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941.
The optical properties of Yb3+ ions in LiTaO3:Nd,Yb crystals 总被引:1,自引:0,他引:1
I. Sokólska W. Ryba-Romanowski S. Gołab T. Lukasiewicz 《Applied physics. B, Lasers and optics》1997,65(4-5):495-498
3+ ions excited by energy transfer from Nd3+ ions in LiTaO3:Nd, Yb crystals are presented. The emission band of Yb3+ ions is broad, due to the strong phonon-coupling and to the relative large Stark-splitting of the ground 2F7/2 multiplet. The emission cross-section was evaluated by the reciprocity method, and a value of 0.53×10-20 cm2 was obtained. The gain coefficients derived for the inversion parameters in the range 0.05 to 0.5 indicate positive gain
in the 985–1070 nm range.
Received: 17 March 1997/Revised version: 10 June 1997 相似文献
942.
Heba Alaa Hosiny Abd Elhameed Ditta Ungor Nra Igaz Mohana Krishna Gopisetty Mnika Kiricsi Edit Csap Bla Gyurcsik 《Macromolecular bioscience》2020,20(7)
Over the past decade, search for novel materials for nucleic acid delivery has prompted a special interest in polymeric nanoparticles (NPs). In this study, the biological applicability of a water‐soluble cationic lipopolymer (WSLP) obtained by the modification of high molecular weight branched poly(ethylenimine) (PEI) with cholesteryl chloroformate is characterized and assessed for better cellular membrane permeability. To test the delivery efficiency of the produced lipopolymer, plasmid DNA (pDNA) encoding the enhanced green fluorescent protein and WSLP are mixed at different charge ratios. WSLP and WSLP/pDNA complexes are characterized by dynamic and static light scattering, particle charge detection, scanning electron microscopy, and transmission electron microscopy. The pDNA loading of WSLP is also verified by agarose gel electrophoresis. Cytotoxicity of PEI, WSLP, and of WSLP/pDNA is evaluated on human A549 and HeLa cells. A remarkable dependence of the toxicity on the dose, cholesterylation, and charge ratio is detected. Transfection is monitored by flow cytometry and by fluorescence microscopy. Importantly, cholesterylation decreases the toxicity of the polymer, while promoting high transfection efficiency in both cell lines. This work indicates a possible optimization mode of the high molecular weight PEI‐based WSLP rendering it a promising candidate for gene delivery. 相似文献
943.
Dra Rdei Judit Hohmann Ferenc Evanics Peter Forgo Pl Szab Imre Mth 《Helvetica chimica acta》2003,86(2):280-289
Five new diterpene polyesters, 1 – 5 , with jatrophane skeletons were isolated from the fresh whole plants of Euphorbia serrulata. The structure elucidation was performed by means of UV/VIS spectroscopy, HR‐ESI‐MS, and advanced two‐dimensional NMR methods, including 1H‐NMR, JMOD, 1H,1H‐COSY, NOESY, HMQC, and HMBC experiments. The relative configurations of 1 – 5 and their conformations in solution were analyzed on the basis of NOESY measurements. As a result of detailed NMR studies, complete 1H and 13C chemical‐shift assignments of the compounds were possible. The isolated compounds differ stereochemically and do not comprise a uniform series regarding the configurations at C(2), C(6), and C(13). Compound 5 possesses the new structural feature of a double bond with (Z)‐configuration in the macrocyclic ring of the jatrophane skeleton, while compound 2 has a C?C bond in the five‐membered ring, this being the first observation of this structural feature in the type of macrocyclic Euphorbiaceae diterpenes. 相似文献
944.
Theoretical calculations employing time-dependent density functional theory (TDDFT) are used to characterize the excited states of Tb(III) β-diketonate complexes. Calculated results are compared directly with experimental results that together show a correlation between relative quantum yields and the excited-state energies that depend on the electronic properties of the p,p'-substituent group associated with the coordinating N-donor neutral ligand. It is found that changes in the electron donating nature of the neutral ligand structure lead to shifts in the lowest triplet energy level of the complex that consequently change the relative quantum yield. This work provides critical direction for the synthesis of high quantum yield terbium complexes. 相似文献
945.
