Range Of CH Research Articles

Estimation of coefficients of consolidation and permeability via piezocone dissipation tests

Measured excess pore pressure dissipation responses always present a different trend from those theoretically expected. A simple hyperbolic equation for estimating the coefficient of consolidation [ch(Hyp)] was thus proposed based on the indirect fit between both responses. The method was applied to dissipation test data in the normally consolidated clay of Nakdong River Delta. The result indicates that ch(Hyp) values vary with the normalized excess pore pressure (U), showing different trends according to the patterns of both curves. The mean values estimated with four theoretical solutions vary within a difference of 200%, and are close to those of the consolidation tests. The coefficients of consolidation obtained using three conventional methods, which are based on the direct fits at U = 50% and between the early or late parts of both curves, lie within or out of the range of ch(Hyp). The coefficients of permeability estimated using the mean values of ch(Hyp) underestimate those of the laboratory permeability test and those of an empirical formula based on the piezocone sounding records.

Inter-Annual Variations of Methane Emission from an Open Fen on the Qinghai-Tibetan Plateau: A Three-Year Study

The study aimed to understand the inter-annual variations of methane (CH4) emissions from an open fen on the Qinghai-Tibetan Plateau (QTP) from 2005 to 2007. The weighted mean CH4 emission rate was 8.37±11.32 mg CH4 m−2 h−1 during the summers from 2005 to 2007, falling in the range of CH4 fluxes reported by other studies, with significant inter-annual and spatial variations. The CH4 emissions of the year of 2006 (2.11±3.48 mg CH4 m−2 h−1) were 82% lower than the mean value of the years 2005 and 2007 (13.91±17.80 mg CH4 m−2 h−1 and 9.44±14.32 mg CH4 m−2 h−1, respectively), responding to the inter-annual changes of standing water depths during the growing season of the three years. Significant drawdown of standing water depth is believed to cause such significant reduction in CH4 emissions from wetlands in the year 2006, probably through changing the methanogen composition and decreasing its community size as well as activating methanotrophs to enhance CH4 oxidation. Our results are helpful to understand the inter-annual variations of CH4 emission and provide a more reasonable regional budget of CH4 emission from wetlands on the QTP and even for world-wide natural wetlands under climate change.

Allosteric effects in a tetrapodal imidazolium-derived calix[4]arene anion receptor

A ditopic tetrapodal imidazolium-based 1,3-alternate calix[4]arene host binds anions as 1 : 2 complexes via a range of CH...anion hydrogen bonds. Allosteric enhancement of the affinity for the second chloride anion is observed. X-Ray crystal structures of the chloride, bromide and nitrate complexes suggest that this behaviour is linked to inter-binding site communication mediated by the calixarene framework. The imidazolium groups exist as either in-out or out-out conformers with respect to the calixarene, with the chloride complex exhibiting conformational isomorphism such that both forms are present in the same crystal structure.

Temperature and performance variations along single chamber solid oxide fuel cells

The catalytic activity of single chamber solid oxide fuel cells (SC-SOFCs) with respect to hydrocarbon fuels induces a major overheating of the fuel cell, temperature variations along its length, and changes in the original fuel/air composition mainly over the anode component. This paper assesses the temperature gradients and the variations in performance along electrolyte-supported Ni-YSZ/YSZ/LSM cells fed with methane gas. The investigations are performed in a useful range of CH 4/O 2 ratios between 1.0 and 2.0, in which the furnace temperature and flow rate of methane–air mixtures are held constant at 700 °C and 450 sccm, respectively. Electrochemical impedance spectroscopy (EIS) is used to sense the temperature at the location where smaller size cathodes are positioned on the opposite side of a full-size anode. Due to temperature increases, cells always perform better when the small cathodes are located at the inlet as well as at a CH 4/O 2 ratio of 1.0. With an increase in ratio, the results show the presence of artefacts due to the use of an active LSM material for the combustion of methane, and open-type gas distribution plates for the single chamber reactor.

