1,502 research outputs found
Tunneling driven tilt modes of the O octahedra in La{2-x}Sr{x}CuO{4}: strong dependence on doping
The anelastic spectrum of La{2-x}Sr{x}CuO{4} (x = 0, 0.008, 0.019, 0.032) has
been measured down to 1.5 K, in order to see the effect of doping on the
intrinsic lattice fluctuations already found in stoichiometric La{2}CuO{4}, and
identified with tunneling driven tilt modes of the O octahedra. Slight doping
with Sr causes a drastic increase of the transition rates and relaxation
strength of the tunneling systems. The influence of doping on the relaxation
rate is interpreted in terms of direct coupling between between the tilts of
the octahedra and the hole excitations. However, the observed fast dependence
of the rate on temperature cannot be explained in terms of the ususal models of
coupling between a tunneling system and the conduction electrons.Comment: LaTeX, 5 figures in a single PostScript file, submitted to Phys. Rev.
Numerical study of the urban geometrical representation impact in a surface energy budget model
The aim of this work is to investigate how both the orientation of the urban canyon and the modeling of the edge effects (i.e. urban canyons of finite length) are important in the numerical simulation of the surface energy budget in urban areas. Starting from the town energy balance scheme, two models of increasing complexity of the canyon geometry are developed. A sensitivity analysis of the role played by the chosen hypothesis and parameterizations is performed by coupling the canyon schemes with the numerical weather prediction model RAMS. The results suggest that a detailed description of the urban geometry could produce non-negligible differences of the energy balances and of the temperature fields with respect to what occurs using simpler schematizations, in particular during the summer
Anelastic relaxation process of polaronic origin in La{2-x}Sr{x}CuO{4}: interaction between the charge stripes and pinning centers
The evolution of an anelastic relaxation process occurring around 80 K in
La{2-x}Sr{x}CuO{4} at a measuring frequency of ~1 kHz has been followed from x
= 0.0075 to the overdoped region, x = 0.2, where it disappears. The dependence
of the peak intensity on doping is consistent with a polaronic mechanism,
identified with the disordered charge stripes overcoming pinning centers. A
marked decrease of the peak amplitude occurs at x > 0.045, the same doping
range where a change of the stripe order from parallel to diagonal with respect
to the Cu-O bonds has been observed by neutron diffraction. Both the energy
barrier and peak amplitude also exhibit a rise near x = 1/8.Comment: 5 pages, 4 figure
The Maternal Lineage: Orality and Language in Natalia Ginzburg\u27s \u3cem\u3eFamily Sayings\u3c/em\u3e
As its title, Family Sayings, suggests, it is through a body of sayings, stories, poems and songs, recalled by her mother, that the author Natalia Ginzburg tells the story of her family before, during and after WWII. Within the turmoil and chaos of the fascist regime and the war, there is a language, a lexicon, capable of establishing a comforting and familiar zone for the members of the family. Through repetitions of sayings and sketches, Natalia Ginzburg will present a work, partly oral and partly written, blurring the relationship between author/reader and storyteller/listener. In a time when consumerism is rampant in post-war Italy, when the family entity and unity is threatened by the individualistic and capitalistic model of prosperity and success, and when television is slowly annulling people’s chances to communicate, Ginzburg establishes the writing of autobiography within immediacy, orality, and relationality, subverting the well-established notion of the genre as the story of an individual and his/her personality. Published in 1968, Family Sayings seems to appear in direct opposition with the revolutionary sentiments of the time. For Italian feminists a critique of any institution began with one of patriarchy, for Ginzburg with a reevaluation of the mother not as guardian of a nation, but as an individual with her own economy of authenticity. In a moment when entire student movements are demanding a deconstruction of institutional and family structures, Ginzburg claims maternal lineage as a transformative experience toward a social, political and literary restoration
Observation of an incoherent thermally activated proton hopping process in calix-[4]-arene by means of anelastic spectroscopy
The anelastic spectrum of calix[4]arene was measured at two different
vibrational frequencies. Three thermally activated peaks were detected. The
lowest temperature peak can be described considering a continous distribution
function of activation energies for the relaxation. This anelastic peak can be
ascribed to a thermally activated hopping process of H atoms of the OH groups,
corresponding to a flip-flop of the OH bond. From the results of the present
study, it seems that anelastic spectroscopy is a good experimental technique to
study atomic motion inside molecules at a mesoscopic (few molecules) level.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Anelastic relaxation and La NQR in LaSrCuO around the critical Sr content x=0.02
Anelastic relaxation and La NQR relaxation measurements in
LaSrCuO for Sr content x around 2 and 3 percent, are presented
and discussed in terms of spin and lattice excitations and ordering processes.
It is discussed how the phase diagram of LaSrCuO at the
boundary between the antiferromagnetic (AF) and the spin-glass phase (x = 0.02)
could be more complicate than previous thought, with a transition to a
quasi-long range ordered state at T = 150 K, as indicated by recent neutron
scattering data. On the other hand, the La NQR spectra are compatible
with a transition to a conventional AF phase around T = 50 K, in agreement with
the phase diagram commonly accepted in the literature. In this case the
relaxation data, with a peak of magnetic origin in the relaxation rate around
150 K at 12 MHz and the anelastic counterparts around 80 K in the kHz range,
yield the first evidence in LaSrCuO of freezing involving
simultaneously lattice and spin excitations. This excitation could correspond
to the motion of charged stripes.Comment: 10 pages, 8 figure
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