42,172 research outputs found
Noncommutative D-Brane in Non-Constant NS-NS B Field Background
We show that when the field strength H of the NS-NS B field does not vanish,
the coordinates X and momenta P of an open string endpoints satisfy a set of
mixed commutation relations among themselves. Identifying X and P with the
coordinates and derivatives of the D-brane world volume, we find a new type of
noncommutative spaces which is very different from those associated with a
constant B field background.Comment: 11 pages, Latex, minor modification
The effect of screening long-range Coulomb interactions on the metallic behavior in two-dimensional hole systems
We have developed a technique utilizing a double quantum well heterostructure
that allows us to study the effect of a nearby ground-plane on the metallic
behavior in a GaAs two-dimensional hole system (2DHS) in a single sample and
measurement cool-down, thereby maintaining a constant disorder potential. In
contrast to recent measurements of the effect of ground-plane screening of the
long-range Coulomb interaction in the insulating regime, we find surprisingly
little effect on the metallic behavior when we change the distance between the
2DHS and the nearby ground-plane.Comment: 5 pages, 4 figures, accepted for publication in PR
Thermal stability of titanium nitride for shallow junction solar cell contacts
To demonstrate the thermal stability of titanium nitride as a high-temperature diffusion barrier, the TiN-Ti-Ag metallization scheme has been tested on shallow-junction (~2000 Å) Si solar cells. Electrical measurements on reference samples with the Ti-Ag metallization scheme show serious degradation after a 600 °C, 10-min annealing. With the TiN-Ti-Ag scheme, no degradation of cell performance is observed after the same heat treatment if the TiN layer is >~1700 Å. The glass encapsulation of cells by electrostatic bonding requires such a heat treatment
Efficient Large-scale Trace Checking Using MapReduce
The problem of checking a logged event trace against a temporal logic
specification arises in many practical cases. Unfortunately, known algorithms
for an expressive logic like MTL (Metric Temporal Logic) do not scale with
respect to two crucial dimensions: the length of the trace and the size of the
time interval for which logged events must be buffered to check satisfaction of
the specification. The former issue can be addressed by distributed and
parallel trace checking algorithms that can take advantage of modern cloud
computing and programming frameworks like MapReduce. Still, the latter issue
remains open with current state-of-the-art approaches.
In this paper we address this memory scalability issue by proposing a new
semantics for MTL, called lazy semantics. This semantics can evaluate temporal
formulae and boolean combinations of temporal-only formulae at any arbitrary
time instant. We prove that lazy semantics is more expressive than standard
point-based semantics and that it can be used as a basis for a correct
parametric decomposition of any MTL formula into an equivalent one with
smaller, bounded time intervals. We use lazy semantics to extend our previous
distributed trace checking algorithm for MTL. We evaluate the proposed
algorithm in terms of memory scalability and time/memory tradeoffs.Comment: 13 pages, 8 figure
Comment on ``Dispersion-Independent High-Visibility Quantum Interference ... "
We show in this Comment that the interpretation of experimental data as well
as the theory presented in Atat\"ure et al. [Phys. Rev. Lett. 84, 618 (2000)]
are incorrect and discuss why such a scheme cannot be used to "recover"
high-visibility quantum interference.Comment: Comment on Atat\"ure et al. [Phys. Rev. Lett. 84, 618 (2000)], 2nd
revision, To appear in Phys. Rev. Lett. April, (2001
Branes from a non-Abelian (2,0) tensor multiplet with 3-algebra
In this paper, we study the equations of motion for non-Abelian N=(2,0)
tensor multiplets in six dimensions, which were recently proposed by Lambert
and Papageorgakis. Some equations are regarded as constraint equations. We
employ a loop extension of the Lorentzian three-algebra (3-algebra) and examine
the equations of motion around various solutions of the constraint equations.
The resultant equations take forms that allow Lagrangian descriptions. We find
various (5+d)-dimensional Lagrangians and investigate the relation between them
from the viewpoint of M-theory duality.Comment: 44+1 pages, reference added, typos corrected, and several discussions
added; v3, reference added, many typos corrected, the language improved; v4,
some typos and references corrected, final version to appear in J. Phys.