A global noise reduction of a high-subsonic jet is achieved by experimental use of an impinging microjets system. The microjet velocity relative to the main jet velocity, the longitudinal distance of injection and the number of microjets are the three parameters examined in order to obtain the maximum noise reduction. This optimized microjet configuration is obtained by a balance between low-frequency attenuation and high-frequency noise generation due to the interaction between the microjets and the main jet mixing layer. To cite this article: T. Castelain et al., C. R. Mecanique 334 (2006). 相似文献
946.
I. Zvára 《Czechoslovak Journal of Physics》2006,56(1):D325-D331
For the volatile (oxo)halides of known elements the energies of desorption from the surface of fused silica measured in radiochemical
gas-solid chromatographic experiments proved close to the sublimation energies. This could hardly be expected for interaction
of isolated molecules with bare surface of ionic SiO2. Because such regularity shows great promise for evaluation of bulk properties of transactinoid compounds we need to understand
the origin of apparent inconsistency. The clue seems to be the real structure of the surface. It is initially rough (from
μm down to nm scale), inherently heterogeneous at the molecular level, and contains atoms and groups with excessive energy.
Exposing to ambient air produces numerous surface ≡SiOH groups. The halogenating agents employed in transactinoid studies
chemically modify such surface: it gets tightly covered by halogen atoms and fragments of the agent molecule attached to the
Si and O atoms. Now the molecules of new compounds cannot touch SiO2 lattice; moreover, in some initially geometric wells (due to roughness), they get surrounded by halogen atoms bonded to the
surface — the situation resembling that in their own bulk condensed phase. Hence, there must be sites with desorption energies up to the sublimation energy. 相似文献
947.
948.
Annamria Szalay Istvn Antal Zsolt Zsigmond Sylvia Marton Istvn Ers Gza Regdon Klra Pintye‐Hdi 《Particle & Particle Systems Characterization》2005,22(3):219-222
Since the particle size distribution is a critical parameter of pharmaceutical excipients used for tablet manufacturing by direct compression, the mean particle size of sieved sorbitol powder was studied by near‐infrared diffuse reflectance spectroscopy (NIRDRS). The aim of this study was to investigate the effect of the particle size (reciprocally proportional to the bulk density) on the reflectance spectrum. The effects of the particle characteristics on the spectral changes were described on the basis of the Kubelka‐Munk theory taking the scattering into consideration. A smaller particle size fraction was associated with a lower spectral value, and at the characteristic wavelength of 1584 nm a linear relationship was established for the particle size range from 125 to 670 μm. The diffuse reflectance measurement was sensitive to the particle characteristics, which offers a fast, non‐destructive alternative test method that can be applied after detailed calibration. 相似文献
949.
Vladimí ra Novotn V ra Hamplov Miroslav Ka par Milada Glogarov Karel Kní ek Siegmar Diele Gerhard Pelzl Chris Jones David Coleman Noel A. Clark 《Liquid crystals》2005,32(8):967-975
New mesogens composed of achiral bent molecules with thermally stable ester linkages, and laterally substituted by a methoxy group symmetrically near the central benzene ring, were synthesized. Texture, calorimetric, electro-optical, X-ray and dielectric measurements were performed. In most of studied compounds the antiferroelectric B2 phase was found on cooling from the isotropic phase, followed by the B7 phase at lower temperatures. Undulation of layers in the B7 phase was confirmed by precise synchrotron studies. 相似文献
950.
D. Kozma Klára Tomor C. Novák G. Pokol E. Fogassy 《Journal of Thermal Analysis and Calorimetry》1996,46(6):1613-1623
Racemic malic acid (I) was resolved by R-α-phenylethylamine(II). The S-(?)-I.R-(+)-II diastereoisomer was in excess in the precipitated salt. DSC curves and X-ray powder diffractograms proved that the diastereoisomeric salt mixture precipitated during the resolution was isomorphous with the optically pure S-(?)-I.R-(+)-II salt. The diastereoisomeric salt mixture containing the R-(?)-I.R-(+)-II salt in abundance bound crystal solvate (water or methanol) when produced by the total evaporation of the mother liquor, while the optically pure R-(?)-I.R-(+)-II salt crystallized without solvate. It is generally assumed that solid solution formation takes place when the two diastereoisomers are alike and the high similarity results in less efficient enantiomer separation. This paper demonstrates that efficient resolution can be accomplished in case of solid solution formation too. The diastereoisomeric salt mixtures can crystallize in isomorphic form even when the physico-chemical properties of the optically pure diastereoisomeric salts are quite different. 相似文献