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81.
Molybdenum carbide (Mo2C) was demonstrated to be highly active for the water–gas shift of a synthetic steam reformer exhaust stream. This catalyst was more active than a commercial Cu–Zn–Al shift catalyst under the conditions employed (220–295°C and atmospheric pressure). In addition, Mo2C did not catalyze the methanation reaction. There was no apparent deactivation or modification of the structure during 48 h on‐stream. The results suggest that high surface area carbides are promising candidates for development as commercial water–gas shift catalysts. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
82.
Jeremy Greer Andrew J. Petruska Arthur W. Mahoney Manikantan Nambi Eberhard Bamberg Jake J. Abbott 《Journal of Materials Engineering and Performance》2014,23(4):1392-1401
This paper focuses on wire electrical discharge machining (WEDM) of devices made from commercially available sintered neodymium-iron-boron (NdFeB) rare-earth magnets that have been magnetized before machining. We conduct an experimental study to quantify the effects of the voltage and capacitance of an RC-type WEDM machine, as well as the magnet polarity, on slicing rate, mean kerf, and variation in kerf. We find that voltage and capacitance affect slicing rate, that voltage affects mean kerf, that no parameters tested affect the variation in kerf, and that the polarity of the magnet being machined does not affect the machining process. Linear regression is used to fit simple predictive models to the data with good agreement. Further analysis is performed to characterize the loss in permanent magnetization on the surface of the magnet due to heating during the machining process, and it is found that the outer layer of approximately 35 μm in depth is demagnetized when using the highest voltage and capacitance values tested. 相似文献
83.
Schönrogge K Napper EK Birkett MA Woodcock CM Pickett JA Wadhams LJ Thomas JA 《Journal of chemical ecology》2008,34(2):168-178
The larva of the hoverfly Microdon mutabilis is a specialist social parasite of the ant Formica lemani that is adapted to local groups of F. lemani colonies but mal-adapted to colonies of the same species situated only a few hundred meters away. At a study site in Ireland,
F. lemani shares its habitat with four other ant species. All nest under stones, making the oviposition choice by M. mutabilis females crucial to offspring survival. In this study, we tested the hypothesis that, as an extreme specialist, M. mutabilis should respond to cues derived from its host rather than from its microenvironment, a phenomenon that has hitherto only been
addressed in the context of herbivorous insects and their parasitoids. In behavioral assays, M. mutabilis females reacted to volatiles from F. lemani colonies by extending their ovipositors, presumably probing for an oviposition substrate. This behavior was not observed
toward negative controls or volatiles from colonies of Myrmica scabrinodis, the host ant of the closely related Microdon myrmicae. Coupled gas chromatography-electroantennography (GC-EAG) that used antennal preparations of M. mutabilis located a single physiologically active compound within an extract of heads of F. lemani workers. Coupled GC-mass spectrometry (GC-MS) tentatively identified the compound as a methylated methylsalicylate. GC co-injection
of the extract with authentic samples showed that of the four possible isomers (methyl 3-, 4-, 5-, and 6-methylsalicylate),
only methyl 6-methylsalicylate co-eluted with the EAG-active peak. Furthermore, the response to methyl 6-methylsalicylate
was four times higher than to those of the other isomers. Coupled GC-EAG and GC-MS also revealed physiological responses to
two constituents, 3-octanone and 3-octanol, of the M. scabrinodis alarm pheromone. However, the behavioral trials did not reveal any behavior that could be attributed to these compounds.
Results are discussed in the context of four phases of host location behavior, and of the characteristics, which volatile
cues should provide to be useful for an extreme specialist such as M. mutabilis. 相似文献
84.
