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排序方式: 共有428条查询结果,搜索用时 15 毫秒
51.
M. Papa F. Amorini M. Cabibbo G. Cardella A. Di Pietro P. Figuera A. Musumarra G. Pappalardo F. Rizzo S. Tudisco 《The European Physical Journal A - Hadrons and Nuclei》1999,4(1):69-82
Recent experimental results on particles-γ coincidence measurements on the systems 12C +64Ni and 35Cl +64Ni at about 8 MeV/nucleon are interpreted as due to the effect of a Dipole pre-equilibrium emission produced during the damping
of the proton-neutron relative collective motion in very deformed intermediate systems formed in the first instants of the
collision. The pre-equilibrium effects are evaluated through semiclassic kinetic theories and through modified statistical
approach to include non-stationary effects in Fusion processes, Massive Transfer reactions (in the 12C +64Ni system) and in Binary Dissipative reactions (in the 35Cl +64Ni system). In particular the study performed on the dipole molecular component allows to establish a link between the above
phenomenon and the charge and mass transfer process in quasi-peripheral reactions.
Received: 15 April 1998 / Revised version: 8 June 1998 相似文献
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Summary The paper deals with the shakedown analysis problem of discrete elastoplastic structures, subjected to variable and repeated quasi-static loads, account being given to the limited structural ductility by imposing a-priori limit values to some relevant parameters of plastic deformation. The key-concept of limited-ductility load amplifier is assessed and the problem is given a unified formulation as a nonlinear mathematical programming problem, where ductility constraints — of generalized character — are obtained by using a so-called perturbation method which leads to a-priori upper bounds of the relevant plastic deformation measures. Lower bounds to the load amplifier are so obtained and three different computationals stratagies are herein outlined: the linear parametric programming one is applied to three case-study structures.
Ricerca finanziata dal CNR e dal MPI. 相似文献
Sommario La memoria affronta lo studio del problema di adattamento elastoplastico di strutture discrete, sottoposte a carichi comunque variabili in modo quasi-statico, tenendo conto di un comportamento a limitata duttilità della struttura, il quale richiede che uno o più parametri della deformazione plastica risultino non superiori di assegnati valori. Del problema di analisi posto, utilizzando il concetto di moltiplicatore dei carichi per l'adattamento con limitata duttilità, viene data una formulazione unitaria come problema di programmazione matematica non lineare, i cui vincoli di duttilità sono ottenuti con tecniche perturbative di maggiorazione a-priori delle deformazioni plastiche. Il metodo conduce a limiti inferiori del moltiplicatore dei carichi dipendenti dal livello assegnato alla deformazione plastica. Tre differenti strategie computazionali vengono delineate per la soluzione del problema, una delle quali di tipo programmazione lineare parametrica viene applicata a tre esempi.
Ricerca finanziata dal CNR e dal MPI. 相似文献
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Methods based on guided ultrasonic waves are gaining increasing attention for the non-destructive inspection and condition
monitoring of multi-wire strands used in civil structures such as prestressing tendons and cable stays. In this paper we examine
the wave propagation problem in seven-wire strands at the level of the individual wires comprising the strand. Through a broad-band,
laser ultrasonic setup and a time—frequency wavelet transform processing, longitudinal and flexural waves are characterized
in terms of dispersive velocity and frequency-dependent attenuation. These vibrating frequencies propagating with minimal
losses are identified as they are suitable for long-range inspection of the strands. In addition, the wave transmission spectra
are found to be sensitive to the load level, suggesting the potential for continuous load monitoring in the field. 相似文献
57.
Aloe plants have been widely documented in artists’ treatises dating from the sixteenth to the nineteenth century as a source
of colorant to achieve lustrous golden glazes on tin- and silver-foiled objects and warm-toned finishes on musical instruments,
such as violins. Aloe extracts contain characteristic anthraquinone and phenolic components which impart a distinctive orange
tone and fluorescence to mixtures containing them. Because of the low concentration of colorant in the coatings and its probable
degradation by high temperature during manufacture, the identification of aloe in heated oil–resin mixtures represents an
analytical challenge. For this reason, the possible presence of aloe in glazes and coatings has been largely overlooked. This
paper describes various analytical approaches to the identification of aloe in historic samples, from comparison with results
obtained from reference standards and mock-up samples. Complementary analytical techniques including thermally assisted hydrolysis
and methylation–gas chromatography–mass spectrometry, high-performance liquid chromatography, laser desorption–mass spectrometry,
matrix-assisted laser desorption-ionization-mass spectrometry and surface-enhanced Raman scattering were used. Different chemical
markers were identified by the individual methods and the advantages and limitations of each technique for the identification
of aloe in oil–resin varnishes are discussed. 相似文献
58.
