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131.
K. Blaum G. Bollen F. Herfurth A. Kellerbauer H.-J. Kluge M. Kuckein E. Sauvan C. Scheidenberger L. Schweikhard 《The European Physical Journal A - Hadrons and Nuclei》2002,15(1-2):245-248
The cyclotron frequencies of singly charged carbon clusters Cn
+ (n ≥ 2) were measured with the Penning-trap mass spectrometer ISOLTRAP at ISOLDE/CERN. The present limit of mass accuracy δm/m = 1.2 . 10-8 and the extent of the mass-dependent systematic shift (δm/m)sys = 1.7(0.6) . 10-10/u
. (m - m
ref) of the setup were investigated for the first time. In addition, absolute mass measurements by use of pure clusters of the
most abundant carbon isotope 12C are now possible at ISOLTRAP.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"Present address: CERN, CH-1211 Geneva 23, Switzerland; e-mail: klaus.blaum@cern.ch 相似文献
132.
We present theoretical results that demonstrate a new technique that can be used to improve the sensitivity of thermal noise measurements: intracavity intensity stabilization. It is demonstrated that electro-optic feedback can be used to reduce intracavity intensity fluctuations, and the consequent radiation pressure fluctuations, by a factor of 2 below the quantum-noise limit. We show that this reduction is achievable in the presence of large classic intensity fluctuations in the incident laser beam. The benefits of this scheme are a consequence of the sub-Poissonian intensity statistics of the field inside a feedback loop and the quantum nondemolition nature of radiation pressure noise as a readout system for the intracavity intensity fluctuations. 相似文献
133.
Ulmer TG Tan RK Zhou Z Ralph SE Kenan RP Verber CM SpringThorpe AJ 《Optics letters》1999,24(11):756-758
Performance-limiting asymmetric distortion is observed in the spectra of fundamental pulses transmitted through GaAs-Al(0.9)Ga(0.1)As multilayer waveguides designed for surface-emitted second-harmonic generation. This behavior is attributed to refractive-index changes resulting from the accumulation of free carriers created by two-photon absorption in the GaAs layers. Numerical simulations of the intensity-dependent spectra by use of the separately measured two-photon absorption coefficient are shown to be in good agreement with the observed spectra. 相似文献
134.
We describe a technique for generating a special class, called QPEC, of mathematical programs with equilibrium constraints, MPEC. A QPEC is a quadratic MPEC, that is an optimization problem whose objective function is quadratic, first-level constraints are linear, and second-level (equilibrium) constraints are given by a parametric affine variational inequality or one of its specialisations. The generator, written in MATLAB, allows the user to control different properties of the QPEC and its solution. Options include the proportion of degenerate constraints in both the first and second level, ill-conditioning, convexity of the objective, monotonicity and symmetry of the second-level problem, and so on. We believe these properties may substantially effect efficiency of existing methods for MPEC, and illustrate this numerically by applying several methods to generator test problems. Documentation and relevant codes can be found by visiting http://www.ms.unimelb.edu.au/danny/qpecgendoc.html. 相似文献
135.
Ralph E. Taylor-Smith Richard A. Register 《Journal of Polymer Science.Polymer Physics》1994,32(12):2105-2114
The nature and extent of phase mixing in blends of hydroxyl-functionalized polystyrene and poly(ethyl acrylate) (PS/PEA), where the driving force for mixing is hydrogen bonding, are characterized by several techniques. Small-angle x-ray scattering (SAXS) shows a reduction in average domain size with increasing functionalization level, a result also evident from scanning electron microscopy (SEM). Together, the two techniques reveal a very broad distribution of domain sizes. At high functionalization levels, both SAXS and SEM indicate a high degree of “in-domain” mixing, with little or no pure PS or PEA remaining in the blends. Mathematical modeling of dynamic mechanical thermal analysis (DMTA) data is employed to quantify this progression. Initially, mixing is primarily interfacial, but as the functionalization level increases, the mixed interphase rapidly grows to occupy the entire material. In agreement with the SAXS and SEM results, DMTA modeling shows that further increases in the functionalization level suppress the amplitude of composition variations in the sample. The onset of extensive in-domain mixing coincides with the marked changes in stress-strain behavior observed previously in these materials. © 1994 John Wiley & Sons, Inc. 相似文献
136.
