226 research outputs found
Microfluidic integration of photonic crystal fibers for online photochemical reaction analysis
Liquid-filled hollow-core photonic crystal fibers (HC-PCFs) are perfect optofluidic channels, uniquely providing low-loss optical guidance in a liquid medium. As a result, the overlap of the dissolved specimen and the intense light field in the micronsized core is increased manyfold compared to conventional bioanalytical techniques, facilitating highly-efficient photoactivation processes. Here we introduce a novel integrated analytical technology for photochemistry by microfluidic coupling of a HC-PCF nanoflow reactor to supplementary detection devices. Applying a continuous flow through the fiber, we deliver photochemical reaction products to a mass spectrometer in an online and hence rapid fashion, which is highly advantageous over conventional cuvette-based approaches
Understanding variability in root zone storage capacity in boreal regions
The root zone storage capacity (Sr) of vegetation is
an important parameter in the hydrological behaviour of a catchment.
Traditionally, Sr is derived from soil and vegetation data.
However, more recently a new method has been developed that uses climate data
to estimate Sr based on the assumption that vegetation adapts its
root zone storage capacity to overcome dry periods. This method also enables
one to take into account temporal variability of derived
Sr values resulting from changes in climate or land cover. The
current study applies this new method in 64 catchments in Finland to
investigate the reasons for variability in Sr in boreal regions.
Relations were assessed between climate-derived Sr values and
climate variables (precipitation-potential evaporation rate, mean annual
temperature, max snow water equivalent, snow-off date), detailed vegetation
characteristics (leaf cover, tree length, root biomass), and vegetation
types. The results show that in particular the phase difference between snow-off
date and onset of potential evaporation has a large influence on the derived
Sr values. Further to this it is found that (non-)coincidence of
snow melt and potential evaporation could cause a division between catchments
with a high and a low Sr value. It is concluded that the climate-derived root zone storage capacity leads to plausible Sr values
in boreal areas and that, apart from climate variables, catchment vegetation
characteristics can also be directly linked to the derived
Sr values. As the climate-derived Sr enables
incorporating climatic and vegetation conditions in a hydrological parameter,
it could be beneficial to assess the effects of changing climate and
environmental conditions in boreal regions.</p
Fiber transport of spatially entangled photons
Entanglement in the spatial degrees of freedom of photons is an interesting
resource for quantum information. For practical distribution of such entangled
photons it is desireable to use an optical fiber, which in this case has to
support multiple transverse modes. Here we report the use of a hollow-core
photonic crystal fiber to transport spatially entangled qubits.Comment: 4 pages, 4 figure
Hybrid-Entanglement in Continuous Variable Systems
Entanglement is one of the most fascinating features arising from
quantum-mechanics and of great importance for quantum information science. Of
particular interest are so-called hybrid-entangled states which have the
intriguing property that they contain entanglement between different degrees of
freedom (DOFs). However, most of the current continuous variable systems only
exploit one DOF and therefore do not involve such highly complex states. We
break this barrier and demonstrate that one can exploit squeezed cylindrically
polarized optical modes to generate continuous variable states exhibiting
entanglement between the spatial and polarization DOF. We show an experimental
realization of these novel kind of states by quantum squeezing an azimuthally
polarized mode with the help of a specially tailored photonic crystal fiber
Rydberg atoms in hollow-core photonic crystal fibres.
The exceptionally large polarizability of highly excited Rydberg atoms-six orders of magnitude higher than ground-state atoms--makes them of great interest in fields such as quantum optics, quantum computing, quantum simulation and metrology. However, if they are to be used routinely in applications, a major requirement is their integration into technically feasible, miniaturized devices. Here we show that a Rydberg medium based on room temperature caesium vapour can be confined in broadband-guiding kagome-style hollow-core photonic crystal fibres. Three-photon spectroscopy performed on a caesium-filled fibre detects Rydberg states up to a principal quantum number of n=40. Besides small energy-level shifts we observe narrow lines confirming the coherence of the Rydberg excitation. Using different Rydberg states and core diameters we study the influence of confinement within the fibre core after different exposure times. Understanding these effects is essential for the successful future development of novel applications based on integrated room temperature Rydberg systems
A new method to measure Bowen ratios using high-resolution vertical dry and wet bulb temperature profiles
The Bowen ratio surface energy balance method is a relatively simple method
to determine the latent heat flux and the actual land surface evaporation.