The Isheyevo meteorite: Mineralogy, petrology, bulk chemistry, oxygen, nitrogen, carbon isotopic compositions, and 40Ar‐39Ar ages

Abstract— Isheyevo is a metal‐rich carbonaceous chondrite that contains several lithologies with different abundances of Fe,Ni metal (7–90 vol%). The metal‐rich lithologies with 50–60 vol% of Fe,Ni metal are dominant. The metal‐rich and metal‐poor lithologies are most similar to the CBb and CH carbonaceous chondrites, respectively, providing a potential link between these chondrite groups. All lithologies experienced shock metamorphism of shock stage S4. All consist of similar components—Fe,Ni metal, chondrules, refractory inclusions (Ca, Al‐rich inclusions [CAIs] and amoeboid olivine aggregates [AOAs]), and heavily hydrated lithic clasts—but show differences in their modal abundances, chondrule sizes, and proportions of porphyritic versus non‐porphyritic chondrules. Bulk chemical and oxygen isotopic compositions are in the range of CH and CB chondrites. Bulk nitrogen isotopic composition is highly enriched in 15N (δ15N = 1122‰). The magnetic fraction is very similar to the bulk sample in terms of both nitrogen release pattern and isotopic profile; the non‐magnetic fraction contains significantly less heavy N. Carbon released at high temperatures shows a relatively heavy isotope signature. Similarly to CBb chondrites, ∼20% of Fe,Ni‐metal grains in Isheyevo are chemically zoned. Similarly to CH chondrites, some metal grains are Ni‐rich (>20 wt% Ni). In contrast to CBb and CH chondrites, most metal grains are thermally decomposed into Ni‐rich and Ni‐poor phases. Similar to CH chondrites, chondrules have porphyritic and non‐porphyritic textures and ferromagnesian (type I and II), silica‐rich, and aluminum‐rich bulk compositions. Some of the layered ferromagnesian chondrules are surrounded by ferrous olivine or phyllosilicate rims. Phyllosilicates in chondrule rims are compositionally distinct from those in the hydrated lithic clasts. Similarly to CH chondrites, CAIs are dominated by the hibonite‐, grossite‐, and melilite‐rich types; AOAs are very rare. We infer that Isheyevo is a complex mixture of materials formed by different processes and under different physico‐chemical conditions. Chondrules and refractory inclusions of two populations, metal grains, and heavily hydrated clasts accreted together into the Isheyevo parent asteroid in a region of the protoplanetary disk depleted in fine‐grained dust. Such a scenario is consistent with the presence of solar wind—implanted noble gases in Isheyevo and with its comparatively old K‐Ar age. We cannot exclude that the K‐Ar system was affected by a later collisional event. The cosmic‐ray exposure (CRE) age of Isheyevo determined by cosmogenic 38Ar is ∼34 Ma, similar to that of the Bencubbin (CBa) meteorite.

Laboratory and Realized Host Ranges of <I>Chaetorellia succinea</I> (Diptera: Tephritidae), an Unintentionally Introduced Natural Enemy of Yellow Starthistle

In 1999, we reported our discovery, in California and Oregon, of Chaetorellia succinea (Costa) (Diptera: Tephritidae) destroying the seeds of yellow starthistle, Centaurea solstitialis L., one of the worst weeds in the western United States. This fly, an unintentional introduction from Greece, dispersed rapidly throughout California and the northwest, and there is interest in using this adventive fly as a classical biological control agent for this weed. Because the host range of Ch. succinea has not been studied, this fly might pose a risk to other members of the thistle tribe Cardueae, especially the many thistle species native to California and other parts of the western United States. We determined the physiological host range of this fly in the laboratory by exposing it under no-choice conditions to 14 potential Cardueae hosts. Two introduced weed species and the native American basketflower (Centaurea americana Nuttall) were laboratory hosts. Under less restrictive choice test conditions, yellow starthistle was highly preferred, but there was a small amount of oviposition, and a few adult Ch. succinea emerged from all three of these plant species. Because Ch. succinea is now widespread throughout California, we collected flower heads from 24 potential host plant species at 111 sites to determine the realized host range in the field. These collections did not include American basketflower, which does not occur naturally in California. Ch. succinea emerged only from the other two known hosts: Ce. melitensis and Ce. sulfurea. Our results suggest that American basketflower growing in the southwestern United States may be at risk if Ch. succinea expands its range into that region.

