40,374 research outputs found
C-14 and Be-10 in dust deposited during the storm of 16-17 April 2006 in Beijing
No full textThe concentrations of Be-10 and C-14 and values of delta C-13 in samples collected during a major dust storm in Beijing on 16-17 April 2006 were studied. The Be-10 concentrations ranged from 1.69 x 10(8) to 2.07 x 10(8) atom/g, C-14 ages for black carbon (BC) ranged from 3001 to 5181 yr BP and for total inorganic carbon (TIC) from 8464 to 9119 yr BP, and delta C-13 values for BC ranged from -23.15% to -23.80% and for TIC from -5.39% to -5.98%. A comparison of BC content and delta C-13 value between the dust, surface soil in the dust source region, and aerosols in Beijing indicated that BC in the dust deposited in Beijing is significantly incorporated by aerosol BC during the dust transportation. Based on the C-14 ages of BC, the proportion of fossil-fuel-derived BC was 0.35-0.49 of the total. In contrast to BC, the TIC deposited in Beijing can be firmly related to the source area and delta C-13 was not significantly modified during its transportation. According to the C-14 ages of TIC, the proportion of the secondary carbonate in the dust was from 0.63 to 0.70. The results confirm that C-14 of TIC is another useful tracer to indicate the source region of dust besides the content and delta C-13 value of TIC from the arid and semi-arid regions of China.Geochemistry & GeophysicsSCI(E)0ARTICLE2-31790-18005
TURNOVER RATE OF SOIL ORGANIC MATTER AND ORIGIN OF SOIL (CO2)-C-14 IN DEEP SOIL FROM A SUBTROPICAL FOREST IN DINGHUSHAN BIOSPHERE RESERVE, SOUTH CHINA
No full textThis paper examines the carbon isotopes (C-13, C-14) of soil organic carbon (SOC) and soil CO2 from an evergreen broadleaf forest in southern China during the rainy season. The distribution of SOC delta C-13, and SOC content with depth, exhibits a regular decomposition of SOC compartments with different turnover rates. Labile carbon is the main component in the topsoil (0-12 cm) and has a turnover rate between 0.1 and 0.01 yr(-1). In the middle section (12-35 cm), SOC was mainly comprised of mediate carbon with turnover rates ranging between 0.01 and 0.025. Below 35 cm depth (underlayer section), the SOC turnover rate is slower than 0.001 yr(-1), indicating that passive carbon is the main component of SOC in this section. The total production of humus-derived CO2 is 123.84 g C m(-2) yr(-1), from which 88% originated in the topsoil. The middle and underlayer sections contribute only 10% and 2% to the total humus-derived CO2 production, respectively. Soil CO2 delta C-13 varies from -24.7 parts per thousand to 24.0 parts per thousand, showing a slight isotopic depth gradient. Similar to soil CO2 delta C-13, Delta C-14 values, which range from 100.0 parts per thousand to 107.2 parts per thousand, are obviously higher than that of atmospheric CO2 (60-70 parts per thousand) and SOC in the middle and underlayer section, suggesting that soil CO2 in the profile most likely originates mainly from SOC decomposition in the topsoil. A model of soil CO2 Delta C-14 indicates that the humus-derived CO2 from the topsoil contributes about 65-78% to soil CO2 in each soil gas sampling layer. In addition, the humus-derived CO2 contributes similar to 81% on average to total soil CO2 in the profile, in good agreement with the field observation. The distribution and origin of soil (CO2)-C-14 imply that soil CO2 will be an important source of atmospheric (CO2)-C-14 well into the future.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000285437900058&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Geochemistry & GeophysicsSCI(E)CPCI-S(ISTP)
Irradiation effect of HfO2 MOS structure under gamma-ray
