11,772 research outputs found
Statistical characterization of phenolic-novolak structures
Three statistical methods of general validity are valuable for characterizing any polymer which results from chain polymerization of multifunctional branching monomers linked through bifunctional monomers
Reentrant nu = 1 quantum Hall state in a two-dimensional hole system
We report the observation of a reentrant quantum Hall state at the Landau
level filling factor nu = 1 in a two-dimensional hole system confined to a
35-nm-wide (001) GaAs quantum well. The reentrant behavior is characterized by
a weakening and eventual collapse of the nu = 1 quantum Hall state in the
presence of a parallel magnetic field component B||, followed by a
strengthening and reemergence as B|| is further increased. The robustness of
the nu = 1 quantum Hall state during the transition depends strongly on the
charge distribution symmetry of the quantum well, while the magnitude of B||
needed to invoke the transition increases with the total density of the system
Generation of spin currents and spin densities in systems with reduced symmetry
We show that the spin-current response of a semiconductor crystal to an
external electric field is considerably more complex than previously assumed.
While in systems of high symmetry only the spin-Hall components are allowed, in
systems of lower symmetry other non-spin-Hall components may be present. We
argue that, when spin-orbit interactions are present only in the band
structure, the distinction between intrinsic and extrinsic contributions to the
spin current is not useful. We show that the generation of spin currents and
that of spin densities in an electric field are closely related, and that our
general theory provides a systematic way to distinguish between them in
experiment. We discuss also the meaning of vertex corrections in systems with
spin-orbit interactions.Comment: 4 page
Static inverters which sum a plurality of waves Patent
Describing static inverter with single or multiple phase outpu
Spin precession and alternating spin polarization in spin-3/2 hole systems
The spin density matrix for spin-3/2 hole systems can be decomposed into a
sequence of multipoles which has important higher-order contributions beyond
the ones known for electron systems [R. Winkler, Phys. Rev. B \textbf{70},
125301 (2004)]. We show here that the hole spin polarization and the
higher-order multipoles can precess due to the spin-orbit coupling in the
valence band, yet in the absence of external or effective magnetic fields. Hole
spin precession is important in the context of spin relaxation and offers the
possibility of new device applications. We discuss this precession in the
context of recent experiments and suggest a related experimental setup in which
hole spin precession gives rise to an alternating spin polarization.Comment: 4 pages, 2 figures, to appear in Physical Review Letter
Determination of Gd concentration profile in UO2-Gd2O3 fuel pellets
A transversal mapping of the Gd concentration was measured in UO2-Gd2O3
nuclear fuel pellets by electron paramagnetic resonance spectroscopy (EPR). The
quantification was made from the comparison with a Gd2O3 reference sample. The
nominal concentration in the pellets is UO2: 7.5 % Gd2O3. A concentration
gradient was found, which indicates that the Gd2O3 amount diminishes towards
the edges of the pellets. The concentration varies from (9.3 +/- 0.5)% in the
center to (5.8 +/- 0.3)% in one of the edges. The method was found to be
particularly suitable for the precise mapping of the distribution of Gd3+ ions
in the UO2 matrix.Comment: 10 pages, 5 figures, 2 tables. Submitted to Journal of Nuclear
Material
Spin interference in silicon three-terminal one-dimensional rings
We present the first findings of the spin transistor effect in the Rashba
gate-controlled ring embedded in the p-type self-assembled silicon quantum well
that is prepared on the n-type Si (100) surface. The coherence and phase
sensitivity of the spin-dependent transport of holes are studied by varying the
value of the external magnetic field and the bias voltage that are applied
perpendicularly to the plane of the double-slit ring. Firstly, the amplitude
and phase sensitivity of the 0.7(2e^2/h) feature of the hole quantum
conductance staircase revealed by the quantum point contact inserted in the one
of the arms of the double-slit ring are found to result from the interplay of
the spontaneous spin polarization and the Rashba spin-orbit interaction.
Secondly, the quantum scatterers connected to two one-dimensional leads and the
quantum point contact inserted are shown to define the amplitude and the phase
of the Aharonov-Bohm and the Aharonov-Casher conductance oscillations.Comment: 8 pages, 5 figure
Spin Density Matrix of Spin-3/2 Hole Systems
For hole systems with an effective spin j=3/2, we present an invariant
decomposition of the spin density matrix that can be interpreted as a multipole
expansion. The charge density corresponds to the monopole moment and the spin
polarization due to a magnetic field corresponds to a dipole moment while heavy
hole-light hole splitting can be interpreted as a quadrupole moment. For quasi
two-dimensional hole systems in the presence of an in-plane magnetic field B
the spin polarization is a higher-order effect that is typically much smaller
than one even if the minority spin subband is completely depopulated. On the
other hand, the field B can induce a substantial octupole moment which is a
unique feature of j=3/2 hole systems.Comment: 8 pages, 1 figure, 3 table
The AGN nature of 11 out of 12 Swift/RXTE unidentified sources through optical and X-ray spectroscopy
The Swift Burst Alert Telescope (BAT) is performing a high Galactic latitude
survey in the 14-195 keV band at a flux limit of ~10^{-11} erg cm^{-2} s^{-1},
leading to the discovery of new high energy sources, most of which have not so
far been properly classified. A similar work has also been performed with the
RXTE slew survey leading to the discovery of 68 sources detected above 8 keV,
many of which are still unclassified. Follow-up observations with the Swift
X-ray Telescope (XRT) provide, for many of these objects, source localization
with a positional accuracy of few arcsec, thus allowing the search for optical
counterparts to be more efficient and reliable. We present the results of
optical/X-ray follow-up studies of 11 Swift BAT detections and one AGN detected
in the RXTE Slew Survey, aimed at identifying their counterparts and at
assessing their nature. These data allowed, for the first time, the optical
classification of 8 objects and a distance determination for 3 of them. For
another object, a more refined optical classification than that available in
the literature is also provided. For the remaining sources, optical
spectroscopy provides a characterization of the source near in time to the
X-ray measurement. The sample consists of 6 Seyfert 2 galaxies, 5 Seyferts of
intermediate type 1.2-1.8, and one object of Galactic nature - an Intermediate
Polar (i.e., magnetic) Cataclysmic Variable. Out of the 11 AGNs, 8 (~70%)
including 2 Seyferts of type 1.2 and 1.5, are absorbed with NH > 10^{22}
cm^{-2}. Up to 3 objects could be Compton thick (i.e. NH > 1.5 x 10^{24}
cm^{-2}), but only in one case (Swift J0609.1-8636) does all the observational
evidence strongly suggests this possibility.Comment: 50 pages, including 16 figures and 7 tables. Accepted for publication
in Ap
Mesoscale simulations of polymer dynamics in microchannel flows
The non-equilibrium structural and dynamical properties of flexible polymers
confined in a square microchannel and exposed to a Poiseuille flow are
investigated by mesoscale simulations. The chain length and the flow strength
are systematically varied. Two transport regimes are identified, corresponding
to weak and strong confinement. For strong confinement, the transport
properties are independent of polymer length. The analysis of the long-time
tumbling dynamics of short polymers yields non-periodic motion with a sublinear
dependence on the flow strength. We find distinct differences for
conformational as well as dynamical properties from results obtained for simple
shear flow
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