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121.
Harro G. Andresen 《Zeitschrift für Physik A Hadrons and Nuclei》1968,210(2):113-141
Hydrogen maser frequency shifts, caused by the multiple quantum transition nonlinearities of a resonant multiple frequency excitation of the atomic hydrogen four level ground state system have been investigated. The oscillation characteristics of hydrogen maser operation with simultaneously excited, low frequencyΔm F =±1 transitions between theF=1 states of the atomic hydrogen ground state have been analysed theoretically and explicit formulas for hydrogen maser frequency shifts and amplitude response have been derived for arbitrary maser oscillation amplitude and a small signal approximation for theΔm F =±1 “Zeeman” transitions. The comparison with experimentally observed hydrogen maser frequency shifts was specialized to small magnetic fields, for which the difference between the resonance frequencies of the two low frequency,Δm F =±1 Zeeman transitions is small compared to the linewidth. Special emphasis was placed on the evaluation of frequency pulling effects for a Zeeman transition excitation at off-resonance conditions. For this case the theoretical formulation of frequency pulling effects becomes insensitive against simplifying assumptions about the radiation damping phenomena and a particular good agreement between experiment and theory can therefore be expected. Experimental conditions have been specified, for which the uncertainty of hydrogen maser frequency due to Zeeman transition induced frequency shifts does not restrict the present frequency stability of a hydrogen maser frequency standard. 相似文献
122.
123.
S. Vratislav J. Zajíček Z. Jirák A.F. Andresen 《Journal of magnetism and magnetic materials》1977,5(1):41-50
Neutron diffraction study on samples MnxCr3?xO4 with x=1.0, 1.2, 1.4 and 1.6 has been performed at temperatures below ~40 K where magnetic ordering is present. At 5 K the structure of the MnCr2O4 compound was found to be a general LKDM magnetic spiral with the propagation vector deviating by 13.3″ from the [110] axis. This results differs from previous findings. At about 16 K the structure becomes collinear. In samples higher content of manganese the magnetic structure is collinear over the whole temperature region (5–40) K, i.e. in the sense of long range ordering. However, a short range ordering of the transverse components of the spins is present both in these samples and in MnCr2O4 above 16 K. 相似文献
124.
Prof. Dr. Harro G. Andresen 《Zeitschrift für Physik A Hadrons and Nuclei》1970,231(4):293-307
Au? ions at anionic places are formed in gold doped crystals by a reducing treatment withF centers. The ultraviolet absorption consists of 4 bands, which are namedA, B, C, andD in analogy to the isoelectronic centers of the s2 type, like Tl+. TheB band oszillator strength strongly increases with temperature in accordance with a phonon allowed transition. The ratio of the dipole strength of theC band to that of theA band as a function of the relative position of theB band is compared with Suganos prediction. Zero phonon lines are found at helium temperatures for theA band in NaCl (2,985 Å), KCl (3,068 Å), and KBr (3,145 Å) and for theC band in KCl (2,329 Å). In KCl the Huang-Rhys factor isg=3.4 for theA band. The vibronic structure comes from the relatively large radius 6s 2 state of the negative ion. Uniaxial stress splits the zero phonon line. The results definitely agree with the stress splitting behaviour of a degenerateΓ 1→Γ 4 transition. Inversion symmetry of the center is confirmed by the absence of a linear Stark effect. 相似文献
125.
Owen S. Fenton Kevin J. Kauffman Rebecca L. McClellan James C. Kaczmarek Manhao D. Zeng Jason L. Andresen Luke H. Rhym Michael W. Heartlein Frank DeRosa Daniel G. Anderson 《Angewandte Chemie (International ed. in English)》2018,57(41):13582-13586
RNAs are a promising class of therapeutics given their ability to regulate protein concentrations at the cellular level. Developing safe and effective strategies to deliver RNAs remains important for realizing their full clinical potential. Here, we develop lipid nanoparticle formulations that can deliver short interfering RNAs (for gene silencing) or messenger RNAs (for gene upregulation). Specifically, we study how the tail length, tail geometry, and linker spacing in diketopiperazine lipid materials influences LNP potency with siRNAs and mRNAs. Eight lipid materials are synthesized, and 16 total formulations are screened for activity in vitro; the lead material is evaluated with mRNA for in vivo use and demonstrates luciferase protein expression in the spleen. In undertaking this approach, not only do we develop synthetic routes to delivery materials, but we also reveal structural criteria that could be useful for developing next‐generation delivery materials for RNA therapeutics. 相似文献
126.
