13,482 research outputs found
Peltier effect in normal metal-insulator-heavy fermion metal junctions
A theoretical study has been undertaken of the Peltier effect in normal metal
- insulator - heavy fermion metal junctions. The results indicate that, at
temperatures below the Kondo temperature, such junctions can be used as
electronic microrefrigerators to cool the normal metal electrode and are
several times more efficient in cooling than the normal metal - heavy fermion
metal junctions.Comment: 3 pages in REVTeX, 2 figures, to be published in Appl. Phys. Lett.,
April 7, 200
Preliminary design of a Primary Loop Pump Assembly (PLPA), using electromagnetic pumps
A preliminary design study of flight-type dc conduction-permanent magnetic, ac helical induction, and ac linear induction pumps for circulating 883 K (1130 F) NaK at 9.1 kg/sec (20 lb/sec) is described. Various electromagnetic pump geometrics are evaluated against hydraulic performance, and the effects of multiple windings and numbers of pumps per assembly on overall reliability were determined. The methods used in the electrical-hydraulic, stress, and thermal analysis are discussed, and the high temperature electrical materials selected for the application are listed
Revivals of Coherence in Chaotic Atom-Optics Billiards
We investigate the coherence properties of thermal atoms confined in optical
dipole traps where the underlying classical dynamics is chaotic. A perturbative
expression derived for the coherence of the echo scheme of [Andersen et. al.,
Phys. Rev. Lett. 90, 023001 (2003)] shows it is a function of the survival
probability or fidelity of eigenstates of the motion of the atoms in the trap.
The echo coherence and the survival probability display "system specific"
features, even when the underlying classical dynamics is chaotic. In
particular, partial revivals in the echo signal and the survival probability
are found for a small shift of the potential. Next, a "semi-classical"
expression for the averaged echo signal is presented and used to calculate the
echo signal for atoms in a light sheet wedge billiard. Revivals in the echo
coherence are found in this system, indicating they may be a generic feature of
dipole traps
Classical mappings of the symplectic model and their application to the theory of large-amplitude collective motion
We study the algebra Sp(n,R) of the symplectic model, in particular for the
cases n=1,2,3, in a new way. Starting from the Poisson-bracket realization we
derive a set of partial differential equations for the generators as functions
of classical canonical variables. We obtain a solution to these equations that
represents the classical limit of a boson mapping of the algebra. The
relationship to the collective dynamics is formulated as a theorem that
associates the mapping with an exact solution of the time-dependent Hartree
approximation. This solution determines a decoupled classical symplectic
manifold, thus satisfying the criteria that define an exactly solvable model in
the theory of large amplitude collective motion. The models thus obtained also
provide a test of methods for constructing an approximately decoupled manifold
in fully realistic cases. We show that an algorithm developed in one of our
earlier works reproduces the main results of the theorem.Comment: 23 pages, LaTeX using REVTeX 3.
Arbitrary-speed quantum gates within large ion crystals through minimum control of laser beams
We propose a scheme to implement arbitrary-speed quantum entangling gates on
two trapped ions immersed in a large linear crystal of ions, with minimal
control of laser beams. For gate speeds slower than the oscillation frequencies
in the trap, a single appropriately-detuned laser pulse is sufficient for
high-fidelity gates. For gate speeds comparable to or faster than the local ion
oscillation frequency, we discover a five-pulse protocol that exploits only the
local phonon modes. This points to a method for efficiently scaling the ion
trap quantum computer without shuttling ions.Comment: 4 page
Robust quantum gates on neutral atoms with cavity-assisted photon-scattering
We propose a scheme to achieve quantum computation with neutral atoms whose
interactions are catalyzed by single photons. Conditional quantum gates,
including an -atom Toffoli gate and nonlocal gates on remote atoms, are
obtained through cavity-assisted photon scattering in a manner that is robust
to random variation in the atom-photon coupling rate and which does not require
localization in the Lamb-Dicke regime. The dominant noise in our scheme is
automatically detected for each gate operation, leading to signalled errors
which do not preclude efficient quantum computation even if the error
probability is close to the unity.Comment: 4 pages, 3 figure
An exactly solvable model of a superconducting to rotational phase transition
We consider a many-fermion model which exhibits a transition from a
superconducting to a rotational phase with variation of a parameter in its
Hamiltonian. The model has analytical solutions in its two limits due to the
presence of dynamical symmetries. However, the symmetries are basically
incompatible with one another; no simple solution exists in intermediate
situations. Exact (numerical) solutions are possible and enable one to study
the behavior of competing but incompatible symmetries and the phase transitions
that result in a semirealistic situation. The results are remarkably simple and
shed light on the nature of phase transitions.Comment: 11 pages including 1 figur
Single grain heating due to inelastic cotunneling
We study heating effects of a single metallic quantum dot weakly coupled to
two leads. The dominant mechanism for heating at low temperatures is due to
inelastic electron cotunneling processes. We calculate the grain temperature
profile as a function of grain parameters, bias voltage, and time and show that
for nanoscale size grains the heating effects are pronounced and easily
measurable in experiments.Comment: 4 pages, 3 figures, revtex4, extended and corrected versio
Analytically solvable potentials for -unstable nuclei
An analytical solution of the collective Bohr equation with a Coulomb-like
and a Kratzer-like unstable potential in quadrupole deformation space
is presented. Eigenvalues and eigenfunctions are given in closed form and
transition rates are calculated for the two cases. The corresponding
SO(2,1)SO(5) algebraic structure is discussed.Comment: 9 pages, 4 figures in one .ps fil
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Training Prospective Abilities through Conversation about the Extended Self
Prospection is an important cognitive achievement, and isrelated to uniquely human abilities such as planning, delay ofgratification, and goal attainment. While prospection developsrapidly during early childhood, little is known about themechanisms that support its development. Here we exploredwhether encouraging children to talk about their extendedselves (self outside the present context) boosts theirprospective abilities. Preschoolers (N = 81) participated in a5-minute interaction with an adult in which they were askedto talk about events in the near future, distant future, nearpast, or present. Compared with children discussing theirpresent and distant future, children asked to discuss events intheir near future or near past displayed better planning andprospective memory. Additionally, those two conditions weremost effective in eliciting self-projection (use of personalpronouns). Results suggest that experience communicatingabout the close-in-time, extended self contributes tochildrenâs future-oriented thinking
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