282 research outputs found
Stacking-order dependent transport properties of trilayer graphene
We report markedly different transport properties of ABA- and ABC-stacked
trilayer graphenes. Our experiments in double-gated trilayer devices provide
evidence that a perpendicular electric field opens an energy gap in the ABC
trilayer, while it causes the increase of a band overlap in the ABA trilayer.
In a perpendicular magnetic field, the ABA trilayer develops quantum Hall
plateaus at filling factors of \nu = 2, 4, 6... with a step of \Delta \nu = 2,
whereas the inversion symmetric ABC trilayer exhibits plateaus at \nu = 6 and
10 with 4-fold spin and valley degeneracy.Comment: 4 pages, 4 figure
Elaboration and characterization of Fe1βxO thin films sputter deposited from magnetite target
Majority of the authors report elaboration of iron oxide thin films by reactive magnetron sputtering from an iron target with ArβO2 gas mixture. Instead of using the reactive sputtering of a metallic target we report here the preparation of Fe1βxOthin films, directly sputtered froma magnetite target in a pure argon gas flow with a bias power applied. This oxide is generally obtained at very low partial oxygen pressure and high temperature.We showed that bias sputtering which can be controlled very easily can lead to reducing conditions during deposition of oxide thin film on simple glass substrates. The proportion of wustite was directly adjusted bymodifying the power of the substrate polarization. Atomic force microscopy was used to observe these nanostructured layers. MΓΆssbauer measurements and electrical properties versus bias polarization and annealing temperature are also reported
Superfluid transition temperature in a trapped gas of Fermi atoms with a Feshbach resonance
We investigate strong coupling effects on the superfluid phase transition in
a gas of Fermi atoms with a Feshbach resonance. The Feshbach resonance
describes a composite quasi-Boson, which can give rise to an additional pairing
interaction between the Fermi atoms. This attractive interaction becomes
stronger as the threshold energy of the Feshbach resonance two-particle bound
state is lowered. In a recent paper, we showed that in the uniform Fermi gas,
this tunable pairing interaction naturally leads to a BCS-BEC crossover of the
Nozi`eres and Schmitt-Rink kind, in which the BCS-type superfluid phase
transition continuously changes into the BEC-type as the threshold energy is
decreased. In this paper, we extend our previous work by including the effect
of a harmonic trap potential, treated within the local density approximation
(LDA). We also give results for both weak and strong coupling to the Feshbach
resonance. We show that the BCS-BEC crossover phenomenon strongly modifies the
shape of the atomic density profile at the superfluid phase transition
temperature Tc, reflecting the change of the dominant particles going from
Fermi atoms to composite Bosons. In the BEC regime, these composite Bosons are
shown to first appear well above Tc. We also discuss the "phase diagram" above
Tc as a function of the tunable threshold energy. We introduce a characteristic
temperature T* describing the effective crossover in the normal phase from a
Fermi gas of atoms to a gas of stable molecules.Comment: 43 pages, 13 figures (submitted to PRA
Unintentional high density p-type modulation doping of a GaAs/AlAs core-multi-shell nanowire
Achieving significant doping in GaAs/AlAs core/shell nanowires (NWs) is of
considerable technological importance but remains a challenge due to the
amphoteric behavior of the dopant atoms. Here we show that placing a narrow
GaAs quantum well in the AlAs shell effectively getters residual carbon
acceptors leading to an \emph{unintentional} p-type doping. Magneto-optical
studies of such a GaAs/AlAs core multi-shell NW reveal quantum confined
emission. Theoretical calculations of NW electronic structure confirm quantum
confinement of carriers at the core/shell interface due to the presence of
ionized carbon acceptors in the 1~nm GaAs layer in the shell.
