784 research outputs found
Sense of Self in Baby Chimpanzees
Philippe Rochat and his colleague tentatively proposed that young infants' propensity to engage in self-perception and systematic exploration of the perceptual consequences of their own action plays and is probably at the origin of an early sense of self: the ecological self. Rochat and Hespos (1997) reported that neonates discriminate between external and self-stimulation. Neonate tended to display significantly more rooting responses (i.e., head turn towards the stimulation with mouth open and tonguing) following external compared to self-stimulation. Rochat et al. (1998) also reported that 2-month-olds showed clear sign of modulation of their oral activity on the pacifier as a function of analog versus non-analog condition. Rochat and his colleague concluded that these observations are interpreted as evidence of self-exploration and the emergence of a sense of self-agency by 2-month-olds. We tried to replicate these findings in infant chimpanzees. We observed rooting responses of three baby chimpanzees in two condition, self-stimulation and external stimulation. In external stimulation condition, the index finger of the experimenter or small stick touched one of the infant's cheeks. In self-stimulation condition, the experimenter took infant's hand and touched his or her cheek with their fingers. In Rochat and Hespos, they recorded and analyzed several measures such as state, head movement, mouth activity and so on. How ever, we analyzed only mouth activities tentatively. We found infant chimpanzees tended to show more rooting responses following external stimulation compared to self-stimulation as well as human infants.
We also carried out sucking experiment with two baby chimpanzees. The experimenter held the pacifier and put the artificial nipple into the infant's mouth. A session started when the infant take the nipple inside the his or her mouth. Auditory stimulus, which was a complex tone comprised of six harmonics with equal intensity, was given to the chimpanzee according to the test condition during their sucking. There were four test conditions and each condition consisted with three types of feedback as follows: 1) silent baseline, contingent, and steady, 2) contingent baseline, 1-sec delay, and 3-sec delay, 3) contingent baseline, 6-sec delay, and 12-sec delay, 4) contingent baseline, 1/2 efficiency, and 1/4 efficiency. In test 1, one infant chimpanzee showed decrease of the minimum pressure of sucking in the contingent condition. In test 2, one subject showed shorter intervals of sucking in 3-sec delay condition. This seems to be similar to human infant's. We may be able to postulate ecological self in baby chimpanzees according to the self-exploration. In test 3 and 4, we did not obtain any effects of stimulus conditions. Results of these studies. These studies were conducted as the parts of the chimpanzee development project in Primate Research Institute, Kyoto University, organized by Professor Tetsuro Matsuzawa
Tomonaga-Luttinger liquid correlations and Fabry-Perot interference in conductance and finite-frequency shot noise in a single-walled carbon nanotube
We present a detailed theoretical investigation of transport through a
single-walled carbon nanotube (SWNT) in good contact to metal leads where weak
backscattering at the interfaces between SWNT and source and drain reservoirs
gives rise to electronic Fabry-Perot (FP) oscillations in conductance and shot
noise. We include the electron-electron interaction and the finite length of
the SWNT within the inhomogeneous Tomonaga-Luttinger liquid (TLL) model and
treat the non-equilibrium effects due to an applied bias voltage within the
Keldysh approach. In low-frequency transport properties, the TLL effect is
apparent mainly via power-law characteristics as a function of bias voltage or
temperature at energy scales above the finite level spacing of the SWNT. The
FP-frequency is dominated by the non-interacting spin mode velocity due to two
degenerate subbands rather than the interacting charge velocity. At higher
frequencies, the excess noise is shown to be capable of resolving the
splintering of the transported electrons arising from the mismatch of the
TLL-parameter at the interface between metal reservoirs and SWNT. This dynamics
leads to a periodic shot noise suppression as a function of frequency and with
a period that is determined solely by the charge velocity. At large bias
voltages, these oscillations are dominant over the ordinary FP-oscillations
caused by two weak backscatterers. This makes shot noise an invaluable tool to
distinguish the two mode velocities in the SWNT.Comment: 20 pages, 9 figure
The mean energy, strength and width of triple giant dipole resonances
We investigate the mean energy, strength and width of the triple giant dipole
resonance using sum rules.Comment: 12 page
Correlation effects in quasi one dimensional electron wires
We explore the role of electron correlation in quasi one dimensional quantum
wires as the range of the interaction potential is changed and their thickness
is varied by performing exact quantum Monte Carlo simulations at various
electronic densities. In the case of unscreened interactions with a long range
1/x tail there is a crossover from a liquid to a quasi Wigner crystal state as
the density decreases. When this interaction is screened, quasi long range
order is prevented from forming, although a significant correlation with 4 k_F
periodicity is still present at low densities. At even lower electron
concentration, exchange is suppressed and the spin-dependent interactions
become negligible, making the electrons behave like spinless fermions. We show
that this behavior is shared by the long range and screened interactions by
studying the spin and charge excitations of the system in both cases. Finally,
