4,183 research outputs found
Fluorescence energy transfer enhancement in aluminum nanoapertures
Zero-mode waveguides (ZMWs) are confining light into attoliter volumes,
enabling single molecule fluorescence experiments at physiological micromolar
concentrations. Among the fluorescence spectroscopy techniques that can be
enhanced by ZMWs, F\"{o}rster resonance energy transfer (FRET) is one of the
most widely used in life sciences. Combining zero-mode waveguides with FRET
provides new opportunities to investigate biochemical structures or follow
interaction dynamics at micromolar concentration with single molecule
resolution. However, prior to any quantitative FRET analysis on biological
samples, it is crucial to establish first the influence of the ZMW on the FRET
process. Here, we quantify the FRET rates and efficiencies between individual
donor-acceptor fluorophore pairs diffusing in aluminum zero-mode waveguides.
Aluminum ZMWs are important structures thanks to their commercial availability
and the large literature describing their use for single molecule fluorescence
spectroscopy. We also compare the results between ZMWs milled in gold and
aluminum, and find that while gold has a stronger influence on the decay rates,
the lower losses of aluminum in the green spectral region provide larger
fluorescence brightness enhancement factors. For both aluminum and gold ZMWs,
we observe that the FRET rate scales linearly with the isolated donor decay
rate and the local density of optical states (LDOS). Detailed information about
FRET in ZMWs unlocks their application as new devices for enhanced single
molecule FRET at physiological concentrations
Nanophotonic enhancement of the F\"orster resonance energy transfer rate on single DNA molecules
Nanophotonics achieves accurate control over the luminescence properties of a
single quantum emitter by tailoring the light-matter interaction at the
nanoscale and modifying the local density of optical states (LDOS). This
paradigm could also benefit to F\"orster resonance energy transfer (FRET) by
enhancing the near-field electromagnetic interaction between two fluorescent
emitters. Despite the wide applications of FRET in nanosciences, using
nanophotonics to enhance FRET remains a debated and complex challenge. Here, we
demonstrate enhanced energy transfer within single donor-acceptor fluorophore
pairs confined in gold nanoapertures. Experiments monitoring both the donor and
the acceptor emission photodynamics at the single molecule level clearly
establish a linear dependence of the FRET rate on the LDOS in nanoapertures.
These findings are applied to enhance the FRET rate in nanoapertures up to six
times, demonstrating that nanophotonics can be used to intensify the near-field
energy transfer and improve the biophotonic applications of FRET
Baryonic matter in the lattice Gross-Neveu model
We investigate the Gross-Neveu model on the lattice at finite temperature and chemical potential in the limit of an infinite number of fermion flavours. We check the universality of the continuum limit of staggered and overlap fermions at finite temperature and chemical potential. We show that at finite density a recently discovered phase of cold baryonic matter emerges as a baryon crystal from a spatially inhomogeneous fermion condensate. However, we also demonstrate that on the lattice, this new phase disappears at large coupling or in small volumes. Furthermore, we investigate unusual finite size effects that appear at finite chemical potential. Finally, we speculate on the implications of our findings for QCD
Plasmonic antennas and zero mode waveguides to enhance single molecule fluorescence detection and fluorescence correlation spectroscopy towards physiological concentrations
Single-molecule approaches to biology offer a powerful new vision to
elucidate the mechanisms that underpin the functioning of living cells.
However, conventional optical single molecule spectroscopy techniques such as
F\"orster fluorescence resonance energy transfer (FRET) or fluorescence
correlation spectroscopy (FCS) are limited by diffraction to the nanomolar
concentration range, far below the physiological micromolar concentration range
where most biological reaction occur. To breach the diffraction limit, zero
mode waveguides and plasmonic antennas exploit the surface plasmon resonances
to confine and enhance light down to the nanometre scale. The ability of
plasmonics to achieve extreme light concentration unlocks an enormous potential
to enhance fluorescence detection, FRET and FCS. Single molecule spectroscopy
techniques greatly benefit from zero mode waveguides and plasmonic antennas to
enter a new dimension of molecular concentration reaching physiological
conditions. The application of nano-optics to biological problems with FRET and
FCS is an emerging and exciting field, and is promising to reveal new insights
on biological functions and dynamics.Comment: WIREs Nanomed Nanobiotechnol 201
Frontal plane stabilization and hopping with a 2DOF tail
The Jerboa, a tailed bipedal robot with two hip-actuated, passive-compliant legs and a doubly actuated tail, has been shown both formally and empirically to exhibit a variety of stable hopping and running gaits in the sagittal plane. In this paper we take the first steps toward operating Jerboa as a fully spatial machine by addressing the predominant mode of destabilization away from the sagittal plane: body roll. We develop a provably stable controller for underactuated aerial stabilization of the coupled body roll and tail angles, that uses just the tail torques. We show that this controller is successful at reliably reorienting the Jerboa body in roughly 150 ms of freefall from a large set of initial conditions. This controller also enables (and appears intuitively to be crucial for) sustained empirically stable hopping in the frontal plane by virtue of its substantial robustness against destabilizing perturbations and calibration errors. The controller as well as the analysis methods developed here are applicable to any robotic platform with a similar doubly-actuated spherical tail joint
Does e-learning policy drive change in Higher Education?: A case study relating models of organisational change to e-learning implementation
Due to the heightened competition introduced by the potential global market and the need for structural changes within organisations delivering e-content, e-learning policy is beginning to take on a more significant role within the context of educational policy per se. For this reason, it is becoming increasingly important to establish what effect such policies have and how they are achieved. This paper addresses this question, illustrating five ways in which change is understood (Fordist, evolutionary, ecological, community of practice and discourse-oriented) and then using this range of perspectives to explore how e-learning policy drives change (both organisational and pedagogic) within a selected higher education institution. The implications of this case are then discussed, and both methodological and pragmatic conclusions are drawn, considering the relative insights offered by the models and ways in which change around e-learning might be supported or promoted
Editorial: water governance in a climate change world: appraising systemic and adaptive effectiveness
and other research outputs Editorial: water governance in a climate change world: appraising systemic and adaptive effectivenes
On the phase diagram of QCD at finite isospin density
Using a canonical formalism, we determine the equation of state and the phase
diagram of eight-flavour QCD, as a function of temperature and isospin density.
Two mechanisms are at work: Bose condensation of pions at high density, and
deconfinement at high temperature. We study their interplay and find that on
our small and coarse lattice the first order deconfinement transition appears
to end at a critical point at finite density. We investigate the strength of
the overlap and of the sign problems and discuss implications for the baryonic
density case.Comment: 7 pages, 4 figures, Contribution to Lattice 2007, Regensburg,
Germany, 30 July - 4 August 200
CVcat: an interactive database on cataclysmic variables
CVcat is a database that contains published data on cataclysmic variables and
related objects. Unlike in the existing online sources, the users are allowed
to add data to the catalogue. The concept of an ``open catalogue'' approach is
reviewed together with the experience from one year of public usage of CVcat.
New concepts to be included in the upcoming AstroCat framework and the next
CVcat implementation are presented. CVcat can be found at http://www.cvcat.org.Comment: 5 pages A&A Latex, 4 figures, accepted for publication in A&
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