372 research outputs found
Constitutional Commitment to Social Security and Welfare Policy
In this paper we explore whether the constitutional text has any practical meaning for welfare policy. To examine the empirical importance of the constitution, we first constructed for 68 countries an index of constitutional commitment to social security in five areas: Old Age, disability and survivors (OASDI), Unemployment, Sickness, Work Injury and Income Support. We find that the extent and coverage of social security laws is not sensitive to the degree of constitutional commitment to social security.Welfare Policy, Social Security, Constitution, Legal Origins
Social Identity and Voter Turnout
This paper uses the unique social structure of Arab communities to examine the effect of social identity on voter turnout. We first show that voters are more likely to vote for a candidate who shares their social group (signified by last name) as compared to other candidates. Using last name as a measure of group affiliation, we find an inverted U-shaped relationship between group size and voter turnout which is consistent with theoretical models that reconcile the paradox of voting by incorporating groups behavior.voter turnout, paradox of voting, social identity, local elections
Atom Interferometry in a Vertical Optical Lattice
We have studied the interference of degenerate quantum gases in a vertical
optical lattice. The coherence of the atoms leads to an interference pattern
when the atoms are released from the lattice. This has been shown for a
Bose-Einstein condensate in early experiments. Here we demonstrate that also
for fermions an interference pattern can be observed provided that the momentum
distribution is smaller then the recoil momentum of the lattice. Special
attention is given to the role of interactions which wash out the interference
pattern for a condensate but do not affect a spin polarized Fermi gas, where
collisions at ultra cold temperatures are forbidden. Comparing the interference
of the two quantum gases we find a clear superiority of fermions for trapped
atom interferometry.Comment: 10 pages, 5 figure
Impact de la télévision par satellite sur une population étrangère en France : cas des immigrés maghrébins (L\u27)
An optical lattice on an atom chip
Optical dipole traps and atom chips are two very powerful tools for the
quantum manipulation of neutral atoms. We demonstrate that both methods can be
combined by creating an optical lattice potential on an atom chip. A
red-detuned laser beam is retro-reflected using the atom chip surface as a
high-quality mirror, generating a vertical array of purely optical oblate
traps. We load thermal atoms from the chip into the lattice and observe cooling
into the two-dimensional regime where the thermal energy is smaller than a
quantum of transverse excitation. Using a chip-generated Bose-Einstein
condensate, we demonstrate coherent Bloch oscillations in the lattice.Comment: 3 pages, 2 figure
Dipole and Bloch oscillations of cold atoms in a parabolic lattice
The paper studies the dynamics of a Bose-Einstein condensate loaded into a 1D
parabolic optical lattice, and excited by a sudden shift of the lattice center.
Depending on the magnitude of the initial shift, the condensate undergoes
either dipole or Bloch oscillations. The effects of dephasing and of atom-atom
interactions on these oscillations are discussed.Comment: 3 pages, to appear in proceeding of LPHYS'05 conference (July 4-8,
2005, Kyoto, Japan
Conduction of Ultracold Fermions Through a Mesoscopic Channel
In a mesoscopic conductor electric resistance is detected even if the device
is defect-free. We engineer and study a cold-atom analog of a mesoscopic
conductor. It consists of a narrow channel connecting two macroscopic
reservoirs of fermions that can be switched from ballistic to diffusive. We
induce a current through the channel and find ohmic conduction, even for a
ballistic channel. An analysis of in-situ density distributions shows that in
the ballistic case the chemical potential drop occurs at the entrance and exit
of the channel, revealing the presence of contact resistance. In contrast, a
diffusive channel with disorder displays a chemical potential drop spread over
the whole channel. Our approach opens the way towards quantum simulation of
mesoscopic devices with quantum gases
Gravity-induced Wannier-Stark ladder in an optical lattice
We discuss the dynamics of ultracold atoms in an optical potential
accelerated by gravity. The positions and widths of the Wannier-Stark ladder of
resonances are obtained as metastable states. The metastable Wannier-Bloch
states oscillate in a single band with the Bloch period. The width of the
resonance gives the rate transition to the continuum.Comment: 5 pages + 8 eps figures, submitted to Phys. Rev.
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