68 research outputs found
TVWS policies to enable efficient spectrum sharing
The transition from analogue to the Digital Terrestrial Television (DTV) in Europe is planned to be completed by the end of the year 2012. The DTV spectrum allocation is such that there are a number of TV channels which cannot be used for additional high power broadcast transmitters due to mutual interference and hence are left unused within a given geographical location, i.e. the TV channels are geographically interleaved. The use of geographically interleaved spectrum provides for the so-called TV white spaces (TVWS) an opportunity for deploying new wireless services. The main objective of this paper is to present the spectrum policies that are suitable for TVWS at European level, identified within the COGEU project. The COGEU project aims the efficient exploitation of the geographical interleaved spectrum (TVWS). COGEU is an ICT collaborative project supported by the European Commission within the 7th Framework Programme. Nine partners from seven EU countries representing academia, research institutes and industry are involved in the project. The COGEU project is a composite of technical, business, and regulatory/policy domains, with the objective of taking advantage of the TV digital switchover by developing cognitive radio systems that leverage the favorable propagation characteristics of the UHF broadcast spectrum through the introduction and promotion of real-time secondary spectrum trading and the creation of new spectrum commons regimes. COGEU will also define new methodologies for compliance testing and certification of TVWS equipment to ensure non-interference coexistence with the DVB-T European standard. The innovation brought by COGEU is the combination of cognitive access to TV white spaces with secondary spectrum trading mechanisms.telecommunications,spectrum management,secondary spectrum market,regulation,TV white spaces,cognitive radio
Trapping Ultracold Atoms in a Time-Averaged Adiabatic Potential
We report the first experimental realization of ultracold atoms confined in a
time-averaged, adiabatic potential (TAAP). This novel trapping technique
involves using a slowly oscillating ( kHz) bias field to time-average the
instantaneous potential given by dressing a bare magnetic potential with a high
frequency ( MHz) magnetic field. The resultant potentials provide a
convenient route to a variety of trapping geometries with tunable parameters.
We demonstrate the TAAP trap in a standard time-averaged orbiting potential
trap with additional Helmholtz coils for the introduction of the radio
frequency dressing field. We have evaporatively cooled 5 atoms of
Rb to quantum degeneracy and observed condensate lifetimes of over
\unit[3]{s}.-Comment: 4 pages, 6 figure
Conditions for spin squeezing in a cold 87Rb ensemble
We study the conditions for generating spin squeezing via a quantum
non-demolition measurement in an ensemble of cold 87Rb atoms. By considering
the interaction of atoms in the 5S_{1/2}(F=1) ground state with probe light
tuned near the D2 transition, we show that, for large detunings, this system is
equivalent to a spin-1/2 system when suitable Zeeman substates and quantum
operators are used to define a pseudo-spin. The degree of squeezing is derived
for the rubidium system in the presence of scattering causing decoherence and
loss. We describe how the system can decohere and lose atoms, and predict as
much as 75% spin squeezing for atomic densities typical of optical dipole
traps.Comment: 9 pages, 3 figures, submitted to J. Opt. B: Quantum Semiclass. Opt.
Proceedings of ICSSUR'0
TVWS policies to enable efficient spectrum sharing
The transition from analogue to the Digital Terrestrial Television (DTV) in Europe is planned to be completed by the end of the year 2012. The DTV spectrum allocation is such that there are a number of TV channels which cannot be used for additional high power broadcast transmitters due to mutual interference and hence are left unused within a given geographical location, i.e. the TV channels are geographically interleaved. The use of geographically interleaved spectrum provides for the so-called TV white spaces (TVWS) an opportunity for deploying new wireless services. The main objective of this paper is to present the spectrum policies that are suitable for TVWS at European level, identified within the COGEU project. The COGEU project aims the efficient exploitation of the geographical interleaved spectrum (TVWS). COGEU is an ICT collaborative project supported by the European Commission within the 7th Framework Programme. Nine partners from seven EU countries representing academia, research institutes and industry are involved in the project. The COGEU project is a composite of technical, business, and regulatory/policy domains, with the objective of taking advantage of the TV digital switchover by developing cognitive radio systems that leverage the favorable propagation characteristics of the UHF broadcast spectrum through the introduction and promotion of real-time secondary spectrum trading and the creation of new spectrum commons regimes. COGEU will also define new methodologies for compliance testing and certification of TVWS equipment to ensure non-interference coexistence with the DVB-T European standard. The innovation brought by COGEU is the combination of cognitive access to TV white spaces with secondary spectrum trading mechanisms
Certified quantum non-demolition measurement of material systems
An extensive debate on quantum non-demolition (QND) measurement, reviewed in
Grangier et al. [Nature, {\bf 396}, 537 (1998)], finds that true QND
measurements must have both non-classical state-preparation capability and
non-classical information-damage tradeoff. Existing figures of merit for these
non-classicality criteria require direct measurement of the signal variable and
are thus difficult to apply to optically-probed material systems. Here we
describe a method to demonstrate both criteria without need for to direct
signal measurements. Using a covariance matrix formalism and a general noise
model, we compute meter observables for QND measurement triples, which suffice
to compute all QND figures of merit. The result will allow certified QND
measurement of atomic spin ensembles using existing techniques.Comment: 11 pages, zero figure
