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961.
The movement of the small ribosomal subunit (30S) relative to the large ribosomal subunit (50S) during translation is widely known, but many molecular details and roles of rRNA and proteins in this process are still undefined, especially in solution models. The functional relationship of modified nucleotides to ribosome activity is one such enigma. To better understand ribosome dynamics and the influence of modified nucleotides on such processes, the focus of this work was helix 69 of 23S rRNA, which contains three pseudouridine residues in its loop region. Ribosome probing experiments with dimethylsulfate revealed that specific base accessibilities and individual nucleotide conformations in helix 69 are influenced differently by pH, temperature, magnesium, and the presence of pseudouridine modifications. 相似文献
962.
Applications of LC/ESI-MS/MS and UHPLC/Qq-TOF-MS for the determination of 141 pesticides in tea 总被引:1,自引:0,他引:1
This paper presents the applications of LC-electrospray ionization (ESI)/MS/MS and ultra-HPLC (UHPLC)/ESI quadrupole (Qq)-time-of-flight (TOF) MS for the determination of 141 pesticides in tea. Pesticides were extracted and cleaned up from tea with a modified quick, easy, cheap, effective, rugged, and safe method using graphitized carbon black and primary-secondary amine sorbents. Quantification was achieved using matrix-matched standard calibration curves with isotopically labeled standards or a chemical analog as internal standards in an analytical range from 5 to 500 microg/kg. The LC/ESI-MS/MS served as a reliable tool to quantify the pesticides due to its superior sensitivity and good repeatability. Its method performance characteristics that include overall recovery, intermediate precision, and measurement uncertainty were evaluated according to a statistically designed experiment, i.e., a nested design. About 87% of the pesticides had recoveries between 81 and 110%; 94% had an intermediate precision < or = 20%; and 90% showed measurement uncertainty < or = 40%. About 92% of the pesticides were able to be detected at 5 microg/kg with an S/N > or = 3. The UHPLC/Qq-TOF-MS showed much less sensitivity and poorer repeatability compared to the LC/ESI-MS/MS, and, therefore, it was primarily used for confirmatory purposes based on the accurate mass measurement and isotopic patterns. 相似文献
963.
Q. Ren X.B. Sun X.Q. Wang G.H. Zhang X.D. Yang F.J. Zhang H.L. Yang Y.T. Chow D. Xu 《Applied Physics A: Materials Science & Processing》2008,90(4):685-688
A novel dmit organometallic complex: [(C2H5)4N]2[Cu(dmit)2] (dmit2-=1,3-dithiole-2-thione-4,5-dithiolate), abbreviated as EtCu, was synthesized. Afterwards its optical nonlinearities in acetone
solution at 532 nm and 1064 nm were studied by the Z-scan technique with laser pulses of picosecond duration. The two-photon absorption at 1064 nm and the saturable absorption
at 532 nm were observed. The Z-scan curves also revealed that EtCu sample solutions exhibited self-defocusing effects at both wavelengths. The origins were
analyzed for the differences between the results. All the outcomes suggest that this material is potential for nonlinear optical
device applications.
PACS 42.65.An; 42.65.Hw; 42.65.Jx; 81.20.Ka; 78.30.Jw 相似文献
964.
We propose and demonstrate an S-band CW dual-wavelength erbium-doped fiber (EDF) dual-ring laser using a compound-ring filter (CRF) with various coupling losses inside the gain cavity. Employing a ring filter combined within the cavity, the fiber laser can lase a dual wavelength without any filter inside the ring loop. The dual-wavelength output exhibits a good performance having optical side-mode suppression ratios (SMSRs) of 31.6 and 31.8 dB and output powers of ?9.6 and ?9.3 dBm at 1505.58 and 1506.43 nm, respectively, when the coupling loss is 30% inside the cavity. In addition, the output stabilities of the dual-wavelength laser have also been analyzed. 相似文献
965.
