Inter-band magnetoplasmons in mono- and bi-layer graphene

Collective excitations spectrum of Dirac electrons in mono and bilayer graphene in the presence of a uniform magnetic field is investigated. Analytical results for inter-Landau band plasmon spectrum within the self-consistent-field approach are obtained. SdH type oscillations that are a monotonic function of the magnetic field are observed in the plasmon spectrum of both mono- and bi-layer graphene systems. The results presented are also compared with those obtained in conventional 2DEG. The chiral nature of the quasiparticles in mono and bilayer graphene system results in the observation of $\pi$ and $2\pi$ Berry's phase in the SdH- type oscillations in the plasmon spectrum.Comment: 9 pages, 2 figure

Superlattice Magnetophonon Resonances in Strongly Coupled InAs/GaSb Superlattices

We report an experimental study of miniband magnetoconduction in semiconducting InAs/GaSb superlattices. For samples with miniband widths below the longitudinal optical phonon energy we identify a new superlattice magnetophonon resonance (SLMPR) caused by resonant scattering of electrons across the mini-Brillouin zone. This new resonant feature arises directly from the drift velocity characteristics of the superlattice dispersion and total magnetic quantisation of the superlattice Landau level minibands.Comment: 9 pages, 8 figures, submitted to Phys. Rev.

Legal guardians understand how children with the human immunodeficiency virus perceive quality of life and stigma

AIM: This aim of this study was to describe how legal guardians assessed health-related quality of life and HIV-related stigma in children with the human immunodeficiency virus (HIV) compared to the children's own ratings. METHODS: A cross-sectional nationwide study was performed to compare how 37 children aged from eight to 16 years of age with perinatal HIV, and their legal guardians, assessed the children's health-related quality of life and HIV-related stigma. Data were collected using the 37-item DISABKIDS Chronic Generic Module and a short eight-item version of the HIV stigma scale. RESULTS: Intraclass correlations indicated concordance between the legal guardians' ratings and the children's own ratings of the child's health-related quality of life and HIV-related stigma. There were no statistically significant differences between the ratings of the two groups and gender did not have any impact on the results. Both groups indicated that the children had concerns about being open about their HIV status. CONCLUSION: The results of this study indicated that legal guardians understood how their children perceived their health-related quality of life and HIV-related stigma. The results also indicated the need for interventions to support both the children and legal guardians when it came to disclosing the child's HIV status

Interaction-induced shift of the cyclotron resonance of graphene using infrared spectroscopy

We report a study of the cyclotron resonance (CR) transitions to and from the unusual $n=0$ Landau level (LL) in monolayer graphene. Unexpectedly, we find the CR transition energy exhibits large (up to 10%) and non-monotonic shifts as a function of the LL filling factor, with the energy being largest at half-filling of the $n=0$ level. The magnitude of these shifts, and their magnetic field dependence, suggests that an interaction-enhanced energy gap opens in the $n=0$ level at high magnetic fields. Such interaction effects normally have limited impact on the CR due to Kohn's theorem [W. Kohn, Phys. Rev. {\bf 123}, 1242 (1961)], which does not apply in graphene as a consequence of the underlying linear band structure.Comment: 4 pages, 4 figures. Version 2, edited for publication. Includes a number of edits for clarity; also added a paragraph contrasting our work w/ previous CR expts. in 2D Si and GaA

The sub-stellar birth rate from UKIDSS

We present a new sample of mid-L to mid-T dwarfs with effective temperatures of 11001700 K selected from the UKIDSS Large Area Survey (LAS) and confirmed with infrared spectra from X-shooter/Very Large Telescope. This effective temperature range is especially sensitive to the formation history of Galactic brown dwarfs and allows us to constrain the form of the sub-stellar birth rate, with sensitivity to differentiate between a flat (stellar like) birth rate and an exponentially declining form. We present the discovery of 63 new L and T dwarfs from the UKIDSS LAS DR7, including the identification of 12 likely unresolved binaries, which form the first complete sub-set from our programme, covering 495 square degrees of sky, complete to J = 18.1. We compare our results for this sub-sample with simulations of differing birth rates for objects of masses 0.10-0.03 M-circle dot and ages 1-10 Gyr. We find that the more extreme birth rates (e. g. a halo type form) can likely be excluded as the true form of the birth rate. In addition, we find that although there is substantial scatter we find a preference for a mass function, with a power-law index a in the range -1 <alpha <0 that is consistent (within the errors) with the studies of late T dwarfs.Peer reviewe

