229 research outputs found
Skyrmions in quantum Hall ferromagnets as spin-waves bound to unbalanced magnetic flux quanta
A microscopic description of (baby)skyrmions in quantum Hall ferromagnets is
derived from a scattering theory of collective (neutral) spin modes by a bare
quasiparticle. We start by mapping the low lying spectrum of spin waves in the
uniform ferromagnet onto that of free moving spin excitons, and then we study
their scattering by the defect of charge. In the presence of this disturbance,
the local spin stiffness varies in space, and we translate it into an
inhomogeneus metric in the Hilbert space supporting the excitons. An attractive
potencial is then required to preserve the symmetry under global spin
rotations, and it traps the excitons around the charged defect. The
quasiparticle now carries a spin texture. Textures containing more than one
exciton are described within a mean-field theory, the interaction among the
excitons being taken into account through a new renormalization of the metric.
The number of excitons actually bound depends on the Zeeman coupling, that
plays the same role as a chemical potencial. For small Zeeman energies, the
defect binds many excitons which condensate. As the bound excitons have a unit
of angular momentum, provided by the quantum of magnetic flux left unbalanced
by the defect of charge, the resulting texture turns out to be a topological
excitation of charge 1. Its energy is that given by the non-linear sigma model
for the ground state in this topological sector, i.e. the texture is a
skyrmion.Comment: 17 pages, 1 figur
Kondo effect in multielectron quantum dots at high magnetic fields
We present a general description of low temperature transport through a
quantum dot with any number of electrons at filling factor . We
provide a general description of a novel Kondo effect which is turned on by
application of an appropriate magnetic field. The spin-flip scattering of
carriers by the quantum dot only involves two states of the scatterer which may
have a large spin. This process is described by spin-flip Hubbard operators,
which change the angular momentum, leading to a Kondo Hamiltonian. We obtain
antiferromagnetic exchange couplings depending on tunneling amplitudes and
correlation effects. Since Kondo temperature has an exponential dependence on
exchange couplings, quantitative variations of the parameters in different
regimes have important experimental consequences. In particular, we discuss the
{\it chess board} aspect of the experimental conductance when represented in a
grey scale as a function of both the magnetic field and the gate potential
affecting the quantum dot
Dynamics of the Compact, Ferromagnetic \nu=1 Edge
We consider the edge dynamics of a compact, fully spin polarized state at
filling factor . We show that there are two sets of collective
excitations localized near the edge: the much studied, gapless, edge
magnetoplasmon but also an additional edge spin wave that splits off below the
bulk spin wave continuum. We show that both of these excitations can soften at
finite wave-vectors as the potential confining the system is softened, thereby
leading to edge reconstruction by spin texture or charge density wave
formation. We note that a commonly employed model of the edge confining
potential is non-generic in that it systematically underestimates the texturing
instability.Comment: 13 pages, 7 figures, Revte
Spin-isospin textured excitations in a double layer at filling factor
We study the charged excitations of a double layer at filling factor 2 in the
ferromagnetic regime. In a wide range of Zeeman and tunneling splittings we
find that the low energy charged excitations are spin-isospin textures with the
charge mostly located in one of the layers. As tunneling increases, the parent
spin texture in one layer becomes larger and it induces, in the other layer, a
shadow spin texture antiferromagnetically coupled to the parent texture. These
new quasiparticles should be observable by measuring the strong dependence of
its spin on tunneling and Zeeman couplings.Comment: 4 pages, 4 figure
Edge Theories for Polarized Quantum Hall States
Starting from recently proposed bosonic mean field theories for fully and
partially polarized quantum Hall states, we construct corresponding effective
low energy theories for the edge modes. The requirements of gauge symmetry and
invariance under global O(3) spin rotations, broken only by a Zeeman coupling,
imply boundary conditions that allow for edge spin waves. In the generic case,
these modes are chiral, and the spin stiffness differs from that in the bulk.
For the case of a fully polarized state, our results agree with
previous Hartree-Fock calculations.Comment: 15 pages (number of pages has been reduced by typesetting in RevTeX);
2 references adde
Wigner Crystalline Edges in nu < 1 Quantum Dots
We investigate the edge reconstruction phenomenon believed to occur in
quantum dots in the quantum Hall regime when the filling fraction is nu < 1.
Our approach involves the examination of large dots (< 40 electrons) using a
partial diagonalization technique in which the occupancies of the deep interior
orbitals are frozen. To interpret the results of this calculation, we evaluate
the overlap between the diagonalized ground state and a set of trial
wavefunctions which we call projected necklace (PN) states. A PN state is
simply the angular momentum projection of a maximum density droplet surrounded
by a ring of localized electrons. Our calculations reveal that PN states have
up to 99% overlap with the diagonalized ground states, and are lower in energy
than the states identified in Chamon and Wen's study of the edge
reconstruction.Comment: 8 pages, 8 figures, to be published in Phys. Rev.
