7,237 research outputs found
Ultrabright Linearly Polarized Photon Generation from a Nitrogen Vacancy Center in a Nanocube Dimer Antenna
We demonstrate an exceptionally bright photon source based on a single
nitrogen- vacancy center (NV-center) in a nanodiamond (ND), placed in the
nanoscale gap between two monocrystalline silver cubes in a dimer
configuration. The system is operated near saturation at a stable photon rate
of 850 kcps, while we further achieve strongly polarized emission and high
single photon purity, evident by the measured auto-correlation with a
g(2)(0)-value of 0.08. These photon source features are key parameters for
quantum technological applications, such as secure communication based on
quantum key distribution. The cube antenna is assembled with an atomic force
microscope, which allows us to predetermine the dipole orientation of the
NV-center and optimize cube positioning accordingly, while also tracking the
evolution of emission parameters from isolated ND to the 1 and 2 cube
configuration. The experiment is well described by finite element modelling,
assuming an instrinsic quantum efficiency of 0.35. We attribute the large
photon rate of the assembled photon source, to increased quantum efficiency of
the NV-center and high antenna efficiency
A webometric analysis of Australian Universities using staff and size dependent web impact factors (WIF)
This study describes how search engines (SE) can be employed for automated, efficient data gathering for Webometric studies using predictable URLs. It then compares the usage of staffrelated Web Impact Factors (WIFs) to sizerelated impact factors for a ranking of Australian universities, showing that rankings based on staffrelated WIFs correlate much better with an established ranking from the Melbourne Institute than commonly used sizedependent WIFs. In fact sizedependent WIFs do not correlate with the Melbourne ranking at all. It also compares WIF data for Australian Universities provided by Smith (1999) for a longitudinal comparison of the WIF of Australian Universities over the last decade. It shows that sizedependent WIF values declined for most Australian universities over the last ten years, while staffdependent WIFs rose
Resonance energy transfer from a fluorescent dye molecule to plasmon and electron-hole excitations of a metal nanoparticle
We study the distance dependence of the rate of electronic excitation energy
transfer from a dye molecule to a metal nanoparticle. Using the spherical
jellium model, we evaluate the rates corresponding to the excitation of l = 1,
2, and 3 modes of the nanoparticle. Our calculation takes into account both the
electron-hole pair and the plasmon excitations of the nanoparticle. The rate
follows conventional R^-6 dependence at large distances while small deviations
from this behavior are observed at shorter distances. Within the framework of
the jellium model, it is not possible to attribute the experimentally observed
d^-4 dependence of the rate to energy transfer to plasmons or e-h pair
excitations.Comment: 4 figure
The dynamics of loop formation in a semiflexible polymer
The dynamics of loop formation by linear polymer chains has been a topic of
several theoretical/experimental studies. Formation of loops and their opening
are key processes in many important biological processes. Loop formation in
flexible chains has been extensively studied by many groups. However, in the
more realistic case of semiflexible polymers, not much results are available.
In a recent study (K. P. Santo and K. L. Sebastian, Phys. Rev. E, \textbf{73},
031293 (2006)), we investigated opening dynamics of semiflexible loops in the
short chain limit and presented results for opening rates as a function of the
length of the chain. We presented an approximate model for a semiflexible
polymer in the rod limit, based on a semiclassical expansion of the bending
energy of the chain. The model provided an easy way to describe the dynamics.
