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41.
L.M. Garcia-Raffi B. Rubio J.L. Tain J. Bea A. Gadea J. Rico P. Kleinheinz R. Menegazzo R. Wirowski P. von Brentano G. Siems A. Dewald 《Zeitschrift für Physik A Hadrons and Nuclei》1997,358(2):205-206
In the present paper we present part of the results obtained in the study of above-yrast states in 145Sm using the 142Nd(α,Xnγ) reaction. γ-γ, angular distribution, polarization, and excitation function measurements were performed. All multiplet members of the and the multiplets have been observed. The unperturbed energies for the multiplet have been estimated using the extensive information existing on one neutron transfer reactions. The results are compared with the 143Nd case. The similarity is remarkable. 相似文献
42.
Al-Saad KA Zabrouskov V Siems WF Knowles NR Hannan RM Hill HH 《Rapid communications in mass spectrometry : RCM》2003,17(1):87-96
Ionization and prompt fragmentation patterns of triacylglycerols, phospholipids (PLs) and galactolipids were investigated using matrix-assisted laser desorption/ionization (MALDI). Positive ions of non-nitrogen-containing lipids appeared only in the sodiated form, while nitrogen-containing lipids were detected as both sodiated and protonated adducts. Lipids containing acidic hydroxyls were detected as multiple sodium adducts or deprotonated ions in the positive and negative modes, respectively, with the exception of phosphatidylcholines. The positive MALDI spectra of triacylglycerols contained prompt fragments equivalent to the loss of RCOO(-) from the neutral molecules. Prompt fragment ions [PL-polar head](+) were observed in the positive MALDI spectra of all phospholipids except phosphatidylcholines. The phosphatidylcholines produced only a minor positive fragment corresponding to the head group itself (m/z 184). Galactolipids did not undergo prompt fragmentation. Post-source decay (PSD) was used to examine the source of prompt fragments. PSD fragment patterns indicated that the lipid prompt fragment ions did not originate from the observed molecular ions (sodiated or protonated), and suggested that the prompt fragmentation followed the formation of highly unstable, probably protonated, precursor ions. Pathways leading to the formation of prompt fragment ions are proposed. 相似文献
43.
Dwivedi P Puzon G Tam M Langlais D Jackson S Kaplan K Siems WF Schultz AJ Xun L Woods A Hill HH 《Journal of mass spectrometry : JMS》2010,45(12):1383-1393
Comprehensive metabolome analysis using mass spectrometry (MS) often results in a complex mass spectrum and difficult data analysis resulting from the signals of numerous small molecules in the metabolome. In addition, MS alone has difficulty measuring isobars and chiral, conformational and structural isomers. When a matrix-assisted laser desorption ionization (MALDI) source is added, the difficulty and complexity are further increased. Signal interference between analyte signals and matrix ion signals produced by MALDI in the low mass region (<1500 Da) cause detection and/or identification of metabolites difficult by MS alone. However, ion mobility spectrometry (IMS) coupled with MS (IM-MS) provides a rapid analytical tool for measuring subtle structural differences in chemicals. IMS separates gas-phase ions based on their size-to-charge ratio. This study, for the first time, reports the application of MALDI to the measurement of small molecules in a biological matrix by ion mobility-time of flight mass spectrometry (IM-TOFMS) and demonstrates the advantage of ion-signal dispersion in the second dimension. Qualitative comparisons between metabolic profiling of the Escherichia coli metabolome by MALDI-TOFMS, MALDI-IM-TOFMS and electrospray ionization (ESI)-IM-TOFMS are reported. Results demonstrate that mobility separation prior to mass analysis increases peak-capacity through added dimensionality in measurement. Mobility separation also allows detection of metabolites in the matrix-ion dominated low-mass range (m/z < 1500 Da) by separating matrix signals from non-matrix signals in mobility space. 相似文献
44.
Plech A Kotaidis V Siems A Sztucki M 《Physical chemistry chemical physics : PCCP》2008,10(26):3888-3894
Time resolved small angle scattering has been employed to follow the formation kinetics of gold nanoparticles from a solution of gold hydrochlorate and tris-sodium citrate at room temperature. While UV irradiation leads to a slow kinetics as observed by optical spectroscopy, the irradiation by the X-rays led to a reduction of the gold within a few minutes. The size and morphology evolution during the radiolytic formation of particles displays the initial nucleation phase and the growth kinetics, which exhibit very nonuniform behavior. They show that the electrostatics of the particle stabilization plays a pronounced role in the repulsive forces and transient clustering of particles. 相似文献
45.
Carotenoids are part of the human diet and a regular low-dose intake of these compounds from natural sources is normally preferred.
