in the Eastern Sichuan Basin mainly originated from carbonate dissolution by acid gases and thermochemical sulfate reduction (TSR). The content of CO2 produced at the early stage of acid gas dissolution is commonly<5%, with δ13CCO2 value<−3.0‰. However, when the CO2 content exceeds 5%, the δ13CCO2 values range from −8‰ to +2‰, and the CO2 and H2S contents demonstrated a positive correlation. The majority of CO2 is generated via TSR as well as acid gas dissolution during the late uplift of the basin. Particularly, the CO2 with δ13CCO2 value<−3‰ is primarily the residual CO2 generated via the TSR after it was partially precipitated to form calcite, while the CO2 with δ13CCO2 value>−3‰ is a mixture of the CO2 produced early via TSR and the CO2 produced by the subsequent carbonate rock dissolution by acid gases.

The origin of abnormally high benzene in light hydrocarbons associated with the gas from the Kuqa depression in the Tarim Basin, China

The chemical and carbon isotopic compositions of C1–C3 and C6–C7 light hydrocarbons were analyzed in 14 natural gas samples from the Kela 2, Dabei and Dina 2 gas fields in the Kuqa depression of the Tarim Basin. The relative content of light aromatic compounds (benzene and toluene) in C6–C7 light hydrocarbons is very high, with benzene as the main peak in the gas chromatogram. The relative content of aromatic compounds generally amounts to over 30% of the C6–C7 light hydrocarbons, especially in the Kela 2 gas field where light aromatics comprise more than 70% of the C6–C7 light hydrocarbons. Compared with 255 coal derived gas samples in many other sedimentary basins in China, an abnormal distribution of hydrocarbon composition is observed in the study area. In order to investigate this abnormal distribution, light hydrocarbon yields generated from low maturity coals at different pyrolysis temperatures were simulated quantitatively. The results showed that the yield of light aromatic compounds (benzene and toluene) gradually increases with increasing pyrolysis temperature. Furthermore, the relative content of aromatic hydrocarbons generated from coal samples at high temperatures, similar to an instantaneous accumulation mode under geologic conditions, can amount to 90% of C6–C7 light hydrocarbons, while that of aromatic hydrocarbons generated cumulatively at high temperatures, similar to a cumulative accumulation mode in natural geologic bodies, and is no more than 46.6%. These phenomena have not yet been reported in the literature. By combining these data with carbon isotopic data for natural gas components, it is proposed that an abnormal distribution of aromatic hydrocarbons in gases from the Kuqa depression may imply that the Kela 2 gas field was mainly formed by instantaneous gas accumulation, while the Dabei and Dina 2 gas fields were largely formed by cumulative gas accumulations.

Pressmud as an Alternate Resource for Hydrocarbons and Chemicals by Thermal Pyrolysis

This report relates to the thermal pyrolysis of pressmud combined with in situ upgradation of the pyrolysis vapor for generation of hydrocarbons and chemicals, up to 873 K, in a batch reactor. The products of the process, comprised of gases (11 wt %), liquids (22 wt %), and solid residues (53 wt %), are well characterized by mass spectroscopy. The gases comprised of C1–C3 hydrocarbons include N2, CO2, CO, and H2, whereas the liquid products were C10–C27 hydrocarbons along with alcohols, acids, aldehydes, and phenolic compounds. The solid char was comprised of macro- and nanoparticles having porous structures and various functionalities. The pyrolysis vapor upgradation by iron is found to be effective in producing hydrocarbon products. A complete mechanism of the product formation during the pressmud pyrolysis is proposed. The investigation shows that pressmud can be a resource of hydrocarbons and valuable chemicals.