UV and IR spectroscopic studies of cold alkali metal ion-crown ether complexes in the gas phase 总被引:1,自引:0,他引:1
Inokuchi Y Boyarkin OV Kusaka R Haino T Ebata T Rizzo TR 《Journal of the American Chemical Society》2011,133(31):12256-12263
We report UV photodissociation (UVPD) and IR-UV double-resonance spectra of dibenzo-18-crown-6 (DB18C6) complexes with alkali metal ions (Li(+), Na(+), K(+), Rb(+), and Cs(+)) in a cold, 22-pole ion trap. All the complexes show a number of vibronically resolved UV bands in the 36,000-38,000 cm(-1) region. The Li(+) and Na(+) complexes each exhibit two stable conformations in the cold ion trap (as verified by IR-UV double resonance), whereas the K(+), Rb(+), and Cs(+) complexes exist in a single conformation. We analyze the structure of the conformers with the aid of density functional theory (DFT) calculations. In the Li(+) and Na(+) complexes, DB18C6 distorts the ether ring to fit the cavity size to the small diameter of Li(+) and Na(+). In the complexes with K(+), Rb(+), and Cs(+), DB18C6 adopts a boat-type (C(2v)) open conformation. The K(+) ion is captured in the cavity of the open conformer thanks to the optimum matching between the cavity size and the ion diameter. The Rb(+) and Cs(+) ions sit on top of the ether ring because they are too large to enter the cavity of the open conformer. According to time-dependent DFT calculations, complexes that are highly distorted to hold metal ions open the ether ring upon S(1)-S(0) excitation, and this is confirmed by extensive low-frequency progressions in the UVPD spectra. 相似文献
59.
Kristensen K Kauczor J Thorvaldsen AJ Jørgensen P Kjærgaard T Rizzo A 《The Journal of chemical physics》2011,134(21):214104
Damped response theory is applied to the calculation of two-photon absorption (TPA) spectra, which are determined directly, at each frequency, from a modified damped cubic response function. The TPA spectrum may therefore be evaluated for selected frequency ranges, making the damped TPA approach attractive for calculations on large molecules with a high density of states, where the calculation of TPA using standard theory is more problematic. Damped response theory can also be applied to the case of intermediate state resonances, where the standard TPA expression is divergent. Both exact damped response theory and its application within density functional theory are discussed. The latter is implemented using an atomic-orbital based density matrix formulation, which makes the approach especially suitable for studies on large systems. A test preliminary study is presented for the TPA spectrum of R-(+)-1,1'-bi(2-naphtol). 相似文献
60.
Radovan Bast Kenneth Ruud Antonio Rizzo Trygve Helgaker 《Theoretical chemistry accounts》2011,129(3-5):685-699
We present the first relativistic study of the electric-field-gradient induced birefringence (Buckingham birefringence), with application to the series of molecules CX2 (X?=?O, S, Se, Te). A recently developed atomic-orbital-driven scheme for the calculation of time-dependent molecular properties using one-, two- and four-component relativistic wave functions (Bast et?al. in Chem Phys 356:177, 2009) is extended to first-order frequency-dependent magnetic-field perturbations, using London atomic orbitals to ensure gauge-origin independent results and to improve basis-set convergence. Calculations are presented at the Hartree?CFock and Kohn?CSham levels of theory and results for CO2 and CS2 are compared with previous high-level coupled-cluster calculations. Except for the heaviest member of the series, relativistic effects are small??in particular for the temperature-independent contribution to the birefringence. By contrast, the effects of electron correlation are significant. However, the reliability of standard exchange-correlation functionals in describing Buckingham birefringence remains unclear based on the comparison with high-level coupled-cluster singles-and-doubles calculations. 相似文献