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161.
RD Harris WS Baker Van Stipdonk MJ RM Crooks EA Schweikert 《Rapid communications in mass spectrometry : RCM》1999,13(14):1374-1380
A suite of keV polyatomic or 'cluster' projectiles was used to bombard unoxidized and oxidized self-assembled monolayer surfaces. Negative secondary ion yields, collected at the limit of single ion impacts, were measured and compared for both molecular and fragment ions. In contrast to targets that are orders of magnitude thicker than the penetration range of the primary ions, secondary ion yields from polyatomic projectile impacts on self-assembled monolayers show little to no enhancement when compared with monatomic projectiles at the same velocity. This unusual trend is most likely due to the structural arrangement and bonding characteristics of the monolayer molecules with the Au(111). Copyright 1999 John Wiley & Sons, Ltd. 相似文献
162.
W. Grimus R. Pfeiffer T. Schwetz 《The European Physical Journal C - Particles and Fields》2000,13(1):125-132
We take as a starting point the Gelmini–Roncadelli model enlarged by a term with explicit lepton number violation in the
Higgs potential and add a neutrino singlet field that is coupled via a scalar doublet to the usual leptons. This scenario
allows us to take into account all three present indications in favor of neutrino oscillations provided by the solar, atmospheric,
and LSND neutrino oscillation experiments. Furthermore, it suggests a model which reproduces naturally one of the two 4-neutrino
mass spectra favored by the data. In this model, the solar neutrino problem is solved by large mixing MSW transitions, and the atmospheric neutrino problem by transitions of into a sterile neutrino.
Received: 11 May 1999 / Published online: 3 February 2000 相似文献
163.
M. Merschdorf W. Pfeiffer A. Thon S. Voll G. Gerber 《Applied Physics A: Materials Science & Processing》2000,71(5):547-552
Two-photon photoemission spectroscopy using femtosecond laser pulses is used to investigate the excitation and decay mechanisms
of the surface plasmon resonance in Ag nanoparticles grown on graphite. The resonant excitation of this collective excitation
leads to a two-orders-of-magnitude-enhanced two-photon photoemission yield from a graphite surface with Ag nanoparticles compared
to the yield from pure graphite. From the shape of the photoemission spectra, the polarization dependence of the photoemission
yield and the excitation probabilities for different excitation pathways we conclude that excitation with 400-nm femtosecond
laser pulses leads to the coherent multiple excitation of the surface plasmon in the Ag nanoparticles. This multiply excited
plasmon mode can decay via the coupling to a single-particle excitation leading to the emission of an electron if its final
state is located in the continuum. The surface plasmon in metallic nanoparticles is a model system to investigate collective
excitations in multiphoton processes.
Received: 26 June 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000 相似文献
164.
165.
S. Kalliakos M. Rontani V. Pellegrini A. Pinczuk A. Shinga C.P. Garcia G. Goldoni E. Molinari L.N. Pfeiffer K.W. West 《Solid State Communications》2009,149(35-36):1436-1442
Low-lying collective excitations above highly correlated ground states of few interacting electrons confined in GaAs semiconductor quantum dots are probed by resonant inelastic light scattering. We highlight that separate studies of the changes in the spin and charge degrees of freedom offer unique access to the fundamental interactions. The case of quantum dots with four electrons is found to be determined by a competition between triplet and singlet ground states that is uncovered in the rich light scattering spectra of spin excitations. These light scattering results are described within a configuration-interaction framework that captures the role of electron correlation with quantitative accuracy. Recent light scattering results that reveal the impact of anisotropic confining potentials in laterally coupled quantum dots are also reviewed. In these studies, inelastic light scattering methods emerge as powerful probes of collective phenomena and spin configurations in quantum dots with few electrons. 相似文献
166.
Na2MnO2 was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursors (Mn2O3, NaN3 and NaNO3) were heated in an appropriate regime up to 390 °C and annealed at this temperature for 20 h, in specially designed silver containers. As the most prominent feature, the crystal structure of Na2MnO2 (C2/c, Z = 12, a = 12.5026(9), b = 12.1006(9), c = 6.0939(4) Å, β = 117.94(0)°, 1556 independent reflections, R1 = 3.83 % (all data)) forms a three dimensional framework polyanion of corner sharing MnO4‐tetrahedra. The connectivity pattern of the tetrahedral building units corresponds to the moganite structure, a rare SiO2 modification. According to measurements of the magnetic susceptibility in the temperature range from 2 to 750 K, Na2MnO2 shows antiferromagnetic ordering below 250 K. Evaluation of the high temperature data employing the Curie‐Weiss law revealed a magnetic moment of μeff = 5.93 μB, confirming the presence of divalent manganese. 相似文献
167.
