Emission Optics of the Steigerwald Type Electron Gun

The emission optics of a Steigerwald type electron gun is re-examined. The virtual and real points of divergence, divergence angles and beam-widths of the electron beams at different telefocusing strength are measured in detail for first time . Two different Wehnelt cylinders are used to establish a contrasting viewpoint. The original `focusing' curves measured by Braucks are reconstructed and will be explained only through a `new' interpretation which is different from the conventional views. While the image of the emitting surface in front of the filament is indeed telefocused beyond the anode, the envelope of the beam does not `focus' as expected. A new model for the emission mechanism is established based on our results.Comment: 14 pages, 10 figure

Composite-fermion crystallites in quantum dots

The correlations in the ground state of interacting electrons in a two-dimensional quantum dot in a high magnetic field are known to undergo a qualitative change from liquid-like to crystal-like as the total angular momentum becomes large. We show that the composite-fermion theory provides an excellent account of the states in both regimes. The quantum mechanical formation of composite fermions with a large number of attached vortices automatically generates omposite fermion crystallites in finite quantum dots.Comment: 5 pages, 3 figure

Evolution of population with sexual and asexual reproduction in changing environment

Using a lattice model based on Monte Carlo simulations, we study the role of the reproduction pattern on the fate of an evolving population. Each individual is under the selection pressure from the environment and random mutations. The habitat ("climate") is changing periodically. Evolutions of populations following two reproduction patterns are compared, asexual and sexual. We show, via Monte Carlo simulations, that sexual reproduction by keeping more diversified populations gives them better chances to adapt themselves to the changing environment. However, in order to obtain a greater chance to mate, the birth rate should be high. In the case of low birth rate and high mutation probability there is a preference for the asexual reproduction.Comment: 11 pages including figs., for Int. J. Mod. Phys. C 15, issue 2 (2004

Half integer quantum Hall effect in high mobility single layer epitaxial graphene

The quantum Hall effect, with a Berry's phase of $\pi$ is demonstrated here on a single graphene layer grown on the C-face of 4H silicon carbide. The mobility is $\sim$ 20,000 cm$^2$/V$\cdot$s at 4 K and ~15,000 cm$^2$/V$\cdot$s at 300 K despite contamination and substrate steps. This is comparable to the best exfoliated graphene flakes on SiO$_2$ and an order of magnitude larger than Si-face epitaxial graphene monolayers. These and other properties indicate that C-face epitaxial graphene is a viable platform for graphene-based electronics.Comment: Some modifications in the text and figures, 7 pages, 2 figure

Magnetothermoelectric transport in modulated and unmodulated graphene

We draw motivation from recent experimental studies and present a comprehensive study of magnetothermoelectric transport in a graphene monolayer within the linear response regime. We employ the modified Kubo formalism developed for thermal transport in a magnetic field. Thermopower as well as thermal conductivity as a function of the gate voltage of a graphene monolayer in the presence of a magnetic field perpendicular to the graphene plane is determined for low magnetic fields (~1 Tesla) as well as high fields (~8 Tesla). We include the effects of screened charged impurities on thermal transport. We find good, qualitative as well as quantitative, agreement with recent experimental work on the subject. In addition, in order to analyze the effects of modulation, which can be induced by various means, on the thermal transport in graphene, we evaluate the thermal transport coefficients for a graphene monolayer subjected to a periodic electric modulation in a magnetic field. The results are presented as a function of the magnetic field and the gate voltage.Comment: 14 pages, 8 figure

BatMeth: improved mapper for bisulfite sequencing reads on DNA methylation

10.1186/gb-2012-13-10-R82Genome Biology1310-GNBL