Hong-Jie Wang Biao Huang Xue-Zheng Shi Jeremy Landon Darilek Dong-Sheng Yu Wei-Xia Sun Yong-Cun Zhao Qing Chang Ingrid Öborn 《Nutrient Cycling in Agroecosystems》2008,81(3):203-218
Balances of major nutrients such as nitrogen (N), phosphorus (P), and potassium (K) in small-scale farming systems are of
critical importance to nutrient management and sustainable agricultural development. Mass balances of N, P, and K and some
of their influencing factors were studied for two years from July 2003 to July 2005 on small-scale vegetable-farming systems
in two contrasting peri-urban areas (Nanjing and Wuxi) of the Yangtze river delta region of China. This balance approach considered
organic fertilizer inputs (cow manure, pig manure, and human biosolids), inorganic fertilizer inputs (urea, composite fertilizer,
and phosphates), irrigation water, and atmospheric deposition; and considered outputs by vegetables. Input via organic fertilizers
was significant for all element balances in the Nanjing area. Inorganic and organic fertilizer, particularly inorganic fertilizer,
contributed major nutrient inputs to the system in the Wuxi area. Compared with nutrient output by vegetables, there were
significant surpluses of N and P on two vegetable farm systems. Furthermore, N surplus in the Nanjing area was higher than
that in the Wuxi area with an inverse relationship to P surplus. In contrast, the general trend of K balances was negative
on both sites; hence, the nutrient use efficiency was significantly lower for N and P than K. The nutrient imbalance may be
attributed to the differences between fertilizer types and management modes driven by social economic status differences among
farmer households. The large N and P net excess creates an environmental threat because of potential losses to ground or surface
waters, whereas negative K balance creates soil fertility risks. The results highlight researchers’ and farmers’ need to develop
rational fertilization technology to optimize nutrient management on vegetable farmlands to promote sustainable agricultural
development in peri-urban areas. 相似文献
85.
Henn A Joachimi A Gonçalves DP Monchaud D Teulade-Fichou MP Sanders JK Hartig JS 《Chembiochem : a European journal of chemical biology》2008,9(16):2722-2729
RNA interference is triggered by small hairpin precursors that are processed by the endonuclease dicer to yield active species such as siRNAs and miRNAs. To regulate the RNAi-mediated suppression of gene expression, we imagined a strategy that relies on the sequence-specific inhibition of shRNA precursor processing by immediate RNA-small molecule interactions. Here, we present a first step in this direction by augmenting shRNAs with guanosine-rich sequences that are prone to fold into four-stranded structures. The addition of small molecules that selectively bind to such quadruplex sequences should allow for the specific inhibition of dicing of shRNAs that contain suitable G-rich elements. In an attempt to find compounds that protect against dicer processing, we have examined the effects of quadruplex-binding compounds on the dicer processing of shRNAs containing G-quadruplexes. Although a variety of small molecules that are known to bind to quadruplexes inhibited in vitro dicing of shRNAs, only two substance classes, namely certain porphyrazines and bisquinolinium compounds, showed selective inhibition of G-rich shRNAs compared to control sequences lacking guanine-rich elements. The G-rich shRNAs displayed a potent knockdown of gene expression in mammalian cell culture, but the effect was not influenced by addition of the respective quadruplex-binding compounds. 相似文献
86.
87.
James McGregor Zhenyu Huang Edward P.J. Parrott J. Axel Zeitler K. Lien Nguyen Jeremy M. Rawson Albert Carley Thomas W. Hansen Jean-Philippe Tessonnier Dang Sheng Su Detre Teschner Elaine M. Vass Axel Knop-Gericke R. Schlögl Lynn F. Gladden 《Journal of Catalysis》2010,269(2):329-339
The catalytic dehydrogenation (DH) and oxidative dehydrogenation (ODH) of light alkanes are of significant industrial importance. In this work both carbonaceous material deposited on VOx/Al2O3 catalysts during reaction and unsupported carbon nanofibres (CNFs) are shown to be active for the dehydrogenation of butane in the absence of gas-phase oxygen. Their activity in these reactions is shown to be dependent upon their structure, with different reaction temperatures yielding structurally different coke deposits. Terahertz time-domain spectroscopy (THz-TDS), among other techniques, has been applied to the characterisation of these deposits – the first time this technique has been employed in coke studies. TEM and other techniques show that coke encapsulates the catalyst, preventing access to VOx sites, without a loss of activity. Studies on CNFs confirm that carbonaceous materials act as catalysts in this reaction. Carbon-based catalysts represent an important new class of potential catalysts for DH and ODH reactions. 相似文献
88.