In this paper, using this model, we investigate the reverse process, i.e., the
loop formation dynamics of a semiflexible polymer chain by describing the
process as a diffusion-controlled reaction. We perform a detailed
multidimensional analysis of the problem and calculate closing times for a
semiflexible chain which leads to results that are physically expected. Such a
multidimensional analysis leading to these results does not seem to exist in
the literature so far.Comment: 37 pages 4 figure
A test of the CPL parameterization for rapid dark energy equation of state transitions
We test the robustness and flexibility of the Chevallier-Polarski-Linder
(CPL) parameterization of the Dark Energy equation of state in recovering a four-parameter step-like fiducial model. We
constrain the parameter space region of the underlying fiducial model where the
CPL parameterization offers a reliable reconstruction. It turns out that non
negligible biases leak into the results for recent () rapid transitions,
but that CPL yields a good reconstruction in all other cases. The presented
analysis is performed with supernova Ia data as forecasted for a space mission
like SNAP/JDEM, combined with future expectations for the CMB shift parameter
and the BAO parameter .Comment: 8 pages, 6 ps figure
Antiferromagnetism of SrFe2As2 studied by Single-Crystal 75As-NMR
We report results of 75As nuclear magnetic resonance (NMR) experiments on a
self-flux grown high-quality single crystal of SrFe2As2. The NMR spectra
clearly show sharp first-order antiferromagnetic (AF) and structural
transitions occurring simultaneously. The behavior in the vicinity of the
transition is compared with our previous study on BaFe2As2. No significant
difference was observed in the temperature dependence of the static quantities
such as the AF splitting and electric quadrupole splitting. However, the
results of the NMR relaxation rate revealed difference in the dynamical spin
fluctuations. The stripe-type AF fluctuations in the paramagnetic state appear
to be more anisotropic in BaFe2As2 than in SrFe2As2.Comment: 4 pages, 5 figures; discussion revised; accepted for publication in
J. Phys. Soc. Jp
Ligand-Enhanced Abiotic Iron Oxidation and the Effects of Chemical versus Biological Iron Cycling in Anoxic Environments
This study introduces a newly isolated, genetically tractable bacterium (Pseudogulbenkiania sp. strain MAI-1) and explores the extent to which its nitrate-dependent iron-oxidation activity is directly biologically catalyzed. Specifically, we focused on the role of iron chelating ligands in promoting chemical oxidation of Fe(II) by nitrite under anoxic conditions. Strong organic ligands such as nitrilotriacetate and citrate can substantially enhance chemical oxidation of Fe(II) by nitrite at circumneutral pH. We show that strain MAI-1 exhibits unambiguous biological Fe(II) oxidation despite a significant contribution (~30–35%) from ligand-enhanced chemical oxidation. Our work with the model denitrifying strain Paracoccus denitrificans further shows that ligand-enhanced chemical oxidation of Fe(II) by microbially produced nitrite can be an important general side effect of biological denitrification. Our assessment of reaction rates derived from literature reports of anaerobic Fe(II) oxidation, both chemical and biological, highlights the potential competition and likely co-occurrence of chemical Fe(II) oxidation (mediated by microbial production of nitrite) and truly biological Fe(II) oxidation
Highest weight state description of the isotropic spin-1 chain
We introduce an overcomplete highest weight state basis as a calculational
tool for the description of the isotropic spin-1 chain with bilinear exchange
coupling J1 and biquadratic coupling J2. The ground state can be expressed
exactly at the three special points in the phase diagram where the Hamiltonian
corresponds to a sum of nearest neighbor total spin projection operators
(J1=0>J2, J1=-J2<0, and J1=-J2/3<0). In particular, at the phase transition
point J1=-J2<0 it is possible to exactly compute the ground states, excited
states, expectation values, and correlation functions by using the new total
spin basis.Comment: 8 pages, 1 figure, the most recent version can be found at
http://www.physik.uni-kl.de/eggert/papers
A webometric analysis of Australian Universities using staff and size dependent web impact factors (WIF)
This study describes how search engines (SE) can be employed for automated, efficient data gathering for Webometric studies using predictable URLs. It then compares the usage of staffrelated Web Impact Factors (WIFs) to sizerelated impact factors for a ranking of Australian universities, showing that rankings based on staffrelated WIFs correlate much better with an established ranking from the Melbourne Institute than commonly used sizedependent WIFs. In fact sizedependent WIFs do not correlate with the Melbourne ranking at all. It also compares WIF data for Australian Universities provided by Smith (1999) for a longitudinal comparison of the WIF of Australian Universities over the last decade. It shows that sizedependent WIF values declined for most Australian universities over the last ten years, while staffdependent WIFs rose
Controlling the elution order of insulin and its analogs in sub-/supercritical fluid chromatography using methanesulfonic acid and 18-crown-6 as mobile phase additives
The purity analysis of therapeutic peptides can often be challenging, demanding the application of more than a single analytical technique. Supercritical fluid chromatography nowadays is a promising alternative to reversed-phase liquid chromatography, providing orthogonal and complementary information. This study investigated its applicability for the separation of human insulin, its analogs and degradation products. A previously published method development protocol for peptides up to 2000 Da was successfully applied to the higher molecular weight insulins (6 kDa). A single gradient method was optimized for all insulins using a Torus DEA column (100 × 3.0 mm, 1.7 μm), carbon dioxide and a modifier consisting of methanol/acetonitrile/water/methanesulfonic acid (65:35:2:0.1, v/v/v/v). Consecutively, the crown ether 18-crown-6, which is well known to complex charged lysine sidechains and other amino functionalities, was added to the modifier to evaluate its impact on selectivity. A decreased retention and a shift in the elution order for the insulins were observed. An inverse effect on retention was found when combined with a neutral stationary phase chemistry (Viridis BEH)
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