276 research outputs found
Quantum Lifetime of Two-Dimensional Holes
The quantum lifetime of two-dimensional holes in a GaAs/AlGaAs double quantum
well is determined via tunneling spectroscopy. At low temperatures the lifetime
is limited by impurity scattering but at higher temperatures hole-hole Coulomb
scattering dominates. Our results are consistent with Fermi liquid theory, at
least up to r_s = 11. At the highest temperatures the measured width of the
hole spectral function becomes comparable to the Fermi energy. A new,
tunneling-spectroscopic, method for determining the in-plane effective mass of
the holes is also demonstrated.Comment: 5 pages, 4 figures. Published versio
Exact Renormalization Group for O(4) Gauged Supergravity
We study exact renormalization group (RG) in O(4) gauged supergravity using
the effective average action formalism. The nonperturbative RG equations for
cosmological and newtonian coupling constants are found. It is shown the
existence of (nonstable) fixed point of these equations. The solution of RG
equation for newtonian coupling constant is qualitatively the same as in
Einstein gravity(i.e. it is growing at large distances).Comment: Latex file, 11 page
Metallothioneins pattern during ontogeny of coastal dolphin, Pontoporia blainvillei, from Argentina
Metallothioneins are signals of metal exposure and widely used in biomonitoring. Franciscana dolphin is an endemic cetacean from the Southwestern Atlantic Ocean, classified as Vulnerable A3d by the IUCN. Metallothionein, copper and zinc in Franciscana were assessed in two geographic groups; one inhabits La Plata River estuary, anthropogenically impacted, and the other inhabits marine coastal ecosystems, with negligible pollution. Despite the environment, hepatic and renal MT concentrations were similar, but there was a declining trend from early to later developmental stages. Metallothionein K/L, Cu and Zn levels corresponded to normal reported ranges. MT was not related with Cd. Fetal concentrations were higher than its mother. These results and the health status of dolphins are suggesting that MT correspond to physiological ranges for the species, and they are closely to homeostasis of Zn and Cu, according to its ontogenetic changes. The information constitutes the first MT information on Franciscana dolphin and can be considered as baseline for the species conservation
New collective states of 2D electrons in high Landau levels
A brief summary of the emerging evidence for a new class of collective states
of two-dimensional electrons in partially occupied excited Landau levels is
presented. Among the most dramatic phenomena described are the large
anisotropies of the resistivity observed at very low temperatures near
half-filling of the third and higher Landau levels and the non-linear character
of the re-entrant integer quantized Hall states in the flanks of the same
levels. The degree to which these findings support recent theoretical
predictions of charge density wave ground states is discussed and a preliminary
comparison to recent transport theories is made.Comment: To be published in Physica E, as part of the proceedings of the 11th
International Winterschool on New Developments in Solid State Physics held in
Mauterndorf, Austria, February, 2000. 25 pages and 9 figures in a single pdf
fil
Nonlocal charges of T-dual strings
We obtain sets of infinite number of conserved nonlocal charges of strings in
a flat space and pp-wave backgrounds, and compare them before and after
T-duality transformation. In the flat background the set of nonlocal charges is
the same before and after the T-duality transformation with interchanging odd
and even-order charges. In the IIB pp-wave background an infinite number of
nonlocal charges are independent, contrast to that in a flat background only
the zero-th and first order charges are independent. In the IIA pp-wave
background, which is the T-dualized compactified IIB pp-wave background, the
zero-th order charges are included as a part of the set of nonlocal charges in
the IIB background. To make this correspondence complete a variable conjugate
to the winding number is introduced as a Lagrange multiplier in the IIB action
a la Buscher's transformation.Comment: 23 pages, 1 figur
The Classical Exchange Algebra of AdS5 x S5 String Theory
The classical exchange algebra satisfied by the monodromy matrix of AdS5 x S5
string theory in the Green-Schwarz formulation is determined by using a
first-order Hamiltonian formulation and by adding to the Bena-Polchinski-Roiban
Lax connection terms proportional to constraints. This enables in particular to
show that the conserved charges of this theory are in involution. This result
is obtained for a general world-sheet metric. The same exchange algebra is
obtained within the pure spinor description of AdS5 x S5 string theory. These
results are compared to the one obtained by A. Mikhailov and S. Schaefer-Nameki
for the pure spinor formulation.Comment: 37 pages; v2: Result on Jacobi identity and Yang-Baxter equation
added in section 3.3; v3: References added; v4: Comparison with ref [12]
clarified in section 3.
