Quantum transport of Dirac electrons in graphene in the presence of a spatially modulated magnetic field

We have investigated the electrical transport properties of Dirac electrons in a monolayer graphene sheet in the presence of a perpendicular magnetic field that is modulated weakly and periodically along one direction.We find that the Landau levels broaden into bands and their width oscillates as a function of the band index and the magnetic field.We determine the $\sigma_{yy}$ component of the magnetoconductivity tensor for this system which is shown to exhibit Weiss oscillations.We also determine analytically the asymptotic expressions for $\sigma_{yy}$.We compare these results with recently obtained results for electrically modulated graphene as well as those for magnetically modulated conventional two-dimensional electron gas (2DEG) system.We find that in the magnetically modulated graphene system cosidered in this work,Weiss oscillations in $\sigma_{yy}$ have a reduced amplitude compared to the 2DEG but are less damped by temperature while they have a higher amplitude than in the electrically modulated graphene system. We also find that these oscillations are out of phase by $\pi$ with those of the electrically modulated system while they are in phase with those in the 2DEG system.Comment: Accepted in PRB: 10 pages, 3 figure

Theory of Weiss oscillations in the magnetoplasmon spectrum of Dirac electrons in graphene

We present the collective excitations spectrum (magnetoplasmon spectrum) of Dirac electrons in a weakly modulated single graphene layer in the presence of a uniform magnetic field. We consider electric modulation in one-dimension and the magnetic field applied perpendicular to graphene.We derive analytical results for the intra-Landau band plasmon spectrum within the self-consistent-field approach. We find Weiss oscillations in the magnetoplasmon spectrum which is the primary focus of this work. Results are presented for the intra-Landau band magnetoplasmon spectrum as a function of inverse magnetic field. These results are also compared with those of conventional 2DEG. We have found that the Weiss oscillations in the magnetoplasmon spectrum are larger in amplitude compared to those in conventional 2DEG for the same modulation strength, period of modulation and electron density.Comment: 9 pages, 1 figure Phys. Rev. B (accepted for publication

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

Evaluating tools to support a new practical classification of diabetes: excellent control may represent misdiagnosis and omission from disease registers is associated with worse control.

To conduct a service evaluation of usability and utility on-line clinical audit tools developed as part of a UK Classification of Diabetes project to improve the categorisation and ultimately management of diabetes

The Effect of 2, 4-Dichlorophenoxy Acetic Acid (2, 4-D) Concentration on Callus Induction in Sugarcane (Saccharum officinarum)

Experiment was designed and conducted to determine the most appropriate concentration of 2, 4-Dichlorophenoxy Acetic Acid suitable for callus induction in sugarcane. Explants were obtained from apical meristems of two sugarcane cultivars (SP726180 and CO-001) and cultured in a modified MS medium supplemented with varying concentrations of 2,4-D. After sterilization, the explants were incubated in the growth chamber at 270C and monitored for callus induction for four Weeks. The resulting calli were sub cultured on a media with a reduced 2,4-D concentration to induce somatic embryogenesis. Percentages of callus formation, embryogenic callus as well as growth coefficient were the parameters monitored. Data generated were analyzed using Chi-square and showed a significant difference among the different 2,4-D concentrations (P≤0.05). Swelling of the explants was observed one week after inoculation while callus initiation begun after two weeks. The calli were found to be yellowish, compact and nodular. Callus induction was found to increase with increase in the concentration of 2,4-D.Keywords: Saccharum officinarum, Explants, Callus Induction, 2,4-Dichlorophenoxy Acetic AcidNigerian Journal of Basic and Applied Science (2011), 19 (2): 213-21

Experimental and Analytical Simulation Analyses on the Electrical Performance of Thermoelectric Generator Modules for Direct and Concentrated Quartz-Halogen Heat Harvesting

The scope of thermoelectric generators (TEGs), in improving the electric vehicle battery performance and glass/steel manufacturing industries, could achieve wider significance by harnessing the unused radiative heat and light conversion to electrical power. This paper experimentally investigates the electrical performance correlated to concentrated quartz-halogen, with acrylic Fresnel lens and heat-light harvesting, coupled with heat sink. This study also experimentally examined the influence of extreme temperature variance on the open circuit generated voltage of the Peltier electrical failure mode, compared to the standard performance parameters of the commercial TEG module. The research results presented provide expedient perception into the testing (open circuit voltage, short circuit current, and full load power) of a commercial heat-stove TEG to understand its performance limitations. The analytical simulation and mathematical model developed in MATLAB compared the electrical performance parameters and its dependencies. The analytical simulation shows that increasing the heat-sink temperature increases the efficiency of not more than 2% at the ΔT of 360 K, due to the limitation of the ZT ̅ of 0.43 at ΔT of 390 K. The maximum ZT ̅ of 0.7 for Bi2Te3, with an achievable efficiency of 4.5% at the Seebeck coefficient of 250 µV/K, was predicted. The design of three experimental setups and results presented demonstrate the functioning of TEG in stable and unstable temperature conditions, confirming the theoretical study and stipulating a quantity of the electrical output power in relation to extreme temperature conditions

The NMR of High Temperature Superconductors without Anti-Ferromagnetic Spin Fluctuations

A microscopic theory for the NMR anomalies of the planar Cu and O sites in superconducting La_1.85Sr_0.15CuO_4 is presented that quantitatively explains the observations without the need to invoke anit-ferromagnetic spin fluctuations on the planar Cu sites and its significant discrepancy with the observed incommensurate neutron spin fluctuations. The theory is derived from the recently published ab-initio band structure calculations that correct LDA computations tendency to overestimate the self-coulomb repulsion for the half-filled Cu d_x2-y2 orbital for these ionic systems. The new band structure leads to two bands at the Fermi level with holes in the Cu d_z2 and apical O p_z orbitals in addition to the standard Cu d_x2-y2 and planar O p_sigma orbitals. This band structure is part of a new theory for the cuprates that explains a broad range of experiments and is based upon the formation of Cooper pairs comprised of a k up spin electron from one band and a -k down spin electron from another band (Interband Pairing Model).Comment: In Press, Journal of Physical Chemistry. See also http://www.firstprinciples.com. Minor changes to references and figure readabilit

Lepton Polarization Asymmetry in B l l(bar) decays in R-parity violating Minimal Supersymmetric Standard Model

We study the implication of R-parity violating Rp Minimal Supersymmetric Standard Model (MSSM) model in lepton polarization asymmetry ALP in B l l(bar) decays . The analysis show that the ALP is significant in a certain phenomenological parametric region of Yukawa couplings. We have also placed indirect bounds on Lambda' lambda couplings as obtained from B t t(bar).Comment: 6 pages, 4 figures Changes of notation in Eq(8-11,17-19),Eq.20 adde

Nonequilibrium Ablation of Phenolic Impregnated Carbon Ablator

In previous work, an equilibrium ablation and thermal response model for Phenolic Impregnated Carbon Ablator was developed. In general, over a wide range of test conditions, model predictions compared well with arcjet data for surface recession, surface temperature, in-depth temperature at multiple thermocouples, and char depth. In this work, additional arcjet tests were conducted at stagnation conditions down to 40 W/sq cm and 1.6 kPa. The new data suggest that nonequilibrium effects become important for ablation predictions at heat flux or pressure below about 80 W/sq cm or 10 kPa, respectively. Modifications to the ablation model to account for nonequilibrium effects are investigated. Predictions of the equilibrium and nonequilibrium models are compared with the arcjet data