No full textthe effect of gamma irradiation upon Al/HfO2/SiO2/Si MOS structure under different doses of Co-60 is studied in this article as a function of total dosage. MOS capacitors with a stacked gate dielectric of 2.8nm thick SiO2 and 15nm thick HfO2 having electrode areas of 1mm*1mm are prepared on the p-Si substrate using thermal oxidation and atomic layer deposition respectively. The MOS capacitors are under zero bias during irradiation under Co-60 gamma ray with total dose of 100Krad (Si)/500Krad (Si)/1Mrad (Si) and dose rate of 50rad (Si)/s. The high frequency Capacitor-Voltage (C-V) and Current-Voltage (I-V) characteristic of each structure are measured at room temperature before and after irradiation. As well as the C-V and I-V property, Atomic Force Microscopy (AFM), Grazing Incidence X-ray Diffraction (GIXRD), and X-ray Photoelectron Spectroscopy (XPS) are also applied to determine the surface morphology, physical, and mechanical properties before and after different doses of radiation. The oxide trapped charge calculated from the high frequency C-V measurement is in the order of 10(12) cm(-2) and increases linearly with the increase of applied total dose. The XRD spectrum exhibits several phases of SiO2 and HfO2 variation under each total dose. The XPS result shows that each different total dosage leads to the binding energy peak drifting to a different degree demonstrating the influence of irradiation on the valence state of the elements, which can be attributed to the gamma-ray induced interface states
Mechanisms of microRNA mediated gene silencing in C. elegans
No full textMechanisms of microRNA mediated gene silencing in C. elegans
Xavier Ding
Dissertation abstract
microRNAs (miRNAs) are a large family of small non-coding RNAs, which post-transcriptionally repress numerous genes; a type of regulation which is important for countless physiological processes of multicellular organisms in health and disease.
miRNAs are genomically encoded and transcribed as long precursors, which undergo a refined and tightly regulated maturation process giving rise to ~22 nucleotide-long RNAs. These small RNAs function as part of an RNA-protein complex termed miRNA induced silencing complex (miRISC). miRNAs, and by extension miRISCs, typically bind partially complementary elements in the 3' untranslated region (UTR) of target messenger RNAs (mRNAs), which become consequently repressed. A large set of studies clearly indicates that miRISC-mediated repression is achieved in metazoans by a variable combination of target mRNA degradation and translational repression. However, the phase of translation that is inhibited is a controversial subject. Various models have been proposed, based mostly on the study of artificial target reporters, which support either an initiation or a post-initiation block model. Argonaute proteins are core component of the miRISC and directly bind miRNAs. The GW182 protein, another miRISC component, has recently emerged as an essential mediator of miRNA-mediated repression action. However, its precise molecular function is still unclear.
The work presented here aimed at understanding the in vivo mechanistic aspects of miRNA-mediated repression in more details, using the nematode Caenorhabditis elegans as a model organism and focusing on the well characterized let-7 miRNA. Initial results from a large-scale genetic screen revealed a strong genetic interaction between let-7 and various translation initiation factors, leading me to propose that C. elegans miRNAs inhibit the initiation of translation on their target mRNAs. Additional genetic experiments uncovered an unsuspected widespread genetic interaction between let-7 and the translation machinery and suggested that let-7 might function by inhibiting the eukaryotic translation initiation factor 3 (eIF3) activity. Biochemical experiments demonstrated that a large set of C. elegans miRNA targets are translationally repressed at the initiation step, sometimes in combination with mRNA degradation, and that the C. elegans GW182 homologs AIN-1 and AIN-2 are essential for these mechanisms. Additional unpublished data revealed that translational repression is specifically mediated by AIN-1, whereas depletion of both AIN-1 and AIN-2 is necessary to prevent miRNA target degradation.