Non-Sequential Double Ionization is a Completely Classical Photoelectric Effect
We introduce a unified and simplified theory of atomic double ionization. Our
results show that at high laser intensities ( watts/cm)
purely classical correlation is strong enough to account for all of the main
features observed in experiments to date
Evidence for a Supermassive Black Hole in the S0 Galaxy NGC 3245
The S0 galaxy NGC 3245 contains a circumnuclear disk of ionized gas and dust with a radius of 1.1" (110 pc), making it an ideal target for dynamical studies with the Hubble Space Telescope (HST). We have obtained spectra of the nuclear disk with the Space Telescope Imaging Spectrograph, using a 0.2" wide slit at five parallel positions. Measurements of the Hα and [N II] emission lines are used to map out the kinematic structure of the disk in unprecedented detail. The data reveal a rotational velocity field with a steep velocity gradient across the innermost 0.4". We construct dynamical models for a thin gas disk in circular rotation, using HST optical images to map out the gravitational potential due to stars. Our modeling code includes the blurring due to the telescope point-spread function and the nonzero slit width, as well as the instrumental shift in measured wavelength for light entering the slit off-center, so as to simulate the data as closely as possible. The Hα+[N II] surface brightness measured from an HST narrowband image is folded into the models, and we demonstrate that many of the apparent small-scale irregularities in the observed velocity curves are the result of the patchy distribution of emission-line surface brightness. Over most of the disk, the models are able to fit the observed radial velocity curves closely, although there are localized regions within the disk that appear to be kinematically disturbed relative to the overall rotational pattern. The velocity dispersion of [N II] λ6584 rises from σ~50 km/s in the outer disk to ~160 km/s at the nucleus, and most of this line width cannot be attributed to rotational or instrumental broadening. To account for the possible dynamical effect of the intrinsic velocity dispersion in the gas, we also calculate models that include a correction for asymmetric drift. This correction increases the derived black hole mass by 12% but leads to slightly poorer fits to the data. A central dark mass of (2.1+/-0.5)×10^8 Msolar is required for the models to reproduce the steep central velocity gradient. This value for the central mass is consistent with recently discovered correlations between black hole mass and bulge velocity dispersion.Peer reviewe
Quantum transport through a deformable molecular transistor
The linear transport properties of a model molecular transistor with
electron-electron and electron-phonon interactions were investigated
analytically and numerically. The model takes into account phonon modulation of
the electronic energy levels and of the tunnelling barrier between the molecule
and the electrodes. When both effects are present they lead to asymmetries in
the dependence of the conductance on gate voltage. The Kondo effect is observed
in the presence of electron-phonon interactions. There are important
qualitative differences between the cases of weak and strong coupling. In the
first case the standard Kondo effect driven by spin fluctuations occurs. In the
second case, it is driven by charge fluctuations. The Fermi-liquid relation
between the spectral density of the molecule and its charge is altered by
electron-phonon interactions. Remarkably, the relation between the
zero-temperature conductance and the charge remains unchanged. Therefore, there
is perfect transmission in all regimes whenever the average number of electrons
in the molecule is an odd integer.Comment: 9 pages, 6 figure
Oscillatory Tunneling between Quantum Hall Systems
Electron tunneling between quantum Hall systems on the same two dimensional
plane separated by a narrow barrier is studied. We show that in the limit where
inelastic scattering time is much longer than the tunneling time, which can be
achieved in practice, electrons can tunnel back and forth through the barrier
continously, leading to an oscillating current in the absence of external
drives. The oscillatory behavior is dictated by a tunneling gap in the energy
spectrum. We shall discuss ways to generate oscillating currents and the
phenomenon of natural ``dephasing" between the tunneling currents of edge
states. The noise spectra of these junctions are also studied. They contain
singularites reflecting the existence of tunneling gaps as well as the inherent
oscillation in the system. (Figures will be given upon requests).Comment: 20 pages, OS
- …