The Bowen ratio method is based on the measurement of air temperature and
vapour pressure gradients. If these measurements are performed at only two
heights, correctness of data becomes critical. In this paper we present the
concept of a new measurement method to estimate the Bowen ratio based on
vertical dry and wet bulb temperature profiles with high spatial resolution.
A short field experiment with distributed temperature sensing (DTS) in a
fibre optic cable with 13 measurement points in the vertical was undertaken.
A dry and a wetted section of a fibre optic cable were suspended on a 6 m
high tower installed over a sugar beet trial plot near Pietermaritzburg
(South Africa). Using the DTS cable as a psychrometer, a near continuous
observation of vapour pressure and air temperature at 0.20 m intervals was
established. These data allowed the computation of the Bowen ratio with a
high spatial and temporal precision. The daytime latent and sensible heat
fluxes were estimated by combining the Bowen ratio values from the DTS-based
system with independent measurements of net radiation and soil heat flux. The
sensible heat flux, which is the relevant term to evaluate, derived from the
DTS-based Bowen ratio (BR-DTS) was compared with that derived from co-located
eddy covariance (<i>R</i><sup>2</sup> = 0.91), surface layer scintillometer
(<i>R</i><sup>2</sup> = 0.81) and surface renewal (<i>R</i><sup>2</sup> = 0.86) systems. By using
multiple measurement points instead of two, more confidence in the derived Bowen
ratio values is obtained
Birefringence and dispersion of cylindrically polarized modes in nanobore photonic crystal fiber
We demonstrate experimentally and theoretically that a nanoscale hollow
channel placed centrally in the solid glass core of a photonic crystal fiber
strongly enhances the cylindrical birefringence (the modal index difference
between radially and azimuthally polarized modes). Furthermore, it causes a
large split in group velocity and group velocity dispersion. We show
analytically that all three parameters can be varied over a wide range by
tuning the diameters of the nanobore and the core
Neural correlates of sexual cue reactivity in individuals with and without compulsive sexual behaviours
Although compulsive sexual behaviour (CSB) has been conceptualized as a "behavioural" addiction and common or overlapping neural circuits may govern the processing of natural and drug rewards, little is known regarding the responses to sexually explicit materials in individuals with and without CSB. Here, the processing of cues of varying sexual content was assessed in individuals with and without CSB, focusing on neural regions identified in prior studies of drug-cue reactivity. 19 CSB subjects and 19 healthy volunteers were assessed using functional MRI comparing sexually explicit videos with non-sexual exciting videos. Ratings of sexual desire and liking were obtained. Relative to healthy volunteers, CSB subjects had greater desire but similar liking scores in response to the sexually explicit videos. Exposure to sexually explicit cues in CSB compared to non-CSB subjects was associated with activation of the dorsal anterior cingulate, ventral striatum and amygdala. Functional connectivity of the dorsal anterior cingulate-ventral striatum-amygdala network was associated with subjective sexual desire (but not liking) to a greater degree in CSB relative to non-CSB subjects. The dissociation between desire or wanting and liking is consistent with theories of incentive motivation underlying CSB as in drug addictions. Neural differences in the processing of sexual-cue reactivity were identified in CSB subjects in regions previously implicated in drug-cue reactivity studies. The greater engagement of corticostriatal limbic circuitry in CSB following exposure to sexual cues suggests neural mechanisms underlying CSB and potential biological targets for interventions
Roadmap on multimode photonics
Multimode devices and components have attracted considerable attention in the last years, and different research topics and themes have emerged very recently. The multimodality can be seen as an additional degree of freedom in designing devices, thus allowing for the development of more complex and sophisticated components. The propagation of different modes can be used to increase the fiber optic capacity, but also to introduce novel intermodal interactions, as well as allowing for complex manipulation of optical modes for a variety of applications. In this roadmap we would like to give to the readers a comprehensive overview of the most recent developments in the field, presenting contributions coming from different research topics, including optical fiber technologies, integrated optics, basic physics and telecommunications
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