4,977 research outputs found
Age-related differences in pointing accuracy in familiar and unfamiliar environments
This study aimed to investigate age-related differences in spatial mental representations of familiar and unfamiliar places. Nineteen young adults (aged 18\u201323) and 19 older adults (aged 60\u201374), all living in the same Italian town, completed a set of visuospatial measures and then pointed in the direction of familiar landmarks in their town and in the direction of landmarks in an unknown environment studied on a map. Results showed that older adults were less accurate in the visuospatial tasks and in pointing at landmarks in an unfamiliar environment, but performed as well as the young adults when pointing to familiar places. Pointing performance correlated with visuospatial tests accuracy in both familiar and unfamiliar environments, while only pointing in an unknown environment correlated with visuospatial working memory (VSWM).
The spatial representation of well-known places seems to be well preserved in older adults (just as well as in young adults), while it declines for unfamiliar environments. Spatial abilities sustain the mental representations of both familiar and unfamiliar environments, while the support of VSWM resources is only needed for the latter
The flank eruption history of Etna (1610-2006) as a constraint on lava flow hazard
Data of the flank eruptions of Etna from over the last 400 years were
extracted from the new geological map for the lava flow extensions and
vent positions, and from the catalogs of historical eruptions for the
eruption durations and lava volumes. The partially or widely hidden lava
fields on the new geological map were retrieved from older geological maps.
The distributions of the eruption durations and lava volumes were
analyzed, with the definition of six eruptive classes for use in numerical
simulations. The threshold values for the eruption durations and lava
volumes were set at 45 days and at 35 × 106 m3 and 100 × 106 m3,
respectively. A global analysis was performed on the whole volcano to
evaluate the recurrence of the classes, and to estimate for each class the
ranges, means and standard deviations of the durations, volumes and
elevations of the main vent. The same analysis was repeated by
subdividing the volcano into three sectors, which were defined on the basis
of the distribution of the eruptive fissures over the last 15 ka. The classes
have different recurrences across these various sectors, and different
distributions of volumes, durations and elevations of the main vent.
Finally, a lava flow resurfacing map that counts the number of lava flows
on each given area of the volcano over the last 400 years was compiled
and then normalized
Study of the magnetic susceptibility in the spin-Peierls system CuGeO
We study numerically, using a one-dimensional Heisenberg model, the
spin-Peierls transition in the linear Cu spin-1/2 chains in the
inorganic compound CuGeO which has been recently observed experimentally.
We suggest that the magnetic susceptibility, the temperature dependence of the
spin gap and the spin-Peierls transition temperature of this material can be
reasonably described by including nearest and next nearest neighbor
antiferromagnetic interactions along the chain. We estimate that the nearest
neighbor exchange parameter J is approximately , and that the next
nearest neighbor exchange parameter is approximately .Comment: 14 pages, Revtex v2.0, 4 figures available upon reques
Strong-coupling expansion for the Hubbard model in arbitrary dimension using slave bosons
A strong-coupling expansion for the antiferromagnetic phase of the Hubbard
model is derived in the framework of the slave-boson mean-field approximation.
The expansion can be obtained in terms of moments of the density of states of
freely hopping electrons on a lattice, which in turn are obtained for
hypercubic lattices in arbitrary dimension. The expansion is given for the case
of half-filling and for the energy up to fifth order in the ratio of hopping
integral over on-site interaction , but can straightforwardly be
generalized to the non-half-filled case and be extended to higher orders in
. For the energy the expansion is found to have an accuracy of better than
for . A comparison is given with an earlier perturbation
expansion based on the Linear Spin Wave approximation and with a similar
expansion based on the Hartree-Fock approximation. The case of an infinite
number of spatial dimensions is discussed.Comment: 12 pages, LaTeX2e, to be published in Phys. Rev.
