Upper Limits on the Pulsed Radio Emission from the Geminga Pulsar at 35 & 327 MHz

We report here our observations at 35 MHz and 327 MHz made in the direction of the Gamma Ray pulsar Geminga. Based on the observed absence of any significant pulsed emission from this source above our detection thresholds at the two frequencies, we obtain useful upper-limits for the average flux to be 75-100 mJy at 35 MHz, and 0.2-0.3 mJy at 327 MHz. We discuss a few possible reasons for the ``radio-quiet'' nature of this pulsar at frequencies other than around 100 MHz.Comment: Accepted for publication in Astronomy & Astrophysic

Characteristic impedance of microstrip lines

The dyadic Green's function for a current embedded in a grounded dielectric slab is used to analyze microstrip lines at millimeter wave frequencies. The dyadic Green's function accounts accurately for fringing fields and dielectric cover over the microstrip line. Using Rumsey's reaction concept, an expression for the characteristic impedance is obtained. The numerical results are compared with other reported results

Rail transit fare collection: Policy and technology assessment

The impact of fare policies and fare structure on the selection of equipment was investigated, fare collection systems are described, hardware and technology related problems are documented, and the requirements of a fare collection simulation model are outlined. Major findings include: (1) a wide variation in the fare collection systems and equipment, caused primarily by historical precedence; (2) the reliability of AFC equipment used at BART and WMATA discouraged other properties from considering use of similar equipment; (3) existing equipment may not meet the fare collection needs of properties in the near future; (4) the cost of fare collection operation and maintenance is high; and (5) the relatively small market in fare collection equipment discourages new product development by suppliers. Recommendations for fare collection R&D programs include development of new hardware to meet rail transit needs, study of impacts of alternate fare policies increased communication among policymakers, and consensus on fare policy issues

Mapping the Dirac point in gated bilayer graphene

We have performed low temperature scanning tunneling spectroscopy measurements on exfoliated bilayer graphene on SiO2. By varying the back gate voltage we observed a linear shift of the Dirac point and an opening of a band gap due to the perpendicular electric field. In addition to observing a shift in the Dirac point, we also measured its spatial dependence using spatially resolved scanning tunneling spectroscopy. The spatial variation of the Dirac point was not correlated with topographic features and therefore we attribute its shift to random charged impurities.Comment: 3 pages, 3 figure

Spatially resolved spectroscopy of monolayer graphene on SiO2

We have carried out scanning tunneling spectroscopy measurements on exfoliated monolayer graphene on SiO$_2$ to probe the correlation between its electronic and structural properties. Maps of the local density of states are characterized by electron and hole puddles that arise due to long range intravalley scattering from intrinsic ripples in graphene and random charged impurities. At low energy, we observe short range intervalley scattering which we attribute to lattice defects. Our results demonstrate that the electronic properties of graphene are influenced by intrinsic ripples, defects and the underlying SiO$_2$ substrate.Comment: 6 pages, 7 figures, extended versio

Electroweak Model Independent Tests for SU(3) Symmetry in Hadronic B Decays

We study effects of new physics beyond the Standard Model on SU(3) symmetry in charmless hadronic two body B decays. It is found that several equalities for some of the decay amplitudes, such as $A(B_d (B_u) \to \pi^+\pi^-,\pi^+ K^- (\pi^- \bar K^0)) =A(B_s \to K^+ \pi^-, K^- K^+ (K^0 \bar K^0))$, $A(B_d \to \pi^+\rho^-, \pi^- \rho^+, K^-\rho^+, \pi^+ K^{*-}) = A(B_s \to K^+ \rho^-, \pi^- K^{*+}, K^- K^{*+}, K^+ K^{*-})$, $A(B_d (B_u) \to \rho^+\rho^-, \rho^+ K^{*-}(\rho^- \bar K^{*0})) =A(B_s \to K^{*+} \rho^-, K^{*-} K^{*+} (K^{*0} \bar K^{*0}))$, predicted by SU(3) symmetry in the SM are not affected by new physics. These relations provide important electroweak model independent tests for SU(3) symmetry in B decays.Comment: 4 pages, revte