we study the effect of electron correlations in the double quantum wire
experiment [Steinberg et al., Phys. Rev. B 77, 113307 (2006)], by introducing
an accurate model for the screening in the experiment and explicitly including
the finite length of the system in our simulations. We find that decreasing the
electron density drives the system from a liquid to a state with quite strong 4
k_F correlations. This crossover takes place around , the
density where the electron localization occurs in the experiment. The charge
and spin velocities are also in remarkable agreement with the experimental
findings in the proximity of the crossover. We argue that correlation effects
play an important role at the onset of the localization transition.Comment: minor improvements, 13 pages, 12 figure
Bose-Fermi Mixtures in One Dimension
We analyze the phase stability and the response of a mixture of bosons and
spin-polarized fermions in one dimension (1D). Unlike in 3D, phase separation
happens for low fermion densities. The dynamics of the mixture at low energy is
independent of the spin-statistics of the components, and zero-sound-like modes
exist that are essentially undamped.Comment: 5 pages; 1 figur
Correlated sequential tunneling through a double barrier for interacting one-dimensional electrons
The problem of resonant tunneling through a quantum dot weakly coupled to
spinless Tomonaga-Luttinger liquids has been studied. We compute the linear
conductance due to sequential tunneling processes upon employing a master
equation approach. Besides the previously used lowest-order golden rule rates
describing uncorrelated sequential tunneling (UST) processes, we systematically
include higher-order correlated sequential tunneling (CST) diagrams within the
standard Weisskopf-Wigner approximation. We provide estimates for the parameter
regions where CST effects can be important. Focusing mainly on the temperature
dependence of the peak conductance, we discuss the relation of these findings
to previous theoretical and experimental results.Comment: replaced with the published versio
Signatures of Strong Correlations in One-Dimensional Ultra-Cold Atomic Fermi Gases
Recent success in manipulating ultra-cold atomic systems allows to probe
different strongly correlated regimes in one-dimension. Regimes such as the
(spin-coherent) Luttinger liquid and the spin-incoherent Luttinger liquid can
be realized by tuning the inter-atomic interaction strength and trap
parameters. We identify the noise correlations of density fluctuations as a
robust observable (uniquely suitable in the context of trapped atomic gases) to
discriminate between these two regimes. Finally, we address the prospects to
realize and probe these phenomena experimentally using optical lattices.Comment: 4 pages, 2 figure
RPAE versus RPA for the Tomonaga model with quadratic energy dispersion
Recently the damping of the collective charge (and spin) modes of interacting
fermions in one spatial dimension was studied. It results from the nonlinear
correction to the energy dispersion in the vicinity of the Fermi points. To
investigate the damping one has to replace the random phase approximation (RPA)
bare bubble by a sum of more complicated diagrams. It is shown here that a
better starting point than the bare RPA is to use the (conserving) linearized
time dependent Hartree-Fock equations, i.e. to perform a random phase
approximation (with) exchange
(RPAE) calculation. It is shown that the RPAE equation can be solved
analytically for the special form of the two-body interaction often used in the
Luttinger liquid framework. While (bare) RPA and RPAE agree for the case of a
strictly linear disperson there are qualitative differences for the case of the
usual nonrelativistic quadratic dispersion.Comment: 6 pages, 3 figures, misprints corrected; to appear in PRB7
First-principles study of the atomic and electronic structure of the Si(111)-(5x2-Au surface reconstruction
We present a systematic study of the atomic and electronic structure of the
Si(111)-(5x2)-Au reconstruction using first-principles electronic structure
calculations based on the density functional theory. We analyze the structural
models proposed by Marks and Plass [Phys. Rev. Lett.75, 2172 (1995)], those
proposed recently by Erwin [Phys. Rev. Lett.91, 206101 (2003)], and a
completely new structure that was found during our structural optimizations. We
study in detail the energetics and the structural and electronic properties of
the different models. For the two most stable models, we also calculate the
change in the surface energy as a function of the content of silicon adatoms
for a realistic range of concentrations. Our new model is the energetically
most favorable in the range of low adatom concentrations, while Erwin's "5x2"
model becomes favorable for larger adatom concentrations. The crossing between
the surface energies of both structures is found close to 1/2 adatoms per 5x2
unit cell, i.e. near the maximum adatom coverage observed in the experiments.
Both models, the new structure and Erwin's "5x2" model, seem to provide a good
description of many of the available experimental data, particularly of the
angle-resolved photoemission measurements
Equivalence of Local and Separable Realizations of the Discontinuity-Inducing Contact Interaction and Its Perturbative Renormalizability
We prove that the separable and local approximations of the
discontinuity-inducing zero-range interaction in one-dimensional quantum
mechanics are equivalent. We further show that the interaction allows the
perturbative treatment through the coupling renormalization.
Keywords: one-dimensional system, generalized contact interaction,
renormalization, perturbative expansion. PACS Nos: 3.65.-w, 11.10.Gh, 31.15.MdComment: ReVTeX 7pgs, doubl column, no figure, See also the website
http://www.mech.kochi-tech.ac.jp/cheon
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