Stereospecific ligands and their complexes. Part XII. Synthesis, characterization and in vitro antiproliferative activity of platinum(IV) complexes with some O,O′-dialkyl esters of (S,S)-ethylenediamine-N,N′-di-2-propanoic acid against colon cancer (HCT-116) and breast cancer (MDA-MB-231) cell lines

Synthesis of three new platinum(IV) complexes C1–C3, with bidentate N,N′-ligand precursors, O,O′-dialkyl esters (alkyl=propyl, butyl and pentyl), of (S,S)-ethylenediamine-N,N′-di-2-propanoic acid, H2-S,S-eddp were reported. The reported platinum(IV) complexes characterized by elemental analysis and their structures were discussed on the bases of their infrared, 1H and 13C NMR spectroscopy. In vitro antiproliferative activity was determined on tumor cell lines: human colon carcinoma HCT-116 and human breast carcinoma MDA-MB-231, using MTT test.

Phenolic metabolites as compliance biomarker for polyphenol intake in a randomized controlled human intervention

Clinical trials are needed to confirm the association between polyphenol consumption and lower incidence of chronic diseases observed in epidemiological studies. However, a reliable evaluation of polyphenol intake is complicated.An 8-week randomized controlled trial (78 subjects) was performed using two isoenergetic diets differing only for polyphenol contents. Then, urinary phenolic metabolite profiles were analysed using gas-chromatography with mass detection. Phenolic metabolites detected in 24-h-urine were hydroxylated phenolic acids with C1–C3 side chain in the group consuming polyphenol-rich diet. The intake of polyphenol-rich foods increases the excretion of phenolic metabolites in urine providing a profile, which may serve as compliance biomarker of polyphenol-rich diet.

Synthetic studies on polymaxenolides: model studies for constructing dihydropyran portion and synthesis of lower portion

With a goal of the total synthesis of polymaxenolide, the first hybrid marine natural product, the model studies for constructing the dihydropyran portion based on the originally proposed biosynthesis (C–C bond formation followed by dehydrative cyclization) and the synthesis of the lower portion (the C1–C3, C7–C17 portion) based on an iodide-induced Morita–Baylis–Hillman type reaction (a three-component assembly) followed by Suzuki–Miyaura cross-coupling are described.

Alcoholysis of canola oil using a short-chain (C1–C3) alcohols

In this study, the conversion characteristics and fuel properties of biodiesel were investigated according to carbon numbers of the short-chain alcohols that were used as reactants in the biodiesel manufacturing process. As the carbon numbers of the short chain alcohols increased, the fatty acid alkyl ester content of biodiesel decreased, and the optimum reaction temperature and time increased. The optimal conditions for short-chain alcoholysis were as follows: methanolysis (55°C, 60min), ethanolysis (65°C, 80min), and propanolysis (85°C, 100min). Also, according to the fuel properties analysis of the manufactured biodiesel with increasing carbon numbers, the heating value increased to 39.6–41.1MJ/kg, and oxidation stability improved with methanolysis (6.68h), ethanolysis (7.03h), and propanolysis (7.51h). But the kinematic viscosity increased from 4.24 to 4.68cSt with increasing carbon numbers of the short chain alcohols.

Hydrocarbons synthesis from syngas by very high pressure plasma

Experimental studies related to chemical processes based on the use of very high pressure plasma are scarce. In the domain of chemical synthesis enhanced by plasma, the influence of pressure has not been yet reported in literature for conversion of syngas into hydrocarbons. This may be attributed to the difficulties of ignition and sustaining a stable electric discharge at pressures higher than 1MPa. Yet, the use of high pressure plasma could constitute a new route to synthesize hydrocarbons in gaseous phase. Thus, this paper presents experimental results of hydrocarbons synthesis from a syngas having a H2:CO ratio of 2.2:1, i.e. close to the one commonly met in the classical Fischer–Tropsch process, in a tip-tip non-thermal arc discharge reactor at very high pressure (in the range 0.5–15MPa) supplied by a high-voltage DC power supply without any catalyst. The molecular synthesis is here studied through the influence of two process setting parameters: operating pressure and supplying current. The results show that C1–C3 molecules can be synthesized by this way and their concentration significantly varies with the two studied parameters. The best results in terms of products concentration after 60s treatment were obtained: (i) for 12MPa pressure at 0.35A current, with concentration of C1 and C2+C3 around 6000ppm and 90ppm respectively, (ii) for 0.2A current at 0.5MPa pressure, with concentration of C1 and C2+C3 around 4500ppm and 5000ppm respectively. In addition, the energy efficiency of the process was evaluated, based on the determination of specific energies as they are defined in the classical Fischer–Tropsch process. The results demonstrate that the optima in terms of chemical conversion and energy efficiency coincide together.