L. Monz R. Hohmann H.-J. Kluge S. Kunze J. Lantzsch E.W. Otten G. Passler P. Senne J. Stenner K. Stratmann K. Swendt K. Zimmer G. Herrmann N. Trautmann K. Walter 《Spectrochimica Acta Part B: Atomic Spectroscopy》1993,48(14):1655-1671
Environmental assessment in the wake of a nuclear accident requires the rapid determination of the radiotoxic isotopes 89Sr and 90Sr. Useful measurements must be able to detect 108 atoms in the presence of about 1018 atoms of the stable, naturally occurring isotopes. This paper describes a new approach to this problem using resonance ionization spectroscopy in collinear geometry, combined with classical mass separation. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an isotopic selectivity of about 106. The ions are then neutralized by charge exchange and the resulting fast strontium atoms are selectively excited into high-lying atomic Rydberg states by narrow-band cw laser light in collinear geometry. The Rydberg atoms are then field-ionized and detected. Thus far, a total isotopic selectivity of S > 1010 and an overall efficiency of ξ = 5 × 10−6 have been achieved. The desired detection limit of 108 atoms 90Sr has been demonstrated with synthetic samples. 相似文献
137.
138.
Atom-probe field-ion microscopy together with X-ray photoelectron spectroscopy and secondary ion mass spectrometry have been applied to the microanalysis of fully ordered NiAl single crystals subjected to 3 keV inert gas ion bombardment. As with the studies of Ni3Al (the companion paper) aluminium was found to be preferentially sputtered by both argon and xenon bombardment. Comparisons between depth profiles through Ni3Al and NiAl targets have provided information about the role of binding energies in the selective sputtering process. These data have also permitted conclusions to be drawn about the correct choice of bombarding species for sample cleaning and depth-profiling applications in surface analysis. Examination of field-ion images from specimens after bombardment suggests that the surface is microroughened and this has been confirmed using transmission electron microscopy. 相似文献
139.
J.D. Petke Gerald M. Maggiora Lester L. Shipman Ralph E. Christoffersen 《Journal of Molecular Spectroscopy》1978,73(2):311-331
Ab initio configuration interaction wavefunctions and energies are reported for the ground state and many low-lying singlet and triplet states of magnesium chlorin and chlorin, and are employed in an analysis of the electronic absorption spectra of these systems.In chlorin, the calculated visible spectrum consists of two states, the lower energy, y-polarized state exhibiting moderate absorption intensity in contrast to the very weak absorption of the higher energy x-polarized state. The configurational composition of both states is well described by the four-orbital model. Five states are responsible for the Soret band envelope. A moderately intense y-state lies under the low energy edge of the band envelope, while two x-polarized states of moderate and strong intensity, respectively, are responsible for the band maximum. The final two states lie at the high energy edge of the Soret band and introduce a measure of asymmetry into the band envelope. Two states of very weak oscillator strength are also found in this region of the spectrum. All the Soret states are of complex configurational composition, and several of the higher lying states contain contributions from doubly excited configurations.The calculated visible spectrum of magnesium chlorin also consists of two states, with the weakly absorbing x-polarized state lying approximately 200 cm?1 lower in energy than the moderately intense y-polarized state. The configurational composition of both states is well described by the four-orbital model. Four states constitute the bulk of the intensity in the Soret band envelope. In distinction to chlorin, the moderately intense state at the low energy edge of the band envelope is x-polarized. Two intense states of y- and x-polarization, respectively, constitute the band maximum region, and a single x-polarized state of moderately strong intensity can be assigned to the high energy shoulder of the band envelope. Two other weakly absorbing states are also found in this region, along with another weakly absorbing state of mixed in-plane and out-of-plane polarization. No clearly defined states are observed. As was the case for chlorin, all the Soret states are of complex configurational composition, and some of the higher energy states contain significant contributions from doubly excited configurations.Chlorin and magnesium chlorin both possess three states which lie below S1 and a single which lies slightly above S2. All four of the low-lying states in each molecule are well described by the four-orbital model, with T1 being essentially a single configuration in each case. The remainder of the states are clustered in the same energetic region as the comparable Soret states, with comparably complex configurational compositions.Dipole moments and charge distributions for low-lying singlet and triplet states are also reported, and are used to rationalize chemical reactivity characteristics. 相似文献
140.
A relatively weak ESR spectrum is observed in single crystals of NaN3 after X-ray irradiation at 77 K. This spectrum, which has an anisotropic g value and exhibits a resolved 5-line hyperfine structure with components in the ratio 1:2:3:2:1, corresponds to a single unpaired electron interacting symmetrically with two spin-one nuclei, in three inequivalent sites. The spin-Hamiltonian parameters are: gx = 2.0054 ± 0.0005, gy = 2.0045 ± 0.0005, gz = 1.9688 ± 0.0005, |Ax| = 4.0 ± 0.2 G, |Ay| = 20.0 ± 0.2 G, and |Az| = 4.9 ± 0.2 G, c-axis, and y is perpendicular to the c-axis. This spectrum, which is clearly different from that of substitutional N2?reported by Gelerinter and Silsbee, is attributed to interstitial N2?. 相似文献