Spin-Peierls transition in an anisotropic two-dimensional XY model
The two-dimensional Jordan-Wigner transformation is used to investigate the
zero temperature spin-Peierls transition for an anisotropic two-dimensional XY
model in adiabatic limit. The phase diagram between the dimerized (D) state and
uniform (U) state is shown in the parameter space of dimensionless interchain
coupling and spin-lattice coupling . It is found
that the spin-lattice coupling must exceed some critical value
in order to reach the D phase for any finite . The dependence of on
is given by for and the transition between U and D
phase is of first-order for at least .Comment: 2 eps figures, considerable revisions were mad
Lattice dynamics and correlated atomic motion from the atomic pair distribution function
The mean-square relative displacements (MSRD) of atomic pair motions in
crystals are studied as a function of pair distance and temperature using the
atomic pair distribution function (PDF). The effects of the lattice vibrations
on the PDF peak widths are modelled using both a multi-parameter Born
von-Karman (BvK) force model and a single-parameter Debye model. These results
are compared to experimentally determined PDFs. We find that the near-neighbor
atomic motions are strongly correlated, and that the extent of this correlation
depends both on the interatomic interactions and crystal structure. These
results suggest that proper account of the lattice vibrational effects on the
PDF peak width is important in extracting information on static disorder in a
disordered system such as an alloy. Good agreement is obtained between the BvK
model calculations of PDF peak widths and the experimentally determined peak
widths. The Debye model successfully explains the average, though not detailed,
natures of the MSRD of atomic pair motion with just one parameter. Also the
temperature dependence of the Debye model largely agrees with the BvK model
predictions. Therefore, the Debye model provides a simple description of the
effects of lattice vibrations on the PDF peak widths.Comment: 9 pages, 11 figure
Frustration induced Raman scattering in CuGeO_3
We present experimental data for the Raman intensity in the spin-Peierls
compound CuGeO_3 and theoretical calculations from a one-dimensional frustrated
spin model. The theory is based on (a) exact diagonalization and (b) a recently
developed solitonic mean field theory. We find good agreement between the
1D-theory in the homogeneous phase and evidence for a novel dimerization of the
Raman operator in the spin-Peierls state. Finally we present evidence for a
coupling between the interchain exchange, the spin-Peierls order parameter and
the magnetic excitations along the chains.Comment: Phys. Rev. B, Rapid Comm, in Pres
Studies of Vibrational Properties in Ga Stabilized d-Pu by Extended X-ray Absorption Fine Structure
Temperature dependent extended x-ray absorption fine structure (EXAFS)
spectra were measured for a 3.3 at% Ga stabilized Pu alloy over the range T= 20
- 300 K at both the Ga K-edge and the Pu L_III-edge. The temperature dependence
of the pair-distance distribution widths, \sigma(T) was accurately modeled
using a correlated-Debye model for the lattice vibrational properties,
suggesting Debye-like behavior in this material. We obtain pair- specific
correlated-Debye temperatures, \Theta_cD, of 110.7 +/- 1.7 K and 202.6 +/- 3.7
K, for the Pu-Pu and Ga-Pu pairs, respectively. These results represent the
first unambiguous determination of Ga-specific vibrational properties in PuGa
alloys, and indicate the Ga-Pu bonds are significantly stronger than the Pu-Pu
bonds. This effect has important implications for lattice stabilization
mechanisms in these alloys.Comment: 7 pages, 4 figures, Phys. Rev. B in pres
Fermented brewers’ spent grain containing dextran and oligosaccharides as ingredient for composite wheat bread and its impact on gut metabolome in vitro
Brewers’ spent grain or BSG is a fiber and protein rich food-grade side stream that has remained underutilized due to its poor technological and sensory characteristics. In this study, BSG was fermented with Weissella confusa A16 in presence of sucrose to induce the synthesis of dextran and maltosyl-isomaltooligosaccharides. Fermented BSG with or without the above polysaccharides was used as ingredient in wheat bread. Digestion of BSG breads was simulated in vitro with Simulator of Human Intestinal Microbial Ecosystem, and levels of fecal metabolites were analyzed. Enrichment of BSG breads with in situ dextran and maltosyl-isomaltooligosaccharides improved the baking quality compared to native BSG. Metabolism of free amino acids and synthesis of short chain fatty acids varied at different stages and parts of colon. The increase in butyric acid was similar in both the proximal and distal colon. In situ dextran and maltosyl-isomaltooligosaccharides, and higher content of proteins and fiber in BSG breads had a positive influence towards gut microbiota functionality. Along with several essential amino acids, an increase in amount of γ-aminobutyric acid was also observed after simulated digestion. BSG breads had a significant effect on the gut metabolome during in vitro digestion, showing increased production of microbial metabolites with potential health benefits
Strong-coupling expansions for the anharmonic Holstein model and for the Holstein-Hubbard model
A strong-coupling expansion is applied to the anharmonic Holstein model and
to the Holstein-Hubbard model through fourth order in the hopping matrix
element. Mean-field theory is then employed to determine transition
temperatures of the effective (pseudospin) Hamiltonian. We find that anharmonic
effects are not easily mimicked by an on-site Coulomb repulsion, and that
anharmonicity strongly favors superconductivity relative to charge-density-wave
order. Surprisingly, the phase diagram is strongly modified by relatively small
values of the anharmonicity.Comment: 34 pages, typeset in ReVTeX, 11 encapsulated postscript files
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