808 research outputs found
Beyond National Institutions: Labor Taxes and Regional Unemployment in Italy
By focusing on the Italian experience, we ask whether the relationship
between labor taxes and unemployment varies across regions. In spite of
similar national labor market institutions, we show that this relationship is
significantly stronger in the highly industrialized North than in the underdeveloped
South, where unemployment is much higher. An important
source of variation in the regional responsiveness of unemployment
originates from the fact that regional gross wages in the North increase
more than in the South in response to a hike in labor taxes. Regional wage
setting affects regional employment (and unemployment) both directly and
indirectly, via its impact on regional profits and the capital stock
Root photosynthesis prevents hypoxia in the epiphytic orchid Phalaenopsis
Orchids (Phalaenopsis spp.) growing in tropical and subtropical regions are epiphytes. As such, they grow on trees with the root system utilised to anchor themselves to tree branches. These roots are highly specialised, display a large diameter and are often green, suggesting the ability to carry out photosynthesis. However, the role of photosynthesis in orchid roots is controversial. Orchids that are leafless can photosynthesise in their roots, thus indicating that some orchid roots carry out photosynthesis in a similar manner to leaves. However, the primary site of photosynthesis in orchids are in their leaves, and the roots of epiphytic orchids may mostly conduct internal refixation of respiratory CO2. Besides contributing to the overall carbon metabolism of orchid plants, oxygen produced through root photosynthesis may also be important by alleviating potential root hypoxia. The bulky tissue of most epiphytic orchid roots suggests that oxygen diffusion in these roots can be limited. Here, we demonstrate that the bulky roots of a widely commercially cultivated orchid belonging to the genus Phalaenopsis are hypoxic in the dark. These roots are photosynthetically active and produce oxygen when exposed to light, thus mitigating root hypoxia
How to measure the Bogoliubov quasiparticle amplitudes in a trapped condensate
We propose an experiment, based on two consecutive Bragg pulses, to measure
the momentum distribution of quasiparticle excitations in a trapped Bose gas at
low temperature. With the first pulse one generates a bunch of excitations
carrying momentum , whose Doppler line is measured by the second pulse. We
show that this experiment can provide direct access to the amplitudes
and characterizing the Bogoliubov transformations from particles to
quasiparticles. We simulate the behavior of the nonuniform gas by numerically
solving the time dependent Gross-Pitaevskii equation.Comment: 12 pages, 4 figures include
Bogoliubov spectrum and Bragg spectroscopy of elongated Bose-Einstein condensates
The behavior of the momentum transferred to a trapped Bose-Einstein
condensate by a two-photon Bragg pulse reflects the structure of the underlying
Bogoliubov spectrum. In elongated condensates, axial phonons with different
number of radial nodes give rise to a multibranch spectrum which can be
resolved in Bragg spectroscopy, as shown by Steinhauer {\it et al.} [Phys. Rev.
Lett. {\bf 90}, 060404 (2003)]. Here we present a detailed theoretical analysis
of this process. We calculate the momentum transferred by numerically solving
the time dependent Gross-Pitaevskii equation. In the case of a cylindrical
condensate, we compare the results with those obtained by linearizing the
Gross-Pitaevskii equation and using a quasiparticle projection method. This
analysis shows how the axial-phonon branches affect the momentum transfer, in
agreement with our previous interpretation of the observed data. We also
discuss the applicability of this type of spectroscopy to typical available
condensates, as well as the role of nonlinear effects.Comment: 8 pages, 7 figures, minor changes, typos correcte
Experimental observation of the Bogoliubov transformation for a Bose-Einstein condensed gas
Phonons with wavevector were optically imprinted into a
Bose-Einstein condensate. Their momentum distribution was analyzed using Bragg
spectroscopy with a high momentum transfer. The wavefunction of the phonons was
shown to be a superposition of +q and -q free particle momentum states, in
agreement with the Bogoliubov quasiparticle picture.Comment: 4 pages, 3 figures, please take postscript version for the best
version of Fig
Critical generalized inverse participation ratio distributions
The system size dependence of the fluctuations in generalized inverse
participation ratios (IPR's) at criticality is investigated
numerically. The variances of the IPR logarithms are found to be
scale-invariant at the macroscopic limit. The finite size corrections to the
variances decay algebraically with nontrivial exponents, which depend on the
Hamiltonian symmetry and the dimensionality. The large- dependence of the
asymptotic values of the variances behaves as according to theoretical
estimates. These results ensure the self-averaging of the corresponding
generalized dimensions.Comment: RevTex4, 5 pages, 4 .eps figures, to be published in Phys. Rev.
Biochemical characterization of a cyanobactin arginine-N-prenylase from the autumnalamide biosynthetic pathway
Cyanobactins are linear and cyclic post-translationally modified peptides. Here we show that the prenyl-D-Arg-containing autum-nalamide A is a member of the cyanobactin family. Biochemical assays demonstrate that the AutF prenyltransferase targets the guanidinium moiety in arginine and homoarginine and is a useful tool for biotechnological applications.Peer reviewe
Bloch oscillations and mean-field effects of Bose-Einstein condensates in 1-D optical lattices
We have loaded Bose-Einstein condensates into one-dimensional, off-resonant
optical lattices and accelerated them by chirping the frequency difference
between the two lattice beams. For small values of the lattice well-depth,
Bloch oscillations were observed. Reducing the potential depth further,
Landau-Zener tunneling out of the lowest lattice band, leading to a breakdown
of the oscillations, was also studied and used as a probe for the effective
potential resulting from mean-field interactions as predicted by Choi and Niu
[Phys. Rev. Lett. {\bf 82}, 2022 (1999)]. The effective potential was measured
for various condensate densities and trap geometries, yielding good qualitative
agreement with theoretical calculations.Comment: 5 pages, 3 figures; accepted for publication in Physical Review
Letter
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