Carotenoid supplementation in various diseases, including cancer, was described to be useful, but evidence has been obtained
that high-dose supplementation of β-carotene may be unsafe, especially to smokers and asbestos-exposed workers, because of
a stastically detected increased cancer risk. The negative effect might be mediated by carotenoid breakdown products having
a high reactivity towards biomolecules. It has been suggested that these compounds originate from nonenzymatic cleavage of
carotenoids by oxidants liberated in large amounts by neutrophils that accumulate in various inflammatory diseases and, in
particular, in pulmonary disorders characterized by profound abnormalities in inflammatory pathways, such as those triggered
by tobacco smoking. Carotenoid breakdown products, in turn, may affect neutrophil response in different ways that depend on
the concentration that is reached by these products in the medium. In vitro studies show that nanomolar and micromolar concentrations of carotenoid derivatives stimulate superoxide production by neutrophils
activated by phorbol myristate acetate (PMA), while a slight inhibition is noticed with cells activated by the chemotactic
tripeptide N-formyl-Met-Leu-Phe (f-MLP). At higher concentrations, carotenoid breakdown products inhibit superoxide production
in the presence of both PMA and f-MLP.
相似文献
46.
C. Kreuter U. Siems P. Nielaba P. Leiderer A. Erbe 《The European physical journal. Special topics》2013,222(11):2923-2939
Over the last decades, colloidal suspensions have been proven as powerful model systems to reveal fundamental questions in soft matter or general physics. In this work, we will focus on the influence of interaction and confinement to the mobility of colloidal particles as well as to the transport behavior of particles over obstacles placed in a micro-channel. Both experiments are supported with Brownian dynamics simulations to complete the experimental work. The paper concludes with the investigation of the behavior of single active swimmers close to a wall. 相似文献
47.
Normal modes, dispersions and spectral densities were calculated for macroscopic layer structures with an arbitrary number of layers per periodicity unit. The influence of the arrangement of layers on the band structure is discussed. 相似文献
48.
R. L. Eatherton M. A. Morrissey W. F. Siems H. H. Hill 《Journal of separation science》1986,9(3):154-160
Using a unidirectional flow ion mobility detector, non-selective detection, tunable selective detection, and complete Fourier transformed ion mobility spectra were successfully obtained after supercritical fluid chromatography on compounds with higher molecular weights than have been previously investigated. In the most selective mode, single oligomers from polymeric material could be independently detected. Using the Fourier transform capabilities of this instrument, complete ion mobility spectra for each oligomer could be obtained in a single chromatographic separation. The collection of individual ion mobility spectra of the components of polymeric material has not been possible prior to the technique described in this paper. Only complex ion mobility spectra of polymeric mixtures are available in the literature. The spectra obtained in this study are all simple, uncomplicated spectra consisting of only one or two product ion peaks. Ko values reported in this work range from 0.633 to 1.61, which are some of the lowest values ever reported in ion mobility spectrometry. With the unidirectional flow design of the detector, the supercritical fluid mobile phase, carbon dioxide, was efficiently eliminated from the detector so that the ion mobility spectrometer could be operated in its normal manner. The fact that CO2 did not interfere with normal ion mobility operation indicates that other supercritical fluids may also be compatible with this sensitive and versatile detection method. 相似文献
49.
The elastic field of centres of dilatation at arbitrary positions in a spherical specimen with cubic elastic constants is studied. The influence of the (free) boundary, which is of central importance due to the long-range nature of the elastic interaction, is included. For materials with small elastic anisotropy expansions in terms of vector spherical harmonics are obtained for the displacements due to one defect, as well as for the interaction energy of two defects. Infinite material expressions and surface contributions are given separately. The general treatment is exemplified by presenting explicit results for the case of hydrogen atoms dissolved in vanadium. 相似文献
50.
Spectroscopic data can deliver force constants only if the exact chain conformation is known. For the longitudinal acoustic modes (LAM), however, simple linear chain models can be used to yield the effective longitudinal chain modulus from spectroscopic data of oligomer crystals. The model of p-coupled linear chain molecules with N masses and only nearest neighbor interactions was used to investigate the longitudinal acoustic modes with s nodes. The frequencies plotted versus s/N fall onto different branches for different s. The intermolecular coupling and the heavier endmasses shift the LAM branches to higher and lower frequencies, respectively. There exists a value x0 depending on the masses and force constants, where the branches cut the dispersion curve of the infinite molecule. For s/N ≥ x0 the effect of endmasses dominates. Low-frequency RAMAN spectra of n-alkanes (N = 20, …, 40 C atoms) were recorded and analyzed. The LAM1 branch runs clearly above a smooth fit through all other LAM data and the origin. This fit approximates to first order the dispersion curve of the infinite PE molecule in an ideal crystal. Its curvature exceeds that of the dispersion curve of the simple linear chain, but is somewhat smaller than that of the dispersion curve of the planar zig-zag chain with rigid bonds. The slope at the origin yields the limiting elastic modulus Ec = 315 GPa in chain direction of crystalline polyethylene. From our measurements on n-alkanes we obtained the frequency shift of LAM1 due to the interlayer coupling and the heavier endmasses. Calculation of the intermolecular coupling constant of the model of a long row of linear chain molecules with the same frequency shift yield the mean value fl = 2.5 N/m. This value decreases with increasing chain length. The relevance and applicability of the model is discussed. © 1997 John Wiley & Sons, Inc. 相似文献