Distributions of Upper PAPR and Lower PAPR of OFDM Signals in Visible Light Communications

Orthogonal frequency-division multiplexing (OFDM) in visible light communications (VLC) inherits the disadvantage of high peak-to-average power ratio (PAPR) from OFDM in radio frequency (RF) communications. The upper peak power and lower peak power of real-valued VLC-OFDM signals are both limited by the dynamic constraints of light emitting diodes (LEDs). The efficiency and transmitted electrical power are directly related with the upper PAPR (UPAPR) and lower PAPR (LPAPR) of VLC-OFDM. In this paper, we will derive the complementary cumulative distribution function (CCDF) of UPAPR and LPAPR, and investigate the joint distribution of UPAPR and LPAPR.Comment: acceptted by IEEE ICASSP 2014. arXiv admin note: text overlap with arXiv:1304.019

Unbalanced edge modes and topological phase transition in gated trilayer graphene

Gapless edge modes hosted by chirally-stacked trilayer graphene display unique features when a bulk gap is opened by applying an interlayer potential difference. We show that trilayer graphene with half-integer valley Hall conductivity leads to unbalanced edge modes at opposite zigzag boundaries, resulting in a natural valley current polarizer. This unusual characteristic is preserved in the presence of Rashba spin-orbit coupling that turns a gated trilayer graphene into a ${Z}_2$ topological insulator with an odd number of helical edge mode pairs.Comment: 5 pages, 4 figure

Clock shifts in a Fermi gas interacting with a minority component: a soluble model

We consider the absorption spectrum of a Fermi gas mixed with a minority species when majority fermions are transferred to another internal state by an external probe. In the limit when the minority species is much more massive than the majority one, we show that the minority species may be treated as static impurities and the problem can be solved in closed form. The analytical results bring out the importance of vertex corrections, which change qualitatively the nature of the absorption spectrum. It is demonstrated that large line shifts are not associated with resonant interactions in general. We also show that the commonly used ladder approximation fails when the majority component is degenerate for large mass ratios between the minority and majority species and that bubble diagrams, which correspond to the creation of many particle--hole pairs, must be taken into account. We carry out detailed numerical calculations, which confirm the analytical insights and we point out the connection to shadowing phenomena in nuclear physics.Comment: 8 pages, 4 figures, NORDITA-2010-

Valley-Hall Kink and Edge States in Multilayer Graphene

We report on a theoretical study of one-dimensional (1D) states localized at few-layer graphene system ribbon edges, and at interfaces between few-layer graphene systems with different valley Hall conductivities. These 1D states are topologically protected when valley mixing is neglected. We address the influence on their properties of stacking arrangement, interface structure, and external electric field perpendicular to the layers. We find that 1D states are generally absent at multilayer ribbon armchair direction edges, but present irrespective of crystallographic orientation at any internal valley-Hall interface of an ABC stacked multilayer.Comment: 5 pages, 3 figure

A variant transfer matrix method suitable for transport through multi-probe systems

We have developed a variant transfer matrix method that is suitable for transport through multi-probe systems. Using this method, we have numerically studied the quantum spin Hall effect (QSHE) on 2D graphene with both intrinsic (Vso) and Rashba (Vr) spin-orbit (SO) couplings. The integer QSHE arises in the presence of intrinsic SO interaction and is gradually destroyed by the Rashba SO interaction and disorder fluctuation. We have numerically determined the phase boundaries separating integer QSHE and spin Hall liquid. We have found that when Vso> 0.2t with t the hopping constant the energy gap needed for the integer QSHE is the largest satisfying |E|<t. For smaller Vso the energy gap decreases linearly. In the presence of Rashba SO interaction or disorders, the energy gap diminishes. With Rashba SO interaction the integer QSHE is robust at the largest energy within the energy gap while at the smallest energy within the energy gap the integer QSHE is insensitive to the disorder

Anderson Localization from Berry-Curvature Interchange in Quantum Anomalous Hall System

We theoretically investigate the localization mechanism of the quantum anomalous Hall effect (QAHE) in the presence of spin-flip disorders. We show that the QAHE keeps quantized at weak disorders, then enters a Berry-curvature mediated metallic phase at moderate disorders, and finally goes into the Anderson insulating phase at strong disorders. From the phase diagram, we find that at the charge neutrality point although the QAHE is most robust against disorders, the corresponding metallic phase is much easier to be localized into the Anderson insulating phase due to the \textit{interchange} of Berry curvatures carried respectively by the conduction and valence bands. At the end, we provide a phenomenological picture related to the topological charges to better understand the underlying physical origin of the QAHE Anderson localization.Comment: 6 pages, 4 figure

Molecular Cloning and Response to Water Temperature and Nutrient Manipulation of Insulin-like Growth Factor (IGF) Genes in Golden Pompano Trachinotus ovatus (Linnaeus 1758) Larvae

In this study, insulin-like growth factor I (IGF I) and IGF II in golden pompano larvae were cloned and analyzed. In the first trial, IGF expression during ontogeny of larvae in the first 18-days of their life was explored, and then the response of IGFs to water temperature (23, 26, and 29oC) on 12 day post hatching (DPH) and 18 DPH were compared. On 28 DPH, the response of IGFs to the manipulation of nutrients was evaluated. The expression of IGF I increased with the increase of fish age, and was not significantly affected by water temperature. The expression of IGF II was affected by water temperature on 12 DPH and 18 DPH. The expression of IGF II at 23oC was significantly higher than at 26oC and 29oC. The expression of IGFs in fish larvae on 28 DPH was not concomitant with nutrient manipulation. This study detected the gene expression of IGFs at the early stage of golden pompano larvae. The time dependent expression of IGF genes in fish larvae is important to understand the ontogenetic development and growth of fish larvae in early life

RESONANCE AND REVIVALS I. QUANTUM ROTOR AND INFINITE-WELL DYNAMICS

Author Institution: Department of Physics, University of Arkansas, Fayetteville, AR 72701; Microelectronics-Photonics, University of Arkansas, Fayetteville, AR 72701Space-time structure of exploding quantum wave packets exhibit a resonate beating phenomena. Such "super-beats" were called "revivals" by J. H. Eberly in connection with numerical studies of Jaynes-Cummings models of atom-in-cavity quantum electrodynamics. The term revival refers to the ability of an initial localized wave packet to dramatically "un-explode" after a period of decoherent quiescence and then more-or-less repeat the process. Analogous revival dynamics can be seen most clearly in a simple 1D rotor or Bohr-ring atomic model, and this provides what is perhaps the clearest understanding so far of the underlying wave mechanics. In this model the main revival and its multitude of sub-revivals repeat perfectly. For this model it is possible predict the space-time location of each revival peak and rank its coherence using a Farey-sum formula so named after a geologist who studied tidal resonance in the early 1800's. Moreover, it is possible to calculate the phases of individual revival peaks using overlapping Cyclic (Cn) group character tables. The resulting interference patterns clearly exhibit all factors of each integer n below a certain Farey-threshold determined by spatial width of the initial packet. A subsequent talk will discuss the revivals observed in Morse oscillator vibrational potential models