30,698 research outputs found
Magnetic Excitations of Stripes and Checkerboards in the Cuprates
We discuss the magnetic excitations of well-ordered stripe and checkerboard
phases, including the high energy magnetic excitations of recent interest and
possible connections to the "resonance peak" in cuprate superconductors. Using
a suitably parametrized Heisenberg model and spin wave theory, we study a
variety of magnetically ordered configurations, including vertical and diagonal
site- and bond-centered stripes and simple checkerboards. We calculate the
expected neutron scattering intensities as a function of energy and momentum.
At zero frequency, the satellite peaks of even square-wave stripes are
suppressed by as much as a factor of 34 below the intensity of the main
incommensurate peaks. We further find that at low energy, spin wave cones may
not always be resolvable experimentally. Rather, the intensity as a function of
position around the cone depends strongly on the coupling across the stripe
domain walls. At intermediate energy, we find a saddlepoint at for
a range of couplings, and discuss its possible connection to the "resonance
peak" observed in neutron scattering experiments on cuprate superconductors. At
high energy, various structures are possible as a function of coupling strength
and configuration, including a high energy square-shaped continuum originally
attributed to the quantum excitations of spin ladders. On the other hand, we
find that simple checkerboard patterns are inconsistent with experimental
results from neutron scattering.Comment: 11 pages, 13 figures, for high-res figs, see
http://physics.bu.edu/~yaodx/spinwave2/spinw2.htm
Magnetic Excitations of Stripes Near a Quantum Critical Point
We calculate the dynamical spin structure factor of spin waves for weakly
coupled stripes. At low energy, the spin wave cone intensity is strongly peaked
on the inner branches. As energy is increased, there is a saddlepoint followed
by a square-shaped continuum rotated 45 degree from the low energy peaks. This
is reminiscent of recent high energy neutron scattering data on the cuprates.
The similarity at high energy between this semiclassical treatment and quantum
fluctuations in spin ladders may be attributed to the proximity of a quantum
critical point with a small critical exponent .Comment: 4+ pages, 5 figures, published versio
Universal Scaling of the Neel Temperature of Near-Quantum-Critical Quasi-Two-Dimensional Heisenberg Antiferromagnets
We use a quantum Monte Carlo method to calculate the Neel temperature T_N of
weakly coupled S=1/2 Heisenberg antiferromagnetic layers consisting of coupled
ladders. This system can be tuned to different two-dimensional scaling regimes
for T > T_N. In a single-layer mean-field theory,
\chi_s^{2D}(T_N)=(z_2J')^{-1}, where \chi_s^{2D} is the exact staggered
susceptibility of an isolated layer, J' the inter-layer coupling, and z_2=2 the
layer coordination number. With a renormalized z_2, we find that this
relationship applies not only in the renormalized-classical regime, as shown
previously, but also in the quantum-critical regime and part of the
quantum-disordered regime. The renormalization is nearly constant; k_2 ~
0.65-0.70. We also study other universal scaling functions.Comment: 4 pages, 4 figure
Twisted quantum affine algebras and solutions to the Yang-Baxter equation
We construct spectral parameter dependent R-matrices for the quantized
enveloping algebras of twisted affine Lie algebras. These give new solutions to
the spectral parameter dependent quantum Yang-Baxter equation.Comment: Latex 24 pages. Misprints in eqs.(4.26) and (A.11) are corrected,
cosmetic changes from "affine Kac-Moody algebras" to "affine Lie algebras"
are made throughout the paper following a suggestion by M.B. Halpern, and one
reference is adde
Synchonisation of Resonances with Thresholds
The mechanism by which a resonance may be attracted to a sharp threshold is
described with several examples. It involves a threshold cusp interfering
constructively with either or both (i) a resonance produced via confinement,
(ii) attractive t- and u-channel exchanges. More generally, it is suggested
that resonances are eigenstates generated by mixing between confined states and
long-range meson and baryon exchanges.Comment: 8 pages, 4 figures. For Meson08 Proceedings. One important typo
correcte
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Two novel nonlinear companding schemes with iterative receiver to reduce PAPR in multi-carrier modulation systems
Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion
Three-band tight-binding model for monolayers of group-VIB transition metal dichalcogenides
published_or_final_versio
Local anaesthetic bupivacaine induced ovarian and prostate cancer apoptotic cell death and underlying mechanisms in vitro
Retrospective studies indicate that the use of regional anesthesia can reduce cancer recurrence after surgery which could be due to ranging from immune function preservation to direct molecular mechanisms. This study was to investigate the effects of bupivacaine on ovarian and prostate cancer cell biology and the underlying molecular mechanisms. Cell viability, proliferation and migration of ovarian carcinoma (SKOV-3) and prostate carcinoma (PC-3) were examined following treatment with bupivacaine. Cleaved caspase 3, 8 and 9, and GSK-3β, pGSK-3β(tyr216) and pGSK-3β(ser9) expression were assessed by immunofluorescence. FAS ligand neutralization, caspase and GSK-3 inhibitors and GSK-3β siRNA were applied to further explore underlying mechanisms. Clinically relevant concentrations of bupivacaine reduced cell viability and inhibited cellular proliferation and migration in both cell lines. Caspase 8 and 9 inhibition generated partial cell death reversal in SKOV-3, whilst only caspase 9 was effective in PC-3. Bupivacaine increased the phosphorylation of GSK-3β(Tyr216) in SKOV-3 but without measurable effect in PC3. GSK-3β inhibition and siRNA gene knockdown decreased bupivacaine induced cell death in SKOV-3 but not in PC3. Our data suggests that bupivacaine has direct ‘anti-cancer’ properties through the activation of intrinsic and extrinsic apoptotic pathways in ovarian cancer but only the intrinsic pathway in prostate cancer
Solutions of the Yang-Baxter Equation with Extra Non-Additive Parameters II: }
The type-I quantum superalgebras are known to admit non-trivial one-parameter
families of inequivalent finite dimensional irreps, even for generic . We
apply the recently developed technique to construct new solutions to the
quantum Yang-Baxter equation associated with the one-parameter family of irreps
of , thus obtaining R-matrices which depend not only on a
spectral parameter but in addition on further continuous parameters. These
extra parameters enter the Yang-Baxter equation in a similar way to the
spectral parameter but in a non-additive form.Comment: 10 pages, LaTex file (some errors in the Casimirs corrected
On Type-I Quantum Affine Superalgebras
The type-I simple Lie-superalgebras are and . We study
the quantum deformations of their untwisted affine extensions
and . We identify additional
relations between the simple generators (``extra -Serre relations") which
need to be imposed to properly define \uqgh and . We
present a general technique for deriving the spectral parameter dependent
R-matrices from quantum affine superalgebras. We determine the R-matrices for
the type-I affine superalgebra in various representations,
thereby deriving new solutions of the spectral-dependent Yang-Baxter equation.
In particular, because this algebra possesses one-parameter families of
finite-dimensional irreps, we are able to construct R-matrices depending on two
additional spectral-like parameters, providing generalizations of the
free-fermion model.Comment: 23 page
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