11,807 research outputs found
A tentative 4- isomeric state in Sr-98
Annual Report 2001, Institut fuer Kernchemie,
Johannes-Gutenberg-Universitaet, Mainz, GermanyComment: 3 pages, 1 figur
Factorizing twists and R-matrices for representations of the quantum affine algebra U_q(\hat sl_2)
We calculate factorizing twists in evaluation representations of the quantum
affine algebra U_q(\hat sl_2). From the factorizing twists we derive a
representation independent expression of the R-matrices of U_q(\hat sl_2).
Comparing with the corresponding quantities for the Yangian Y(sl_2), it is
shown that the U_q(\hat sl_2) results can be obtained by `replacing numbers by
q-numbers'. Conversely, the limit q -> 1 exists in representations of U_q(\hat
sl_2) and both the factorizing twists and the R-matrices of the Yangian Y(sl_2)
are recovered in this limit.Comment: 19 pages, LaTe
Explicit solution of the linearized Einstein equations in TT gauge for all multipoles
We write out the explicit form of the metric for a linearized gravitational
wave in the transverse-traceless gauge for any multipole, thus generalizing the
well-known quadrupole solution of Teukolsky. The solution is derived using the
generalized Regge-Wheeler-Zerilli formalism developed by Sarbach and Tiglio.Comment: 9 pages. Minor corrections, updated references. Final version to
appear in Class. Quantum Gra
Competition Between Fractional Quantum Hall Liquid, Bubble and Wigner Crystal Phases in the Third Landau Level
Magnetotransport measurements were performed in a ultra-high mobility
GaAs/AlGaAs quantum well of density . The
temperature dependence of the magnetoresistance was studied in detail
in the vicinity of . In particular, we discovered new minima in
at filling factor and , but only at
intermediate temperatures mK. We interpret these as
evidence for a fractional quantum Hall liquid forming in the N=2 Landau level
and competing with bubble and Wigner crystal phases favored at lower
temperatures. Our data suggest that a magnetically driven insulator-insulator
quantum phase transition occurs between the bubble and Wigner crystal phases at
T=0.Comment: Phys. Rev. Lett.93 266804 (2004
Evidence for Skyrmion crystallization from NMR relaxation experiments
A resistively detected NMR technique was used to probe the two-dimensional
electron gas in a GaAs/AlGaAs quantum well. The spin-lattice relaxation rate
was extracted at near complete filling of the first Landau level by
electrons. The nuclear spin of As is found to relax much more
efficiently with and when a well developed quantum Hall state with
occurs. The data show a remarkable correlation between the
nuclear spin relaxation and localization. This suggests that the magnetic
ground state near complete filling of the first Landau level may contain a
lattice of topological spin texture, i.e. a Skyrmion crystal
Matrix-free calcium in isolated chromaffin vesicles
Isolated secretory vesicles from bovine adrenal medulla contain 80 nmol of Ca2+ and 25 nmol
of Mg2+ per milligram of protein. As determined with a Ca2+-selective electrode, a further accumulation
of about 160 nmol of Ca2+/mg of protein can be attained upon addition of the Ca2+ ionophore A23187.
During this process protons are released from the vesicles, in exchange for Ca2+ ions, as indicated by the
decrease of the pH in the incubation medium or the release of 9-aminoacridine previously taken up by the
vesicles. Intravesicular Mg2+ is not released from the vesicles by A23 187, as determined by atomic emission
spectroscopy. In the presence of N H Q , which causes the collapse of the secretory vesicle transmembrane
proton gradient (ApH), Ca2+ uptake decreases. Under these conditions A23 187-mediated influx of Ca2+
and efflux of H+ cease at Ca2+ concentrations of about 4 pM. Below this concentration Ca2+ is even released
from the vesicles. At the Ca2+ concentration at which no net flux of ions occurs the intravesicular matrix
free Ca2+ equals the extravesicular free Ca2+. In the absence of NH4C1 we determined an intravesicular
pH of 6.2. Under these conditions the Ca2+ influx ceases around 0.15 pM. From this value and the known
pH across the vesicular membrane an intravesicular matrix free Ca2+ concentration of about 24 pM was
calculated. This is within the same order of magnitude as the concentration of free Ca2+ in the vesicles
determined in the presence of NH4C1. Calculation of the total Ca2+ present in the secretory vesicles gives
an apparent intravesicular Ca2+ concentration of 40 mM, which is a factor of lo4 higher than the free
intravesicular concentration of Ca2+. It can be concluded, therefore, that the concentration gradient of free
Ca2+ across the secretory vesicle membrane in the intact chromaffin cells is probably small, which implies
that less energy is required to accumulate and maintain Ca2+ within the vesicles than was previously
anticipated
Localization Transition in a Ballistic Quantum Wire
The many-body wave-function of an interacting one-dimensional electron system
is probed, focusing on the low-density, strong interaction regime. The
properties of the wave-function are determined using tunneling between two
long, clean, parallel quantum wires in a GaAs/AlGaAs heterostructure, allowing
for gate-controlled electron density. As electron density is lowered to a
critical value the many-body state abruptly changes from an extended state with
a well-defined momentum to a localized state with a wide range of momentum
components. The signature of the localized states appears as discrete tunneling
features at resonant gate-voltages, corresponding to the depletion of single
electrons and showing Coulomb-blockade behavior. Typically 5-10 such features
appear, where the one-electron state has a single-lobed momentum distribution,
and the few-electron states have double-lobed distributions with peaks at . A theoretical model suggests that for a small number of particles (N<6),
the observed state is a mixture of ground and thermally excited spin states.Comment: 10 pages, 4 figures, 1 tabl
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