Ten years of atmospheric methane observations at a high elevation site in Western China

Abstract In this paper, the continuous (1994–2001) and discrete air sample (1991–2001) measurements of atmospheric CH 4 from the Waliguan Baseline Observatory located in western China (36°17′N, 100°54′E, 3816 m asl) are presented and characterized. The CH 4 time series show large episodic events on the order of 100 ppb throughout the year. During spring, a diurnal cycle with average amplitude of 7 ppb and a morning maximum and late afternoon minimum is observed. In winter, a diurnal cycle with average amplitude of 14 ppb is observed with an afternoon maximum and morning minimum. Unlike most terrestrial observational sites, no obvious diurnal patterns are present during the summer or autumn. A background data selection procedure was developed based on local horizontal and vertical winds. A selected hourly data set representative of “baseline” conditions was derived with approximately 50% of the valid hourly data. The range of CH 4 mixing ratios, annual means, annual increases and mean annual cycle at Waliguan during the 1992–2001 were derived from discrete and continuous data representative of “baseline” conditions and compared to air samples collected at other Northern Hemisphere sites. The range of CH 4 monthly means of 1746–1822 ppb, average annual means of 1786.7±10.8 ppb and mean annual increase of 4.5±4.2 ppb yr −1 at Waliguan were inline with measurements from sites located between 30° and 60°N. There were variations observed in the CH 4 annual increase patterns at Waliguan that were slightly different from the global pattern. The mean CH 4 annual cycle at Waliguan shows an unusual pattern of two gentle peaks in summer and February along with two small valleys in early winter and spring and a mean peak-to-peak amplitude of ∼11 ppb, much smaller than amplitudes observed at most other mid- and high-northern latitude sites. The Waliguan CH 4 data are strongly influenced by continental Asian CH 4 emissions and provide key information for global atmospheric CH 4 models.

Kinase inhibitors and the case for CH...O hydrogen bonds in protein-ligand binding.

Although the hydrogen bond is known to be an important mediator of intermolecular interactions, there has yet to be an analysis of the role of CH...O hydrogen bonds in protein-ligand complexes. In this work, we present evidence for such nonstandard hydrogen bonds from a survey of aromatic ligands in 184 kinase crystal structures and 358 high-resolution structures from the Protein Data Bank. CH groups adjacent to the positively charged nitrogen of nicotinamide exhibit geometric preferences strongly suggestive of hydrogen bonding interactions, as do heterocyclic CH groups in kinase ligands, while other aromatic CH groups do not exhibit these characteristics. Ab initio calculations reveal a considerable range of CH...O hydrogen bonding potentials among different aromatic ring systems, with nicotinamide and heterocycles preferred in kinase inhibitors showing particularly favorable interactions. These results provide compelling evidence for the existence of CH...O hydrogen bonds in protein-ligand interactions, as well as information on the relative strength of various aromatic CH donors. Such knowledge will be of considerable value in protein modeling, ligand design, and structure-activity analysis.