Micro-photoluminescence in high magnetic field shows a clear signature of
avoided crossings of the Landau level emission line with the Landau
level TO phonon replica. The coupling is caused by the resonant hole-phonon
interaction, which points to a large 2D hole density in the structure.Comment: just published in Nano Letters
(http://pubs.acs.org/doi/full/10.1021/nl500818k
Giant Electroresistance in Edge Metal-Insulator-Metal Tunnel Junctions Induced by Ferroelectric Fringe Fields
An enormous amount of research activities has been devoted to developing new types of non-volatile memory devices as the potential replacements of current flash memory devices. Theoretical device modeling was performed to demonstrate that a huge change of tunnel resistance in an Edge Metal-Insulator-Metal (EMIM) junction of metal crossbar structure can be induced by the modulation of electric fringe field, associated with the polarization reversal of an underlying ferroelectric layer. It is demonstrated that single three-terminal EMIM/Ferroelectric structure could form an active memory cell without any additional selection devices. This new structure can open up a way of fabricating all-thin-film-based, high-density, high-speed, and low-power non-volatile memory devices that are stackable to realize 3D memory architectureope
Effects of the protein kinase inhibitors wortmannin and KN62 on cellular radiosensitivity and radiation-activated S phase and G1/S checkpoints in normal human fibroblasts
Wortmannin is a potent inhibitor of phosphatidylinositol (PI) 3-kinase and PI 3-kinase-related proteins (e.g. ATM), but it does not inhibit the activity of purified calmodulin-dependent protein kinase II (CaMKII). In the present study, we compared the effects of wortmannin and the CaMKII inhibitor KN62 on the response of normal human dermal fibroblast cultures to Ξ³ radiation. We demonstrate that wortmannin confers a phenotype on normal fibroblasts remarkably similar to that characteristic of cells homozygous for the ATM mutation. Thus wortmannin-treated normal fibroblasts exhibit increased sensitivity to radiation-induced cell killing, lack of temporary block in transition from G1 to S phase following irradiation (i.e. impaired G1/S checkpoint), and radioresistant DNA synthesis (i.e. impaired S phase checkpoint). Wortmannin-treated cultures display a diminished capacity for radiation-induced up-regulation of p53 protein and expression of p21WAF1, a p53-regulated gene involved in cell cycle arrest at the G1/S border; the treated cultures also exhibit decreased capacity for enhancement of CaMKII activity post-irradiation, known to be necessary for triggering the S phase checkpoint. We further demonstrate that KN62 confers a radioresistant DNA synthesis phenotype on normal fibroblasts and moderately potentiates their sensitivity to killing by Ξ³ rays, without modulating G1/S checkpoint, p53 up-regulation and p21WAF1 expression following radiation exposure. We conclude that CaMKII is involved in the radiation responsive signalling pathway mediating S phase checkpoint but not in the p53-dependent pathway controlling G1/S checkpoint, and that a wortmannin-sensitive kinase functions upstream in both pathways. Β© 1999 Cancer Research Campaig
Enhancement of immune response of HBsAg loaded poly(L-lactic acid) microspheres against Hepatitis B through incorporation of alum and chitosan
Purpose: Poly (L-lactic acid) (PLA) microparticles encapsulating Hepatitis B surface antigen (HBsAg) with alum and chitosan were investigated for their potential as a vaccine delivery system.
Methods: The microparticles, prepared using a water-in-oil-in-water (w/o/w) double emulsion solvent evaporation method with polyvinyl alcohol (PVA) or chitosan as the external phase stabilising agent showed a significant increase in the encapsulation efficiency of the antigen.
Results: PLA-Alum and PLA-chitosan microparticles induced HBsAg serum specific IgG antibody responses significantly higher than PLA only microparticles and free antigen following subcutaneous administration. Chitosan not only imparted a positive charge to the surface of the microparticles but was also able to increase the serum specific IgG antibody responses significantly.
Conclusions: The cytokine assays showed that the serum IgG antibody response induced is different according to the formulation, indicated by the differential levels of interleukin 4 (IL-4), interleukin 6 (IL-6) and interferon gamma (IFN-Ξ³). The microparticles eliciting the highest IgG antibody response did not necessarily elicit the highest levels of the cytokines IL-4, IL-6 and IFN-Ξ³
A Kinome RNAi Screen Identified AMPK as Promoting Poxvirus Entry through the Control of Actin Dynamics
Poxviruses include medically important human pathogens, yet little is known about the specific cellular factors essential for their replication. To identify genes essential for poxvirus infection, we used high-throughput RNA interference to screen the Drosophila kinome for factors required for vaccinia infection. We identified seven genes including the three subunits of AMPK as promoting vaccinia infection. AMPK not only facilitated infection in insect cells, but also in mammalian cells. Moreover, we found that AMPK is required for macropinocytosis, a major endocytic entry pathway for vaccinia. Furthermore, we show that AMPK contributes to other virus-independent actin-dependent processes including lamellipodia formation and wound healing, independent of the known AMPK activators LKB1 and CaMKK. Therefore, AMPK plays a highly conserved role in poxvirus infection and actin dynamics independent of its role as an energy regulator
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