127 research outputs found
Controlled formation of isolated miniband in bilayer graphene on almost commensurate √3 × √3 substrate
We investigate theoretically the interplay between the effects of a
perpendicular electric field and incommensurability at the interface on the
electronic properties of a heterostructure of bilayer graphene and a
semiconducting substrate with a unit cell almost three times larger then that
of graphene. It is known that the former introduces an asymmetry in the
distribution of the electronic wave function between the layers and opens a
band gap in the electronic spectrum. The latter generates a long wavelength
periodic moir\'{e} perturbation of graphene electrons which couples states in
inequivalent graphene Brillouin zone corners and leads to the formation of
minibands. We show that, depending on the details of the moir\'{e}
perturbation, the miniband structure can be tuned from that with a single band
gap at the neutrality point and over-lapping minibands on the
conduction/valence band side to a situation where a single narrow miniband is
separated by gaps from the rest of the spectrum.Comment: 7 pages, 3 figure
Infrared absorption of closely-aligned heterostructures of monolayer and bilayer graphene with hexagonal boron nitride
We model optical absorption of monolayer and bilayer graphene on hexagonal
boron nitride for the case of closely-aligned crystal lattices. We show that
perturbations with different spatial symmetry can lead to similar absorption
spectra. We suggest that a study of the absorption spectra as a function of the
doping for almost completely full first miniband is necessary to extract
meaningful information about the moire characteristics from optical absorption
measurements and to distinguish between various theoretical proposals for the
physically realistic interaction. Also, for bilayer graphene, the ability to
compare spectra for the opposite signs of electric-field-induced interlayer
asymmetry might provide additional information about the moire parameters.Comment: 7 pages, 6 figures, minor changes, version accepted to PR
Preclinical antitumour activity of F 11782, a novel dual catalytic inhibitor of topoisomerases
F 11782 is a novel inhibitor of topoisomerases I and II, with an original mechanism of action (Perrin et al, 2000). This study, aimed to define its anticancer efficacy against a series of murine and human tumour models, has provided evidence of major antitumour activity for F 11782. This was demonstrated as a high level of activity against the P388 leukaemia, as reflected by increased survival of 143–457%, when administered i.p., p.o. or i.v. as single or multiple doses, and proved consistently superior to etoposide or camptothecin tested concurrently. Single or multiple i.p. doses of F 11782 also proved highly active against the s.c. grafted B16 melanoma, significantly increasing survival (P < 0.001) and inhibiting tumour growth (T/C of 0.3%), again superior to etoposide tested concurrently. Furthermore, F 11782 inhibited the number of pulmonary metastatic foci of the B16F10 melanoma by 99%. In human tumour xenograft studies, multiple i.p. doses of F 11782 resulted in major inhibitory activity against MX-1 (breast) tumours (T/C of 0.1%), as well as causing definite tumour regressions, whereas none resulted from similar experimental treatments with etoposide. Significant activity was also recorded with F 11782 against the relatively refractory LX-1 (lung) xenografts, with an optimal T/C value of 19%. It was notable that the antitumour activity of F 11782 was consistently demonstrated over a wide range of 2–6 dose levels, providing evidence of its good overall tolerance. In conclusion, these results emphasize the preclinical interest of this novel molecule and support its further preclinical development. © 2000 Cancer Research Campaign http://www.bjcancer.co
Band dispersion in the deep 1s core level of graphene
Chemical bonding in molecules and solids arises from the overlap of valence
electron wave functions, forming extended molecular orbitals and dispersing
Bloch states, respectively. Core electrons with high binding energies, on the
other hand, are localized to their respective atoms and their wave functions do
not overlap significantly. Here we report the observation of band formation and
considerable dispersion (up to 60 meV) in the core level of the carbon
atoms forming graphene, despite the high C binding energy of 284
eV. Due to a Young's double slit-like interference effect, a situation arises
in which only the bonding or only the anti-bonding states is observed for a
given photoemission geometry.Comment: 12 pages, 3 figures, including supplementary materia
ARPES signatures of few-layer twistronic graphenes
Diverse emergent correlated electron phenomena have been observed in twisted
graphene layers due to electronic interactions with the moir\'e superlattice
potential. Many electronic structure predictions have been reported exploring
this new field, but with few momentum-resolved electronic structure
measurements to test them. Here we use angle-resolved photoemission
spectroscopy (ARPES) to study the twist-dependent () electronic band structure of few-layer graphenes, including twisted
bilayer, monolayer-on-bilayer, and double-bilayer graphene (tDBG). Direct
comparison is made between experiment and theory, using a hybrid
model for interlayer coupling and implementing
photon-energy-dependent phase shifts for photo-electrons from consecutive
layers to simulate ARPES spectra. Quantitative agreement between experiment and
theory is found across twist angles, stacking geometries, and back-gate
voltages, validating the models and revealing displacement field induced gap
openings in twisted graphenes. However, for tDBG at ,
close to the predicted magic-angle of , a flat band is found
near the Fermi-level with measured bandwidth of meV. Analysis of
the gap between the flat band and the next valence band shows significant
deviations between experiment (meV) and the theoretical model
(meV), indicative of the importance of lattice relaxation in this
regime
Vinflunine: a new active drug for second-line treatment of advanced breast cancer. Results of a phase II and pharmacokinetic study in patients progressing after first-line anthracycline/taxane-based chemotherapy
