129 research outputs found
Electron transport in nanotube--molecular wire hybrids
We study contact effects on electron transport across a molecular wire
sandwiched between two semi-infinite (carbon) nanotube leads as a model for
nanoelectrodes. Employing the Landauer scattering matrix approach we find that
the conductance is very sensitive to parameters such as the coupling strength
and geometry of the contact. The conductance exhibits markedly different
behavior in the two limiting scenarios of single contact and multiple contacts
between the molecular wire and the nanotube interfacial atoms. In contrast to a
single contact the multiple-contact configuration acts as a filter selecting
single transport channels. It exhibits a scaling law for the conductance as a
function of coupling strength and tube diameter. We also observe an unusual
narrow-to-broad-to-narrow behavior of conductance resonances upon decreasing
the coupling.Comment: 4 pages, figures include
Photoionization of ultracold and Bose-Einstein condensed Rb atoms
Photoionization of a cold atomic sample offers intriguing possibilities to
observe collective effects at extremely low temperatures. Irradiation of a
rubidium condensate and of cold rubidium atoms within a magneto-optical trap
with laser pulses ionizing through 1-photon and 2-photon absorption processes
has been performed. Losses and modifications in the density profile of the
remaining trapped cold cloud or the remaining condensate sample have been
examined as function of the ionizing laser parameters. Ionization
cross-sections were measured for atoms in a MOT, while in magnetic traps losses
larger than those expected for ionization process were measured.Comment: 9 pages, 7 figure
Students as co-creators of teaching approaches, course design and curricula: implications for academic developers
Within higher education, studentsâ voices are frequently overlooked in the design of teaching approaches, courses and curricula. In this paper we outline the theoretical background to arguments for including students as partners in pedagogical planning processes. We present examples where students have worked collaboratively in design processes along with the beneficial outcomes of these examples. Finally we focus on some of the implications and opportunities for academic developers of proposing collaborative approaches to pedagogical planning
Coherent multiple light scattering in Faraday active materials
Wave propagation in multiple scattering media shows various kinds of coherent phenomena such as coherent backscattering [1, 2] or Anderson localization [3], both of which are intimately connected to the concept of reciprocity. Manipulating reciprocity in such media is a powerful tool to study these phenomena in experiments [4]. Here we discuss the manipulation of reciprocity in reflection and transmission geometry for the case of light propagation in magneto-optical media. We show new experiments on coherent backscattering and speckle correlations in strongly scattering samples containing Faraday active materials (CeF3) with transport mean free path in the ÎŒm range, at low temperatures (T < 10âK) and high fields (B = 18âT). Under such conditions we observe the effect of a Faraday rotation saturation in multiple scattering measurements.publishe
Tight-binding parameters for charge transfer along DNA
We systematically examine all the tight-binding parameters pertinent to
charge transfer along DNA. The molecular structure of the four DNA bases
(adenine, thymine, cytosine, and guanine) is investigated by using the linear
combination of atomic orbitals method with a recently introduced
parametrization. The HOMO and LUMO wavefunctions and energies of DNA bases are
discussed and then used for calculating the corresponding wavefunctions of the
two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO
and LUMO energies of the bases are in good agreement with available
experimental values. Our results are then used for estimating the complete set
of charge transfer parameters between neighboring bases and also between
successive base-pairs, considering all possible combinations between them, for
both electrons and holes. The calculated microscopic quantities can be used in
mesoscopic theoretical models of electron or hole transfer along the DNA double
helix, as they provide the necessary parameters for a tight-binding
phenomenological description based on the molecular overlap. We find that
usually the hopping parameters for holes are higher in magnitude compared to
the ones for electrons, which probably indicates that hole transport along DNA
is more favorable than electron transport. Our findings are also compared with
existing calculations from first principles.Comment: 15 pages, 3 figures, 7 table
Pequenas espĂ©cies de Parmeliaceae ciliadas no Parque Estadual da Cantareira, SĂŁo Paulo, SP, Brasil: gĂȘneros Bulbothrix, Parmelinella e Parmelinopsis (Parmeliaceae, Ascomycota)
Pequenas espĂ©cies de Parmeliaceae (Ascomycota) eciliadas no Parque Estadual da Cantareira, estado de SĂŁo Paulo, Brasil: gĂȘneros Canoparmelia e Crespoa
GĂȘneros de macroliquens do campus da Universidade Federal de SĂŁo Carlos, Brasil - UFSCar, municĂpio de SĂŁo Carlos, estado de SĂŁo Paulo
Espécies de Parmotrema (Parmeliaceae, Ascomycetes liquenizados) com rizinas dimórficas do litoral centro-sul do estado de São Paulo
EspĂ©cies de Parmotrema (Parmeliaceae, Ascomycota) do litoral centro-sul do Estado de SĂŁo Paulo: II. Grupos quĂmicos norstĂctico e salazĂnico
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