Kristin Engels Dr. Carsten Beyer Dr. Maria L. Suárez Fernández Frank Bender Michael Gaßel Dr. Gottfried Unden Prof. Dr. Richard J. Marhöfer Dr. Jeremy C. Mottram Prof. Dr. Paul M. Selzer Prof. Dr. 《ChemMedChem》2010,5(8):1259-1271
Apicomplexan parasites encompass several human‐ and animal‐pathogenic protozoans such as Plasmodium falciparum, Toxoplasma gondii, and Eimeria tenella. E. tenella causes coccidiosis, a disease that afflicts chickens, leading to tremendous economic losses to the global poultry industry. The considerable increase in drug resistance makes it necessary to develop new therapeutic strategies against this parasite. Cyclin‐dependent kinases (CDKs) are key molecules in cell‐cycle regulation and are therefore prominent target proteins in parasitic diseases. Bioinformatics analysis revealed four potential CDK‐like proteins, of which one—E. tenella CDK‐related kinase 2 (EtCRK2)—has already been characterized by gene cloning and expression. 1 By using the CDK‐specific inhibitor flavopiridol in EtCRK2 enzyme assays and schizont maturation assays (SMA), we could chemically validate CDK‐like proteins as potential drug targets. An X‐ray crystal structure of human CDK2 (HsCDK2) served as a template to build protein models of EtCRK2 by comparative homology modeling. Structural differences in the ATP binding site between EtCRK2 and HsCDK2, as well as chicken CDK3, were addressed for the optimization of selective ATP‐competitive inhibitors. Virtual screening and “wet‐bench” high‐throughput screening campaigns on large compound libraries resulted in an initial set of hit compounds. These compounds were further analyzed and characterized, leading to a set of four promising lead compounds for development as EtCRK2 inhibitors. 相似文献
89.
Flexible piezoresistive films, such as, carbon black/polydimethylsiloxane (C-PDMS) composites, are often used as skin analogs and integrated into complex array sensors for tactile sensing. The uniformity of the sensor characteristics heavily depends on the homogeneity of the composite. Therefore, the ability to locally characterize a film that will be integrated into a complex force sensor could be critical. Here, a method to characterize the local sensitivity of flexible piezoresistive films is presented. Using a conductive sphere, which was chosen over a flat probe to eliminate misalignment issues, the surface of a thin film composite is indented to characterize the change in resistivity in terms of average strain. Experiments were performed with 15 and 18 wt% carbon black C-PDMS films of varying thickness. The contact radius of the probe with the piezoresistive film was estimated using the Johnson-Roberts-Kendall contact theory. Theoretical contact area estimates were found to agree with contact radius measurements carried out using optically transparent PDMS films observed through an optical microscope. Results show that C-PDMS with 15 wt% carbon black exhibit a higher rate if change of resistivity and gauge factor than films of same thickness with 18 wt% carbon black. On the other hand, thicker films exhibit higher gauge factors for the two tested carbon black contents. Tests carried out at multiple locations yielded consistent sensitivity values, making these types of composites suitable for array type force sensors. 相似文献
90.
Eric W. Neuman Benjamin J. Lai Jeremy L. Watts Gregory E. Hilmas William G. Fahrenholtz Laura Silvestroni 《International Journal of Applied Ceramic Technology》2021,18(6):2224-2236
Densification behavior, microstructure, and mechanical properties of zirconium diboride (ZrB2) ceramics modified with a complex Zr/Si/O-based additive were studied. ZrB2 ceramics with 5–20 vol.% additions of Zr/Si/O-based additive were densified to >95% relative density at temperatures as low as 1400°C by hot-pressing. Improved densification behavior of ZrB2 was observed with increasing additive content. The most effective additive amount for densification was 20 vol.%, hot-pressed at 1400°C (∼98% relative density). Microstructural analysis revealed up to 7 vol.% of residual second phases in the final ceramics. Improved densification behavior was attributed to ductility of the silicide phase, liquid phase formation at the hot-pressing temperatures, silicon wetting of ZrB2 particles, and reactions of surface oxides. Room temperature strength ranged from 390 to 750 MPa and elastic modulus ranged from 440 to 490 GPa. Vickers hardness ranged from 15 to 16 GPa, and indentation fracture toughness was between 4.0 and 4.3 MPa·m1/2. The most effective additive amount was 7.5 vol.%, which resulted in high relative density after hot-pressing at 1600°C and the best combination of mechanical properties. 相似文献