Real-World Delivery of Rucaparib to Patients with Ovarian Cancer: Recommendations Based on an Integrated Safety Analysis of ARIEL2 and Study 10
Treatment options for women with recurrent ovarian cancer who have received two or more prior lines of chemotherapy have recently expanded with the U.S. Food and Drug Administration (FDA) and European Commission (EC) approvals of the poly(ADPâribose) polymerase (PARP) inhibitor rucaparib. As more oncologists begin to use rucaparib and other PARP inhibitors as part of routine clinical practice, awareness of possible side effects and how to adequately manage toxicities is crucial. In this review, we summarize the safety and tolerability of rucaparib reported in an integrated safety analysis that supported the FDA's initial approval of rucaparib in the treatment setting. Additionally, drawing on clinical data and our personal experience with rucaparib, we provide our recommendations on the management of common side effects observed with rucaparib, including anemia, blood creatinine elevations, alanine aminotransferase and aspartate aminotransferase elevations, thrombocytopenia, gastrointestinalârelated events (e.g., nausea, vomiting), and asthenia and fatigue. These side effects, many of which appear to be class effects of PARP inhibitors, are often selfâlimiting and can be managed with adequate interventions such as treatment interruption and/or dose reduction and the use of supportive therapies. Supportive therapies may include blood transfusions for patients with anemia, prophylactic medications to prevent nausea and vomiting, or behavioral interventions to mitigate fatigue. Understanding and appropriate management of potential side effects associated with rucaparib may allow patients with ovarian cancer to continue to benefit from rucaparib treatment.
Implications for Practice.
Rucaparib was recently approved in the U.S. and European Union for use as treatment or maintenance for recurrent ovarian cancer. This review focuses on the safety and tolerability of rucaparib in the treatment setting. Similar side effects are observed in the maintenance setting. Drawing on the authorsâ clinical experience with rucaparib, rucaparib prescribing information, and published supportive cancer care guidelines, this review discusses how to optimally manage common rucaparibâassociated side effects in patients with advanced ovarian cancer in the realâworld oncology setting. Adequate management of such side effects is crucial for allowing patients with ovarian cancer to remain on treatment to receive optimal efficacy benefit
Pushmepullyou: An efficient micro-swimmer
The swimming of a pair of spherical bladders that change their volumes and
mutual distance is efficient at low Reynolds numbers and is superior to other
models of artificial swimmers. The change of shape resembles the wriggling
motion known as {\it metaboly} of certain protozoa.Comment: Minor rephrasing and changes in style; short explanations adde
Baryon Asymmetry, Dark Matter and Quantum Chromodynamics
We propose a novel scenario to explain the observed cosmological asymmetry
between matter and antimatter, based on nonperturbative QCD physics. This
scenario relies on a mechanism of separation of quarks and antiquarks in two
coexisting phases at the end of the cosmological QCD phase transition: ordinary
hadrons (and antihadrons), along with massive lumps (and antilumps) of novel
color superconducting phase. The latter would serve as the cosmological cold
dark matter. In certain conditions the separation of charge is C and CP
asymmetric and can leave a net excess of hadrons over antihadrons in the
conventional phase, even if the visible universe is globally baryon symmetric
. In this case an equal, but negative, overall baryon charge must be
hidden in the lumps of novel phase. Due to the small volume occupied by these
dense lumps/antilumps of color superconducting phase and the specific features
of their interaction with "normal" matter in hadronic phase, this scenario does
not contradict the current phenomenological constrains on presence of
antimatter in the visible universe. Moreover, in this scenario the observed
cosmological ratio within an order of magnitude
finds a natural explanation, as both contributions to originated from
the same physics during the QCD phase transition. The baryon to entropy ratio
would also be a natural outcome, fixed by the
temperature T_f \simlt T_{QCD} at which the separation of phases is
completed.Comment: New paragraph added in subsection II.D; version to appear in Physical
Review
Parameter in 2 Color QCD at Finite Baryon and Isospin Density
We use 2-color QCD as a model to study the effects of simultaneous presence
of the so-called parameter, chemical potentials for baryon number,
and for isospin charge, . We pay special attention to ,
, dependence of different vacuum condensates, including chiral
and diquark condensates, as well as the gluon condensate, , and the
topological susceptibility. We find that two phase transitions of the second
order will occur when relaxes from to , if
is of order of the pion mass. We demonstrate that the transition to the
superfluid phase at occurs at a much lower chemical potential
than at . We also show that the strong dependence present
near in vacuum (Dashen's phenomenon), becomes smoothed out in
the superfluid phase. Finally, we comment on the relevance of this study for
the real world with N_c=3
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