Graphene: Kinks, Superlattices, Landau levels, and Magnetotransport

We review recent work on superlattices in monolayer and bilayer graphene. We highlight the role of the quasiparticle chirality in generating new Dirac fermion modes with tunable anisotropic velocities in one dimensional (1D) superlattices in both monolayer and bilayer graphene. We discuss the structure of the Landau levels and magnetotransport in such superlattices over a wide range of perpendicular (orbital) magnetic fields. In monolayer graphene, we show that an orbital magnetic field can reverse the anisotropy of the transport imposed by the superlattice potential, suggesting possible switching-type device applications. We also consider topological modes localized at a kink in an electric field applied perpendicular to bilayer graphene, and show how interactions convert these modes into a two-band Luttinger liquid with tunable Luttinger parameters. The band structures of electric field superlattices in bilayer graphene (with or without a magnetic field) are shown to arise naturally from a coupled array of such topological modes. We briefly review some bandstructure results for 2D superlattices. We conclude with a discussion of recent tunneling and transport experiments and point out open issues.Comment: Invited Review Article for Special Issue on Graphene, References added, Typos correcte

Gauging the mass of metals in the gas phase of galaxies from the Local Universe to the Epoch of Reionization

The chemical enrichment of dust and metals are vital processes in constraining the star formation history of the universe. Previously, the dust masses of high-redshift star-forming galaxies have been determined through their far-infrared continuum, however, equivalent, and potentially simpler, approaches to determining the metal masses have yet to be explored at $z\gtrsim 2$. Here, we present a new method of inferring the metal mass in the interstellar medium (ISM) of galaxies out to $z\approx 8$, using the far-infrared [CII]$-158\mu$m emission line as a proxy. We calibrated the [CII]-to-$M_{\rm Z,ISM}$ conversion factor based on a benchmark observational sample at $z\approx 0$, in addition to gamma-ray burst sightlines at $z>2$ and cosmological hydrodynamical simulations of galaxies at $z\approx 0$ and $z\approx 6$. We found a universal scaling across redshifts of $\log (M_{\rm Z,ISM}/M_\odot) = \log (L_{\rm [CII]}/L_\odot) - 0.45,$ with a 0.4 dex scatter, which is constant over more than two orders of magnitude in metallicity. We applied this scaling to recent surveys for [CII] in galaxies at $z\gtrsim 2$ and determined the fraction of metals retained in the gas-phase ISM, $M_{\rm Z,ISM} / M_\star$, as a function of redshift showing that an increasing fraction of metals reside in the ISM of galaxies at higher redshifts. We place further constraints on the cosmic metal mass density in the ISM ($\Omega_{\rm Z,ISM}$) at $z\approx 5$ and $\approx 7$, yielding $\Omega_{\rm Z,ISM} = 6.6^{+13}_{-4.3}\times 10^{-7}\,M_\odot\, {\rm Mpc}^{-3}$ ($z\approx 5$) and $\Omega_{\rm Z,ISM} = 2.0^{+3.5}_{-1.3}\times 10^{-7}\,M_\odot\, {\rm Mpc}^{-3}$ ($z\approx 7$). These results are consistent with the expected metal yields from the integrated star formation history at the respective redshifts. This suggests that the majority of metals produced at $z\gtrsim 5$ are confined to the ISM of galaxies.Comment: Accepted in A&A, abstract abridge

Topological confinement in an antisymmetric potential in bilayer graphene in the presence of a magnetic field

We investigate the effect of an external magnetic field on the carrier states that are localized at a potential kink and a kink-antikink in bilayer graphene. These chiral states are localized at the interface between two potential regions with opposite signs

Extreme damped Lyman-α\alpha absorption in young star-forming galaxies at z=9−11z=9-11

The onset of galaxy formation is thought to be initiated by the infall of neutral, pristine gas onto the first protogalactic halos. However, direct constraints on the abundance of neutral atomic hydrogen (HI) in galaxies have been difficult to obtain at early cosmic times. Here we present spectroscopic observations with JWST of three galaxies at redshifts $z=8.8 - 11.4$, about $400-600$ Myr after the Big Bang, that show strong damped Lyman-$\alpha$ absorption ($N_{\rm HI} > 10^{22}$ cm$^{-2}$) from HI in their local surroundings, an order of magnitude in excess of the Lyman-$\alpha$ absorption caused by the neutral intergalactic medium at these redshifts. Consequently, these early galaxies cannot be contributing significantly to reionization, at least at their current evolutionary stages. Simulations of galaxy formation show that such massive gas reservoirs surrounding young galaxies so early in the history of the universe is a signature of galaxy formation in progress.Comment: Submitte

Bilateral Breast Involvement In Acute Lymphoblastic-Leukemia - Color Doppler Sonography Findings

WOS: A1995RW13800059PubMed ID: 767695

Color Doppler imaging of choroidal circulation in patients with asymmetric age-related macular degeneration

WOS: 000181458300010PubMed ID: 12592053We aimed at evaluating the possible role of choroidal perfusion abnormalities in the development of choroidal neovascularisation (CNV) in patients with age-related macular degeneration (AMD). Twenty-six patients who had non-exudative AMD in the first eye and CNV secondary to AMD in the fellow eye were enrolled. Blood flow velocities, vessel pulsatilities and resistivities were measured from ophthalmic artery, nasal and temporal posterior ciliary arteries using colour Doppler imaging. Systolic and diastolic velocities were lower in eyes with CNV for all vessels, except for the systolic velocity of the nasal posterior ciliary artery (p >0.05). Pulsatility and resistivity indices were higher in eyes with CNV for all vessels. This difference was statistically significant for the resistivity index of the nasal and temporal posterior ciliary arteries (p = 0.032 and p = 0.021, respectively) and the pulsatility index of the nasal posterior ciliary artery (p = 0.035). We have shown that in patients with AMD choroidal blood flow is more impaired in the eyes with CNV than in the fellow eyes

Radical treatment for hepatic echinococcosis

Background: Hydatid liver surgery is associated with a high incidence of recurrence. Combined medical and surgical treatment should decrease the recurrence rates. Methods: In a retrospective study, 75 patients receiving operative treatment for hepatic echinococcosis with or without albendazole therapy were invited to enter a follow-up survey. Patients were examined clinically, and hydatid serology and B-mode ultrasound were performed. The initial results were evaluated by a panel and patients with equivocal results were further studied with diagnostic aspiration and direct microscopic examination for protoscolices. Results: Thirty-nine patients (52%) responded and 36 were followed up (22 in Group I with operation plus albendazole; 14 in Group 2 with operation alone). Although recurrence could not be excluded in 24 of these patients (18 Group I, 6 Group 2) when the initial results were evaluated, diagnostic aspiration revealed protoscolices in only two of them. One of these patients was excluded from the study because of inapproriate usage of albendazole. The recurrence rate was therefore 5%. Discussion: The recurrence rate in this study is lower than that obtained in our previous experience, but it does not represent a significant benefit for combined ('radical') treatment of echinococcosis. Data obtained from the follow-up studies are confusing for most of the parameters and indicate that the present methods for assessment are unsatisfactory for evaluating the treatment of hepatic echinococcosis