Liquid-phase dehydration of d-xylose over silica–alumina catalysts with different alumina contents

The dehydration of d-xylose into furfural was examined using SiO2–Al2O3 catalysts with varying alumina contents to determine the effects of surface acidity on the catalytic performance. For comparison, SiO2 and Al2O3 catalysts were also examined. d-Xylose conversion increased with increasing alumina content in the SiO2–Al2O3 catalysts. Conversely, furfural selectivity at a similar d-xylose conversion decreased with increasing alumina content in the SiO2–Al2O3 catalyst. Lewis acid sites appeared to catalyze the isomerization of d-xylose into lyxose and xylulose, decomposition of d-xylose into C1–C3 products, and polymerization of d-xylose and furfural into humin.

Characterization of oil complex hydrocarbon mixtures by HSQC‐NMR spectroscopy and PCA

The degree of changes in complex mixtures from crude oil (CO) and from oil residues in soils was determined by using heteronuclear single quantum coherence–nuclear magnetic resonance (HSQC‐NMR) spectroscopy. The HSQC‐NMR spectra of crude oil samples and two oil residues with natural attenuation (E1 and E2), and two biopiles (B1 and B2) were recorded using a 500‐MHz spectrometer. The spectra could be divided into major regions according to the different types of protons and carbons. Twenty‐three regions (A1–A5, B1–B11, C1–C3, D1–D3, and E) were defined on the basis of signal assignments. A multivariate method, the principal component analysis (PCA), was used to search the change in the structural parameters during the environmental exposure time. The first two principal components (PCs) accounted for the 83.3% of the total variance (51.8% and 31.5% for PC1 and PC2, respectively). The euclidean distances (3D) between the samples are 2.80 (CO–E2), 2.37 (CO–E1), 1.62 (CO–BP1), and 1.72 (CO–BP2). This suggests that the environmental transformation during exposure time follows the order E2 &gt; E1 &gt; BP2 &gt; BP1 &gt; CO. The disappearance of the signals (−CH, −CH2, and −CH3) in the HSCQ‐NMR spectra compared with the crude oil spectrum was conveniently quantified by PCA, and it helps in the characterization of the fate of the oil spills. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Dehydrogenation of alkane to light olefin over PtSn/θ-Al2O3 catalyst: Effects of Sn loading

Pt0.5Snx.x/θ-Al2O3 catalysts with different amount of tin (0.5, 0.75, 1.0 and 1.5wt%) were prepared by a co-impregnation method. Propane dehydrogenation was performed at 873K and a GHSV of 53,000mL/(gcath). The Pt0.5/θ-Al2O3 catalyst showed severe deactivation in alkane dehydrogenation reaction. The Sn addition decreased the cracking products of C1–C2 and the Pt0.5Sn0.75 catalyst with the highest Pt dispersion showed the highest C3 yield and C3 selectivity. n-Butane dehydrogenation was performed at 823K and a GHSV of 18,000mL/(gcath). Similarly to propane dehydrogenation, the Sn addition to the Pt0.5/θ-Al2O3 catalyst decreased the cracking products of C1–C3. However, the Pt0.5Sn1.0 showed the highest n-C4 yield and the catalyst was steadily deactivated even at 823K differently from propane dehydrogenation at 873K.The small amount of Sn addition improved the C3 and n-C4 selectivity by blocking the cracking sites of Pt catalyst. The PtSn alloy formed after the reduction at 500°C. The PtSn formation can enhance the C3 and n-C4 selectivity. The Pt dispersion on the Pt0.5/θ-Al2O3 catalyst increased with the Sn addition up to 0.75 wt%. The highest Pt metal dispersion was observed on the Pt0.5Sn0.75 catalyst. The conclusion was given to the Sn effects on the increase of Pt dispersion to enhance the activity as well as on the electronic and geometric effect of PtSn alloy to increase the stability and olefin selectivity.

