2,709 research outputs found
Strongly correlated bosons and fermions in optical lattices
These lectures are an introduction to the physics of strongly correlated
fermions and bosons. They are specially targeted for the experimental
realizations that have been provided by cold atomic gases in optical lattices.Comment: Lectures presented at the Les Houches summer school 2010: "Many-Body
Physics with Ultracold Gases", organized by C. Salomon and G. V. Shlyapniko
How many double squares can a string contain?
Counting the types of squares rather than their occurrences, we consider the
problem of bounding the number of distinct squares in a string. Fraenkel and
Simpson showed in 1998 that a string of length n contains at most 2n distinct
squares. Ilie presented in 2007 an asymptotic upper bound of 2n - Theta(log n).
We show that a string of length n contains at most 5n/3 distinct squares. This
new upper bound is obtained by investigating the combinatorial structure of
double squares and showing that a string of length n contains at most 2n/3
double squares. In addition, the established structural properties provide a
novel proof of Fraenkel and Simpson's result.Comment: 29 pages, 20 figure
Modeling and simulation of drying operation in PVC powder production line: a pneumatic dryer model
A one-dimensional steady-state model is developed to simulate drying of PVC powder in a pneumatic dryer. In this model, a two-phase continuum model was used to describe the steady-state flow of a dilute dispersed phase (wet PVC powder) and a continuous phase (humid air) through dryer. The particle scale kinetics was obtained by immersion of a fixed mass of wet PVC’s particles (cake) in a batch dense fluidized bed containing inert hot particles (glass bead). The drying kinetics was described by a shrinking core type model and integrated in pneumatic dryer model. The results show that the inlet temperature is the most important parameter
in the operation. The drying rate is controlled by a two-stage process. The first stage corresponds to the surface water evaporation, and the second to the pore water evaporation
Experimental observation of a strong mean flow induced by internal gravity waves
We report the experimental observation of a robust horizontal mean flow
induced by internal gravity waves. A wave beam is forced at the lateral
boundary of a tank filled with a linearly stratified fluid initially at rest.
After a transient regime, a strong jet appears in the wave beam, with
horizontal recirculations outside the wave beam. We present a simple physical
mechanism predicting the growth rate of the mean flow and its initial spatial
structure. We find good agreement with experimental results
Measurement of the Angular Dependence of the Dipole-Dipole Interaction Between Two Individual Rydberg Atoms at a F\"orster Resonance
We measure the angular dependence of the resonant dipole-dipole interaction
between two individual Rydberg atoms with controlled relative positions. By
applying a combination of static electric and magnetic fields on the atoms, we
demonstrate the possibility to isolate a single interaction channel at a
F\"orster resonance, that shows a well-defined angular dependence. We first
identify spectroscopically the F\"orster resonance of choice and we then
perform a direct measurement of the interaction strength between the two atoms
as a function of the angle between the internuclear axis and the quantization
axis. Our results show good agreement with the expected angular dependence
, and represent an important step towards quantum
state engineering in two-dimensional arrays of individual Rydberg atoms.Comment: 5 pages, 4 figure
Direct measurement of the van der Waals interaction between two Rydberg atoms
We report on the direct measurement of the van der Waals interaction between
two isolated, single Rydberg atoms separated by a controlled distance of a few
micrometers. By working in a regime where the single-atom Rabi frequency of the
laser used for excitation to the Rydberg state is comparable to the interaction
energy, we observe a \emph{partial} Rydberg blockade, whereby the
time-dependent populations of the various two-atom states exhibit coherent
oscillations with several frequencies. A quantitative comparison of the data
with a simple model based on the optical Bloch equations allows us to extract
the van der Waals energy, and to observe its characteristic
dependence. The magnitude of the measured coefficient agrees well with an
\emph{ab-initio} theoretical calculation, and we observe its dramatic increase
with the principal quantum number of the Rydberg state. Our results not
only allow to test an important physical law, but also demonstrate a degree of
experimental control which opens new perspectives in quantum information
processing and quantum simulation using long-range interactions between the
atoms.Comment: 4 pages, 3 figures, published versio
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