A numerical-derivative method, employing a running cubic spline, has been developed to infer coefficients in power series expansions of total vapor pressure vs. composition data. The technique makes it possible to determine values of the coefficients individually, avoiding a generic problem in least squares analysis, viz., that the regression parameters are highly coupled and that their derived values depend strongly on the number of constants used in fitting data. The numerical derivative method also indicates when errors of measurements will preclude the determination of meaningful values of higher-order terms in polynomical representations of data. 相似文献
127.
128.
The LD-method of inclined incidence was found useful in the study of the orientations of probe chromophores (carotene, anthracene) solubilized in lamellar mesophases of the systems sodium octanoate/decanol/water and sodium di-2-ethylhexylsulphosuccinate/water, respectively. The results suggest the existence of two competing molecular orientation mechanisms aligning the longest axis of the probe molecule either parallel with the lamellar surface or perpendicular to it. 相似文献
129.
C. Kohstall D. Belic P. von Brentano C. Fransen R. -D. Herzberg J. Jolie U. Kneissl H. Lehmann A. Linnemann P. Matschinsky A. Nord N. Pietralla H. H. Pitz M. Scheck F. Stedile V. Werner S. W. Yates 《Physics of Atomic Nuclei》2001,64(6):1141-1146
Low-lying dipole excitations in the medium-weight vibrational nuclei of the Cd isotopic chain were investigated by means of nuclear resonance fluorescence experiments performed at the bremsstrahlung beam of the Stuttgart Dynamitron accelerator (endpoint energy 4.1 MeV). Detailed information has been obtained on excitation energies, spins, decay widths, and transition probabilities of numerous excited states in 110–114,116Cd. Additionally, the use of two Compton polarimeters enabled model-independent parity assignments for excitations in the even-even isotopes. Strongly excited J π = 1? states are found in all even-even Cd nuclei at excitation energies near the sumof the energies of the first 2+ and 3? states. These excitations are interpreted as the 1? member of the quadrupole-octupole coupled quintuplet (2+?3?). The fragmented strength observed in the odd isotopes 111,113Cd is compared with the strength distributions in the neighboring even-even Cd isotopes. 相似文献
130.
Lind JU Acikgöz C Daugaard AE Andresen TL Hvilsted S Textor M Larsen NB 《Langmuir : the ACS journal of surfaces and colloids》2012,28(15):6502-6511
A versatile procedure is presented for fast and efficient micropatterning of multiple types of covalently bound surface chemistry in perfect register on and between conductive polymer microcircuits. The micropatterning principle is applied to several types of native and functionalized PEDOT (poly(3,4-ethylenedioxythiophene)) thin films. The method is based on contacting PEDOT-type thin films with a micropatterned agarose stamp containing an oxidant (aqueous hypochlorite) and applying a nonionic detergent. Where contacted, PEDOT not only loses its conductance but is entirely removed, thereby locally revealing the underlying substrate. Surface analysis showed that the substrate surface chemistry was fully exposed and not affected by the treatment. Click chemistry could thus be applied to selectively modify re-exposed alkyne and azide functional groups of functionalized polystyrene substrates. The versatility of the method is illustrated by micropatterning cell-binding RGD-functionalized PEDOT on low cell-binding PMOXA (poly(2-methyl-2-oxazoline)) to produce cell-capturing microelectrodes on a cell nonadhesive background in a few simple steps. The method should be applicable to a wide range of native and chemically functionalized conjugated polymer systems. 相似文献