Four new T dwarfs identified in PanSTARRS 1 commissioning data

A complete well-defined sample of ultracool dwarfs is one of the key science programs of the Pan-STARRS 1 optical survey telescope (PS1). Here we combine PS1 commissioning data with 2MASS to conduct a proper motion search (0.1--2.0\arcsec/yr) for nearby T dwarfs, using optical+near-IR colors to select objects for spectroscopic followup. The addition of sensitive far-red optical imaging from PS1 enables discovery of nearby ultracool dwarfs that cannot be identified from 2MASS data alone. We have searched 3700 sq. deg. of PS1 y-band (0.95--1.03 um) data to y$\approx$19.5 mag (AB) and J$\approx$16.5 mag (Vega) and discovered four previously unknown bright T dwarfs. Three of the objects (with spectral types T1.5, T2 and T3.5) have photometric distances within 25 pc and were missed by previous 2MASS searches due to more restrictive color selection criteria. The fourth object (spectral type T4.5) is more distant than 25 pc and is only a single-band detection in 2MASS. We also examine the potential for completing the census of nearby ultracool objects with the PS1 3$\pi$ survey.Comment: 25 pages, 8 figures, 5 table, AJ accepted, updated to comply with Pan-STARRS1 naming conventio

Lanthanoid Biphenolates as a Rich Source of Lanthanoid-Main Group Heterobimetallic Complexes

Several new trivalent dinuclear rare earth 2,2’-methylenebis(6-tert-butyl-4-methylphenolate) (mbmp²¯) complexes with the general form [Ln₂(mbmp)₃(thf)n] (Ln=Sm 1, Tb 2 (n=3), and Ho 3, Yb 4 (n=2), and a tetravalent cerium complex [Ce(mbmp)₂(thf)₂] (5) have been synthesised by RTP (redox transmetallation/protolysis) reactions from lanthanoid metals, Hg(C₆F₅)₂ and the biphenol mbmpH₂. These new complexes and some previously reported partially protonated rare earth biphenolate complexes [Ln(mbmp)(mbmpH)(thf)n] react with lithium, aluminium, potassium and zinc organometallic reagents to form lanthanoid-main group heterobimetallic species. When reaction mixtures containing the Ln biphenolate complexes were treated with n-butyllithium, both molecular ([Li(thf)₂Ln(mbmp)₂(thf)n] (Ln=La 6, Pr 7 (n=2) and Er 8, Yb 9, and Lu 10 (n=1)) and charge separated ([Li(thf)₄][Ln(mbmp)₂(thf)₂] (Ln=Y 11, Sm 12, Dy 13, and Ho 14) complexes were isolated. Treatment with trimethylaluminium also led to isolation of molecular ([AlMe₂Ln(mbmp)₂(thf)₂] (Ln=Pr 15, Sm 16, and Tb 17)) and ionic [La(mbmp)(thf)₅][AlMe₂(mbmp)] (18) complexes. One gadolinium-potassium ([K(thf)₃Gd(mbmp)₂(thf)₂] (19)), and one ytterbium-zinc species ([ZnEtYb(mbmp)₂(thf)] (20)) were isolated from treatment of reaction mixtures with potassium bis(trimethylsilyl)amide and diethylzinc respectively

Non-linear electromagnetic response of graphene

It is shown that the massless energy spectrum of electrons and holes in graphene leads to the strongly non-linear electromagnetic response of this system. We predict that the graphene layer, irradiated by electromagnetic waves, emits radiation at higher frequency harmonics and can work as a frequency multiplier. The operating frequency of the graphene frequency multiplier can lie in a broad range from microwaves to the infrared.Comment: 5 pages, 3 figure