In this demonstration, we propose and experimentally investigate a wavelength-selection erbium-doped fiber (EDF) laser in
single-longitudinal-mode (SLM) by using simple fiber ring scheme design. We use a tunable bandpass filter (TBF) inside the
gain cavity to restrict the lasing frequency. The proposed ring cavities can also serve as the mode filters for side mode
suppression. Based on the simple ring cavity design, the mode hopping can be avoided to achieve SLM output. The TBF inside
the laser scheme also obtains the wavelength tuning in the range of 1520.02 to 1562.02 nm. In addition, the output performance
of the proposed fiber laser has also been discussed. 相似文献
966.
The ability of natural and simulated soils to take up radioisotopes of cesium, strontium and ruthenium was examined. Uptakes
were assessed by distribution coefficients measured in the presence of different concentrations of Na, Ca, Mg and HN4 cations, and from synthetic groundwaters. Peat was included in similar studies for comparison purposes. Conclusions were
drawn as to the effect of soil and ground water compositions on isotope uptake taking into account the results described in
Part 1 of this series1 which estimated the distribution coefficients for137Cs,89Sr and106Ru (as chloride or nitrosyl) shown by illite and montmorillonite clays. These, or similar, clays were soil components in this
study. 相似文献
967.
Additive Partitions and Continued Fractions 总被引:1,自引:0,他引:1
A set S of positive integers is avoidable if there exists a partition of the positive integers into two disjoint sets such that no two distinct integers from the same set sum to an element of S. Much previous work has focused on proving the avoidability of very special sets of integers. We vastly broaden the class of avoidable sets by establishing a previously unnoticed connection with the elementary theory of continued fractions. 相似文献
968.
X. Q. Wang D. Xu Y. T. Chow X. F. Cheng W. L. Liu W. T. Yu G. H. Zhang Q. Ren M. K. Lü D. R. Yuan S. R. Zhao 《Crystal Research and Technology》2004,39(8):732-738
The growth morphology of MMTG (manganese mercury thiocyanate glycol monomethyl ether, MnHg(SCN)4(C3H8O2)) crystal was indexed according to the X‐ray powder diffraction spectroscopy. The density and Mohs hardness were determined at room temperature. The specific heat of the crystal is 458.6 J.mol‐1K‐1 at 300 K. The thermal expansion coefficient (TEC) along the a, b and c axis is a1=6.89 × 10‐5 K‐1, a2=6.78 × 10‐5 K‐1 and a3=2.08 × 10‐5 K‐1, respectively. The sameness and difference of the TECs are interpreted on the basis of crystal structure. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
969.
T. S. Chow 《Macromolecular theory and simulations》1998,7(2):257-261
New scaling laws for chain networks are derived to describe the fundamental relationships between the viscosity exponent (k), viscoelastic exponent (m), stretched exponent (β), spatial dimension (d). fractal dimension (df), and a universal constant (γ). The scaling of the total number of monomers and the radius of gyration is defined by df. We have discovered γ = m/β to be a universal constant which relates the shear modulus of a polymer gel melt to the shear modulus near the glass transition. Analyzing the size-dependent shear viscosity, we have determined γ = 3dfcd/(7d−5dfc) = 2.647 for d = 3 where dfc is the fractal dimension of critical clusters at the gel point. By using γ, the present theory extends previous work pertaining to systems near the sol-gel transition, and shows how properties far from the critical point can be explained. The theoretical prediction is in good agreement with viscoelastic measurements. 相似文献
970.
Incomplete LU factorizations are among the most effective preconditioners for solving general large, sparse linear systems arising from practical engineering problems. This paper shows how an ILU factorization may be easily computed in sparse skyline storage format, as opposed to traditional row-by-row schemes. This organization of the factorization has many advantages, including its amenability when the original matrix is in skyline format, the ability to dynamically monitor the stability of the factorization and the fact that factorizations may be produced with symmetric structure. Numerical results are presented for Galerkin finite element matrices arising from the standard square lid-driven cavity problem. © 1997 John Wiley & Sons, Ltd. 相似文献