54,675 research outputs found
Engineering Negative Differential Conductance with the Cu(111) Surface State
Low-temperature scanning tunneling microscopy and spectroscopy are employed
to investigate electron tunneling from a C60-terminated tip into a Cu(111)
surface. Tunneling between a C60 orbital and the Shockley surface states of
copper is shown to produce negative differential conductance (NDC) contrary to
conventional expectations. NDC can be tuned through barrier thickness or C60
orientation up to complete extinction. The orientation dependence of NDC is a
result of a symmetry matching between the molecular tip and the surface states.Comment: 5 pages, 4 figures, 1 tabl
Mesoscopic Kondo effect of a quantum dot embedded in an Aharonov-Bohm ring with intradot spin-flip scattering
We study the Kondo effect in a quantum dot embedded in a mesoscopic ring
taking into account intradot spin-flip scattering . Based on the finite-
slave-boson mean-field approach, we find that the Kondo peak in the density of
states is split into two peaks by this coherent spin-flip transition, which is
responsible for some interesting features of the Kondo-assisted persistent
current circulating the ring: (1) strong suppression and crossover to a sine
function form with increasing ; (2) appearance of a "hump" in the
-dependent behavior for odd parity. -induced reverse of the persistent
current direction is also observed for odd parity.Comment: 7 pages,6 figures, to be published by Europhys. Let
Quantum Phase Transitions in Josephson Junction Chains
We investigate the quantum phase transition in a one-dimensional chain of
ultra-small superconducting grains, considering both the self- and junction
capacitances. At zero temperature, the system is transformed into a
two-dimensional system of classical vortices, where the junction capacitance
introduces anisotropy in the interaction between vortices. This leads to the
superconductor-insulator transition of the Berezinskii-Kosterlitz-Thouless
type, as the ratios of the Josephson coupling energy to the charging energies
are varied. It is found that the junction capacitance plays a role similar to
that of dissipation and tends to suppress quantum fluctuations; nevertheless
the insulator region survives even for arbitrarily large values of the junction
capacitance.Comment: REVTeX+5 EPS figures, To appear in PRB Rapid
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Cirmtuzumab inhibits Wnt5a-induced Rac1 activation in chronic lymphocytic leukemia treated with ibrutinib.
Signaling via the B cell receptor (BCR) plays an important role in the pathogenesis and progression of chronic lymphocytic leukemia (CLL). This is underscored by the clinical effectiveness of ibrutinib, an inhibitor of Bruton's tyrosine kinase (BTK) that can block BCR-signaling. However, ibrutinib cannot induce complete responses (CR) or durable remissions without continued therapy, suggesting alternative pathways also contribute to CLL growth/survival that are independent of BCR-signaling. ROR1 is a receptor for Wnt5a, which can promote activation of Rac1 to enhance CLL-cell proliferation and survival. In this study, we found that CLL cells of patients treated with ibrutinib had activated Rac1. Moreover, Wnt5a could induce Rac1 activation and enhance proliferation of CLL cells treated with ibrutinib at concentrations that were effective in completely inhibiting BTK and BCR-signaling. Wnt5a-induced Rac1 activation could be blocked by cirmtuzumab (UC-961), an anti-ROR1 mAb. We found that treatment with cirmtuzumab and ibrutinib was significantly more effective than treatment with either agent alone in clearing leukemia cells in vivo. This study indicates that cirmtuzumab may enhance the activity of ibrutinib in the treatment of patients with CLL or other ROR1+ B-cell malignancies
Inelastic scattering in a monolayer graphene sheet; a weak-localization study
Charge carriers in a graphene sheet, a single layer of graphite, exhibit much
distinctive characteristics to those in other two-dimensional electronic
systems because of their chiral nature. In this report, we focus on the
observation of weak localization in a graphene sheet exfoliated from a piece of
natural graphite and nano-patterned into a Hall-bar geometry. Much stronger
chiral-symmetry-breaking elastic intervalley scattering in our graphene sheet
restores the conventional weak localization. The resulting carrier-density and
temperature dependence of the phase coherence length reveal that the
electron-electron interaction including a direct Coulomb interaction is the
main inelastic scattering factor while electron-hole puddles enhance the
inelastic scattering near the Dirac point.Comment: 12 pages, 3 figures, submitted to PR
Cosmological Luminosity Evolution of QSO/AGN Population
We apply the observed optical/X-ray spectral states of the Galactic black
hole candidates (GBHCs) to the cosmological QSO luminosity evolution under the
assumptions that QSOs and GBHCs are powered by similar accretion processes and
that their emission mechanisms are also similar. The QSO luminosity function
(LF) evolution in various energy bands is strongly affected by the spectral
evolution which is tightly correlated with the luminosity evolution. We
generate a random sample of QSOs born nearly synchronously by allowing the QSOs
to have redshifts in a narrow range around an initial high redshift, black hole
masses according to a power-law, and mass accretion rates near Eddington rates.
