582 research outputs found
Fractal light from lasers
Fractals, complex shapes with structure at multiple scales, have long been observed in Nature: as symmetric fractals in plants and sea shells, and as statistical fractals in clouds, mountains and coastlines. With their highly polished spherical mirrors, laser resonators are almost the precise opposite of Nature, and so it came as a surprise when, in 1998, transverse intensity cross-sections of the eigenmodes of unstable canonical resonators were predicted to be fractals [Karman et al., Nature 402, 138 (1999)]. Experimental verification has so far remained elusive. Here we observe a variety of fractal shapes in transverse intensity cross-sections through the lowest-loss eigenmodes of unstable canonical laser resonators, thereby demonstrating the controlled generation of fractal light inside a laser cavity. We also advance the existing theory of fractal laser modes, first by predicting 3D self-similar fractal structure around the centre of the magnified self-conjugate plane, second by showing, quantitatively, that intensity cross-sections are most self-similar in the magnified self-conjugate plane. Our work offers a significant advance in the understanding of a fundamental symmetry of Nature as found in lasers
Entangled Bessel beams
Orbital angular momentum (OAM) entanglement is investigated in the
Bessel-Gauss (BG) basis. Having a readily adjustable radial scale, BG modes
provide a more favourable basis for OAM entanglement over Laguerre-Gaussian
(LG) modes. The OAM bandwidth in terms of BG modes can be increased by
selection of particular radial modes and leads to a flattening of the spectrum.
The flattening of the spectrum allows for higher entanglement. We demonstrate
increased entanglement in terms of BG modes by performing a Bell-type
experiment and violating the appropriate Clauser Horne Shimony Holt (CHSH)
inequality. In addition, we reconstruct the quantum state of BG modes entangled
in high-dimensions.Comment: 8 pages, 4 figure
Keck Spectroscopy of Candidate Proto-globular Clusters in NGC 1275
Keck spectroscopy of 5 proto-globular cluster candidates in NGC 1275 has been
combined with HST WFPC2 photometry to explore the nature and origin of these
objects and discriminate between merger and cooling flow scenarios for globular
cluster formation. The objects we have studied are not HII regions, but rather
star clusters, yet their integrated spectral properties do not resemble young
or intermediate age Magellanic Cloud clusters or Milky Way open clusters. The
clusters' Balmer absorption appears to be too strong to be consistent with any
of the standard Bruzual & Charlot evolutionary models at any metallicity. If
these models are adopted, an IMF which is skewed to high masses provides a
better fit to the data. A truncated IMF with a mass range of 2-3 Mo reproduces
the observed Balmer equivalent widths and colors at about 450 Myr. Formation in
a continuous cooling flow appears to be ruled out since the age of the clusters
is much larger than the cooling time, the spatial scale of the clusters is much
smaller than the cooling flow radius, and the deduced star formation rate in
the cooling flow favors a steep rather than a flat IMF. A merger would have to
produce clusters only in the central few kpc, presumably from gas in the
merging galaxies which was channeled rapidly to the center. Widespread shocks
in merging galaxies cannot have produced these clusters. If these objects are
confirmed to have a relatively flat, or truncated, IMF it is unclear whether or
not they will evolve into objects we would regard as bona fide globular
clusters.Comment: 30 pages (AAS two column style, including 9 tables and 7 figures) to
appear in the AJ (August issue), also available at
http://www.ucolick.org/~mkissler/Sages/sages.html (with a full resolution
Fig.1) Revised Version: previous posted version was an uncorrect ealier
iteration, parts of the text, tables and figures changed. The overall
conclusions remain unchange
MOCVD of ultra-thin PV solar cell devices using a pyrite based p-i-n structure
Ultra-thin photovoltaic (PV) devices were produced by atmospheric pressure metal organic chemical vapour deposition (AP-MOCVD) incorporating a highly absorbing intermediate sulphurised FeSₓ layer into a CdS/CdTe structure. X ray diffraction (XRD) confirmed a transitional phase change to pyrite FeS₂ after post growth sulphur (S) annealing of the FeSₓ layer between 400⁰C and 500⁰C. Devices using a superstrate configuration incorporating a sulphurised or non sulphurised FeSₓ layer were compared to p-n devices with only a CdS/CdTe structure. Devices with sulphurised FeSₓ layers performed least efficiently, even though pyrite fractions were present. Rutherford back scattering (RBS) confirmed deterioration of the CdS/FeSₓ interface due to S inter-diffusion during the annealing process
Bridging the gap between low and high mass dwarf galaxies
While the dark matter content within the most massive giant and smallest
dwarf galaxies has been probed -- spanning a range of over one million in mass
-- an important observational gap remains for galaxies of intermediate mass.
This gap covers K band magnitudes of approximately -16 > M_K > -18 (for which
dwarf galaxies have B--K ~ 2). On the high mass side of the gap are dwarf
elliptical (dE) galaxies, that are dominated by stars in their inner regions.
While the low mass side includes dwarf spheroidal (dSph) galaxies that are dark
matter-dominated and ultra compact dwarf (UCD) objects that are star-dominated.
Evolutionary pathways across the gap have been suggested but remain largely
untested because the `gap' galaxies are faint, making dynamical measurements
very challenging. With long exposures on the Keck telescope using the ESI
instrument we have succeeded in bridging this gap by measuring the dynamical
mass for five dwarf galaxies with M_K ~ -17.5 (M_B ~ --15.5). With the
exception of our brightest dwarf galaxy, they possess relatively flat velocity
dispersion profiles of around 20 km/s. By examining their 2D scaling relations
and 3D fundamental manifold, we found that the sizes and velocity dispersions
of these gap galaxies reveal continuous trends from dE to dSph galaxies. We
conclude that low-luminosity dwarf elliptical galaxies are dominated by stars,
not by dark matter, within their half light radii. This finding can be
understood if internal feedback processes are operating most efficiently in gap
galaxies, gravitationally heating the centrally-located dark matter to larger
radii. Whereas external environmental processes, which can strip away stars,
have a greater influence on dSph galaxies resulting in their higher dark matter
fractions. Abridged.Comment: 20 pages, includes 12 figures, accepted for publication in MNRA
HOSPICIJ-POTREBA HUMANOG DRUŠTVA
Hrvatsko zakonodavstvo i regulativa palijativne skrbi imaju postavljene neke smjernice za razvoj u Republici Hrvatskoj. Međutim, da uhvatimo korak s razvijenim zemljama treba puno toga pravno i organizacijski urediti. Imamo znanje, imamo volju , imamo svijest nesebičnog djelovanja, ali nemamo financijske mogućnosti u ovom trenutku.O palijativnoj skrbi svaki pojedinac počinje razmišljati tek onda kada mu se razboli član njegove obitelji. Da smo u stanju podići ovu djelatnost u prioritete, našla bi se i sredstva za nju. Da bismo mogli iskoristiti znanje koje imamo treba odmah djelovati. To neće biti jednostavan proces, no u svijetu postoji puno modela i primjera, pa bi se uz iskustvo drugih, naš stručni kadar, te djelovanje na fleksibilnost hrvatske birokracije, okolnosti mogle promijeniti u pozitivnom smislu. Ne zbog nas, ali možda i za nas
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