527 research outputs found
Super-resolving multi-photon interferences with independent light sources
We propose to use multi-photon interferences from statistically independent
light sources in combination with linear optical detection techniques to
enhance the resolution in imaging. Experimental results with up to five
independent thermal light sources confirm this approach to improve the spatial
resolution. Since no involved quantum state preparation or detection is
required the experiment can be considered an extension of the Hanbury Brown and
Twiss experiment for spatial intensity correlations of order N>2
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Buoys with looming eyes deter seaducks and could potentially reduce seabird bycatch in gillnets.
Bycatch of seabirds in gillnet fisheries is a global conservation issue with an estimated 400 000 seabirds killed each year. To date, no underwater deterrents trialled have consistently reduced seabird bycatch across operational fisheries. Using a combination of insights from land-based strategies, seabirds' diving behaviours and their cognitive abilities, we developed a floating device exploring the effect of large eyespots and looming movement to prevent vulnerable seabirds from diving into gillnets. Here, we tested whether this novel above-water device called 'Looming eyes buoy' (LEB) would consistently deter vulnerable seaducks from a focal area. We counted the number of birds present in areas with and without LEBs in a controlled experimental setting. We show that long-tailed duck Clangula hyemalis abundance declined by approximately 20-30% within a 50 m radius of the LEB and that the presence of LEBs was the most important variable explaining this decline. We found no evidence for a memory effect on long-tailed ducks but found some habituation to the LEB within the time frame of the project (62 days). While further research is needed, our preliminary trials indicate that above-water visual devices could potentially contribute to reduce seabird bycatch if appropriately deployed in coordination with other management measures
Buoys with looming eyes deter seaducks and could potentially reduce seabird bycatch in gillnets.
Bycatch of seabirds in gillnet fisheries is a global conservation issue with an estimated 400 000 seabirds killed each year. To date, no underwater deterrents trialled have consistently reduced seabird bycatch across operational fisheries. Using a combination of insights from land-based strategies, seabirds' diving behaviours and their cognitive abilities, we developed a floating device exploring the effect of large eyespots and looming movement to prevent vulnerable seabirds from diving into gillnets. Here, we tested whether this novel above-water device called 'Looming eyes buoy' (LEB) would consistently deter vulnerable seaducks from a focal area. We counted the number of birds present in areas with and without LEBs in a controlled experimental setting. We show that long-tailed duck Clangula hyemalis abundance declined by approximately 20-30% within a 50 m radius of the LEB and that the presence of LEBs was the most important variable explaining this decline. We found no evidence for a memory effect on long-tailed ducks but found some habituation to the LEB within the time frame of the project (62 days). While further research is needed, our preliminary trials indicate that above-water visual devices could potentially contribute to reduce seabird bycatch if appropriately deployed in coordination with other management measures
Active laser frequency stabilization using neutral praseodymium (Pr)
We present a new possibility for the active frequency stabilization of a
laser using transitions in neutral praseodymium. Because of its five outer
electrons, this element shows a high density of energy levels leading to an
extremely line-rich excitation spectrum with more than 25000 known spectral
lines ranging from the UV to the infrared. We demonstrate the active frequency
stabilization of a diode laser on several praseodymium lines between 1105 and
1123 nm. The excitation signals were recorded in a hollow cathode lamp and
observed via laser-induced fluorescence. These signals are strong enough to
lock the diode laser onto most of the lines by using standard laser locking
techniques. In this way, the frequency drifts of the unlocked laser of more
than 30 MHz/h were eliminated and the laser frequency stabilized to within
1.4(1) MHz for averaging times >0.2 s. Frequency quadrupling the stabilized
diode laser can produce frequency-stable UV-light in the range from 276 to 281
nm. In particular, using a strong hyperfine component of the praseodymium
excitation line E = 16 502.616_7/2 cm^-1 -> E' = 25 442.742_9/2 cm^-1 at lambda
= 1118.5397(4) nm makes it possible - after frequency quadruplication - to
produce laser radiation at lambda/4 = 279.6349(1) nm, which can be used to
excite the D2 line in Mg^+.Comment: 10 pages, 14 figure
Connectivity between countries established by landbirds and raptors migrating along the African–Eurasian flyway
The conservation of long-distance migratory birds requires coordination between the multiple countries connected by the movements of these species. The recent expansion of
tracking studies is shedding new light on these movements, but much of this information
is fragmented and inaccessible to conservation practitioners and policy makers. We synthesized current knowledge on the connectivity established between countries by landbirds
and raptors migrating along the African–Eurasian flyway. We reviewed tracking studies to
compile migration records for 1229 individual birds, from which we derived 544 migratory links, each link corresponding to a species’ connection between a breeding country in
Europe and a nonbreeding country in sub-Saharan Africa. We used these migratory links
to analyze trends in knowledge over time and spatial patterns of connectivity per country
(across species), per species (across countries), and at the flyway scale (across all countries
and all species). The number of tracking studies available increased steadily since 2010 (particularly for landbirds), but the coverage of existing tracking data was highly incomplete.
An average of 7.5% of migratory landbird species and 14.6% of raptor species were tracked
per country. More data existed from central and western European countries, and it was
biased toward larger bodied species. We provide species- and country-level syntheses of the
migratory links we identified from the reviewed studies, involving 123 populations of 43
species, migrating between 28 European and 43 African countries. Several countries (e.g.,
Spain, Poland, Ethiopia, Democratic Republic of Congo) are strategic priorities for future
tracking studies to complement existing data, particularly on landbirds. Despite the limitations in existing tracking data, our data and results can inform discussions under 2 key
policy instruments at the flyway scale: the African–Eurasian Migratory Landbirds Action Plan and the Memorandum of Understanding on the Conservation of Migratory Birds of
Prey in Africa and Eurasia.Fundação para a Ciência e Tecnologia - FCTinfo:eu-repo/semantics/publishedVersio
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