The QSOs evolve as a single long-lived population on the cosmological time
scale. The pure luminosity evolution results in distinct luminosity evolution
features due to the strong spectral evolution. Most notably, different energy
bands (optical/UV, soft X-ray, and hard X-ray) show different evolutionary
trends and the hard X-ray LF in particular shows an apparent reversal of the
luminosity evolution (from decreasing to increasing luminosity) at low
redshifts, which is not seen in the conventional pure luminosity evolution
scenario without spectral evolution. The resulting mass function of black holes
(BHs), which is qualitatively consistent with the observed QSO LF evolution,
shows that QSO remnants are likely to be found as BHs with masses in the range
10**8-5x10**10 solar masses. The long-lived single population of QSOs are
expected to leave their remnants as supermassive BHs residing in rare, giant
elliptical galaxies.Comment: 9 pages, 2 figures, ApJ
Signature of high temperature superconductivity in electron doped Sr2IrO4
Sr2IrO4 was predicted to be a high temperature superconductor upon electron
doping since it highly resembles the cuprates in crystal structure, electronic
structure and magnetic coupling constants. Here we report a scanning tunneling
microscopy/spectroscopy (STM/STS) study of Sr2IrO4 with surface electron doping
by depositing potassium (K) atoms. At the 0.5-0.7 monolayer (ML) K coverage, we
observed a sharp, V-shaped gap with about 95% loss of density of state (DOS) at
EFand visible coherence peaks. The gap magnitude is 25-30 meV for 0.5-0.6 ML K
coverage and it closes around 50 K. These behaviors exhibit clear signature of
superconductivity. Furthermore, we found that with increased electron doping,
the system gradually evolves from an insulating state to a normal metallic
state, via a pseudogap-like state and possible superconducting state. Our data
suggest possible high temperature superconductivity in electron doped Sr2IrO4,
and its remarkable analogy to the cuprates.Comment: 11 pages, 5 figure
Slow relaxation in the Ising model on a small-world network with strong long-range interactions
We consider the Ising model on a small-world network, where the long-range
interaction strength is in general different from the local interaction
strength , and examine its relaxation behaviors as well as phase
transitions. As is raised from zero, the critical temperature also
increases, manifesting contributions of long-range interactions to ordering.
However, it becomes saturated eventually at large values of and the
system is found to display very slow relaxation, revealing that ordering
dynamics is inhibited rather than facilitated by strong long-range
interactions. To circumvent this problem, we propose a modified updating
algorithm in Monte Carlo simulations, assisting the system to reach equilibrium
quickly.Comment: 5 pages, 5 figure
Skyrmions in a Doped Antiferromagnet
Magnetization and magnetoresistance have been measured in insulating
antiferromagnetic La_{2}Cu_{0.97}Li_{0.03}O_{4} over a wide range of
temperatures, magnetic fields, and field orientations. The magnetoresistance
step associated with a weak ferromagnetic transition exhibits a striking
nonmonotonic temperature dependence, consistent with the presence of skyrmions.Comment: 4+ pages, 3 figures (some low resolution), supplementary material (3
pages); discussion expanded, references added; as publishe
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