4,949 research outputs found
Consistent thermodynamics for spin echoes
Spin-echo experiments are often said to constitute an instant of
anti-thermodynamic behavior in a concrete physical system that violates the
second law of thermodynamics. We argue that a proper thermodynamic treatment of
the effect should take into account the correlations between the spin and
translational degrees of freedom of the molecules. To this end, we construct an
entropy functional using Boltzmann macrostates that incorporates both spin and
translational degrees of freedom. With this definition there is nothing special
in the thermodynamics of spin echoes: dephasing corresponds to Hamiltonian
evolution and leaves the entropy unchanged; dissipation increases the entropy.
In particular, there is no phase of entropy decrease in the echo. We also
discuss the definition of macrostates from the underlying quantum theory and we
show that the decay of net magnetization provides a faithful measure of entropy
change.Comment: 15 pages, 2 figs. Changed figures, version to appear in PR
Efficient Model Learning for Human-Robot Collaborative Tasks
We present a framework for learning human user models from joint-action
demonstrations that enables the robot to compute a robust policy for a
collaborative task with a human. The learning takes place completely
automatically, without any human intervention. First, we describe the
clustering of demonstrated action sequences into different human types using an
unsupervised learning algorithm. These demonstrated sequences are also used by
the robot to learn a reward function that is representative for each type,
through the employment of an inverse reinforcement learning algorithm. The
learned model is then used as part of a Mixed Observability Markov Decision
Process formulation, wherein the human type is a partially observable variable.
With this framework, we can infer, either offline or online, the human type of
a new user that was not included in the training set, and can compute a policy
for the robot that will be aligned to the preference of this new user and will
be robust to deviations of the human actions from prior demonstrations. Finally
we validate the approach using data collected in human subject experiments, and
conduct proof-of-concept demonstrations in which a person performs a
collaborative task with a small industrial robot
Coulomb Blockade of Tunneling Through a Double Quantum Dot
We study the Coulomb blockade of tunneling through a double quantum dot. The
temperature dependence of the linear conductance is strongly affected by the
inter-dot tunneling. As the tunneling grows, a crossover from
temperature-independent peak conductance to a power-law suppression of
conductance at low temperatures is predicted. This suppression is a
manifestation of the Anderson orthogonality catastrophe associated with the
charge re-distribution between the dots, which accompanies the tunneling of an
electron into a dot. We find analytically the shapes of the Coulomb blockade
peaks in conductance as a function of gate voltage.Comment: 11 pages, revtex3.0 and multicols.sty, 4 figures uuencode
On the droplet size and application of wettability analysis for the development of ink and printing substrates
The role of the equation of state and the space-time dimension in spherical collapse
We study the spherically symmetric collapse of a fluid with non-vanishing
radial pressure in higher dimensional space-time. We obtain the general exact
solution in the closed form for the equation of state ()
which leads to the explicit construction of the root equation governing the
nature (black hole versus naked singularity) of the central singularity. A
remarkable feature of the root equation is its invariance for the three cases:
(),
() and () where is the
dimension of space-time. That is, for the ultimate end result of the collapse,
-dimensional dust, - AdS (anti de Sitter)-like and - dS-like
are absolutely equivalent.Comment: 4 Pages, RevTeX, no figures, minor changes, new references added,
Detailed version to follo
Effects of Novel Ryegrass Endophytes on Pasture Production and Milk Production from Dairy Cows in Northern New Zealand
Tunneling Conductance and Coulomb Blockade Peak Splitting of Two Quantum Dots Connected by a Quantum Point Contact
By using bosonization method and unitary transformation, we give a general
relation between the dimensionless tunneling conductance and the fractional
Coulomb blockade conductance peak splitting which is valid both for weak and
strong transmission between two quantum dots, and show that the tunneling
conductance has a linear temperature dependence in the low energy and low
temperature limit.Comment: 12 pages, Revtex, no figures, to appear in Phys. Rev.
TUNNELING SPECTROSCOPY OF QUANTUM CHARGE FLUCTUATIONS IN THE COULOMB BLOCKADE
We present a theory of Coulomb blockade oscillations in tunneling through a
pair of quantum dots connected by a tunable tunneling junction. The positions
and amplitudes of peaks in the linear conductance are directly related,
respectively, to the ground state energy and to the dynamics of charge
fluctuations. We study analytically both strong and weak interdot tunneling. As
the tunneling decreases, the period of the peaks doubles, as observed
experimentally. In the strong tunneling limit, we predict a striking power law
temperature dependence of the peak amplitudes.Comment: 4 pages, revtex3.0, 1 figure uuencode
Spherically symmetric static solution for colliding null dust
The Einstein equations are integrated in the presence of two (incoming and
outgoing) streams of null dust, under the assumptions of spherical symmetry and
staticity. The solution is also written in double null and radiation
coordinates and it is reinterpreted as an anisotropic fluid. Interior matching
with a static fluid and exterior matching with the Vaidya solution along null
hypersurfaces is discussed. The connection with two-dimensional dilaton gravity
is established.Comment: 12 pages, 7 figures, to appear in Phys. Rev.
Relation between Barrier Conductance and Coulomb Blockade Peak Splitting for Tunnel-Coupled Quantum Dots
We study the relation between the barrier conductance and the Coulomb
blockade peak splitting for two electrostatically equivalent dots connected by
tunneling channels with bandwidths much larger than the dot charging energies.
We note that this problem is equivalent to a well-known single-dot problem and
present solutions for the relation between peak splitting and barrier
conductance in both the weak and strong coupling limits. Results are in good
qualitative agreement with the experimental findings of F. R. Waugh et al.Comment: 19 pages (REVTeX 3.0), 3 Postscript figure
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