13,685 research outputs found
Generalised Marcus Theory for Multi-Molecular Delocalised Charge Transfer
Although Marcus theory is widely used to describe charge transfer in
molecular systems, in its usual form it is restricted to transfer from one
molecule to another. If a charge is delocalised across multiple donor
molecules, this approach requires us to treat the entire donor aggregate as a
unified supermolecule, leading to potentially expensive quantum-chemical
calculations and making it more difficult to understand how the aggregate
components contribute to the overall transfer. Here, we show that it is
possible to describe charge transfer between groups of molecules in terms of
the properties of the constituent molecules and couplings between them,
obviating the need for expensive supermolecular calculations. We use the
resulting theory to show that charge delocalisation between molecules in either
the donor or acceptor aggregates can enhance the rate of charge transfer
through a process we call supertransfer (or suppress it through subtransfer).
The rate can also be enhanced above what is possible with a single molecule by
judiciously tuning energy levels and reorganisation energies. We also describe
bridge-mediated charge transfer between delocalised molecular aggregates. The
equations of generalised Marcus theory are in closed form, providing
qualitative insight into the impact of delocalisation on charge dynamics in
molecular systems
Generalized parton distributions from neutrino experiments
The analysis of deeply virtual meson production is extended to
neutrino-production of the pseudo-Goldstone mesons (pions, kaons, eta-mesons)
on nucleons, with the flavor content of the recoil baryon either preserved, or
changed to a hyperon from the same SU(3) octet. We rely on the SU(3) relations
and express all the cross-sections in terms of the proton generalized parton
distributions (GPDs). The corresponding amplitudes are calculated at the
leading twist level and in the leading order in \alpha_{s}, using a
phenomenological parametrization of GPDs. We also included in the analysis the
electromagnetic O(alpha_{em})-corrections to neutrino-induced deeply virtual
meson production (\nuDVMP). We found that such electromagnetic corrections
decrease with Q^2 in the Bjorken regime less than the standard \nuDVMP handbag
contribution, so the electromagnetic mechanism dominates at large Q^2. The
electromagnetic corrections give rise to an angular correlation between the
lepton and hadron scattering planes with harmonics sensitive to the real and
imaginary parts of the DVMP amplitude. These corrections constitute a few
percent effect in the kinematics of the forthcoming MINERvA experiment at
Fermilab and should be taken into account in precise tests of GPD
parametrizations. For virtualities Q^2~100 GeV^2 these corrections become on a
par with \nuDVMP handbag contributions.Comment: 5 pages, 3 figures, to appear in the proceedings of the DIS 2013
Workshop, Marseille, France, 22-26 April 201
Key Generation in Wireless Sensor Networks Based on Frequency-selective Channels - Design, Implementation, and Analysis
Key management in wireless sensor networks faces several new challenges. The
scale, resource limitations, and new threats such as node capture necessitate
the use of an on-line key generation by the nodes themselves. However, the cost
of such schemes is high since their secrecy is based on computational
complexity. Recently, several research contributions justified that the
wireless channel itself can be used to generate information-theoretic secure
keys. By exchanging sampling messages during movement, a bit string can be
derived that is only known to the involved entities. Yet, movement is not the
only possibility to generate randomness. The channel response is also strongly
dependent on the frequency of the transmitted signal. In our work, we introduce
a protocol for key generation based on the frequency-selectivity of channel
fading. The practical advantage of this approach is that we do not require node
movement. Thus, the frequent case of a sensor network with static motes is
supported. Furthermore, the error correction property of the protocol mitigates
the effects of measurement errors and other temporal effects, giving rise to an
agreement rate of over 97%. We show the applicability of our protocol by
implementing it on MICAz motes, and evaluate its robustness and secrecy through
experiments and analysis.Comment: Submitted to IEEE Transactions on Dependable and Secure Computin
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