Electrochemical investigation of Pd nanoparticles and MWCNTs supported Pd nanoparticles-coated electrodes for alcohols (C1–C3) oxidation in fuel cells

Incorporation of palladium nanoparticles (PdNPs) and multi-walled carbon nanotubes (MWCNTs) into chitosan-coated glassy carbon (GC) electrode for alcohols (methanol, ethanol, and isopropanol) electrooxidation has been studied. PdNPs–chitosan and MWCNTs–PdNPs–chitosan nanocomposites are successfully prepared and characterized by transmission electron microscopy images and UV–Vis spectroscopy. Based on the results, PdNPs–chitosan nanocomposite indicates high electrochemical activity and excellent catalytic characteristic for alcohol (C1–C3) electrooxidation on a GC electrode in an alkaline medium. The current density of the alcohols oxidation at GC–PdNPs–chitosan electrode is investigated in optimized conditions and compared with that obtained at the GC-modified electrode by Pd with different polymers. Also, our results show that the dispersion of Pd nanoparticles on the MWCNTs significantly improved the performance of the PdNPs/chitosan composite for electrooxidation of the C1–C3 alcohols.

Distribution of PARAFAC modeled CDOM components in the North Pacific Ocean, Bering, Chukchi and Beaufort Seas

The spatial and vertical distribution of colored dissolved organic matter (CDOM) in the North Pacific Ocean, Bering, Chukchi and Beaufort Seas was investigated with respect to water circulation. Four fluorescent components were identified in 546 samples using parallel factor analysis (PARAFAC): terrestrially-derived humic-like (C1), UV humic-like (C2), microbially derived humic-like (C3) and proteinaceous/tryptophan-like (C4) components. Deep water upwelling upon contact with the Aleutian Islands influenced optical properties of CDOM in Bering Sea surface water, where higher absorption coefficient at 355nm (a355), fluorescence intensities of all CDOM components and lower spectral slope (S275–295) were found compared to surface waters of the Gulf of Alaska (p<0.01). Further north, a marked increase in bioprocessed material (C4) was found in surface waters in Chukchi Sea. This finding was attributed to elevated biological activity in surface Chukchi water. Humic-like C1–C3 showed considerable dilution with increasing latitude from coastal to offshore regions in surface Beaufort Sea, suggesting a terrestrial predominance. This contrasts well with protein-like C4 where no significant gradient was found in Beaufort Sea surface water, supporting in situ generation. Finally, the vertical decrease of protein-like C4 relative to humic-like components C1–3 suggests that humic-like CDOM is produced at depth as a byproduct of remineralization.

Electrocatalytic conversion of CO2 on carbon nanotube-based electrodes for producing solar fuels

The behavior of Fe, Co, Cu (mono-, bi- and trimetallic) on carbon nanotube (CNT) electrocatalysts in the solventless conversion of CO2 to C1–C3 hydrocarbons/organics (HO) has been studied as a part of the general objective of developing novel photoelectrocatalytic (PEC) solar cells to convert CO2 to solar fuels. The comparison of commercial conductive carbon black support is also analyzed, as well as the role of CNT. FeCu bimetallic electrocatalysts double the productivity to C1–C3 HO with respect to iron monometallic electrocatalysts, and the use of CNTs as conductive carbon support allows to double productivity to C1–C3 HO with respect to commercial conductive carbon black supports. The parallelism between solventless operations at atmospheric pressure and high-pressure operations in the electrocatalytic reduction of CO2 in liquid electrolyte was evidenced. The results show that Fe and other metals, which is different from Cu are inactive in forming HO during the electroreduction of CO2 at atmospheric pressure in a liquid aqueous electrolyte, are instead active and superior to copper under solventless conditions. The results indicate that the inhibition of the surface reactivity toward H2 formation rather than minimizing the energy barriers in CO2 electroreduction is the key to improve the performances and realize selective electrocatalysts.

