3,418 research outputs found
Grafted Rods: A Tilting Phase Transition
A tilting phase transition is predicted for systems comprising rod like
molecules which are irreversibly grafted to a flat surface, so that the non
interacting rods are perpendicularly oriented. The transition is controlled by
the grafting density . It occurs as increases as a result of the
interplay between two energies. Tilt is favoured by the van-der-Waals
attraction between the rods. It is opposed by the bending elasticity of the
grafting functionality. The role of temperature is discussed, and the tilting
mechanism is compared to other tilting transitions reported in the literature.Comment: 21 pages, 2 figures, to appear in Journal de Physique I
Scenario for Fractional Quantum Hall Effect in Bulk Isotropic Materials
We investigate the possibility of a strongly correlated Fractional Quantum
Hall (FQH) state in bulk three dimensional isotropic (not layered) materials.
We find that a FQH state can exist at low densities only if it is accompanied
by a staging transition in which the electrons re-organize themselves in
layers, perpendicular to the magnetic field, at distances of order the magnetic
length apart. The Hartree energy associated to the staging transition is
off-set by the correlation Fock energy of the 3D FQH state. We obtain the phase
diagram of bulk electrons in a magnetic field subject to Coulomb interactions
as a function of carrier density and lattice constant. At very low densities,
the 3D FQH state exhibits a transition to a 3D Wigner crystal state stabilized
by phonon correlations
Anti-Fall: A Non-intrusive and Real-time Fall Detector Leveraging CSI from Commodity WiFi Devices
Fall is one of the major health threats and obstacles to independent living
for elders, timely and reliable fall detection is crucial for mitigating the
effects of falls. In this paper, leveraging the fine-grained Channel State
Information (CSI) and multi-antenna setting in commodity WiFi devices, we
design and implement a real-time, non-intrusive, and low-cost indoor fall
detector, called Anti-Fall. For the first time, the CSI phase difference over
two antennas is identified as the salient feature to reliably segment the fall
and fall-like activities, both phase and amplitude information of CSI is then
exploited to accurately separate the fall from other fall-like activities.
Experimental results in two indoor scenarios demonstrate that Anti-Fall
consistently outperforms the state-of-the-art approach WiFall, with 10% higher
detection rate and 10% less false alarm rate on average.Comment: 13 pages,8 figures,corrected version, ICOST conferenc
Broken symmetry, excitons, gapless modes and topological excitations in Trilayer Quantum Hall systems
We study the interlayer coherent incompressible phase in Trilayer Quantum
Hall systems (TLQH) at total filling factor from three
approaches:
Mutual Composite Fermion (MCF), Composite Boson (CB) and wavefunction
approach.
Just like in Bilayer Quantum Hall system, CB approach is superior than
MCF approach in studying TLQH with broken symmetry. The Hall and Hall drag
resistivities are found to be quantized at . Two neutral gapless
modes with linear dispersion relations are identified and the ratio of the two
velocities is close to .
The novel excitation spectra are classified into two classes: Charge neutral
bosonic
2-body bound states and Charge fermionic 3-body bound states.
In general, there are two 2-body Kosterlize-Thouless (KT) transition
temperatures and one 3-body KT transition. The Charge 3-body
fermionic bound states may be the main dissipation source of transport
measurements.
The broken symmetry in terms of algebra is studied. The structure
of excitons and their flowing patterns are given. The coupling between the two
Goldstone modes may lead to the broadening in the zero-bias peak in the
interlayer correlated tunnelings of the TLQH. Several interesting features
unique to TLQH are outlined.
Limitations of the CB approach are also pointed out.Comment: 10 pages, 3 figures, Final version to be published in Phys. Rev.
Microscopic analytical theory of a correlated, two-dimensional N-electron gas in a magnetic field
We present a microscopic, analytical theory describing a confined N-electron
gas in two dimensions subject to an external magnetic field. The number of
electrons N and strength of the electron-electron interaction can be
arbitrarily large, and all Landau levels are included implicitly. A possible
connection with the Integer and Fractional Quantum Hall Effects is proposed.Comment: The revised version contains minor changes to text. To be published
in J. Phys: Condens. Mat
Stacking Faults, Bound States, and Quantum Hall Plateaus in Crystalline Graphite
We analyze the electronic properties of a simple stacking defect in Bernal
graphite. We show that a bound state forms, which disperses as |\bfk-\bfK|^3
in the vicinity of either of the two inequivalent zone corners \bfK. In the
presence of a strong c-axis magnetic field, this bound state develops a Landau
level structure which for low energies behaves as E\nd_n\propto |n B|^{3/2}.
We show that buried stacking faults have observable consequences for surface
spectroscopy, and we discuss the implications for the three-dimensional quantum
Hall effect (3DQHE). We also analyze the Landau level structure and chiral
surface states of rhombohedral graphite, and show that, when doped, it should
exhibit multiple 3DQHE plateaus at modest fields.Comment: 19 page
Tunneling effect on composite fermion pairing state in bilayer quantum Hall system
We discuss the composite fermion pairing state in bilayer quantum Hall
systems. After the evaluation of the range of the inter-layer separation in
which the quantum Hall state is stabilized, we discuss the effect of
inter-layer tunneling on the composite fermion pairing state at \nu=1/2. We
show that there is a cusp at the transition point between the Halperin (3,3,1)
state and the Pfaffian state.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev.
The Geography of Non-formal Manifolds
We show that there exist non-formal compact oriented manifolds of dimension
and with first Betti number if and only if and
, or and . Moreover, we present explicit
examples for each one of these cases.Comment: 8 pages, one reference update
The Hartree-Fock state for the 2DEG at filling factor 1/2 revisited: analytic solution, dynamics and correlation energy
The CDW Hartree-Fock state at half filling and half electron per unit cell is
examined. Firstly, an exact solution in terms of Bloch-like states is
presented. Using this solution we discuss the dynamics near half filling and
show the mass to diverge logarithmically as this filling is approached. We also
show how a uniform density state may be constructed from a linear combination
of two degenerate solutions. Finally we show the second order correction to the
energy to be an order of magnitude larger than that for competing CDW solutions
with one electron per unit cell.Comment: 14 pages, no figures, extended acknowledgements, two new references
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