Ultrastructural response of arcuate nucleus neurons to fasting in aged rats
The arcuate nucleus of the hypothalamus (ARH) is involved in the control of
energy homeostasis. Leptin - an adipocyte derived hormone - is known to
act on the hypothalamic nuclei and thus to control body weight by food intake
reduction. Oxidative stress is believed to be implicated in leptin signalling. However,
its relevance for leptin-induced signal transduction within ARH remains
unclear. The goal of the study was to investigate the effect of fasting on morphological
alterations of the neuronal endoplasmic reticulum/Golgi network as
well as on the expression of leptin receptors in the arcuate nucleus of aged
rats. Male Wistar rats, aged 24 months, were fasted for 96 hours. The control
animals were fed ad libitum. Membranous whorls in the ARH neurons were
visualized using the electron microscopy technique. Leptin receptors in the
membranes of ARH neurons were determined immunohistochemically (IHC),
and soluble leptin receptors in the plasma as well as plasma isoprostanes were
quantified immunochemically (ELISA). An intense formation of membranous
whorls was observed, directly associated with the cisternae of the rough endoplasmic
reticulum, as well as lamellar bodies. Interestingly, the whorls were
often localized near a well-developed Golgi complex. Moreover, some Golgi
complexes displayed an early stage of whorl formation. Groups of residual
lipofuscin granules were found in the immediate proximity of the whorls. An
increased immunoreactivity with neuronal leptin receptors suggests that hypersensitive
neurons may still effectively respond to the fasting serum levels of
leptin, mediating ultrastructural transformation of ARH neurons during short-term fasting. Having observed a significant accumulation of lipofuscin granules
and a marked increase of total 8-isoprostane serum level in the fasting rats, we
hypothesize that signal transduction within the neurons of ARH is dependent
on oxidative stress phenomena
Non-Destructive Probing of Rabi Oscillations on the Cesium Clock Transition near the Standard Quantum Limit
We report on non-destructive observation of Rabi oscillations on the Cs clock
transition. The internal atomic state evolution of a dipole-trapped ensemble of
cold atoms is inferred from the phase shift of a probe laser beam as measured
using a Mach-Zehnder interferometer. We describe a single color as well as a
two-color probing scheme. Using the latter, measurements of the collective
pseudo-spin projection of atoms in a superposition of the clock states are
performed and the observed spin fluctuations are shown to be close to the
standard quantum limit.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Interaction-based quantum metrology showing scaling beyond the Heisenberg limit
Quantum metrology studies the use of entanglement and other quantum resources
to improve precision measurement. An interferometer using N independent
particles to measure a parameter X can achieve at best the "standard quantum
limit" (SQL) of sensitivity {\delta}X \propto N^{-1/2}. The same interferometer
using N entangled particles can achieve in principle the "Heisenberg limit"
{\delta}X \propto N^{-1}, using exotic states. Recent theoretical work argues
that interactions among particles may be a valuable resource for quantum
metrology, allowing scaling beyond the Heisenberg limit. Specifically, a
k-particle interaction will produce sensitivity {\delta}X \propto N^{-k} with
appropriate entangled states and {\delta}X \propto N^{-(k-1/2)} even without
entanglement. Here we demonstrate this "super-Heisenberg" scaling in a
nonlinear, non-destructive measurement of the magnetisation of an atomic
ensemble. We use fast optical nonlinearities to generate a pairwise
photon-photon interaction (k = 2) while preserving quantum-noise-limited
performance, to produce {\delta}X \propto N^{-3/2}. We observe super-Heisenberg
scaling over two orders of magnitude in N, limited at large N by higher-order
nonlinear effects, in good agreement with theory. For a measurement of limited
duration, super-Heisenberg scaling allows the nonlinear measurement to overtake
in sensitivity a comparable linear measurement with the same number of photons.
In other scenarios, however, higher-order nonlinearities prevent this crossover
from occurring, reflecting the subtle relationship of scaling to sensitivity in
nonlinear systems. This work shows that inter-particle interactions can improve
sensitivity in a quantum-limited measurement, and introduces a fundamentally
new resource for quantum metrology
4-OH-TEMPO prevents the morphological alteration of rat thymocytes primed to apoptosis by oxidative stress inducer ButOOH
Thymocytes exposed to the pro-oxidant tert–butyl-hydroperoxide (ButOOH) display
a number of dramatic changes in morphology similar to those observed in
the case of dexamethasone-treated cells. Both reagents induce nuclear chromatin
peripheral aggregation below the nuclear membrane. Some nuclei themselves
break up producing two or more fragments. ButOOH-treated cells are
morphologically characterised by cell shrinkage, extensive surface blebbing and,
finally, fragmentation into membrane–bound apoptotic bodies composed of
cytoplasm and tightly packed with or without nuclear fragments. An increased
level of lipid hydroxyperoxides was detected after exposure of thymocytes to
ButOOH. Both oxidative stress markers and morphological damage to cells were
prevented by the antioxidant 4-OH-TEMPO
Hamiltonian Design in Atom-Light Interactions with Rubidium Ensembles: A Quantum Information Toolbox
We study the coupling between collective variables of atomic spin and light
polarization in an ensemble of cold 87Rb probed with polarized light. The
effects of multiple hyperfine levels manifest themselves as a rank-2 tensor
polarizability, whose irreducible components can be selected by means of probe
detuning. The D1 and D2 lines of Rb are explored and we identify different
detunings which lead to Hamiltonians with different symmetries for rotations.
As possible applications of these Hamiltonians, we describe schemes for spin
squeezing, quantum cloning, quantum memory, and measuring atom number.Comment: 6 pages, 4 figures; added reference
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