To evaluate the single agent activity, pharmacokinetics and tolerability of the novel tubulin targeted agent vinflunine (VFL) (320 mg m−2 q 21 days) as second-line chemotherapy in patients with metastatic breast carcinoma (MBC). All patients had disease progression after anthracycline/taxane (A/T) therapy. They could have received a nonanthracycline adjuvant treatment and subsequently received a first-line A/T combination for advanced/metastatic disease; or relapsed >6 months after completion of adjuvant A/T therapy and were subsequently treated with the alternative agent; or relapsed within 6 months from an adjuvant A/T combination. Objective response was documented in 18 of 60 patients enrolled (RR: 30% (95% confidence interval (CI): 18.9–43.2%)). Among the responders, seven patients had relapsed during a period of <3 months from taxane-based regimen yielding a RR of 33.3%. The median duration of response was 4.8 months (95% CI: 4.2–7.2), median progression-free survival was 3.7 months (95% CI: 2.8–4.2) and median overall survival was 14.3 months (95% CI: 9.2–19.6). The most frequent adverse event was neutropenia (grade 3 in 28.3% and grade 4 in 36.7% of patients). No febrile neutropenia was observed. Fatigue (grade 3 in 16.7% of patients) and constipation (grade 3 in 11.7% of patients) were also common; these were non-cumulative and manageable permitting achievement of a good relative dose intensity of 93.5%. Vinflunine is an active agent with acceptable tolerance in the management of MBC patients previously treated with (A/T)-based regimens. These encouraging phase II results warrant further investigation of this novel agent in combination with other active agents in this setting or in earlier stages of disease
Characterization of cell death induced by vinflunine, the most recent Vinca alkaloid in clinical development
Vinflunine, the most recent Vinca alkaloid in clinical development, demonstrated superior antitumour activity to other Vincas in preclinical tumour models. This study aimed to define its molecular mechanisms of cell killing in both parental sensitive and vinflunine-resistant P388 leukaemia cells. Vinflunine treatment of these cells resulted in apoptosis characterized by DNA fragmentation and proteolytic cleavage of poly-(ADP-ribose) polymerase. Apoptosis-inducing concentrations of vinflunine caused c-Jun N-terminal kinase 1 stimulation, as well as caspases-3/7 activation. This activation of caspases and the induction of apoptosis could be inhibited by the caspase inhibitor acetyl-Asp-Glu-Val-Asp-aldehyde. Interestingly, the apoptosis signal triggered by vinflunine in these P388 cells was not mediated through Bcl-2 phosphorylation. In addition, when vinflunine resistance was developed in P388 cells, it was associated with resistance to vinflunine-induced apoptosis, as reflected by a loss of capacity to induce DNA fragmentation and PARP degradation, and characterized by increased levels of Bcl-2 and Bfl-1/A1. Therefore, these data indirectly implicate Bcl-2 and Bfl-1/A1 in vinflunine-induced cell death mechanisms
Graphene-based modulation-doped superlattice structures
The electronic transport properties of graphene-based superlattice structures
are investigated. A graphene-based modulation-doped superlattice structure
geometry is proposed and consist of periodically arranged alternate layers:
InAs/graphene/GaAs/graphene/GaSb. Undoped graphene/GaAs/graphene structure
displays relatively high conductance and enhanced mobilities at elevated
temperatures unlike modulation-doped superlattice structure more steady and
less sensitive to temperature and robust electrical tunable control on the
screening length scale. Thermionic current density exhibits enhanced behaviour
due to presence of metallic (graphene) mono-layers in superlattice structure.
The proposed superlattice structure might become of great use for new types of
wide-band energy gap quantum devices.Comment: 5 figure
Transport Spectroscopy of Symmetry-Broken Insulating States in Bilayer Graphene
The flat bands in bilayer graphene(BLG) are sensitive to electric fields
E\bot directed between the layers, and magnify the electron-electron
interaction effects, thus making BLG an attractive platform for new
two-dimensional (2D) electron physics[1-5]. Theories[6-16] have suggested the
possibility of a variety of interesting broken symmetry states, some
characterized by spontaneous mass gaps, when the electron-density is at the
carrier neutrality point (CNP). The theoretically proposed gaps[6,7,10] in
bilayer graphene are analogous[17,18] to the masses generated by broken
symmetries in particle physics and give rise to large momentum-space Berry
curvatures[8,19] accompanied by spontaneous quantum Hall effects[7-9]. Though
recent experiments[20-23] have provided convincing evidence of strong
electronic correlations near the CNP in BLG, the presence of gaps is difficult
to establish because of the lack of direct spectroscopic measurements. Here we
present transport measurements in ultra-clean double-gated BLG, using
source-drain bias as a spectroscopic tool to resolve a gap of ~2 meV at the
CNP. The gap can be closed by an electric field E\bot \sim13 mV/nm but
increases monotonically with a magnetic field B, with an apparent particle-hole
asymmetry above the gap, thus providing the first mapping of the ground states
in BLG.Comment: 4 figure
Lorentz violation, Gravity, Dissipation and Holography
We reconsider Lorentz Violation (LV) at the fundamental level. We show that
Lorentz Violation is intimately connected with gravity and that LV couplings in
QFT must always be fields in a gravitational sector. Diffeomorphism invariance
must be intact and the LV couplings transform as tensors under coordinate/frame
changes. Therefore searching for LV is one of the most sensitive ways of
looking for new physics, either new interactions or modifications of known
ones. Energy dissipation/Cerenkov radiation is shown to be a generic feature of
LV in QFT. A general computation is done in strongly coupled theories with
gravity duals. It is shown that in scale invariant regimes, the energy
dissipation rate depends non-triviallly on two characteristic exponents, the
Lifshitz exponent and the hyperscaling violation exponent.Comment: LateX, 51 pages, 9 figures. (v2) References and comments added.
Misprints correcte
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