V. Vijayasundaram V. Ramasamy PL. RM. Palaniappan 《Journal of Thermal Analysis and Calorimetry》2009,98(1):183-188
The paper presents the changes in the thermal properties of control, arsenic exposed and DMSA treated Labeo rohita bones by using thermo analytical techniques. The result shows that the mass loss due to the thermal decomposition occurs
in three distinct steps due to loss of water, organic and inorganic materials. The arsenic exposed bones present a different
thermal behaviour compared to the control bones. The residue masses are increased due to arsenic exposure, while the DMSA
treatment reduces the residue mass level. These thermal characteristics can be used as a qualitative method to check the metal
accumulation in samples. 相似文献
168.
We review structure data obtained by decay spectroscopy of neutron-rich nuclei of mass close to 100. Emphasis is put on the contribution of experiments at IGISOL in the nineties. They confirmed the earlier postulated shape coexistence in the fast shape-transition region between N = 58 (spherical ground states and low collectivity) and N = 60 (strong axial deformation). A detailed spectroscopic study of the A = 99 chain established the upper-Z limit of the N = 56 shell closure region with 99Nb, owing to striking similarities with 97Y. A consequence of the N = 56 closure is that the s 1/2 odd-neutron becomes the ground state of the most neutron-rich N = 57 isotones, starting with 99Mo, instead of the degenerated d 5/2 and g 7/2 subshells familiar in the tin region. Consequences on the change of spin on astrophysical r-process calculations are briefly discussed. Finally, we say a few words about neutron-rich rhodium and palladium isotopes near the neutron midshell where regular and intruder states coexist very close to each other. 相似文献
169.
We present here a high-performance liquid chromatography−tandem mass spectrometry (LC-MS/MS) method for quantifying phytoestrogenic
isoflavones (daidzein, equol, genistein, and O-desmethylangolensin) and lignans (enterodiol and enterolactone) in urine without the use of extraction or the preconcentration
techniques inherent in existing methods. The development of this concept was made possible by use of atmospheric pressure
photoionization (APPI); an ionization technique that we found to improve analyte sensitivity relative to electrospray ionization
and atmospheric pressure chemical ionization for this particular group of compounds. The analytical performance of this method
was equal to or exceeded that of comparable methods. Between-run coefficients of variation (CVs) across three quality control
(QC) pool levels analyzed in duplicate over 20 days were 3.1–5.8% CV; within-run CVs were 2.3–6.0%. Accuracy, as determined
by average spike recovery in QC pools, was generally within ±10% of being quantitative (100%). Relative limits of detection
were 0.04–0.4 ng/mL urine, with absolute detection limits as low as 0.1 pg. This method was applied to the analysis of >2,500
urine specimens for the 2005–2006 Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey
(NHANES). The method was capable of quantifying these compounds in 95–100% of study samples. This work is the first ever report
of using APPI for the LC-MS/MS determination of these compounds in urine. It is also the first method of its kind to do so
without any need for analyte extraction or preconcentration prior to analysis. 相似文献
170.
Friedrich Pfeiffer 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(1):47-56
Many machine and mechanism processes are accompanied by impacts with friction. They arise by short-time contacts between two
or more bodies, and they generate energy losses mainly due to friction in tangential contact directions. During the last two
decades, a couple of impact models based on the theory of rigid body contact were established connected with the names of
Moreau, Frémond, and Glocker, which all work quite satisfactorily with respect to practical applications, although some examples
indicate deviations requiring more investigations with respect to the impact models and the type of examples considered. We
shall focus on Glocker’s model, for which some experimental verifications are available by Beitelschmidt. A missing link are
energy considerations, which are available, but nevertheless do not provide us with a complete information for all possible
cases. The paper tries to fill a bit this gap by founding the investigations on a combined phenomenological and theoretical
basis. 相似文献