Characterization of the stereochemical structure of poly(tert-butyl acrylate) by one- and two-dimensional NMR spectroscopy

Two samples of poly(tert-butyl acrylate) (PtBuA) prepared by group-transfer and anionic polymerization were studied by a combination of one- and two-dimensional NMR methods. Lines in 1 H and 13 C NMR spectra of PtBuA solutions could be assigned to the configurational triads (CH range) and tetrads (CH 2 range). For analysis of the CH 2 range, the application of the inverse HETCOR (HMQC) technique was essential. The results obtained by the analysis of line intensities at tetrad level confirm that both PtBuA samples obey Bernouillian statistics

Study of the soot nucleation zone of rich methane-oxygen flames

Some aspects of the soot nucleation processes which take place in the reaction zone of an atmospheric pressure premixed flat methane/oxygen flame have been studied using a laser light scattering method and a gas chromatographic technique. A range of CH 4 /O 2 ratios of 0.9 to 1.27 was covered and the temperatures of the flames were varied by altering the inlet flow rate; in some experiments small amounts of ethylene or acetylene were added to the feeding mixtures. The maximum concentration of C 2 H 2 , C 4 H 2 and C 4 H 4 is increased when a higher R =CH 4 /O 2 ratio is used and, for the same R ratio, when the flame has a higher combustion temperature. The addition of C 2 H 2 and C 2 H 4 to the feeding mixtures increases the concentrations of all the unsaturated hydrocarbons. The angular patterns of the vertically and horizontally polarized components of the scattered light at λ 0 =514.5 nm were determined at different heights in the flame. It was found that in the reaction zone the vertical Q ˙ VV polarized components were due both to Rayleigh scattering by gas phase combustion products and to a contribution due to higher molecular weight substances. Higher combustion temperatures decrease the contribution of soot particles to the measured Q ˙ VV intensity, which is higher for richer mixtures. The depolarized Q ˙ HV component was much higher in the reaction zone than that predicted by the depolarization of the gas phase compounds. The Q ˙ VV / Q ˙ HV ratios pass through a maximum which is more pronounced and displaced toward the burner for higher CH 4 /O 2 mixtures. The extinction coefficients at λ 0 =514.5 nm in the reaction zone have also been measured and compared with the scatter results. The analysis of the experimental results shows that the formation and evolution of C 2 , C 3 and C 4 unsaturated hydrocarbons does not appear to be a process which takes place before soot nucleation. A part of the scattered signals in the first reaction zone is due to highly depolarized “anelastic” effects, whereas the depolarization in the burned gas region is due mainly to the anistropy of the soot particles. The minimum particle size observed, determined by the scatter/extinction method, is around 20 and the initial soot number concentration has a maximum of 10 13 cm −3 for the richest flame studied.

Methylmercury as a reversible denaturing agent for agarose gel electrophoresis

A method for agarose gel electrophoresis under denaturing conditions, with methylmercuric hydroxide as the denaturing agent, is described. Methylmercuric hydroxide is a strong and reversible denaturing agent. It appears that complete denaturation of any base-paired secondary structural feature of a nucleic aicd can be achieved at practical concentrations of CH 3 HgOH. The method has been tested by showing that singly nicked circular duplex PM2 DNA is dissociated into more rapidly migrating linear and circular single-strand forms by a CH 3 HgOH concentration within the 2.5–5.0 m m range. The mobilities of single-strand RNA molecules are decreased in the presence of sufficient CH 3 HgOH because their secondary structure is disrupted. For HeLa 28S rRNA, the melting transition occurs mainly in 2–3 m m range of CH 3 HgOH. For a series of RNA's, at 5 m m CH 3 HgOH, corresponding to complete denaturation, there is a linear dependence of log (molecular weight) on electrophoretic mobility and of log (mobility) on agarose concentration, just as in other gel electrophoresis systems.

Direct Measurements of Predissociation Probabilities in CH and CD Molecules

Quantitative measurements of nonradiative decay rates in the $C^{2}\ensuremath{\Sigma}^{+}$ state of CH and CD molecules are presented via absolute phase shift versus frequency data and are interpreted as direct measures of predissociation probabilities. The $C$-state decay rates measured in CH are approximately three times larger than those in CD and comparison with absorption oscillator strength measurements shows that the predissociation probabilities of the rotational levels observed in CH range from approximately 3\ifmmode\times\else\texttimes\fi{}${10}^{7}$ to 1.6\ifmmode\times\else\texttimes\fi{}${10}^{8}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, i.e., approximately 3 to 18 times the radiative transition probability.