Batch fermentative hydrogen production by enriched mixed culture: Combination strategy and their microbial composition

The effect of individual and combined mixed culture on dark fermentative hydrogen production performance was investigated. Mixed cultures from cow dung (C1), sewage sludge (C2), and pig slurry (C3) were enriched under strict anaerobic conditions at 37°C with glucose as the sole carbon source. Biochemical hydrogen production test in peptone-yeast-glucose (PYG) and basal medium was performed for individual mixed cultures (C1, C2 and C3) and their combinations (C1-C2, C2-C3, C1-C3 and C1-C2-C3) at a glucose concentration of 10 g/L, 37°C and initial pH 7. Maximum hydrogen yields (HY) of 2.0 and 1.86 [Formula: see text] by C2, and 1.98 and 1.95 mol(H2)/mol(glucose) by C2-C3 were obtained in PYG and basal medium, respectively. Butyrate and acetate were the major soluble metabolites produced by all the cultures, and the ratio of butyrate to acetate was ∼2 fold higher in basal medium than PYG medium, indicating strong influence of media formulation on glucose catabolism. The major hydrogen-producing bacterial strains, observed in all mixed cultures, belonged to Clostridium butyricum, C. saccharobutylicum, C. tertium and C. perfringens. The hydrogen production performance of the combined mixed culture (C2-C3) was further evaluated on beverage wastewater (10 g/L) at pH 7 and 37°C. The results showed an HY of 1.92 mol(H2)/mol(glucose-equivalent). Experimental evidence suggests that hydrogen fermentation by mixed culture combination could be a novel strategy to improve the HY from industrial wastewater.

Pt nanoparticles synthesized with new surfactants: improvement in C1–C3 alcohol oxidation catalytic activity

Platinum electrocatalysts were prepared using PtCl4 as a starting material and 1-decylamine, N,N-dimethyldecylamine, 1-dodecylamine, N,N-dimethyldodecylamine, 1-hexadecylamine, and 1-octadecylamine as surfactants. These surfactants were used for the first time in this synthesis to determine whether the primary and/or tertiary structure and/or chain length of the surfactants, affects the size and/or activity of the catalysts in C1–C3 alcohol electro-oxidation reactions. Electrochemical measurements (cyclic voltammetry and chronoamperometry) indicated that the highest electrocatalytic performance was observed for the Pt nanocatalysts that were stabilized by N,N-dimethyldecylamine, and this has a tertiary amine structure with a short chain length (R = C10H21). The high performance may be due to the high electrochemical surface area, Pt(0)/Pt(IV) ratio, %Pt utility, and roughness factor (Rf). X-ray photoelectron spectroscopy, X-ray diffraction, atomic force microscopy, and transmission electron microscopy were used to determine the parameters that affect the catalytic activities.

Measurements of C1–C4 alkyl nitrates and their relationships with carbonyl compounds and O3 in Chinese cities

