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1.
Dielectric effect on the rf characteristics of a helical groove travelling wave tube 总被引:1,自引:0,他引:1 下载免费PDF全文
A new type of partial-dielectric-loaded helical groove slow-wave structure (SWS) for millimetre wave travelling wave tube (TWT) is presented in this paper.The radio-frequency characteristics including the dispersion properties,the longitudinal electric field distribution and the beam-wave coupling impedance of this structure are analysed.The results show that the dispersion of the helical groove circuit is weakened,the phase velocity is reduced and the position of the maximum Ez is moved from the mouth to the inside of the groove after partially filling the dielectric materials in the helical groove SWS.Therefore,the dielectric-loaded helical groove SWS is suitable for a multi-beam TWT with broad band and high gain. 相似文献
2.
3.
Dalip Kumar 《Tetrahedron letters》2004,45(14):2887-2889
Standard procedures for elaborating a quinone methide precursor for conjugation to a DNA ligand was not compatible with the presence of a vinyl group. Instead, an acrylate linker was attached by Heck coupling subsequent to o-substitution of the phenolic precursor. This transformation required protection of the phenolic group and use of ethyl acrylate rather than acrylic acid. The presence of the vinyl group also rendered the quinone methide precursor more labile to alkaline conditions than its equivalent saturated derivative and required mild conditions for coupling to the pyrrole-imidazole polyamide. 相似文献
4.
Dimers of the pyrrole amino acid (Paa), 5-(aminomethyl)pyrrole-2-carboxylic acid, and its derivatives having Lys anchored on N- and C-termini bind in the minor groove of DNA with considerable apparent binding affinities. When the Lys unit is attached to the C-terminus, the resulting ligand binds to ds-DNA with twice the affinity, of the order of 105, than the one carrying two positive charges at the same end. 相似文献
5.
The nonintercalative binding of an aliphatic and an aromatic bisguanylhydrazone (BGH) to the minor groove of double-stranded (dA-dT)
n
oligomers is investigated by means of theoretical computations. The preferred binding arrangements of both BGHs are stabilized by a number of H-bonding interactions with sites O2(T), N3(A) and o1 on the two strands, and require limited conformational rearrangements of the BGHs around their C-C single bonds. The intermolecular interaction energy is larger with the aliphatic BGH than with the aromatic one. The energy difference is, however, considerably reduced when the oligomer is lengthened: it passes from 16.1 kcal/mole at the heptamer level, to 7.9 kcal/mole at the undecamer level and to 4.6 kcal/mole when each strand of the undecamer is flanked with a complementary complete helical turn of phosphates, on both the 3 and 5 termini.The interaction energies of the BGHs with water molecules in the first hydration shell are, however, also larger with the aliphatic BGH, than with the aromatic BGH. This energy difference is further enhanced when one considers also the water molecules in the second shell. It becomes greater than the difference in the interaction energy of the two BGHs with (dA-dT)
n
for large values of n. When the dehydration energy of BGHs is taken into account the overall energy balance is then more favorable for the interaction of the aromatic than of the aliphatic BGH with the polynucleotide. This last conclusion is in agreement with experimental results. 相似文献
6.
Two new water soluble oxovanadium(IV) complexes with formulae Na[VO(his)(met)SO4] (1) and Na[VO(gly)(met)SO4] (2), (gly=glycine his=histidine, and met=metformin) were synthesized and characterized by LCMS, UV‐Visible absorption, infrared spectra, magnetic moment, elemental analysis, thermal analysis and electronic spectral studies. The metal center was found in an octahedral geometry. DNA binding interaction of these complexes with CT DNA has been explored by UV‐Visible absorption, fluorescence, viscosity measurements and cleavage studies. Finally the binding of the complexes with CT‐DNA could be surface binding, mainly in the groove binding. The complexes were docked in to B‐DNA sequence, 5’(D*AP*CP*CP*GP*AP*CP*GP*TP*CP*GP*GP*T)‐3’ retrieved from protein data bank (PDB ID: 423D), using Discovery Studio 2.1 software. 相似文献
7.
Guralchuk GY Sorokin AV Katrunov IK Yefimova SL Lebedenko AN Malyukin YV Yarmoluk SM 《Journal of fluorescence》2007,17(4):370-376
Optical spectroscopy experiments were used to study the features of cyanine dye 3,3′-dimethyl-9-(2-thienyl)-thiacarbocyanine
iodide (L-21) aggregation in binary solutions DMF:Tris–HCl buffer (pH = 8) containing nucleic acids (DNA or RNA). The appearance
of absorption and luminescence bands associated with J-aggregates and dimers that are formed within the minor groove of DNA
has been observed. The model of L-21 J-aggregate structure is proposed. It has been found that dimers are the building blocks
of L-21 J-aggregates. Disorientation in dimers caused by the minor groove curvature is reason of observation of Davydov splitting
in absorption spectrum of L-21 J-aggregates. In the solution containing DNA the absorption and luminescence bands of L-21
J-aggregates exhibit the specific properties that allows the dye L-21 to be used as a fluorescent probe for DNA detection. 相似文献
8.
Xiu-Jun Wang Ming-Li Yang Lan-Ping Zhang Tong Yao Cheng Chen Lian-Gang Mao Yin Wang Jie Wu 《中国化学快报》2014,25(4):589-592
A new series of bis-benzimidazole derivatives were designed and synthesized.In vitro cytotoxicity evaluation showed that these compounds exhibited high activity against the selected tumor cells.Among them,compound 9 owned the best potential,its IC_(50) values being 5.95 μmol/L(mononuclear tumor cell line(U937)) and 5.58 μmol/L(cervical cancer cell(HeLa)).Fluorescence and UV-vis studies showed that compound 9 could bind into the minor groove of DNA. 相似文献
9.
Jochen Schölhammer Brigitte Baretzky Wolfgang Gust Eric Mittemeijer Boris Straumal 《Interface Science》2001,9(1-2):43-53
The atomic force microscopy (AFM) was used to study the grain boundary (GB) groove profiles far away from the melting temperature T
m. It is shown that AFM allows one to measure the temperature dependence of the GB energy in a rather broad temperature interval (from 0.85 T
m to T
m). The GB energy and GB segregation of Bi were measured at 1123 K in the interval of the Bi bulk concentration x
v
Bi from 5 to 140 ppm Bi. The transition from monolayer to multilayer adsorption is observed for the 19a GB at 1123 K and x
v
Bi = 60 at. ppm Bi. At the same point (1123 K and x
v
Bi = 60 at. ppm Bi) a discontinuity of the first derivative of the GB energy is observed. These features were explained using the model of GB prewetting phase transformation developed previously. 相似文献
10.
Summary. A convenient synthesis method was developed for the preparation of C-stapled homodimeric bis-lexitropsins connected through
the nitrogen atoms of the central pyrrole ring with a bis-methylene linker. This lexitropsin is designed as a standard for
other bis-lexitropsins with longer chains in biological evaluation and NMR studies. The key step in this method is the treatment
of ethyl 4-nitropyrrole-2-carboxylate with flame-dried potassium carbonate in DMF followed by the addition of 1,2-dibromoethane to form the 1,2-dipyrroloethane derivative. 相似文献