Collectively, these results show that C. elegans miRNAs employ at least two mechanisms in vivo, i.e. target degradation and inhibition of translation initiation, which are likely to be independent pathways
Ding projective and Ding injective modules over trivial ring extensions
No full textsummary:Let be a trivial extension of a ring by an --bimodule such that , , and have finite flat dimensions. We prove that is a Ding projective left -module if and only if the sequence is exact and is a Ding projective left -module. Analogously, we explicitly describe Ding injective -modules. As applications, we characterize Ding projective and Ding injective modules over Morita context rings with zero bimodule homomorphisms
Gamma-irradiation effect on electrical properties of SiO2 gate dielectric of MOS structure
No full textThe total dose effect of 60Co gamma-irradiation on MOS (metal-oxide-semiconductor) structure of Al/SiO2/p-Si with different insulation layer thickness has been investigated in this article. MOS capacitors with oxide layer thickness of 5nm/19nm/29nm and electrode area of 1mm 2 were prepared using thermal oxidation method. Each structure was stressed with no bias during 60Co gamma-source irradiation with the total dose of 100k/500k/1Mrad. The low and high frequency C-V characteristic of each structure was measured at room temperature before and after gamma-irradiation. Besides of the electric properties, Atomic Force Microscopy (AFM), Grazing Incidence X-ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) with Ar+ etching were also measured before and after different total dose gamma-irradiation. AFM results showed that the surface of the oxide was relatively smooth with the roughness under 5%. Low and high frequency C-V results indicated that the interfacial states between Si and SiO2 and oxide traps varied with insulation layer thickness and different total dose. On the other hand, the XRD property change under gamma irradiation differs with oxide layer thickness. And the Si 2p peak and O 1s peak result derived from the XPS drifted with different total dose and oxide layer thickness. These results offered necessary theory assistance for the nuclear hardening of the microelectronic devices with ultrathin insulation layer, which can advance the safety of weapons in the high-tech warfare. © 2012 IEEE
Bis(arylimido) molybdenum(VI) amidinate and guanidinate complexes; Molecular structures of [(ArN)(2)MoMe{N(Cy)C[N(i-Pr)(2)]N(Cy)}] (Ar=2,6-i-Pr2C6H3; Cy = cyclohexyl) and [(2,6-i-Pr2C6H3N)(2)MoCl2]center dot[NH=C(C6H5)CH(SiMe3)(2)]
No full textThe reaction of [(ArN)(2)MoCl2]. DME (Ar = 2,6-i-Pr6C6H3) (1) with lithium amidinates or guanidinates resulted in molybdenum(VI) complexes [(ArN)(2)-MoCl(N(R-1)C(R-2)N(R-1))] (R-1 = Cy (cyclohexyl), R-2 = Me (2); R-1 = Cy, R-2 = N(i-Pr)(2) (3); R-1 = Cy, R-2 = N(SiMe3)(2) (4); R-1 = SiMe3, R-2 = C6H5 (5)) with five coordinated molybdenum atoms. Methylation of these compounds was exemplified by the reactions of 2 and 3 with MeLi affording the corresponding methylates [(ArN)(2)MoMe(N(R-1)C(R-2)N(R-1))] (R-1 = Cy, R-2 = Me (6); R-1 = Cy, R-2 = N(i-Pr)(2) (7)). The analogous reaction of 1 with bulky [N(SiMe3)C(C6H5)-C(SiMe3)(2)]Li . THF did not give the corresponding metathesis product, but a Schiff base adduct [(ArN)(2)MoCl2]. [NH=C(C6H5)CH(SiMe3)(2)] (8) in low yield. The molecular structures of 7 and 8 are established by the X-ray single crystal structural analysis
Modeling adsorption of CO2 on Ni(110) surface
No full textThe adsorption of CO2 on Ni(110) surface is simulated within the framework of density functional theory using ab-initio pseudopotentials. Beyond possible adsorbed geometries with C,, symmetry, suggested by analogy with the formate adsorption, a geometry with lower symmetry but higher adsorption energy is found and analyzed. Common features of the adsorbed geometries are non-negligible electronic charge transfers from the metal to the molecule ranging from 0.5 to 0.9 electrons in different cases and bending of the molecule with C atom closest to the surface. In the clean surface case we found an enhancement of the magnetic moments of surface and subsurface Ni atoms with respect to bulk, which is partially attenuated by CO, chemisorption. Both local spin density (LSDA) and generalized gradient correction (GGA) approximations are used for the exchange-correlation functionals: at variance with GGA, LSDA functional is not reliable for energetics, although the results concerning geometric and some electronic properties are almost similar with the two functionals
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