Ambient alkyl nitrates (RONO2) are important byproducts of O3 formation. Although concern about O3 pollution has increased recently, few studies have investigated RONO2 chemistry and distributions in China. In this study, ambient levels of C1–C4 RONO2 were measured in Chinese cities, and their relationships with parent hydrocarbons (RH), carbonyls, and total oxidant (Ox = O3 + NO2) were investigated. Our measurements showed that 2-butyl nitrate (2-BuONO2) was the most abundant RONO2 species, with mixing ratios of 48–88 pptv, followed by 2-propyl nitrate (2-PrONO2), ethyl nitrate (EtONO2), methyl nitrate (MeONO2), and 1-propyl nitrate (1-PrONO2). The measured RONO2 species exhibited maximum levels in the early afternoon (13:00–14:00) of summer, suggesting the importance of RONO2 photochemical production. Relative to 2-BuONO2/n-butane, the measured 1-PrONO2/propane agreed well with the modeled ratio based on laboratory kinetic data, suggesting that propane was the dominant precursor of ambient 1-PrONO2. However, the measured ratios for MeONO2/methane, EtONO2/ethane, and summertime 2-PrONO2/propane showed significant positive deviations from the predicted values, indicating the existence of additional sources other than OH oxidation of the parent hydrocarbons. Initial mixing ratios of C1–C3 carbonyls during 08:00–12:00 in summer at the PKU site exhibited significant correlations with RONO2 levels, suggesting the importance of secondary sources for ambient carbonyls. The measured ratios of formaldehyde/MeONO2 were close to the theoretical ratio, whereas the derived ratios for acetaldehyde/EtONO2, propanal/1-PrONO2, and acetone/2-PrONO2 were higher than the kinetic ratios, indicating that these carbonyls might be produced from sources other than the reaction of alkoxy radicals with O2. Carbonyls are important precursors of Ox, but their photochemical reactions do not result in RONO2 production. Therefore, Ox/RONO2 could indicate the relative importance of carbonyls to Ox formation. On the basis of the measured ratios of Ox/2-BuONO2, we estimated the maximum contributions of secondary carbonyls to Ox at the PKU site to be 25–32% during 12:00–16:00 in summer.

A numerical study on the ability to predict the heat release rate using CH* chemiluminescence in non-sooting counterflow diffusion flames

Numerical studies on 1-D, non-sooting counterflow diffusion flames were performed to determine the precision with which the total heat release rate can be calculated using light emission, namely, chemiluminescence, from the reaction zone. A detailed reaction mechanism, incorporating sub-reaction models for excited state radicals (CH* and OH*, where * denotes the excited state), was employed in this study. A set of 1-D, steady state conservation equations was solved under standard atmospheric conditions over a counterflow configuration utilizing the CHEMKIN-PRO package. A variety of fuels (CH4 and C3H8), velocities (0.1m/s − near the extinction condition), diluents (N2, H2O, CO2, and Ar), detailed reaction mechanisms for C1–C3 hydrocarbons (GRI-Mech 3.0, Hai Wang’s-, and San Diego-mechanism), different sub-reaction models for excited radicals, and excited radical transport properties were examined for the current purpose. It was found that a one-to-one correlation between total chemiluminescence from CH* and the total heat release rate cannot be sustained when the flame experiences a relatively high stretch and dilution, even though the condition is still far away from extinction. This trend is consistent with the different types of fuels, and it is understood that the reduction of the ethynyl radical (C2H), a potential precursor of CH*, is the main cause of the one-to-one correlation not being sustained. To this end, it was concluded that the observable light emission can only be used to predict the total heat release rate when non-sooting diffusion flames exist under velocity conditions from 0.1m/s to 1.5m/s. In other words, the chemiluminescence intensity does not always correlate with the total heat release rate of highly stretched flames found in practical combustors.

Optimum extraction equilibria of the systems (water + carboxylic acid + 1-hexanol/Alamine): Thermodynamic modeling

Extraction equilibria of the systems (water+carboxylic acid+1-hexanol/Alamine 300) have been investigated at T=298.2K. Among the studied C1–C3 carboxylic acids, propanoic acid gives the largest distribution ratio and separation factors, as compared to formic and acetic acids. The equilibrium data of monocarboxylic acids are used to establish the basis to an analytical structure for optimum extraction. Some aspects of selection of an appropriate criterion for designing optimum extraction are discussed. Solvation energy relation (SERLAS) with five parameters has been performed to estimate the properties of extraction systems containing a protic alcohol solvent. The tie-lines of the present systems have been predicted by the UNIFAC-original model. The reliability analysis of both models has been made statistically against the experimental extraction factors.