40,783 research outputs found
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
Towards understanding broad degeneracy in non-strange mesons
The spectroscopic regularities of modern empirical data on the non-strange
mesons up to 2.4 GeV can be summarized as a systematic clustering of states
near certain values of energy. It is getting evident that some unknown
X-symmetry triggers the phenomenon. We review the experimental status of this
symmetry and recent theoretical attempts put forward for explanation of broad
degeneracy.Comment: Brief review, 16 pages, 1 figur
A Practical Guide for X-Ray Diffraction Characterization of Ga(Al, In)N Alloys
Ga(In, Al)N alloys are used as an active layer or cladding layer in light
emitting diodes and laser diodes. x-ray diffraction is extensively used to
evaluate the crystalline quality, the chemical composition and the residual
strain in Ga(Al,In)N thin films, which directly determine the emission
wavelength and the device performance. Due to the minor mismatch in lattice
parameters between Ga(Al, In)N alloy and a GaN virtual substrate, x-ray
diffraction comes to a problem to separate the signal from Ga(Al,In)N alloy and
GaN. We give a detailed comparison on different diffraction planes. In order to
balance the intensity and peak separation between Ga(Al,In)N alloy and GaN,
(0004) and (1015) planes make the best choice for symmetric scan and asymmetric
scan, respectively.Comment: 9 pages, 5 figure
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
Steady-state MreB helices inside bacteria: dynamics without motors
Within individual bacteria, we combine force-dependent polymerization
dynamics of individual MreB protofilaments with an elastic model of
protofilament bundles buckled into helical configurations. We use variational
techniques and stochastic simulations to relate the pitch of the MreB helix,
the total abundance of MreB, and the number of protofilaments. By comparing our
simulations with mean-field calculations, we find that stochastic fluctuations
are significant. We examine the quasi-static evolution of the helical pitch
with cell growth, as well as timescales of helix turnover and denovo
establishment. We find that while the body of a polarized MreB helix treadmills
towards its slow-growing end, the fast-growing tips of laterally associated
protofilaments move towards the opposite fast-growing end of the MreB helix.
This offers a possible mechanism for targeted polar localization without
cytoplasmic motor proteins.Comment: 7 figures, 1 tabl
Adiabatic Quantum Search in Open Systems
Adiabatic quantum algorithms represent a promising approach to universal
quantum computation. Whilst in a closed system these algorithms are limited by
avoided level crossings, where the gap becomes exponentially small in the
system size, their robustness in open systems remains unresolved. We study the
dynamics in the proximity of such an avoided level crossing associated with the
adiabatic quantum search algorithm in a quantum system that is coupled to a
generic environment. At zero temperature, we find that the algorithm remains
scalable provided the noise spectral density of the environment decays
sufficiently fast at low frequencies. At finite temperature, however,
scattering processes render the algorithm inefficient and no quantum speedup
can be achieved. Owing to the generic nature of our model, we expect our
results to be widely applicable to other adiabatic quantum algorithms.Comment: Accepted version. 6 pages, 2 figures, 10 pages supplemental material
Holographic classification of Topological Insulators and its 8-fold periodicity
Using generic properties of Clifford algebras in any spatial dimension, we
explicitly classify Dirac hamiltonians with zero modes protected by the
discrete symmetries of time-reversal, particle-hole symmetry, and chirality.
Assuming the boundary states of topological insulators are Dirac fermions, we
thereby holographically reproduce the Periodic Table of topological insulators
found by Kitaev and Ryu. et. al, without using topological invariants nor
K-theory. In addition we find candidate Z_2 topological insulators in classes
AI, AII in dimensions 0,4 mod 8 and in classes C, D in dimensions 2,6 mod 8.Comment: 19 pages, 4 Table
Casimir Invariants from Quasi-Hopf (Super)algebras
We show how to construct, starting from a quasi-Hopf (super)algebra, central
elements or Casimir invariants. We show that these central elements are
invariant under quasi-Hopf twistings. As a consequence, the elliptic quantum
(super)groups, which arise from twisting the normal quantum (super)groups, have
the same Casimir invariants as the corresponding quantum (super)groups.Comment: 24 pages, Latex fil
Two-player quantum pseudo-telepathy based on recent all-versus-nothing violations of local realism
We introduce two two-player quantum pseudo-telepathy games based on two
recently proposed all-versus-nothing (AVN) proofs of Bell's theorem [A.
Cabello, Phys. Rev. Lett. 95, 210401 (2005); Phys. Rev. A 72, 050101(R)
(2005)]. These games prove that Broadbent and Methot's claim that these AVN
proofs do not rule out local-hidden-variable theories in which it is possible
to exchange unlimited information inside the same light-cone (quant-ph/0511047)
is incorrect.Comment: REVTeX4, 5 page
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