Quantum Gravitational Corrections to the Real Klein-Gordon Field in the Presence of a Minimal Length
The (D+1)-dimensional -two-parameter Lorentz-covariant
deformed algebra introduced by Quesne and Tkachuk [C. Quesne and V. M. Tkachuk,
J. Phys. A: Math. Gen. \textbf {39}, 10909 (2006).], leads to a nonzero minimal
uncertainty in position (minimal length). The Klein-Gordon equation in a
(3+1)-dimensional space-time described by Quesne-Tkachuk Lorentz-covariant
deformed algebra is studied in the case where up to first order
over deformation parameter . It is shown that the modified Klein-Gordon
equation which contains fourth-order derivative of the wave function describes
two massive particles with different masses. We have shown that physically
acceptable mass states can only exist for which
leads to an isotropic minimal length in the interval . Finally, we have shown that the above estimation of
minimal length is in good agreement with the results obtained in previous
investigations.Comment: 10 pages, no figur
Holocene black carbon in Antarctica paralleled Southern Hemisphere climate
Black carbon (BC) and other biomass-burning (BB) aerosols are critical components of climate forcing but quantification, predictive climate modeling, and policy decisions have been hampered by limited understanding of the climate drivers of BB and by the lack of long-term records. Prior modeling studies suggested that increased Northern Hemisphere anthropogenic BC emissions increased recent temperatures and regional precipitation, including a northward shift in the Inter-Tropical Convergence Zone (ITCZ). Two Antarctic ice cores were analyzed for BC and the longest record shows that the highest BC deposition during the Holocene occurred ~8-6k years before present in a period of relatively high austral burning season and low growing season insolation. Atmospheric transport modeling suggests South America (SA) as the dominant source of modern Antarctic BC and, consistent with the ice-core record, climate model experiments using mid-Holocene and preindustrial insolation simulate comparable increases in carbon loss due to fires in SA during the mid-Holocene. SA climate proxies document a northward shifted ITCZ and weakened SA Summer Monsoon (SASM) during this period, with associated impacts on hydroclimate and burning. A second Antarctic ice core spanning the last 2.5k years documents similar linkages between hydroclimate and BC, with the lowest deposition during the Little Ice Age characterized by a southerly shifted ITCZ and strengthened SASM. These new results indicate that insolation-driven changes in SA hydroclimate and BB, likely linked to the position of the ITCZ, modulated Antarctic BC deposition during most of the Holocene and suggests connections and feedbacks between future BC emissions and hydroclimate.
Plain Language Summary
Future anthropogenic-driven climate change may impact wildfires, yet predicting future changes is hampered by few long-term records of natural wildfires, particularly for the Southern Hemisphere. We document large variations in black carbon deposition during the past 14,000 years from an Antarctic ice core. Black carbon is a tracer for wildfires and a significant climate forcing agent. We show that black carbon in Antarctica closely followed Southern Hemisphere hydroclimate and strength of the South American Summer Monsoon. With future predictions showing significant low-latitude changes in precipitation under increased emissions, the climate-fire linkages presented here suggest future changes South American biomass burning
Resonant Enhancement of Inelastic Light Scattering in the Fractional Quantum Hall Regime at
Strong resonant enhancements of inelastic light scattering from the long
wavelength inter-Landau level magnetoplasmon and the intra-Landau level spin
wave excitations are seen for the fractional quantum Hall state at .
The energies of the sharp peaks (FWHM ) in the profiles of
resonant enhancement of inelastic light scattering intensities coincide with
the energies of photoluminescence bands assigned to negatively charged exciton
recombination. To interpret the observed enhancement profiles, we propose
three-step light scattering mechanisms in which the intermediate resonant
transitions are to states with charged excitonic excitations.Comment: 5 pages, 5 figure
Gain in a quantum wire laser of high uniformity
A multi-quantum wire laser operating in the 1-D ground state has been
achieved in a very high uniformity structure that shows free exciton emission
with unprecedented narrow width and low lasing threshold. Under optical pumping
the spontaneous emission evolves from a sharp free exciton peak to a
red-shifted broad band. The lasing photon energy occurs about 5 meV below the
free exciton. The observed shift excludes free excitons in lasing and our
results show that Coulomb interactions in the 1-D electron-hole system shift
the spontaneous emission and play significant roles in laser gain.Comment: 4 pages, 4 figures, prepared by RevTe
- …